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1. TRM RED670 61 6U BC 9 O Eo b w ei 7 Lad Ww 20 Y a 21 rte NO NO N p Article Mo RK 926 315 BC Comment RTXP 24 Figure C 9 Connection Diagram RED670 Current and Voltage Leads between TRM and Test Switch 5 13A a ee TRM REG670 61 6U AH 14A 14B X401 2 CH1 1 15A 15B X401 3 16A 16B X401 4 CH2 I 17A 17B X401 5 18A gt 18B X401 6 CH3 1 19A A B 19B X401 7 3 20A gt 20B X401 8 CH4 1 Faa T 21A 21B X401 9 I5 i CH5 1 22B X401 10 7 a 23A 23B X401 11 7 24A 24B X401 12 CH6 1 1A 1B X401 13 e 2A 2B X401 14 CH7 U 3A 3B X401 15 e 4A 4B X401 16 CH8 U 5A 5B X401 17 J 6A 6B xX401 18 CH9 U wo 20 Y 21 23 oe B X401 19 e B X401 20 3 CH10 U B X401 21 e B X401 22 3 CH11 U Article No B X401 23 RK 926 315 AH B X401 24 CH12 U RTXP 24 l Figure C 10 Connection Diagram REG670 Current and Voltage Leads between TRM and Test Switch 5 CH1 I CH2 I ff X401 5 Q e X401 6 O CH3 I CH4 1 CHS I CH6 I 1A 1B X401 13 J 2A 2B X401 14 CH7 U 3A 3B X401 15 J 4A 4B X401 16 CH8 U 5A 5B X401 17 e 6A 6B X401 18 CH9 U B X401 19 B X401 20 CH10 U B X401 21 B X401 22 CH11 U B X401 23 B X401 24 CH12 U Figure C 11 Connection Diagram RET670 Current and Voltage Leads between TRM and Test Switch 5 D Appendix Equipment List Description Li
2. 6 1 2 3 1 Coupling Capacitor Voltage Transformers 2 4 Power System Protection Attributes 3 Short Circuits and Abnormal Conditions 3 1 Three Phase to Ground Faults 3 2 Phase to Ground Faults 2 0 eos ob eek ok ge a eh be 8 3 3 Phase to Phase Faults ek ode Se eee a ee SS a er Ee Th ed 3 4 Double Phase to Ground Faults 4 Protection Principles As AUIS CS wae ot Ue tie tay ent Mas ie et nln Gh Sark halt Gh Gar oe oo Te UP eR E 4 2 Overcurrent Relay 2 0 2005000008 4 3 Directional Overcurrent Relay ay aes es avete de 8 ae Pe ad 4A Wistances clayey cea due wind ai ea ie ee a DA ee DHS 4 5 Differential Relay 2 4 gos 22 id BR ed ee ee a ee ee 4 5 1 Generator Differential Protection 4 5 2 Transformer Differential Protection 2 2 4 5 3 Busbar Differential Protection 20 Modern Relay Technology Relay Testing Testing Relay Tester 2 0 0 ee ee 6 1 1 Manual Testing ae kee ee ee ee a 6 1 2 Software Routine Testing 6 1 3 Event Recording Simulated Waveform Playback 10 11 A B C D 6 2 Testing Fault Simulator 4 lt 6 oa a a ee Oe 8 6 3 Testing Scaled Physical Network aoaaa 6A Testine SUMMAT i oe oA Bae OS T a a aT ee 6 5 Test Procedures ooa hw alg a Oo Bd Software 7 1 Short Circuit Calculation Software o o ooa a
3. The protection of power system consists of zones of protection as seen in Fig ure 2 7 One protected component normally has its own zone and it is nor mally defined by the location of the CTs at each end The zones overlap each other and this is one important feature of a well designed protection system Parts of a power system has more than one relaying protecting it primary and back up protection Back up protection is normally divided between local and remote back up Local back up is provided by the same relay providing primary protection however it uses a different relay principle or setting i e overcurrent function as local back up for a primary differential function Remote back up is provided by a relay at another location zone and it utilizes the same or a different relay principle as the primary relay The remote relay may again have the primary relay as its remote back up 21 BUS PROTECTION BUS PROTECTION y n f 1 menn 4 l De ay I I I awe ee ee eS N Se 7 GENERATORI TRANSFORMER PROTECTION TTT PROTECTION Figure 2 7 Protection Zones of a Power System 10 CHAPTER 2 POWER SYSTEM PROTECTION Relay Coordination In many parts of the power system two or more relays are able to detect a fault in a given component location i e a primary relay and one or remotes back up relays Making sure that the primary relay gets the first attempt to clear the fault is important to ensure high sel
4. 7 2 Relay Configuration and Parameter Setting Software Relay Lab 8 1 Relay Lab at Michigan Technological University 8 2 Expansion Steps of Relay Lab 04 8 3 Practical Set Up of Lab hey doth chy Sane he BAP eke 7E WP Pare AL 8 3 1 Test Switch Test Handle ers any arpee ow BY eee 4 8 4 Configuration of ABB Relays ac606 cn ww al we a eg Lab Exercise Proposals 9 1 Introduction to Relay Function and Overcurrent Protection 9 2 Distance Protection ode ae oe ea a ture Bae Ue ae ae a Conclusion Further Work Appendix Symmetrical Components Appendix Wide Area Measurement Systems Appendix Connection Diagrams Appendix Equipment List Bibliography VI 77 79 80 81 91 93 List of Figures 2 1 Principles of Power System Protection 2 2 2 Conceptual Illustration of a Current Transformer 4 2 3 Equivalent Circuit for a Current Voltage Transformer 5 2 4 Excitation Curve for a Multi Ratio CT 21 6 2 5 Simplified Equivalent Circuit for Coupling Capacitive Voltage Trans former with Tuning Inductor ooa a 7 2 6 Cross Section of a Coupling Capacitive Voltage Transformer from Alstom Grid 11 S628 ok eee hae eh eh ee hd Be 8 2 7 Protection Zones of a Power System 2 9 2 8 Example Relay Coordination for Adjacent Lines Fault at Line 3 10 3 1 Simple Two Bus Network with Fault on Line
5. 14 3 2 Three Phase to Ground Fault 0 14 3 3 Reduced Sequence Networks Interconnection for Three Phase Fault No Negative or Zero Sequence Network Component 15 3 4 Phase to Ground Fault oe 8 8 ee ke oh A Be A 16 3 5 Reduced Sequence Networks Interconnection for Phase to Ground FAs No ae Cons ee See ht ea ee oy RE A a ee ie Se 16 3 6 Phase to Phase Fault wh a ceki bane fs OS eee Uh ee ado ke Hh Se bee 18 3 7 Reduced Sequence Networks Interconnection for Phase to Phase Fault No Zero Sequence Network Component 18 3 8 Double Phase to Ground Fault a a bose eee ee es ae ES 19 3 9 Reduced Sequence Networks Interconnection for Double Phase to Phases Pats ea Pork ee ne oe ao ble a a aap tied inh 4 20 4 1 Time Current Characteristics fora Fuse 19 21 4 2 Connection of Current Transformers for Overcurrent Relay 22 4 3 Inverse Time and Instantaneous Characteristics Overcurrent Protection 4 4 Simplified One Line Diagram of Substation with Directional Over current Relay nae oe hark a habe ol Gis Seg 24 4 5 Phasor Diagram for Directional Relay using Voltage Reference 25 4 6 Distance Relay Principle 2 004 26 4 7 Line 1 from Figure 4 6 with Mid Line Fault 27 4 8 Corresponding RX diagrams with Zone Settings Line Load and Fault Impedances for Line 1 in Figure 4 7 21 4 9 Protection of Line with Distance Relay at Both Ends of the Line
6. 28 4 10 Differential Relay Principle oaa aa a 29 4 11 Percentage Differential Relay Current Characteristics 30 VII 23 4 12 Secondary Current Waveforms with without CT Saturation 31 5 1 5 2 5 3 5 4 6 1 6 2 6 3 6 4 6 5 6 6 6 7 6 8 6 9 7 1 7 2 8 1 8 2 8 3 8 4 8 5 8 6 9 1 9 2 A 1 C 1 C 2 C 3 VI Architecture of Modern Relays 04 36 Sampling of Analog Signal to Digital Values by an Analog to Dig ital Converter AJD re Ste hia gh hokey ake oe eal die eh 37 Signal and Function Blocks for Overcurrent Protection in ABB HOE POCO Welay 4G aa eile Sek hd gs eg tt BID ae hi B e Slide Sod 38 IEC61850 Framework Substation Communication System 40 Front Panel of Omicron CMC 356 Relay Tester 23 43 Connection Diagram for Three Phase Testing of Relays using a Relay Tester s metir a Gta a a e a Se gd Be ak Se a 44 Screenshot from Omicron Test Universe 1 61 SR1 QuickCMC Control Panel var e ara a Serta Beeler a RES Bh A e e G e aren Y 45 Screenshot from Overcurrent Relay Test Doble F6Test 3 12 0 47 Screenshot from Differential Relay Test Omicron Test Universe Iba DSA g Sage oh et aad a a a aa i a a de AA R 48 Screenshot from Playback of pl4 file in Doble Protection Suite 3 0 Displays Currents and Voltages in a Three Phase System During a Phase to Ground Fault a0 a a a a 49 Front Panel of Fault Simulato
7. MMS ease lite In Control Au tomation and Systems 2007 ICCAS 07 International Conference on pages 1873 1877 October 2007 Omicron CMC 356 https www omicron at typo3temp pics CMC 356 1_bbf 8 3db84 png 24 Inc Operation Technology ETAP http etap com industries etap user list htm 25 Zo Electrical Engineering Portal Symmetrical Components http electrical engineering portal com resources knowledge electrical formulas symmetrical components 26 M A Redfern X Sun Wen An P A Crossley Li Yang and H Grasset IEC61850 and Designs for Future Relays In Developments in Power Sys tem Protection DPSP 2010 Managing the Change 10th IET International Conference on pages 1 5 March 2010 27 M Harry Hesse Robert C Degeneff Principles of Power Engineering Anal ysis CRC Press First edition 2012 28 Anthony F Sleva Protective Relay Principles CRC Press First edition 2009 29 smartgrids no http smartgrids no nytt nasjonalt laboratorium for smartgrid i trondheim November 4th 2013 30 Torstein Stadheim Implementering av rel vern i ATPDraw Master s thesis NTNU June 2012 31 Arun G Phadke Stanley H Horowitz Power System Relaying Research Studies Press Ltd Second edition 1995 32 Chris Werstiuk The Relay Testing Handbook Relay Testing Fundamentals Valence Electrical Training Services LLC 2012 33 A Wright and C Christopoulos Electrical Pow
8. Phase System During a Phase to Ground Fault 6 2 Testing Fault Simulator Simpler devices that can be used for certain types of relay tests e g logic testing and simple overcurrent tests exist They are autonomous devices and not de pendent on an auxiliary computer and software package As relay testers they produce secondary currents and voltages at one location of the power system Amplitudes of currents and voltages as well as phase angles are adjustable for two states pre fault and fault It can normally just produce symmetrical values in other words it can simulate steady state symmetrical conditions and three phase faults However this is sufficient when one is only looking to trig a trip signal Figure 6 7 shows the front panel of a fault simulator from Cebec AB It is able to deliver up to 2 A line currents and line voltages up to 130 V The major benefit of a fault simulator versus a relay tester is that it is only a fraction of the cost 50 CHAPTER 6 RELAY TESTING Figure 6 7 Front Panel of Fault Simulator from Cebec AB 6 3 Testing Scaled Physical Network An alternative to using a relay tester is to use a scaled physical network Here one uses known characteristics of power system components and try to implement them with reduced size Normally variable resistance inductance and capaci tance are used this allows modeling of e g lines with different lengths types 6 3 TESTING SCALED PHYSICAL NETWORK
9. a parallel port interface newer models use an Ethernet or USB interface Some high end models also have 44 CHAPTER 6 RELAY TESTING Wi Fi capabilities Combined with its software the relay tester is a very powerful tool The testing routines of the relay tester and software can be divided in three main parts e Manual Testing e Software Routine Testing e Event Recording Simulated Waveform Playback The voltages and currents induced by the relay tester is wired to the CT and VT inputs of the relay i e the test object Connections between digital inputs and outputs to indicate trip signals and breaker positions are made as shown in Figure 6 2 This is vital since it among other things allows the relay tester to record the trip time of the relay and to compare the value with an expected result Test Object Relay Relay Tester Figure 6 2 Connection Diagram for Three Phase Testing of Relays using a Relay Tester 6 1 TESTING RELAY TESTER 45 6 1 1 Manual Testing The software for relay testers normally comes with a control panel function where the current and voltage outputs can be set manually Figure 6 3 shows a screen shot from the control panel function of Omicron s software Test Universe The control panel gives the user full control over amplitude phase angle and ampli tude of the relay testers current and voltage outputs A phase diagram with the corresponding phasors provides the user with a visual o
10. be described closer in this report 28 5 Modern Relay Technology The technology behind microprocessors continuously improves leading to them becoming more powerful faster and smaller Todays modern relays commonly referred to as Intelligent Electronic Devices IEDs are microprocessor based devices This technology development has allowed relay manufacturers to make complex devices containing several protective functions as well as metering event recording functions and communication features This all in one philosophy lets one device replace the functions of several stand alone devices significantly decreasing investment costs Should one protective function not operate as intended during a fault another function will detect and cause the relay to trip For instance if there is problems with a VT leading to the distance protection not being dependable the relay should detect this and disable the distance function the overcurrent protection function will detect the fault and operate This is in Chapter 2 4 referred to as local back up However should the entire relay fail one is left without protection unless there is a separate relay similar or different model providing redundancy Digi tal relays have two main sources of error hardware and software software being introduced by the transition into digital relays Periodic maintenance testing of relays to ensure their reliability especially after software updates revisio
11. be recorded events from a relay IED Relay testing using waveforms from a real fault scenario can be very interesting for students The waveforms can also be created by simulation programs e g EMTP programs as shown in Figure 6 6 This is a useful feature as the user can verify a relays reliability The relay tester can play back a scenario where the relay tripped when it was not supposed to giving the user an opportunity to locate the reasoning behind the mis operation and improve the protection systems security in future events whether it was a hardware software error or simply an error in the setting of the relay Another significant event is when a relay does not trip for a fault it was supposed to trip for i e the relays dependability was not sufficient Studies of such scenarios are important to improve the overall reliability of protection systems 6 2 TESTING FAULT SIMULATOR 49 X XAA A bi E Readouts M S D A Legend Edt v E show Only Assigned Channels Secondary v Harmonics 00048 X00018 A PLD PPP PDLPPLPPDPPLPDPPL PIP PPL PPPPPIPPL PLP PLPLPLPLPLPLDIPPLIIN eo004C xO001C A LELLPLLLLL LEE PELL ikiss eneyt gie State 2F mm r T T T T f T T T T T T T T T T T T T a o0 a4 ors 02 025 o3 oss os ous os os os 08s a7 o7s os oss os 095 Total samples 10 001 Senge time ins Figure 6 6 Screenshot from Playback of pl4 file in Doble Protection Suite 3 0 Displays Currents and Voltages in a Three
12. be wired to CTs VTs and circuit breakers However for the purpose of the relay lab the A side will normally be wired to a relay tester The alternative to using a test switch is connecting the relay tester directly to the relays This solution is used at the lab course at MTU The students must then read the relay manual to figure out the connections each time the lab is used For students on a university level this is not optimal use of time in the lab The test switch test handle solution saves time since it will be well documented allowing students to easily connect banana plug leads correctly without having to browse a relay manual Between the A and B side there can be three types of switches all shown in Figure 8 5 The three switches have different characteristics tailored to the function they are supposed to have Figure 8 5a illustrates the switch used for trip signals it is normally closed i e trip signals are forwarded to CB s When the switch is opened the trip signal will be blocked 68 CHAPTER 8 RELAY LAB Figure 8 4 ABB RTXP24 Test Switch right and RTXH24 Test Handle left 4 As mentioned in Chapter 2 2 the secondary side of a CT should never be left open Current inputs are therefore wired to the types of switches shown in Figure 8 5b This switch is normally closed but in its other position it will short circuit the current circuit The three phase current circuits can be short circuited sepa rat
13. course consists of 9 sessions with different topics including directional overcurrent distance and differential protection Some of the sessions are more advanced e g one session focuses on challenges with distributed generation and distance protection In the lab exercises the stu dents face practical challenges they are handed a relay with no cables connected and have to use the manual to figure how to connect input and outputs The lab exercises also consists of a pre lab part which should be completed before the actual lab session This part makes the students prepared for the exercise making the session itself more efficient One of the most interesting features of the MTU lab is how it has been ex panded in steps vertically and horizontally over the years with different types of equipment and added parallel work benches It is important to build a lab which is capable of being gradually expanded with up to date and desired fea tures and this is something which should be a focus when designing the lab at NTNU However since the lab at NTNU is not supposed to be used in a sepa rate lab course but as a smaller lab part of standard course it should not be as demanding when it comes to practical challenges A focus on principles and an overall understanding of power system protection and the relays role is essential 62 CHAPTER 8 RELAY LAB 8 2 Expansion Steps of Relay Lab As mentioned earlier building the lab graduall
14. dealing with In addition the playback function is very useful for lab exercises purposes as it allows the students to simulate a fault scenario and play it back on the relay tester and check the relay response Using software capable of simulat ing relay operations and comparing it with real relay behavior is also a possibility with the relay tester 6 5 Test Procedures Test procedures for relays can be separated in three parts 32 e Pick up Testing This testing involves applying the current voltage corresponding to the relays pick up setting and check that pick up is indicated by the relay The next step is to slowly decrease the current voltage un til pick up is no longer indicated Then increase the current voltage again until the relay indicates pick up Logging the actual values calculating the error with these values and the expected values and comparing them with the manufacturers data is the final step ActualV alue ExpectedV alue ExpectedV alue 100 error 6 1 6 5 TEST PROCEDURES 53 Current A Pick up on Setting Time s Figure 6 9 Pick up Indication Testing e Timing Testing This test is performed to measure the time difference delay between test initiation applying a current voltage within the pick up region and when the relay output indicates trip The relay output contact should preferably be the same contact as used in service The error is again calculated according to
15. exciting magnetizing force Uef and the excitation current Te Sarri oon Mo oom cei tint i asad mm N Ze I PN r aae a it aa J Te ino nespre Pt ttt ttt en Ht TIAA Baa tA WA F mar LZ Si 7 Exciting Magnetizing Force U V l 001 Excitation Current A Figure 2 4 Excitation Curve for a Multi Ratio CT 21 2 3 VOLTAGE TRANSFORMERS 7 2 3 Voltage Transformers Voltage transformers are used in the same way as CTs but their task is to step down the high voltage of the power system to a low voltage which the relays can handle The basic design is similar to the one of CTs so the equivalent circuit in Figure 2 3a is still valid VTs in contrary to CTs normally have two or more windings on the secondary side and multiple windings on the primary side N gt Ns The burden here becomes y2 Zy Q 2 a 2 3 2 3 1 Coupling Capacitor Voltage Transformers For voltages up to roughly 115 kV electromagnetic VTs Equvialent Circuit shown in Figure 2 3 are used while for higher voltages capacitive dividers are intro duced to the transformer design It is referred to as a coupling capacitor voltage transformer CCVT 15 An equivalent circuit can be seen in Figure 2 5 while a cross section illustation of a CCVT from Alstom Grid is shown in Figure 2 6 Figure 2 5 Simplified Equivalent Circuit for Coupling Capacitive Voltage Trans former with Tuning
16. its own protection which is not illustrated here The green arrows illustrate how the current in the network will flow during normal operation 4 3 DIRECTIONAL OVERCURRENT RELAY 25 If a fault were to occur at one of the transmission lines e g at Line A as illustrated current will flow from Line B via the busbar and upstream in Line A towards the fault while still supplying load current to the feeders The current flow during this fault is illustrated with the red arrows In other words Relay B will see a higher current than the relay in Line A during this scenario If the relays have pick up and time current characteristics similar to each other and initially assume they have no directional element it is possible that Relay B will trip before Relay A However ideally Relay A is supposed to operate first as it is the primary protection for Line A Assuming the relays now are directional with forward tripping directions i e towards protected object Relay B will be blocked during the fault due to the direction of the current it sees This will lead to high selectivity as Relay B will trip first and clear the fault A reference commonly referred to as polarizing quantity is used to provide the directional function This reference either voltage or current is utilized by the relay to compare the angle between the measured current Jor and the reference to determine the direction of the current flow Normally a voltage qua
17. near a generator switchyard and or substation it will be on the high end and vice versa The different fault types can be divided into four groups Looking at all faults over a statistical significant time and area the different faults will have the fol lowing approximate percentage distribution 15 e Three Phase to Ground Faults 2 3 e Phase to Ground Faults 70 80 e Phase to Phase Faults 8 10 e Double Phase to Ground Faults 10 17 Short circuits can be classified by whether they are symmetrical or asymmetri cal In this chapter the different fault types will be examined The simple network in Figure 3 1 will be used to illustrate how symmetrical component networks can be used to calculate fault currents Background for symmetrical components can be found in Appendix A The network consists of two buses with respective loads and generation as well as a line between the buses for power transmission The fault situations below describe bolted faults and where Phase a is used as ref erence In this situation current can flow from both buses to the fault area in contrary to a radial system where the current flows in one direction 13 14 CHAPTER 3 SHORT CIRCUITS AND ABNORMAL CONDITIONS Zo B f B Ze Line Z U U P jQ P jQ Figure 3 1 Simple Two Bus Network with Fault on Line e Z Z Respective Generator Impedances e U U Respective Generator Voltages e P jQ P jQ Respec
18. of overcurrent relays are currents from CTs which continuously measure currents flowing in the system Normally in a three phase system there are three CTs per location one per phase This supplies the relay with information about current in each phase as well as the current flowing in the neutral ground The current in the neutral is normally measured by joining the three phase leads inside the physical relay itself as illustrated in Figure 4 2 In a perfectly symmetrical system the current in the neutral will be zero Kirchoff s law During an asymmetrical fault this current will be of significantly higher magnitude This principle is therefore used as a fault indicator in overcurrent relays Figure 4 2 Connection of Current Transformers for Overcurrent Relay Overcurrent relays operate with inverse definite time and instantaneous char acteristics The relays have a set pick up current J and when the current reaches and or surpasses this value a timer starts The relationship between the magnitude of the current and the time needed for tripping is inverse or definite When the timer reaches its corresponding point on the time current curve with out the current dropping the relay will trip The relay will trip instantaneously if the current reaches the instantaneous trip setting An example is shown in Figure 4 3 The inverse curves are usually divided into normal very or extreme inverse characteristics ANSI and IEC have
19. relays The card slots can be equipped with different modules Figure C 1 Card Slots ABB Relion 670 6U 1 2 19 The following card slots modules are relevant e X11 Power Supply Module Connection of 48 V DC supply e X31 X32 Binary Input Module BIM Input of Binary Signals Not used in the first step of the relay lab Should be included for more advanced relay testing X41 X42 Binary Output Module BOM Output of Binary Signals e X401 Transformer Input Module TRM Input of currents and voltages The power to the relays is provided through rectifiers as shown in Figures C 2 and C 3 The equipment is protected with a residual current circuit breaker RCCB one for each rack 81 In Figure C 4 C 7 similar connection diagrams of wiring between the BOM and test switch is displayed Two binary output signals have been forwarded through the test switch for each relay The two letter combination at the end of top text in each figure represents the respective model configuration for the test switch Figure C 8 C 11 contains connection diagrams of the wiring between the TRM and test switch Notice how different test switch configurations have been used and how it affects the wiring Power Supply RED670 aed PSM X11 4 X11 5 RED670 PSM X11 4 To Wall Socket X11 5 PE also connected to chassis of components Figure C 2 Connection Diagram Power Supply Rack 1 Power Supply Ra
20. remote back up protection for Relay C With communication simple boolean or IEC61850 compliant between the relays relay coordination can become easier and operating times can become faster As soon as the primary relay detects it failed to clear the fault for instance due to CB malfunction it can forward a trip signal to the remote back up protection The operating times will then decrease improving the overall protection system 2 4 POWER SYSTEM PROTECTION ATTRIBUTES 11 Speed Naturally we want to clear a fault in a power system as quickly as possible Relays rely on continuous monitoring of current and voltage waveforms A fault will cause the values and shape of these waveforms to change In the transient stage after a fault the waveforms will be significantly distorted The relay must be able to filter out the useful information and use it to make a reasoned decision as fast as possible If the relay decides to trip it should send a signal to the circuit breaker momentarily so that it can operate We can generally classify relays according to their operation speed as given below 31 e Instantaneous Instant operation as soon as a secure decision has been made by the relay e Time Delay Time delay is introduced after the relay decision and before trip signal is sent Introduced to increase reliability and or coordinate with other relays e High Speed Capable of operating in less than a set time Modern re
21. to every relevant signal e g start trip disturbance record start stop etc Finally the display is configured with a one line diagram of the surrounding power system normally a substation In addition to this there are several other small parts in the configuration that must be made correctly however the procedure describes the most important steps generally although somewhat simplified The step after the configuration is made which is a vital one is setting the parameters of the relay according to the surrounding power system protected device 8 4 CONFIGURATION OF ABB RELAYS 71 As mentioned the relays are also capable of displaying a one line diagram of the surrounding power system for instance a substation The configurations made for the relays include one line diagrams of their respective parts of a power plant substation The power plant substation consists of one generator REG670 one transformer RET670 and two transmission lines 2xRED670 connected by double busbars as shown in Figure 8 6 The purpose of the one line diagrams is to display how the relays would be used in real life Another benefit is that the one line diagram will display a simulated opening of the circuit breaker if the relay trips as it would in real life The display also shows the measured currents voltages and other relevant values The measurements have been configured in such a way that if the circuit breaker is open the currents and othe
22. 1 STL3 GRP1L3 TRM_40 CHECU GRPIN j W1_VT_UL3 ST2L30 TRM_40 CH9 U Figure 5 3 Signal and Function Blocks for Overcurrent Protection in ABB RET670 Relay 5 4 COMMUNICATION 39 The output signals of the protective function blocks are binary signals most importantly trip and start signals e g W1_TOC1 TRIP and W1_TOC1 START shown in Figure 5 3 These signals are forwarded to tripping logic schemes which typically contains AND OR and NOR blocks used to combine several signals to achieve the desired functions The signals are also connected to other function blocks controlling LEDs on the HMI Human Machine Interface and most importantly the binary output signals which is the communication between the relay and the circuit breaker This description is simplified as the logic of modern relays is quite complex however it explains the general principles 5 4 Communication The possibilities for communication is a major benefit of digital relays Com munication allows relays to cooperate in real time e g communication between distance relays at each end of a line will provide excellent reliability Continuous monitoring of entire protection systems with communication between relays and central data systems in the substation or at a remote location is beneficiary for the system operator It also allows the system operator to make changes to relay parameter settings all from remote locations if desirable Communication i
23. 14 244 2 If Zi Z Z then the relay will see the a current of the same magnitude during a Three Phase to Ground Fault as during a Phase to Ground Fault 3 7 18 CHAPTER 3 SHORT CIRCUITS AND ABNORMAL CONDITIONS 3 3 Phase to Phase Faults Figure 3 7 Reduced Sequence Networks Interconnection for Phase to Phase Fault No Zero Sequence Network Component When two phases in a three phase system comes in contact with each other it is called a phase to phase fault This is an asymmetrical fault Consider a case where Phase a and b are the faulted phases Then the currents in the phases 3 4 DOUBLE PHASE TO GROUND FAULTS 19 would be of equal amplitude with reverse polarity and the current in Phase c will be zero I I I Ip IL 0 Assuming the respective positive and negative sequence impedances are equal Equation A 1 yields the following expression for the magnitude of the fault cur rent _ v3U v3U 22 27 This shows va the magnitude of the fault current during a bolted phase to phase fault is 2 0 866 to the one of a bolted three phase fault 3 9 In the same way as before the relay will only see the current contribution from bus B which in this case is J and Jj 3 4 Double Phase to Ground Faults B B Figure 3 8 Double Phase to Ground Fault Double Phase to Ground faults occur when two phases come in contact with each other and ground at the same time It occurs
24. 51 Naturally a construction like this is expensive nor built overnight The best solution is to cooperate with other parties who would have interest in using such a scaled network for testing on other similar fields At NTNU such a scaled network exists in the form of a renewable energy smart grid wind power lab SG Lab The lab is quite comprehensive and includes several types of generator models a distribution network model lines transformers loads energy storage capabilities and a short circuit emulator as shown in Figure 6 8 qesey Renewable energy lab Smartgrid Lab Windpower lab __NTNU siNTEF Ny Lab supply grid 400V AC 225A 225A PM generator 50kVA gee 771 pa Cii induction general GA A siorago Z GA GA St N Synchronous generator 17kVA 2013 04 03 wd Figure 6 8 One Line Diagram of SG Lab at NTNU The lab provides several opportunities for relay testing the short circuit emu lator is especially of importance It allows the emulation of different fault scenar ios i e phase to ground and three phase faults with corresponding fault currents flowing in the network However traditional CTs and VTs does not exist in the lab today Transducers outputting current values scaled as a mV A signal is in stalled The currents from these transducers are also sampled and used for other purposes than protective relaying today Traditional CTs and VTs could possibly be installed however the amou
25. Equation 6 1 and compared with data specified by the manufacturer e Logic Testing This testing is made without changing relay settings or monitor any relay output contacts The first step is to make sure all drawings match the settings of the relay by checking the documentation of the site and the appropriate relay settings Checking for logic impossibilities and other possible errors is important here The output logic of each contact should be listed with simple AND OR statements The main testing then consists of checking that the output is correct according to what is expected To make relay testing faster and more efficient it is common to combine test procedures and make a test plan As mentioned modern relay testers are in combination with its software powerful tools capable of automating test plans This makes testing of relays efficient as it is possible to make standardized plans tailored to relay models types where only minor adjustments have to be made for each test case T Software This chapter includes an overview and study of the different software that is relevant for the relay lab Software for relay testers have already been discussed in Chapter 6 1 That leaves a section regarding short circuit and relay coordination software as well as a section on the software used to communicate with and configure the relays 7 1 Short Circuit Calculation Software The fault currents in a power system will vary dependin
26. ION AND PARAMETER SETTING SOFTWARE 59 RET670_TOC Signal Matrix 4b BOM_4 bl a BLOCK W1 CB QA1TRIP W1_TOC1_TRIP W1_TOC1_START F_QA1_CLOSE W1 BFP TRIP W1 BFP TRIP W2 BFP TRIP F_QC9_ CLOSE QB9_OPEN Not used FNKEYMD1 1 FNKEYMD1 1 FKEYOUT1 FNKEYMD2 1 FNKEYMD2 4 FKEYOUT2 i i FNKEYMD3 1 ae a Si eS aes FNKEYMD3 1 FKEYOUT3 FNKEYMD5 1 FNKEYMD5 1 FKEYOUTS W1 CB SMBO 1 H i W1 CB SMBO 1 CBTRIP d x TRIP LOCKOUT TCS ALARM CB CLOSED CB SPRING UNC Not used Not used Not used Not used Not used W1 PROT SMBO 8 W1 PROT SMBO 8 Bot i ii i TOC TRIP l i x TOC START i l i x TOC START L1 TOC START L2 TOC START L3 IEF TRIP q REF TRIP REF START REF DIROK Figure 7 2 Screenshot Signal Matrix PCM600 2 6 The communication between the computer and the relay is also configured in PCM600 To achieve communication between the two devices the user has to connect an Ethernet cable between the front panel of the relay and the computers network card and input the IP address and the technical key of the relay into PCM600 The technical key is a unique ID for each relay The user can now read from write to the relay 8 Relay Lab After talking to relay engineers from utility companies Tr nderEnergi NTE R ros E verk Statkraft Statnett and from the ind
27. Inductor Based on Figure 3 7a 3 8 in 33 Since the output voltage at the secondary terminal normally is set to a fixed value e g 120 V the ratio N Ns in the transformer is proportional to the voltage level at the high voltage terminal Uyy When the voltage is higher than a certain value commonly around 115 kV 15 the cost of the additional turns makes a CCVT a more economical choice The capacitance C in Figure 2 5 is in reality constructed of a stack of capacitors connected in series i e Cy lt Co This means most of the high voltage Uyy will be distributed over C4 with the remaining lower proportion over C2 This allows the voltage over the primary side of the transformer to be relatively low The number of primary windings needed to achieve an output voltage low enough for the connected relays can 8 CHAPTER 2 POWER SYSTEM PROTECTION then be reduced substantially Assuming the CCVT is unloaded the voltage over Cy becomes Cl Ci C2 L in Figure 2 5 is a tuning inductor that is introduced to cancel out the impedance caused by the capacitors C and Ch i e setting the source impedance to zero The CCVT will then provide the relay with the actual voltage measured To achieve this the value of L is selected as follows 33 Uc Unv 2 4 1 L i gt m w2 C C2 Equation 2 5 assumes the secondary leakage inductance L is negligible Lm is the magnetizing inductance of the VT while L is the primary
28. NTNU Trondheim Norwegian University of Science and Technology Relay Lab at NINU Emil Anthonsen Dyrstad Master of Energy and Environmental Engineering Submission date June 2014 Supervisor Hans Kristian Hgidalen ELKRAFT Norwegian University of Science and Technology Department of Electric Power Engineering Problem Description Relay protection is essential for reliable operation of power supply Distributed generation increased complexity of power systems and new communication so lutions require increased focus on protection Protective relays and their settings are commonly tested in hardware Simulation results typically fault currents and voltages are through an amplifier applied to the actual relay and its re sponse is verified or settings adjusted Traditionally only sinusoidal steady state responses are used but transients may be of importance At NTNU there is a plan to expand and build competence in relay protection with a relay lab and a future specialization course The simple relay protection lab planned at NTNU should include a test bench with distance over current and differential relays and a relay tester for applying simulated waveforms to the relays A strategic co operation with Michigan Technological University Statnett SF and ABB is under establishment and ABB is gifting four Relion 670 relays for transformer generator and line protection The project will consist of e Study and document power system p
29. Open the project file Lab2 pcmp and select the corresponding RED670 configuration a e Study the parameters needed to set the distance protection Calculate the zone settings for a 2 zone distance protection Zone 1 should cover 85 of the line while Zone 2 should cover 125 Remember the time delay between the zones Write the calculated values to the relay using PCM600 Use the relay tester to apply currents and voltages as before Apply the calculated fault currents Note the trip time Use the event recorder playback to apply currents and voltages sim ulated in ATPDraw same pl4 files as before Note the trip time Compare trip times for both simulated and calculated values Explain any differences Compare trip times for overcurrent protection and distance protection Which one is faster Why is that 10 Conclusion A relay lab consisting of modern relays is an essential component to educate stu dents in the field of power system protection The relay lab should function as an arena to demonstrate protection principles and practical challenges Further developing of the lab to include communication especially IEC61850 compli ant communication is vital as this is important for the future of power system protection Utility companies in Norway have a conservative protection strategy which is not feasible in the long run with a trend shift from radial grids to more complex power systems Students should be educated w
30. Parameter Setting as shown in Figure 9 2 RET670 is used as 74 CHAPTER 9 LAB EXERCISE PROPOSALS an example in this case Make sure the communication between the computer and the relay is online it should be if not ask the scien tific student assistant s is Local Server Lab_1 F File Edit View Tools Window Help iD L ele 5 e obec Types 9 Emajegi RR Generic IEC61850IED 5 ae ciao a a T Substation Sub Transmission IEDs amp J E 22kV Transmission IEDs 2 g F Qo xa RET670_TOC EE Application Configuration Properties Figure 9 2 Screenshot Plant Structure PCM600 2 6 e Scroll down to Current Protection and Step 1 This is where you input the parameters for the overcurrent protection a To confirm that the logic and the digital outputs of the relay is func tioning and correctly configured simple logic testing should be per formed This means having the relay trip and checking that the correct digital output contact closes Configure the relay so that it will trip on a set of given input currents and voltages this is a challenge try before asking Use the Signal Matrix module in PCM600 to check where the trip signals are assigned in the Binary Output Module Write the configuration to the relay b Open the relay tester software and the manual control panel ref Chapter 6 1 1 Set the relay tester with current and voltag
31. Principle Figure 4 10 illustrates the basic principle of differential relay protection This relay has an input of two currents however it is possible for a differential relay to have additional inputs if protection of the zone equipment requires it The protection of a busbar with a differential relay is an example which may require more than two current inputs I is the current that flows through the zone during normal operation The relay s input is the secondary current from both sides i e the primary current times CT ratio minus the respective excitation current The CT ratios will be equal unless there is a transformer within the protected zone If that is the case the CT ratios will be set so that secondary currents will be equal Kirchoff s law yields that the relay will have zero contribution from the secondary currents The excitation currents however e1 e2 can not be considered to be equal at all times They are dependent on the burdens R and R which is proportional to the length of the cables between CTs and the relay If the respective length of the cables are significantly different the excitation currents may differ In 30 CHAPTER 4 PROTECTION PRINCIPLES addition the excitation currents is inversely proportional to the CT ratios as shown in Chapter 2 2 If they are different the excitation currents characteristics may also be different The operating current Jop which the relay sees will then be the diffe
32. ance Protection 1x ABB RET670V2 0 Transformer Differential Protection 1x ABB REG670V2 0 Generator Protection e Racks e Power Supply with Accessories Input 100 240 VAC Output 48 V DC e Relay Tester e Test Switches e Test Handles e Lab Computer ABB has decided to supported the relay lab and gift new modern relays from their Relion 670 series The relays are IEC61850 compliant in other words they are ready for the proposed expansions However for the first part of the lab they can be used as simple stand alone devices The RED670 relays is also equipped with a GPS unit which can be used for time synchronization The relays from ABB comes with one Transformer Input Module TRM ca pable of handling up to 12 current and voltage inputs in this case six current and six voltage inputs 6I 6U The current and voltage inputs are rated at 1 A and 110 220 V respectively They are all capable of receiving 16 binary signals via the Binary Input Module BIM and output 24 binary signals through the Binary Output Module BOM To make the lab mobile two racks on wheels is used This is useful as the lab can be used to demonstrate relay functionality for instance during a lecture The relays are mounted together with their respective test switch to the racks two relays on each rack An illustration is shown in Figure 8 1 Connection diagrams of the wiring between the relays and the test switches is located in Appendix C Figur
33. ansformer itself during energizing of a nearby trans former or during other faults in the network which causes a momentary voltage dip Initially the magnetizing current may be up to 8 30 times higher than full load current The current decays to normal exciting current after some time typically the time constant can be everything from 10 cycles to 1 minute de pending on several factors most notably the resistance and stray losses in the transformer This phenomena is important to be aware about when applying differential protection to a transformer is at can cause unbalance to the currents measured by the CTs and falsely indicating an internal fault and leading to un necessary tripping The differential relay should therefore be able to detect the phenomena when it happens and block the relay for the required period 15 Overexcitation Overexcitation is caused by overvoltage and or underfrequency and it may lead to saturation of the transformer and subsequent heat buildup and internal dam age Larger transformers usually have separate protection for overexcitation as differential protection is not practical to use explicitly for this However overexcitation is a concern for differential protection as it can lead to tripping on overexcitation far below dangerous values The relay should in this case be blocked from operating currents caused by overexcitation 15 Different CT Characteristics due to Different Voltage Levels A transfor
34. around 1 ps For the measurement of a 50 Hz AC phasor where a 360 rotation equals 20 103us the maximum angle error becomes 16 360 20 10 ys The GPS signals are provided by satellites orbiting the earth and they are transferred to the IEDs via an external GPS receiver system The antenna of the GPS system needs to be located where it has a clear path to the sky Lus 0 018 0 005 B 1 Phasor Measurement Unit PMU A Phasor Measurement Unit is a device used under WAMS which is capable of measuring phases of currents and voltages in a power system The unit is supplied with analogue data containing current voltage values for the three phases from CTs and VTs The analogue data is then filtered by an anti aliasing filter and the data is converted into digital samples by an analogue digital converter At the same time the data is time stamped with the GPS synchronized clock of the PMU The three phase phasors are then transformed into positive sequence components The time stamped positive sequence components are then stored with a fixed interval typically every 40 or 100 ms and sent to other WAMS devices Modern digital relays with micro processors are theoretically capable of functioning as a PMU in addition to its protective functions The relays must then have firmware software that supports it 16 80 C Appendix Connection Diagrams Figure C 1 shows the numbering and placement of card slots for the Relion 670
35. ars transformers and generators however some extra considerations must be made for these components 32 CHAPTER 4 PROTECTION PRINCIPLES 4 5 1 Generator Differential Protection A generator is normally protected with several types of protective relay functions in addition to differential protection e g volts per Hertz overexcitation ther mal overload and overvoltage protection The number and types of protection will vary with the size type location and significance of the generator However differential protection is almost always a part of the protection system for gener ators as it provides fast and sensitive protection for internal generator faults It is not always used on generators under 1 MVA 15 Differential protection needs two sets of current transformers one at the gen erator terminals and one in the neutral leads It is common that they have the same ratio and preferably be of the same model to reduce potential mismatch errors for external faults Since a generator can be wye or delta connected it is important that this is taken into consideration when setting the relay The percentage characteristics or gradients m mz2 are usually set to a relatively low value typically to 10 25 to increase sensitivity 4 5 2 Transformer Differential Protection For the protection of transformers over 10 MVA differential protection is widely used This is due to the same reasons as to why they are used for generato
36. asors ref Equation A 2 In this case the relay at bus B will not see the entire fault current it will see the current contribution flowing from bus B fanaa 3 2 a 3 2 16 CHAPTER 3 SHORT CIRCUITS AND ABNORMAL CONDITIONS 3 2 Phase to Ground Faults Figure 3 5 Reduced Sequence Networks Interconnection for Phase to Ground Fault Single Phase to Ground faults are the most common fault types in common three phase networks They may be caused by direct or indirect lightning strokes leading to transient overvoltages Falling trees or other objects may also lead 3 2 PHASE TO GROUND FAULTS 17 to a short circuit between phase and ground 15 In a situation where Phase a experiences a bolted fault to ground as illustrated in Figure 3 4 the current in Phase b and c becomes zero while Phase a will carry the entire fault current I Ip I 0 3 3 I 0 Inserting this into Equation A 1 leads to the following relationship a U U Ia la Ha 3 4 ON 3 LEE EEL LY Z Z G The currents can be divided up in to the two parts as earlier Ia I I Ia T L I e 3 5 Iaz Tie Tv Ia Ia Ko za Ko The fault current may then be expressed as follows aU 3U7 l i lahs B l i 3 6 TT Ty S E This can be represented by connecting all of the sequence networks in series as shown in Figure 3 5 Again the relay will only see the current from bus B 3U 24
37. b Notice Some of the content was included in the authors specialization project report with the same title in the 2013 fall semester This was deliberate as it functions as pre project for the Master s thesis The content has been edited where deemed necessary June 2014 Trondheim Norway Fud AD Emil Anthonsen Dyrstad II Abstract This thesis presents background on power system protection relay principles modern relay technology and relay testing to support the design practical set up and proposals for use of a new relay lab at NTNU The paper includes a theoretical part describing the components of power sys tem protection their function and attributes To better the understanding of the importance of power system protection a short study of the different types of faults that may occur in a power system and how they can be calculated has been made One chapter covering the principles of protective relaying functions relevant for the lab is included It covers the theory of overcurrent including directional distance and differential protection as well as challenges one may encounter when applying these protective functions A chapter on modern relay technology describing the possibilities and benefits of micro processor based relays especially with regards to communication is a part of the report This chapter also includes sections describing the inputs and outputs logic and function of modern relays The e
38. cation can be simple with transferring of one or more boolean variables i e trip signals and breaker positions This type of communication can be made over radio wave copper wire or fiber optic cables For more advanced communication with transmission of for instance time stamped current and voltage values fiber optic communication according to the IEC61850 standard ref Chapter 5 4 5 5 is used Binary Line Communication i For Sending Receiving Remote Trip Signals i Fiber Copper Radio Wave Interface Figure 4 9 Protection of Line with Distance Relay at Both Ends of the Line 4 5 DIFFERENTIAL RELAY 29 4 5 Differential Relay Differential relay protection is considered to be one of the most versatile protection techniques available today 15 A differential relay compare two or more currents flowing into and out of the protected zone equipment The basic principle relies on the fact that under normal conditions the current s entering the zone should be equal to the current s leaving it If this condition is not satisfied it is an in dication that there is a fault within the zone This makes differential relays ideal for the protection of generators transformers busbars and transmission lines 15 l IpsNoi Nou lei l2 l Np2 Ns2 leo lhe le Npa Nsi leer i lz Np2 Ns2 lee Ires Maya x 14 13 2 Ikesr Mayo X lae be 2 Figure 4 10 Differential Relay
39. cess bus however the main principles remains the same 18 26 5 6 THE FUTURE OF RELAY TECHNOLOGY AND POWER SYSTEM PROTECTION Al GOOSE Generic Object Oriented Substation Events is a high speed peer to peer communication model used to transmit status information e g trip signals and breaker positions GOOSE is a part of the IEC61850 standard and it allows this vital information to be prioritized and transferred with minimum delay 34 5 6 The Future of Relay Technology and Power System Protection IEC61850 is designed with future sub station communication designs in mind There will be a shift from separate devices for each protection metering and con trol function into more integrated solutions where all functions have access to the same real time information As computer technology develops we will likely see scenarios where have a main processor system with dedicated computer power for each function However the increasing integration and complexity of system will also lead increased vulnerability It is therefore important to have redundancy in the system maybe also back up of the most vital functions at a different loca tion In the future we will also see more electronic transducers which can feed digital data directly to merging units process bus This is a major development from conventional transducers as the distance from the relay to the transducers becomes irrelevant Today many relays are hard wired to transducers
40. ck 2 RET670 PSM X11 4 X11 5 REG670 PSM X11 4 To Wall Socket X11 5 PE also connected to chassis of components Figure C 3 Connection Diagram Power Supply Rack 2 BOM RED670 AK 2A 28 X41 1 3A BO1 k 8 x3 BO2 B X41 4 BO3 BO4 B X41 7 BOS BO6 B X41 10 BO7 BOS B X41 13 BO9 BO10 B X41 16 BO11 BO12 B X42 1 BO13 BO14 B X42 4 BO15 BO16 B X42 7 BO17 BO18 B X42 10 BO19 BO20 B X42 13 BO21 BO22 B X42 16 BO23 BO24 Figure C 4 Connection Diagram RED670 1 Current and Voltage Leads between BOM and Test Switch BOM RED670 BC 2A 28 X41 1 B X42 1 9A BO1 BO13 poe 1 x43 BO2 BO14 B X41 4 B X42 4 BO3 B015 BO4 BO16 B X41 7 B X42 7 BOS BO17 BO6 BO18 B X41 10 B X42 10 BO7 BO19 BO8 BO20 B X41 13 B X42 13 BO9 BO21 BO10 BO22 B X41 16 B X42 16 BO11 BO23 BO12 BO24 Figure C 5 Connection Diagram RED670 2 Current and Voltage Leads between BOM and Test Switch t 8B X41 1 BOM REG6 70 AH BO1 O t 10B X41 3 BO2 B X41 4 BO3 BO4 B X41 7 BOS BO6 B X41 10 BO7 BO8 B X41 13 BO9 BO10 B X41 16 BO11 BO12 BOM and Test Switch B X42 1 BO13 BO14 B X42 4 BO15 BO16 B X42 7 BO17 BO18 B X42 10 BO19 BO20 B X42 13 BO21 BO22 B X42 16 BO23 BO24 Figure C 6 Connection Diagram RET670 Current and Voltag
41. course is a golden opportunity to educate students with knowledge of and a drive for the opportunities that lay within modern relaying technologies However most of the old protection principles strategies are valid and still being practiced by the utilities The students should therefore also have a fundamental knowledge of traditional power system protection to be aware of the limitations and challenges of adapting to modern protection schemes Students graduating from NTNU with this competence can be a valuable contribution to utility companies as it may lead to broaden their view of power system protection and the possibilities of modern relay technology It is therefore vital that the relay lab is designed and used in such a way that students gain the knowledge of past and future strategies and their advantages and limitations 60 8 1 RELAY LAB AT MICHIGAN TECHNOLOGICAL UNIVERSITY 61 8 1 Relay Lab at Michigan Technological University When designing a university relay lab it might be a good idea to contact other uni versities which has such lab facilities Michigan Technological University MTU and NTNU cooperate in several areas and MTU is in possession of a well devel oped relay lab primarily used for a power system protection lab course The lab at MTU consists of six parallel work benches each equipped with a relay tester from Doble where students work in pairs i e 12 students can work in the lab simultaneously The lab
42. d by several utility companies in Norway as it provides fool proof testing capabilities On the front of the test handle you can access both the A and B side connections of the test switch via banana plug slots This is where you connect the outputs and inputs of your relay tester The banana plug option makes this solution ideal for lab purposes since it makes for easy wiring between the relay tester and the relay In addition it displays how relay testing is performed in real life 8 4 Configuration of ABB Relays Modern relays are usually delivered with a configuration and functions corre sponding to the needs of the end user Pre made configurations for relatively simple lab exercises at a university are not supplied by ABB since most configurations are delivered with many more functions than needed for this purpose To avoid confusion for students when they are in the lab testing basic protection principles e g overcurrent protection it is a good idea to have the configurations as simple as possible in each case In other words this means stripping the relay configuration down to a level where there is only the desired functions left This has been a very time consuming task as one needs to be very careful when removing a signal or a function block in the configuration One wrong step can make the relay performance unreliable In many cases the signals have to be reassigned to other function blocks in correct order The relay con
43. d have knowledge of the lab exercise topic before entering the lab A pre lab part is a good way for the students to refresh their knowledge and come prepared to the lab It is vital that the scientific assistant and the student assistants are familiar with the software and the different components most notably the relay and the relay tester Before the lab session starts the relay should be connected to the lab computer through an Ethernet connection and it should be verified that it is working correctly This will allow students to get the most out of their session without spending too much time on practicalities outside the focus of the exercise 9 1 Introduction to Relay Function and Overcurrent Protection The purpose of this exercise is to get an introduction to the non directional overcurrent protection function of a modern relay It includes parameter setting of relay based on fault current calculations for a radial system The relay with the set parameters will be tested using a relay tester The results of the tests will be analyzed to see whether the relay performed as required Pre lab Work PC Value Unit Min Max DirModel Non directional Characterist 1 I gt IB 5 2500 t1 s 0 000 60 000 IMin1 IB 1 10000 1 Mult 1 0 10 0 Table 9 1 Parameter Settings for Overcurrent Protection Relevant QQ 9 1 INTRODUCTION TO RELAY FUNCTION AND OVERCURRENT PROTECTION is Ug 22
44. e overstr m distanse og differensial er beskrevet i rapporten Utfordringer med bruken av disse er ogsa diskutert I tillegg er moderne mikroprosessor baserte rel vern og deres virkemate forklart Fordeler med denne teknologien spesielt med tanke pa kommunikasjon har blitt diskutert Forskjellige metoder for rel verntesting er diskutert Det inkluderer testing i skalerte kraftsystem testing ved bruk av rel tester og bruk av feilsimulator Pro gramvare relevant for laben og lab vinger er ogsa beskrevet Den praktiske delen av oppgaven det vil si design og montering av rel vern laben er en viktig del av rapporten Dette kapittelet inneholder diskusjon rundt laben beskrivelse av komponenter forslag til fremtidige utvidelser og konfig urering av rel vernene Slutten av rapporten inneholder forslag til labovinger samt forslag til videre arbeid IV Contents Introduction Power System Protection 2 1 Power System Protection Components 2 2 Current Transformers 4 2 0 9 eA goes be ee bane be A ee ES 2 3 Voltage Transformers 2 s 0 2 ce sok BR ee he ek Ae 5 1 Transducer Input and A D Sampling 5 2 Digital Inputs and Outputs ecto oo be te Ge bee ak ee 5 37 Logic and Function ie slats ieai a hia ale Be ae ete ate ae A 5 4 Communication oo a a 5 5 IEC61850 Standard for Design of Substation Automation 5 6 The Future of Relay Technology and Power System Protection
45. e 8 2 displays the backside of the relays and the test switch in the rack 8 3 PRACTICAL SET UP OF LAB 65 Figure 8 2 Backside of Relay and Test Switch The terminals on the right side of the relay is the TRM i e current and voltage inputs The green long terminal blocks are the BOM right and the BIM left The Power Supply Module PSM is in the top left corner with the black and red wire connected to a green terminal block 66 CHAPTER 8 RELAY LAB The relays require a 48 V DC supply and AC DC converters is therefore needed This voltage level is selected mainly for personnel safety reasons 2 The relays have one converter each which are connected to the AC power supply through power strips Between the power strips and their plug a residual current circuit breaker has been installed which also is for personnel safety reasons The power supply can be seen in Figure 8 3 schematics over it is shown in Appendix C Figure 8 3 Relay Power Supply For safety purposes the chassis of the relays are grounded can be seen in Fig ure C 1 The grounding wires from the relays are fastened to terminal blocks in its respective rack The protective earth PE lead is wired to the terminal blocks and provides the grounding potential 8 3 PRACTICAL SET UP OF LAB 67 As discussed in Chapter 6 using a relay tester is the best testing tool for the first step of the relay lab The relay tester NTNU currently owns an Omic
46. e Leads between BOM RET670 AM B 8A 38 X41 1 9A BO1 ae 1 x3 BO2 B X41 4 BO3 BO4 B X41 7 BOS BO6 B X41 10 BO7 BOS B X41 13 BO9 BO10 B X41116 BO11 BO12 B B B B B X42 1 X42 4 X42 7 X42 10 X42 13 X42 16 BO13 BO14 BO15 BO16 BO17 BO18 BO19 BO20 BO21 BO22 BO23 BO24 Figure C 7 Connection Diagram REG670 Current and Voltage Leads between BOM and Test Switch TRM RED670 61 6U AK CH1 I CH2 I CH3 I B X401 7 e B X401 8 CH4 I B X401 9 e B X401 10 CH5 I B X401 11 e B X401 12 CH6 I 7A 7B X401 13 J SA 8B X401 14 CH7 U 21A 21B X401 15 22A 22B X401 16 CH8 U j 23A 23B X401 17 24A 24B X401 18 CH9 U B X401 19 B X401 20 CH10 U B X401 21 B X401 22 CH11 U Article No Comment B X401 24 CH12 U Figure C 8 Connection Diagram RED670 Current and Voltage Leads between TRM and Test Switch 5 i 13A 13B X401 1 14A 14B X401 2 CH1 15A 15B X401 3 16A e 16B X401 4 CH2 1 17A 17B X401 5 18A 18B X401 6 CH3 I 19B X401 7 J 20B X401 8 CH4 1 21B X401 9 e 22B X401 10 CH5 1 23B X401 11 e 24B X401 12 CH6 I 3A 3B X401 13 4A s 4B X401 14 CH7 U 7A 7B X401 15 8A 8B X401 16 CH8 U 21A 21B X401 17 22A 22B X401 18 CH9 U B X401 19 B X401 20 CH10 U B X401 21 B X401 22 CH11 U B X401 23 i B X401 24 CH12 U
47. e of a modern relay with hard wired conven tional transducers The number of current and voltage inputs can be specified according to the buyers needs as most modern relays have interchangeable in put output modules This is as long as practical restrictions of the relay models are followed All currents must be converted to voltage signals which are suit able for digital sampling usually done by shunt resistors The digital sampling is done by the Analog to Digital Converter A D whose inputs are in parallel with the shunt resistors The A D normally has a peak voltage restriction of 10 V Voltage inputs from VTs CCVTs must therefore be scaled according to this input range It is worth mentioning that if electronic transducers are used the internal architecture will be different The data is then sampled in the transducers and can then be directly input to the microprocessor 8 Figure 5 2 illustrates a continuous sinusoidal signal being sampled to discrete values 5 2 DIGITAL INPUTS AND OUTPUTS 37 A D Figure 5 2 Sampling of Analog Signal to Digital Values by an Analog to Digital Converter A D Before reaching the A D the currents and voltages pass through surge filters whose role is to block potentially harmful transients These transients can be signals in the order of mega Hertz created by arcing or switching off compo nents The cut off frequency of a surge filters are therefore in the range of several hundred kilo He
48. ectivity see below If the relay and or its corresponding circuit breaker s fail to clear the fault for some reason the back up relay should clear the fault In other words the relays need to be coordinated both upstream and downstream to ensure that they operate in the correct order Relay coordination is normally made by introducing time delays to the relay op eration The time delay will vary depending on the ambient power system but it should be as small as possible while still giving the primary protection enough time to operate i e initiation of trip signal from relay and circuit breaker s opening A security margin for relay CT accuracy is also added Typically the added time delay is in the order of 300 500 ms 21 28 Line 3 Relay B Relay A Figure 2 8 Example Relay Coordination for Adjacent Lines Fault at Line 3 Figure 2 8 illustrates three adjacent lines with their respective protection sys tem If a fault occurs at Line 3 the primary protection is Relay C i e it should operate first without any intentional time delay Relay B should have an added time delay so that it will function as remote back up protection if the primary protection fails At the same time Relay A should be coordinated with both relays typically the intentional time delay will here be double the one for Relay B This is due to the fact that Relay A should function as remote back up for Re lay B meaning it indirectly has the role as
49. eloped by DIgSILENT Germany 9 e Common users include Statkraft PSS E Power System Simulator for Engineering e Developed by Siemens AG Germany 7 e Common users include Statnett ASPEN OneLiner e Developed by Advanced Systems for Power Engineering Inc 6 e Used by Michigan Technological University for Relay Lab Exercises ETAP Electrical Transient Analyzer Program e Developed by Operation Technology Inc USA e Popular among utility companies in North America Ontario Power Gen eration Hydro Quebec 24 ATPDraw e Graphical preprocessor to ATP 13 e Developed by Hans Kristian H idalen at NTNU For some of the programs it has only been possible to obtain trial versions with various limitations however they gave a fair overview of their functionality and user interface The table below summarizes how well the different software meet the set requirements 56 CHAPTER 7 SOFTWARE PowerFactory PSS E ETAP Aspen ATPDraw OneLiner Easy to Use SC Calc Relay Models Licence Cost Relevancy Table 7 1 Summary of Short Circuit Calculation Software Green Good Yel low Fair Red Poor For the purpose of software use for lab exercises PowerFactory PSSQE and ETAP are considered too complex It takes a significant amount of time more than what should be required for lab exercises to reach a sufficient level of profi ciency in these programs However when the user is
50. ely or to a common point If the relay is the last in a chain of relays using the same currents the short circuiting is made to a common point Else it is made separately to allow the currents to flow to the relay s downstream in the chain The third type of switch shown in Figure 8 5c is used to open the voltage circuits It is normally closed b Short Circuiting of Cur c Opening of Voltage Cir Blocking of Trip Circuit i a Bloceng of dup Oren rent Circuit ou Figure 8 5 Contact Functions ABB RTXP 24 Test Switch Handle 8 4 CONFIGURATION OF ABB RELAYS 69 The test handle is used to operate the switches It operates the different types of switches depending on the test handle position It can be in three positions out half in Out is the normal position the test handle is then not attached to the test switch If you insert the test handle into the test switch it will first stop at one position this is the half position Pushing a lever and fully inserting the test handle yields the in position At half position the trip circuit blocking switching will occur while fully in serting the test handle to the in position will result in switching of the two other types of switches The reason behind this logic i e to block trip signals first is to prevent any mis operation as the relay may trip due to the short circuiting of the current and opening of the voltage circuits 4 The test switch test handle solution is use
51. er System Protection Chap man amp Hall First edition 1993 34 Zengli Yang Dongyuan Shi and Xianzhong Duan Study on flexible power system protection relay coordination software based on user defined princi ple In Universities Power Engineering Conference 2007 UPEC 2007 42nd International pages 277 282 Sept 2007 35 esi Gerhard Ziegler Numerical Distance Protection Publicis Corporate Pub lishing Second edition 2006
52. es nec essary for the relay to trip c Connect the relay tester to the relay according to Figure 6 2 and the connection diagrams in Appendix C Apply to set currents and volt ages to the relay If things are set correctly the relay should trip Check which binary outputs forwards the trip signal 9 2 DISTANCE PROTECTION 75 2 Calculated values a Input the values from Table 9 1 into the corresponding relay in PCM600 b Select IEC Definite Time Characteristics Write configuration to relay Use the relay tester to apply the calculated currents and voltages Note the trip time c Select IEC Inverse Time Characteristics the exact parameters of the curve is not vital but remember them Write configuration to relay Use the relay tester to apply the calculated currents and voltages Note the trip time 3 ATPDraw a Use the Event Recorder Playback function of the relay tester to apply the currents and voltages simulated with ATP Draw both fault types Use the same relay settings as IEC Def Time and IEC Inv Time Compare trip times for both simulated and calculated values Explain any differences 9 2 Distance Protection The purpose of this lab task is to get an introduction to distance protection Calculation of zone settings and comparison of trip times between overcurrent and distance protection is vital 1 Consider the same network and fault scenarios as used in the previous lab exercise see Figure 9 1
53. familiar with the programs and their capabilities they are very useful tools Aspen OneLiner is used by MTU in their relay lab exercises It is fairly easy to get to know for first time users and has a good module for coordination of overcurrent protection The drawbacks of the program is that is not common in Norway and that the licensing fee is high The program also has a relay database available for an extra significant fee ATPDraw is an EMTP with a graphical user interface The benefits of ATP Draw is that it is free and being developed at NTNU it includes relay models and that it is fairly easy for students to get to know Most students will also have encountered the program in a previous course The closeness to the program de velopers is a major benefit both for the users of the relay lab and the developers of the program The relay lab can among other things be used to verify the relay models in the program ATPDraw is a good choice for using together with the relay lab 7 2 RELAY CONFIGURATION AND PARAMETER SETTING SOFTWARE 57 7 2 Relay Configuration and Parameter Setting Software This section describes the use and functionality of ABBs software for configuring and setting ABB relays officially named PCM600 2 6 ABB Protection and Control IED Manager Although it is specific for ABB and their relays the principles are similar for software from other relay manufacturers ABB PCM600 2 6 ABB Protection and Contro
54. figurations have been made in ABBs software PCM600 Three projects pemp files have been created containing configuration files for the relays relevant for the lab 70 CHAPTER 8 RELAY LAB Lab 1 Overcurrent Protection RET670_ TOC REG670 TOC Lab 2 Distance Protection RED670_TOC_IMP x2 Lab 3 Differential Protection RET670_ TOC DIFF REG670 TOC DIFF The main parts of the relay configurations are created in the following procedural way see also Chapter 5 3 Currents and voltages from hard wired CT s and VT s are assigned to the physical hardware channels of the relay i e phase current Iz from CT1 is connected to hardware channel 1 It is important that the type of input i e current or voltage match the assigned hardware channel Binary inputs if relevant are also assigned a hardware channel The hardware channels are then connected to function blocks SMAI Blocks which outputs signals with the sampled currents and voltages These sig nals are forwarded to several function blocks most notably the protection measuring disturbance recording function blocks The output signals of the protection function blocks of significant impor tance are two binary signals start signals and trip signals The trip signals are then assigned a binary output channel They may pass through other logic elements merging comparing several trip signals beforehand Next step is to assign front panel LEDs
55. g on the location of the fault and the characteristics of the power system itself For small simple and radial power system the calculations may be performed by hand However when the system is larger and more complex hand calculations are close to impossible Here calculations are made by computer software In most software programs you build a model of the power system input known data measured or provided by manufacturers simulate different fault scenarios and the software outputs the fault currents Some programs also include models of relays and a database of different relay types from different manufacturers where one can simulate re lay operations For the purpose of the teaching part of the lab i e for the lab exercises this is an important feature For the lab exercises software that meet the following requirements e Simple intuitive and user friendly e Short circuit calculation and protection coordination capabilities e Relay models database e Reasonable licensing costs NTNU already have licenses for some programs e Relevance of software use in Norway previously used in university courses On the market today there exist several different software 10 with varying degree of complexity and features that cover the set requirements A study of selected programs and how good they meet requirements have been made The selected programs include 54 7 1 SHORT CIRCUIT CALCULATION SOFTWARE 55 PowerFactory e Dev
56. gh surge and anti aliasing filters 38 CHAPTER 5 MODERN RELAY TECHNOLOGY Digital outputs are similar to the digital inputs and their purpose is mainly to send trip signals to circuit breakers if the relay detects a fault The number of digital inputs and outputs will vary with models and specific needs from the buyer 5 3 Logic and Function Modern relays are logic devices constantly processing input values to check whether they represent a normal or faulted system The input values are pro cessed in different function blocks with a fixed time interval giving the sampling rate of the values The most notable function blocks represent the protective functions e g overcurrent as shown in Figure 5 3 as OC4PTOC and distance protection The protective function blocks contains advanced algorithms designed to operate with highest possible speed and reliability and this is a well kept secret of the relay manufacturers as this is what separates them from each other TIME OVERCURRENT PROTECTION WINDING 1 SIDE Curent inputs E W1_CT_IL1 m O W1_TOC1 TRIP TRM_40 CHI T wa_cT1L2 GI2Ale TRM_40 2 E GRP12L3 SA W1_CT_IL3 TRL 3E Analog Signals TR2L2 Binary Digital Signals TRM_40 CH3 T TR2L39 a Blocks Voltage Inputs REALZERO TR4L30 START re W1_TOC1 START ST3e 7 ST4e TRM_40 CH Ea STL1 gt W1_TOC1 STL1 W1_VT_UL2 RPL STL2e gt W1_T0C1 STL2 GRP1L2 STL3 gt _ W1_T0C
57. ings accordingly Then the relay should be re tested to ensure the new settings are correct There are three different methods to test relays however only two of them are feasible in this context testing with relay tester with full scale physical network not feasible or with a scaled physical network 6 1 Testing Relay Tester A relay tester is a device that is able to induce secondary currents and voltages at one location of a power system It is able to induce and output currents and voltages as if they were provided by transducers connected to a real three phase system Commonly testers have three voltage and three current outputs Some high end models may have additional current outputs e g for the testing of differential relays The tester also has binary outputs e g to simulate breaker positions and inputs e g to receive trip signals from relay Some relay testers also have the capability of producing the current and voltage output as sampled digital values instead of live currents and voltages The sampled values are then fed directly to a compatible relay according to the IEC61850 standard mentioned in Chapter 5 5 An illustration of a front panel with inputs and outputs of relay tester from Omicron is shown in Figure 6 1 Figure 6 1 Front Panel of Omicron CMC 356 Relay Tester 23 The relay tester is normally connected to a computer that runs the software to control and use the relay tester Earlier versions had
58. ioned may have multiple tap settings but their intention is not to be remotely controlled e g to accommo date tap changing transformers By setting the CT ratio according to the center of the voltage range the error is minimized to half of the overall voltage range For a transformer with a tap changing voltage range of 10 the maximum error caused by the tap changer is 10 Selecting the percentage characteristics for the differential protection accordingly to prevent mis operation is therefore vital when dealing with tap changing transformers 15 4 5 3 Busbar Differential Protection The main challenge when applying differential protection of busbars is achiev ing sufficient selectivity to avoid mis operation during close in faults i e faults in close proximity of the bus but outside the bus protection zone CT satura tion may occur during close in faults and the busbar differential protection must therefore be accordingly delayed to coordinate with the relay providing the pri mary protection function for the adjacent faulted line In some cases distributed devices for each line connected to the bus which transmits measured values to a central unit The differential function is then performed in the central unit which compares the values from all lines continuously There exist other types of busbar differential protection which are commonly used e g low impedance and high impedance differential protection however they will not
59. itation current Ie is of significant value In other words Ie represents the degree of error in a CT Designing a CT so that becomes insignificant for expected fault conditions is therefore important Ie is non zero as long as the CT is energized and is dependent on the magnetiz ing impedance here represented by the magnetizing inductance Lm and the loss resistance R The magnetizing impedance varies with the flux in the core which is needed to provide exciting magnetizing force Uef Uep is the force that pushes 6 CHAPTER 2 POWER SYSTEM PROTECTION I through the secondary circuit The core flux has a non linear characteristic meaning that the excitation current Ie also will have a non linear characteristic In addition Ie is inversely proportional to the CT ratio This can be seen from Equation 2 2 J a function of the current from the primary side I x and Uer is the driving force for J And as shown above J is indirectly dependent on Uef This also indicates that Ie is dependent of the burden Z A CT may also have several different tap settings commonly referred to as a multi ratio CT MRCT which allows the end user to select whichever tap is most beneficial for each case i e which tap setting will give the smallest error Typically the ratio Np Ns for the different taps can be 600 5 500 5 400 5 and 450 5 15 Figure 2 4 below illustrates the excitation curve for a MRCT i e the relationship between the
60. ith knowledge of the pos sibilities within modern relay technology After graduation they can contribute to a shift in protection strategies within utility companies to meet the demands for power system protection in the future Using a relay tester as a testing tool for the relay lab is a good versatile and flexible solution It is easy to use for the beginner while having advanced fea tures for the more advanced user A new relay tester should be acquired as the Omicron CMC 56 NTNU currently owns is quite old and is not supported by the newest software It is also limited by the fact that it has only three current and three voltage outputs The relays have been mounted in the mobile racks and wired to the test switches and power supply as discussed in 8 3 and according to the connection diagrams in Appendix C The lab stands in a fully operational condition however getting to know the equipment and software will take some effort for someone new to the lab The relay configurations as described in Chapter 8 4 have been written to the relays and successfully tested The relays are currently configured with Lab 1 RET670 REG670 and Lab 2 RED670 configurations ref Chapter 8 4 If utilized properly the relay lab can contribute to increased interest and knowl edge of power system protection among students at NTNU for many years to come Educating future engineers with this knowledge is important for the protection and reliability of futu
61. kV 1 2 Z 0 3 j1 Q km Zoa 50 j1Q 10 km Z 0 3 j10 lt gt 20 km Figure 9 1 Network Lab Exercise 1 A fault occurs on the system in Figure 9 1 Calculate the fault currents analytically ref Chapter 3 during a a Phase to Ground Fault b Three Phase Fault c The current magnitudes are equal why Is this realistic Hint Chap ter 3 2 2 What happens to the fault currents if the fault occurs at the very end of the line 3 To protect the line an overcurrent relay is placed at bus 1 The relevant parameters for the relay is shown in Table 9 1 a The relay can have an inverse or definite time current curve What is the difference between the two Sketch a graph illustrating the difference b Use the calculated values to fill Table 9 1 IB 1200 A 4 Use ATPDraw to model the network in Figure 9 1 a Simulate Phase to Ground Fault and Three Phase Fault Pre fault time in the simulation should be around one second Store the pl4 files on a memory stick and bring it to the lab exercise b Compare the simulated currents with your calculations Are they equal Lab Work 1 The first part of the lab includes using software on the lab computer to communicate with and set the parameters of the relay e Open PCM600 2 6 Software for communicating with ABB relays e Open the project file Labl pcmp expand the plant structure match ing the relay configuration with the relay model you are working on Select
62. l IED The screenshot in Figure 7 1 displays the user interface of PCM600 Normally the user would create one project for each substation and set up the project according to the one line diagram of the substation This means creating a folder for each voltage level and folders for each bay inside these Inside the bay folders the relay configurations are placed They can be made from scratch or templates can be imported The most important modules in the software for relay engineers are described on the following pages File Edit View Tools IED Window Help alo EPPS 4 5 8 GBD lols BB viivleparametes H A i 4 RET670_TOC Parameter Setting v 4 b X Object Properties vax Group Parameter Name TED Value PC Value Unit Min Max zul 3 CYA ci a a 000 Appearance i i cotsn ira TEM TOC Description RET670 Transform ka a i 020 Addresses anaes Collapse i IP Address 10 1 150 3 A aaa IP GATEWAY 192 0 2 1 5 5 Api E signal Monitoring aatia IP SUBNET 255 255 255 0 a _ Eg Disturbance Handling 1 1 6 4 030 Communication Control e Connection T Fixed 8 vent Viewer ey 4 080 Authentication a x Is Authenticati True aramee Saing Is Password u False Application Configuration Password Signal Matrix 1 29 2014 8 17 14 AM a 100 SCL information Co RET670ver2 0 0 a g 670 series a B ee March ed E a A g IED Users Sunday E Last H sj IED C
63. lays are in most cases high speed relays 2 Selectivity An important feature of a well designed protection system is how it should be designed to discriminate between a fault within a given zone of protection and a fault outside of the protected zone This attribute conflicts with speed and dependability Dependability A relays dependability is given by the probability it will operate when it is sup posed to This is a vital attribute a relay without dependability is as good as useless It can be considered as worse than not having a relay installed at all since it gives a false assurance of protection 12 CHAPTER 2 POWER SYSTEM PROTECTION Security The certainty a relay will not operate when it is not supposed to Security conflicts with a relays dependability Protection systems today are normally set towards high dependability to obtain this it is sacrificing some level of security This is done deliberately as most power systems today have several paths to deliver power from generator to consumer However one should be careful with this relationship when looking at a power system with limited re routing options for power transfer e g in a radial power system Reliability Reliability describes the relationship between dependability and security i e the probability a relay will perform as required High reliability is desirable however how it is achieved may vary from scenario to scenario Economics As with mos
64. le eas C 8 Connection Diagram RED670 Current and Voltage Leads between TRM and Test Switeh 5 22 d amp gactengin b SES we 2 ere Bee C 9 Connection Diagram RED670 Current and Voltage Leads between TRM and Test Switeh 5 v 2 5s Kehoe se Bee a C 10 Connection Diagram REG670 Current and Voltage Leads between TRM and Test Switch sk ee eS a oe ee Be C 11 Connection Diagram RET670 Current and Voltage Leads between TRM and Test Switeh 5 coco Se ee a ee ee a ee 85 86 87 88 89 Ix Abbreviations ANSI IEEE IEC NTNU MTU A D AC BIM BOM CB CCVT COMTRADE CT CTR DC DFT EMTP GOOSE GPS HF HMI IED LED MRCT PE PMU PSM RCCB SG TCC TRM USB VT VTR WAMS WAP American National Standards Institute Institute of Electrical and Electronics Engineers International Electrotechnical Commission Norges teknisk naturvitenskapelige universitet Norwegian University of Science and Technology Michigan Technological University Analog to Digital Converter Alternating Current Binary Input Module Binary Output Module Circuit Breaker Coupling Capacitive Voltage Transformer Common format for Transient Data Exchange for power systems Current Transformer Current Transformer Ratio Direct Current Discrete Fourier Transformation ElectroMagnetic Transients Program Generic Object Oriented Substation Event Global Positioning System High Frequency Human Machine Interface Intelligent E
65. leakage induc tance es 2 5 Primary terminal Cast aluminum bellow housing Stainless steel expansion bellow Compression spring Insulated voltage connection Capacitor elements Insulator porcelain or composite Voltage divider tap connection wo On ono FP Wo NY Cast epoxy bushing HF terminal connection PB e oO Ferro resonance suppression device Re N Secondary terminals m e UJ Oil level sight glass e P Aluminum terminal box Intermediate transformer Oil air block Oil sampling device PPP e oN on Compensating reactor 19 Aluminum cover plate Figure 2 6 Cross Section of a Coupling Capacitive Voltage Transformer from Alstom Grid 11 2 4 POWER SYSTEM PROTECTION ATTRIBUTES 9 2 4 Power System Protection Attributes Power system protection is supposed to operate in such a way that the conse quences of a fault in the network is reduced to a minimum Relays cannot operate before a fault as a fault is a condition for it to operate Therefore we want it to detect the fault and operate accordingly as soon as possible Protection systems should also be designed so that isolating a faulted area is as easy as possible We can therefore identify certain wanted attributes when talking about protective relaying Some of these attributes conflict with each other and should therefore be considered accordingly for each type of relays 15 Zones of Protection
66. lectronic Device Light Emitting Diode Multi Ratio Current Transformer Protective Earth Phasor Measurement Unit Power Supply Module Residual Current Circuit Breaker Smart Grid Time Current Curve Transformer Input Module Universal Serial Bus Voltage Transformer Voltage Transformer Ratio Wide Area Measurement Systems Wide Area Protection ANSI Device Numbers 21 50 51 52 67 87 Distance Relay Instantaneous Overcurrent Relay AC Inverse Time Overcurrent Relay AC Circuit Breaker AC Directional Overcurrent Relay Differential Protective Relay XI 1 Introduction Electrical energy is one of the cornerstones of modern society Having access to electrical energy with stable nominal values is something we take for granted every day Trying to have a normal day without electrical energy is close to im possible Why can we take it for granted Why is electrical energy so reliable Protective relaying is an important part of the answer to these questions Pro tective relaying has the role of quickly detecting and clearing faults in power systems Without protective relaying a fault could lead to major damage to power system components causing outage of electric power for long periods of time The objective of protective relays is to isolate the smallest possible area af ter a fault whilst clearing it as fast as possible This minimizes the consequences of the fault Protective relays are becoming more advanced to keep u
67. lts per Hertz however they are not the scope of this thesis 4 1 Fuses The first type of protection for electrical networks were fuses As they are simple and cheap they are still commonly used for protection purposes today The most common type of fuses consists of a short conducting wire inside a casing capa ble of carrying the current permitted for the protected zone The cross section and material of the wire decides how much current the fuse can conduct without melting The wire will melt if the temperature increase caused by the current going through the fuse which has some resistance becomes higher than the melt ing temperature of the wire material The fuse can melt almost instantaneously or with some time delay as seen in Figure 4 1 A melted fuse will need to be manually replaced and this is one of the drawbacks of using fuses for protection Overcurrent relays which will be looked at later in this chapter can have a time current characteristic similar to fuses 33 10 tt Minimum Melting Time Total Clearing Time Time s 0 001 000 Current A Figure 4 1 Time Current Characteristics for a Fuse 19 21 22 CHAPTER 4 PROTECTION PRINCIPLES 4 2 Overcurrent Relay In most cases fault currents are several times higher than load currents In other words currents significantly higher than load currents equals fault This simple principle is what overcurrent relays is based on The inputs
68. mer will have different voltage levels at the different terminals To compensate for this the ratio of the CTs at each terminal is chosen accordingly so that secondary currents i e the current that the relay sees has the same base value on all terminals Due to the needed difference in CT ratio one may come across sets of CTs of a different type model and or from a different manufacturer This can also mean that the CTs will have different performance characteristics This is another factor that must be taken into account 15 34 CHAPTER 4 PROTECTION PRINCIPLES Phase Shifts Depending on how the transformer windings are connected to each other on each side there may be a phase shift from one side to the other For instance will a delta wye connected transformer experience a phase shift where the delta side will lead the wye side with 30 It is therefore important to input correct information about each respective winding when setting the relay 15 28 Tap Changing Transformers Selected transformers can have the possibility of adjusting the ratio with built in tap changers This feature is used for voltage control to achieve desired power system operation e g controlling reactive power flow and is in most cases con trolled remotely Normally the tap changers are able to adjust the voltage ratio by 10 Since CTs are set at a fixed ratio this is a concern for the purpose of differential protection Some CTs as previously ment
69. ne Differential Protection Relay Generator Protection Relay Transformer Protection Relay Test Switch Test Switch Test Switch Test Switch Test Handle Relay Mounting Kit Mobile Lab Rack Rack Shelf AC DC Converter Power Strip Residual Current Circuit Breaker Relay Tester Name ABB RED670V2 0 ABB RET670V2 0 ABB REG670V2 0 ABB RTXP24 ABB RTXP24 ABB RTXP24 ABB RTXP24 ABB RTXH24 ABB 19 Mounting Kit Schroff 19 Cabinet Schroff 19 XP Power LCL150P548 Bachmann 6 fach Schneider El DCP H Vigi Omicron CMC 56 Model Info IEC 6U 1 2 19 61 6U IEC 6U 1 2 19 91 3U IEC 6U 1 2 19 71 5U RK926315 AH RK926315 AK RK926315 AM RK926315 BC RK926016 AA 1MRK002930 BB 36U 10117 498 2U Depth 400 mm 100 240VAC 48VDC 150 W 19 16 A 230 VAC 30mA MGN19752 3U 3I 91 Bibliography ABB AB Relion 670 series Generator protection REG670 Pre configured Product Guide 2012 ABB AB Relion 670 series Line differential protection RED670 Pre configured Product Guide 2012 ABB AB Relion 670 series Transformer protection RET670 Pre configured Product Guide 2012 ABB AB Test system COMBITEST BuyerOs guide 1MRK 512 001 BEN Revision E http www05 abb com global scot scot354 nsf veritydisplay c60fcdc986d039fcc1257b6000485353 file 1MRK512001 BEN_E_en_Test_System_COMBITEST pdfs 2013 ABB AB Specification Test switch RTXP 24 Symbol Catalogue IMRK 001 024 CA h
70. ng too complicated 2 Power System Protection This chapter provides a theoretical background of the components and attributes for the protection of a power system 2 1 Power System Protection Components A power system protection scheme consists of several elements that work together for the detection and clearing of faults and other abnormal conditions Figure 2 1 illustrates the key components of a protection system Transducers CTs VTs relays power supply and circuit breakers CBs 28 31 SUPPLY al Figure 2 1 Principles of Power System Protection Transducers The transducers i e the current CT and voltage transformers VT are the sensors of the protection system feeding the relays with continuous current and voltage values reflecting the state of the power system They step down the values to a level that is safe for the relays 2 1 POWER SYSTEM PROTECTION COMPONENTS 3 Relays Relays are the physical devices that interpret the data from the transducers If the data indicates a fault the relay will trip and forward an operating signal to the circuit breaker s Traditional protective relays were electromechanical de vices which utilized the relationship between electricity and magnetism In these relays a measured current would flow through a coil creating a magnetic force which would then act on mechanical parts such as an induction disk or clapper contact These relays were quite slow compared
71. ns is therefore key To avoid potential recurring problems it might be beneficial to install relays of a different model series or perhaps even better from a different manufacturer A redundant protection system is also important to have since re lays has to been to taken out of service for maintenance testing The alternative testing relays while leaving the system unprotected is not viable The increased complexity of modern digital relays provides challenges for relay operators Software allows the number of settings for the different integrated protective functions to be substantial It is therefore important that the relay operator is well known with the capabilities of the relay and its software to pre vent misapplications The software of the relays are also frequently updated and it requires the operator to stay up to date as software updates may bring new and added functions but also change existing functions 32 35 36 CHAPTER 5 MODERN RELAY TECHNOLOGY Binary Binary Contact Contact Currents Voltages Inputs Outputs Surge Filters Surge Filters Signal Conditioning Signal Conditioning Digital Output Signal GPS Signal Conditioning Sampling Clock A D Sampling Microprocessor Communications Figure 5 1 Architecture of Modern Relays based on Figure 1 1 in 8 and Figure 1 6 in 32 5 1 Transducer Input and A D Sampling Figure 5 1 illustrates the architectur
72. nt of space in the switchgear cabinet is limited Because of this using the sampled values in an IEC61850 compliant lab system might be a good idea This is a possible future step for the relay lab and not the focus of this report Any further studies of this opportunity will not be made in this report 52 CHAPTER 6 RELAY TESTING 6 4 Testing Summary For the purpose of the relay lab using a relay tester for testing of relays is a safe start It is a powerful tool capable of doing tests with varying degrees of complexity which suits a lab with prospective expansions perfectly NTNU cur rently owns an old relay tester from Omicron CMC 56 whose functionality and software is somewhat limited only three current and three voltage outputs in other words three phase differential testing is not possible In addition the software support for this model was discontinued in 2004 A new and up to date relay tester should therefore be acquired as soon as possible For simple tests it could also be possible to acquire fault simulators which is much cheaper but with limited functionality In the future the expanding SG Lab could be used for testing possibly the relay lab could be integrated to this lab However for the first part of the lab using a relay tester is considered the best option For the lab exercises manual testing using the control panel is a good way to make the students understand what kinds of currents and voltages they are
73. ntity is used as a reference as seen in Figure 4 4 and shown in the phasor diagram in Figure 4 5 as U es since a current reference may not be non zero at all times Reverse Figure 4 5 Phasor Diagram for Directional Relay using Voltage Reference Based on Figure 194 in 2 The tripping direction of the directional overcurrent relay can be set to forward reverse or it can be both i e having a regular overcurrent function Forward direction is usually defined towards the protected object which normally also is towards the grounded side of the CT as in the example in Figure 4 4 Reverse direction is naturally the opposite 26 CHAPTER 4 PROTECTION PRINCIPLES 4 4 Distance Relay Distance relays sometimes referred to as impedance relay measure the impedance of its protected unit e g a line using current and voltages supplied by CTs and VTs The relay have been provided with the calculated impedance of the line and continuously compare the two Should the measured impedance at any time drop below the known line impedance it will know that there is a fault and trip Relay Trip Time Zone 3 Figure 4 6 Distance Relay Principle Since the relay relies on measured values from transducers and compares it with a calculated value some safety margin is necessary It is common to let the relay under reach the line by 15 20 to make sure it does not operate before other relays downstream when i
74. ocation The impedance between two possible fault locations can be small i e the fault currents are similar compared to the impedance back to the CT location This can make it hard for the relays to discriminate between a fault inside or outside its zone 24 CHAPTER 4 PROTECTION PRINCIPLES 4 3 Directional Overcurrent Relay A regular overcurrent relay is not sensitive to the direction of the measured current An overcurrent relay only looks at the magnitude of the current and will initiate pick up and trip according to its time current characteristics regardless of the way the current is flowing In many power system scenarios it can be very beneficial to have an overcurrent relay that is sensitive to both magnitude and direction of the current flow i e a directional overcurrent relay This can increase the selectivity and the reliability ref Chapter 2 4 of an overcurrent relay application significantly Line A Line B Tripping R Tripping a Direction S Direction f Forward Relay A Forward Relay B eT be 4 CB Radial Feeders cB cB c cB cB Wi wW wW wW Figure 4 4 Simplified One Line Diagram of Substation with Directional Over current Relay Figure 4 4 illustrates a substation with two main transmission lines i e Line A and Line B supplying four radial feeders with power The main transmission lines are protected with a directional overcurrent relay i e Relay A and Relay B the busbar will have
75. ompare asi a E Fa TEC 61850 Configuration 1 0 i Communication Management oj a B E License Update Tool October fan REG670_T e Set Technical Key Sunday 7 RED670_1 Create Template Last 03 Import 100 REDE port Read from IED a Write to IED Report Parameters 1 00 Configuration Language Communication Port amp Cut Copy Of Delete of Rename SNTP Server Properties Fast Caption Figure 7 1 Screenshot PCM600 2 6 ABB Protection and Control IED Man ager 58 CHAPTER 7 SOFTWARE Parameter Setting The parameter setting module is used to set all changeable parameters of the relay This includes time and date global base values HMI and communication settings The most importing settings however are the parameters for the pro tective functions This module also allows the user to read the values from the relay e g for comparison or verification The table format view of the parameter setting module is shown in the background in Figure 7 1 The table view gives the user a good overview of the parameters including units and min max for the parameters Application Configuration In the application configuration module the relay engineer can tailor the functions and logic of the relays This means assigning currents and voltages to hardware channels selecting function and logic blocks and forwarding analog and digitals signals according to the desired relay functionality The ap
76. on of the relay lab to include IEC61850 com munication and WAP PMU capability as described in Chapter 8 2 The possibilities of use for the lab will increase significantly when it becomes fully IEC61850 compliant A lot of interesting topics could be studied Benefits of using communication for relay coordination is an example ref Chapter 2 4 TT A Appendix Symmetrical Components Line currents and voltages in a three phase system can be represented by a phasor sum of a balanced positive sequence vectors balanced negative sequence vectors and identical zero sequence vectors as illustrated in Figure A 1 These sets of vectors systems are referred to as symmetrical components 25 Figure A 1 Positive Negative and Zero Sequence Vectors Sequence Equations The sequence equations Equation A 1 and A 2 are used to go from one repre sentation to the other Ip 1 1 1 es a h l 1 a l h A 1 Ty 3 1 al Ia 1 1 ell it Jy fd al A 2 I 1 a b 79 B Appendix Wide Area Measurement Systems Wide Area Measurement Systems abbreviated WAMS transmits time stamped analogue and or digital information via telecommunication protocols Time stamping is the key word as it allows information from several IEDs to be com pared at a central unit Time Synchronization GPS The time in each device is synchronized with GPS Global Positioning System signals The GPS signals provide a time reference with an accuracy of
77. ones are normally shown using an impedance or RX diagram Modern numerical distance relays have the ability to let the impedance characteristics have whichever shape is desirable however they normally have a quadrilateral or circular shape 35 Figure 4 8a displays an exam ple of the settings of a distance relay with three zones During normal operation the distance relay will see the impedance of the line Z plus the impedance of the load Zloaa Under a fault the relay will see the impedance of the line to the fault location Zjr and the impedance of the fault itself here illustrated with an arc flash resistance Rr This yields the total fault impedance Zp 28 CHAPTER 4 PROTECTION PRINCIPLES A common application for distance protection of a line is to have two distance relays at both ends of the line looking towards each other as seen in Figure 4 9 The zone settings of the relays are set equal and in opposite direction with Zone 1 normally being set to 80 85 of the line length The main purpose of using dual relays is to improve reliability for far bus faults i e faults outside of Zone 1 Assuming a fault occurs close to bus B Relay A will see the fault in Zone 2 while Relay B will see it in its Zone 1 This means Relay A will have longer operating time than Relay B due to the added time delay To improve operating time and allow both relays to operate instantaneously communication between the relays can be added The communi
78. p with more complex and integrated power systems From a traditional radial design where the flow of power moves in one direction the design of power systems has been transformed into a design with a higher number of interconnections and where the power flows in both directions The future of power systems is smart grids meaning more complex designs with distributed generation smart meters and continuous surveillance to ensure optimal operation and power flow at every instant The electrical engineers of the future should be educated with this in mind To enlighten today s and future students about protective relaying a solid theoreti cal background part is a fundamental first step To complement the theory and to better the understanding of the topic a practical component to understand how power system protection works in real life is vital A protective relay lab can be the foundation of such a practical hands on component Designing the lab at NTNU to make it useful for students and easy to grasp is therefore crucial Designing it with a future specialization course for last year Master s students in mind as well as for integrating it into current courses is important Creating a lab which is well documented and ready for future expansions to accommodate future protective trends is important to keep in mind The motivation should be that lab is to provide the students with a practical understanding of protective relays without bei
79. plication configuration module is therefore normally used exclusively before the relay is set into opera tion while the signal matrix and parameter setting modules are used to adjust the relay during operation However the application configuration module can be used after commissioning if an error in the configuration is discovered Most configurations errors should be detected during the commissioning test The use of the application configuration module is more closely described in Chapter 8 4 and 5 3 Signal Matrix The signal matrix provides a good overview over the signals out of the binary output module BOM and into the binary input module BIM The signal matrix is an easier way of assigning binary signals e g trip signals to the BOM and BIM than using the application configuration module Figure 7 2 displays a screenshot of the Signal Matrix in PCM600 Graphical Display Editor The graphical display editor is used to create single line diagrams of the sur rounding power system to be shown on the relay display Templates of the most relevant components are included in the editor Examples of a single line diagram can be seen in Figure 8 6 In addition to single line diagrams the display can include measured values e g currents and voltages The single line diagram can also show updated breaker positions and with the the front panel buttons the user can select and operate breakers if user is permitted 7 2 RELAY CONFIGURAT
80. ppendix B 40 CHAPTER 5 MODERN RELAY TECHNOLOGY 5 5 IEC61850 Standard for Design of Substation Automation The standard for communication between IEDs is provided by the International Electrotechnical Commission s standard IEC61850 Standard for Design of Sub station Automation The main purpose of IEC61850 are to meet the increasing demand for communication by creating standards for communication between devices from different manufacturers while reducing investment operating and maintenance costs 26 Management and Control Systems Protection IEDs Control IEDs Metering IEDs Merging Units Merging Units Figure 5 4 IEC61850 Framework Substation Communication System Based on Figure 1 in 26 Figure 5 4 illustrates a substation communication system in compliance with the framework defined in IEC61850 The information from transducers actua tors and status contacts are gathered and sampled if necessary in a merging unit and distributed to the protection control and metering devices via a process bus The IEDs are now reduced to just a processing element with a human interface as they get all their data via the process bus The IEDs are connected to the overseeing management and control system through a station bus The buses are normally fiber optic Ethernet networks The design of a sub station communi cation system will vary e g the merging units can be directly connected to the IEDs not via a pro
81. protected object and may cause the corresponding CTs to satu rate creating distorted waveforms leading to an unnecessary tripping Carefully selecting CTs for each protection scenario is therefore important Figure 4 12 displays how the secondary current affected by CT saturation compared to the actual secondary current Real Secondary Current Secondary Current due A to CT Saturation Figure 4 12 Secondary Current Waveforms with without CT Saturation Another limitation for differential relays are that they can not protect a zone where the distances from CTs to the relay is long or varies too much This is because the error of the CTs are dependent on the burden which again is pro portional to the length of the cables connecting the CTs and the relay For the protection of a long line it is therefore common to have two differential relays with corresponding CTs on each side of the line and communication able to trans fer current values between the two relays For the protection of transmission and distribution lines the relay engineer must be aware of the challenges occurring when energizing a line Due to the shunt capacitance length dependent of a line a significant capacitive current will flow in the line during energizing de energizing This current contribution may not be equal at both sides so the relay should block during this phenomena The described principles and challenges are valid for differential protection of busb
82. r from Cebec AB aaa aa 50 One Line Diagram of SG Lab at NTNU 51 Pick up Indication Testing oa aa GA lt 8 ace on Ee 53 Screenshot PCM600 2 6 ABB Protection and Control IED Man IEEE aaar a A a aa Seen G ea Sk bal Aa a 8 we i we a 57 Screenshot Signal Matrix PCM6002 6 59 Conceptual Illustration of Relays in Mobile Rack 63 Backside of Relay and Test Switch 0 65 Relay Power Supply eos 4 2 6 BS 4k Ge Fa oes ee OA 66 ABB RTXP24 Test Switch right and RTXH24 Test Handle left 4 68 Contact Functions ABB RTXP 24 Test Switch Handle 68 One Line Diagrams for ABB Relion 670 Relays re Network Lab Exercise 2 a 73 Screenshot Plant Structure PCM60026 74 Positive Negative and Zero Sequence Vectors 79 Card Slots ABB Relion 670 6U 1 219 81 Connection Diagram Power Supply Rack 1 2 82 Connection Diagram Power Supply Rack 2 82 C 4 Connection Diagram RED670 1 Current and Voltage Leads between BOM and Test Switch 00 C 5 Connection Diagram RED670 2 Current and Voltage Leads between BOM and Test Switch 0 C 6 Connection Diagram RET670 Current and Voltage Leads between BOM and Test Switch a 44 0204 AG ce ee kd BOR Dk oe Os C 7 Connection Diagram REG670 Current and Voltage Leads between BOM and Test Owitel e3 s orea Kobe a alg wea ee
83. r values which is a function of current will be zero The different breakers are also interlocked as they would be if they were used in a real substation For instance disconnectors can not be opened before the corresponding circuit breaker is open These features are useful as they give students a better understanding of how modern relays are used for more than just protection they are also an important part of substation automation and control T1_C_o04 U tieriae kV C_QA1 Ny I geeRR BR A U ggggR tt kU U ggggR ee kU P seese nt MU OAL I geneeee A I seeetee A a Caco Q teeeeee MVAr P gggam ee MU P en ee MU Q ggenm eR MVAr Q gggeR ee MVA Cam L aco aco QB9 QB9 y RED670 p RED670 RET670 To Transformer U gggge ee kV I geneeen A P settaee MU Q gngem ee MVAr f gugemee Hz i PF gggnm eR REG670 Figure 8 6 One Line Diagrams for ABB Relion 670 Relays I Possible interconnection for line differential bi A P R 1 line distance protection testing with one relay I at each end of line end to end testing o an en m e e en n mt 9 Lab Exercise Proposals The lab exercises should give students insight in the practical world of power system protection The exercises should demonstrate the different protection principles and the function of modern relays Setting of parameters for the relays based on calculated values is also an important part The students shoul
84. raw The graphical preprocessor to ATP http www atpdraw net Hans Kr H idalen Lecture Notes Over Current Protection In TET4115 Power System Analysis Norwegian University of Science and Technology 2013 Thomas J Domin J Lewis Blackburn Protective Relaying Principles and Applications CRC Press Third edition 2007 James R Bumby Jan Machowski Janusz W Balek Power System Dynamics Stability and Control Wiley Second edition 2012 Il Dong Kim Experiences and future prospects on the digital relay applica tion and substation automation In Transmission and Distribution Confer ence and Exhibition 2002 Asia Pacific IEEE PES volume 1 pages 613 617 vol 1 Oct 2002 R E Mackiewicz Overview of IEC 61850 and Benefits In Power Engineering Society General Meeting 2006 IEEE pages 8 pp 2006 Juan A Martinez Velasco Jacinto Martin Arnedo and Ferley Castro Aranda Modeling Protective Devices for Distribution Systems with Dis tributed Generatio Using an EMTP Type Tool Ingeniare Revista chilena de ingenier a 18 259 274 August 2010 C Russell Mason The Art amp Science of Protective Relaying General Elec tric 1956 http www gedigitalenergy com multilin notes artsci Mukesh Nagpal and Charles Henville Lecture Notes In EECE 497 Power System Protection University of British Columbia 2013 Nhat Nguyen Dinh Gwan Su Kim and Hong Hee Lee A study on GOOSE communication based on IEC 61850 using
85. re power systems If the lab is well maintained and expanded to keep up with trends in the field it could last many years 76 11 Further Work As mentioned the relay lab should be further developed to keep up with emerging technologies and to act as a useful supplement to future power system protection courses at NTNU Further work to ensure the development of the relay lab should include e Testing and verification of the contents in the proposed lab exercises with the relays in the lab Modification of exercise proposals where necessary Draft solutions to exercises e Develop more advanced lab exercises Interesting topics could be challenges with differential protection as described in Chapter 4 5 especially with re gards to CT saturation Exercises focusing on communication between line differential relays is also a possibility Comparing simulated relay opera tions from ATPDraw with results in the lab is another interesting topic Using the event recorder to playback waveforms from real fault scenarios e Creating a simple user manual for use of the relay lab This will make it easier for students to use the lab for research purposes It should include information on how to communicate with the relay and the relay tester as well as other practical information e Perform a study of different models of relay testers to be able to make a recommendation for a future purchase acquisition of a new tester e Continue with the expansi
86. relatively rarely nevertheless it should be mentioned 20 CHAPTER 3 SHORT CIRCUITS AND ABNORMAL CONDITIONS J I Z laa laa Z lt Ug Figure 3 9 Reduced Sequence Networks Interconnection for Double Phase to Phase Fault Figure 3 8 illustrates a Double Phase to Ground Fault where Phase a and b are faulted The current in Phase c becomes zero 0 This fault can be represented by interconnecting the three sequence networks in parallell This gives 1 n Ha Ka a Ta 1 a Z 1 e i Bo T Bh Z gu er ee en a eT Oe 3 10 2 a2 T a2 1 z Zi Z z Z g Io Loth 2 2 0 a0 F a0 1 z Zi z Z The relay at bus B will also here just see the proportion of the fault currents coming from bus B I and Jj 4 Protection Principles There exists several different protection techniques and principles Fuses are the simplest and cheapest technology however they need to be manually replaced when they melt operate Protective relays are used when fuses are not feasible Different relays can have different inputs and they will treat the information differently but their objective is shared to correctly detect and clear a fault as soon as possible A closer look at overcurrent distance and differential relay principles will be made in this chapter as they are the most common protection applications in power systems today Other protection principles also exists e g overvoltage undervoltage vo
87. rence between the two An important design criteria for differential protection systems is therefore to take this into account when placing sizing and setting the components 21 During an internal fault both fault currents will flow into the zone The magnitude of the currents will also in most cases be much higher than normal operation currents The fault currents will not necessarily be equal as they are dependent on the external system on both sides This will lead to an increased operating current Jopr Percentage differential relays are the most common type of differential relays 15 They compare a restrain current with the operating current if the operating cur rent Top is greater than the restrain current rgs times a gradient m it will operate A lower gradient will increase the sensitivity of the relay Figure 4 11 shows the current characteristics of a typical fixed percentage differential relay It has two gradients m and m2 M is greater to improve security at high restrain currents To add security at low restrain currents the operating current has a minimum pick up value lop ae m 70 Restrain Region Pick up ee lees Figure 4 11 Percentage Differential Relay Current Characteristics 4 5 DIFFERENTIAL RELAY 31 One of the main problems with differential protection is that the CTs may ex perience different degrees of saturation External faults may lead to high through currents of the
88. rent Transformers The basic design and behavior of current transformers CTs are similar to other two winding transformers They are used to step up or down voltage and cur rent The power entering the primary side must be equal to the power out of the secondary side i e Up Ip Us Is Current transformers are used in protection systems to step down the high currents that flows in the network to values that are sufficiently low and safe for the relays In other words they have a single turn or few primary turns and several secondary turns Np lt Ns O O To Relay Figure 2 2 Conceptual Illustration of a Current Transformer Figure 2 2 illustrates conceptually how a CT is connected to the power system In contrary to regular power transformers CTs are connected in series with con ductors of the power system Because of this the voltage over both sides of a CT is independent of the system voltage Under normal steady state operation the voltage on the primary side is usually less than 1 volt and under 10 volts on the secondary depending on the turns ratio A fault will lead to an increase in the voltages on both sides typically to a couple of hundred volts on the secondary side and up to a few volts on the primary 28 These values are valid when the secondary side is short circuited as an open secondary circuit will lead to very high voltages only limited by saturation of the core on the secondary side Thus should the seconda
89. ricated relay or tests a new software revision for a relay model End users may perform type testing to check that the relay operates as promised and within their needs e Acceptance Testing The relay is tested to prove that is the correct model and that all features are working as they should It consists functional tests of in puts outputs displays communcation and in some cases pre defined pick up and timing tests Acceptance tests are generic and its main purpose is to prove that model ordered has been delivered without damage during transportation e Commissioning Commissioning is a site specific test and is considered the most impor tant test during the lifetime of a relay It confirms that all protective elements and logic settings are correct for its intended use e Maintenance Testing To ensure a relay continues to operate as it should maintenance tests are performed at set intervals Modern digital relays have internal self testing that check for many errors Maintenance testings is therefore not as crucial as it used to be with electromechanical relays which were less reliable e g due to functions drifting 42 6 1 TESTING RELAY TESTER 43 e Troubleshooting Troubleshooting is important to perform after a fault if the relay did not operate or if the relay operated when the system was operating in normal steady state conditions This entails checking the log of the relay and adjust sett
90. ron CMC 56 as previously mentioned is somewhat limited due to its age and the fact that it only has three current and three voltage outputs However it can still be used until a new and up to date tester is acquired Since different software is required to communicate with both the relays and the relay tester the lab should have a designated computer with the required soft ware installed A computer is required to control and use the relay tester The relays parameter settings can be adjusted using the HMI however the computer software provides a better overview and is more efficient if a group of parameters are being set It is also required for more advanced configurations of the relay e g application configuration The CMC 56 requires a parallel port for commu nication This is no longer standard on most computer motherboards as it has been superseded by the USB port However parallel to USB port adapters exist which means the CMC 56 can be used with most computers Since the lab is supposed to be mobile a laptop computer would be ideal 8 3 1 Test Switch Test Handle The test switch test handle solution provides the user of the lab with easy access to the relay inputs and outputs The test switch is wired to the relay i e cur rent voltage inputs digital inputs and digital outputs The test switches in this case consists of 24 connection points each with an A and a B side The B side is wired to the relay while the A side would
91. rotection principles e Study the different software available to obtain the simulated values e Develop lab exercise tasks for a future specialization course with inspiration from a Michigan Technological University e Design and arrange the practical set up of the laboratory including docu mentation and proposals for future expansions e Test the preliminary laboratory set up and create plug and play relay con figuration files to be used in the different lab exercises Preface This report is the result of the authors Master s thesis at the Department of Elec tric Power Engineering at the Norwegian University of Science and Technology The work for the thesis was performed and written in the spring semester of 2014 I would like to express gratitude towards my supervisor Professor Hans Kris tian H idalen for providing guidance during the semester and towards Professor Bruce Mork for providing useful input I would like to thank ABB for their contribution to the relay lab with new and modern protective relays I am very grateful for the help guidance and training I have received from Odd Werner Erichsen at ABB in Vasteras Sweden during the spring of 2014 Siemens Norway also deserves some gratitude on my behalf for letting me participate in their relay seminar for new employees as a third party in October 2013 I would also like to thank Bard Almas Vladimir Klubicka and Aksel Hanssen for assisting me with the set up of the relay la
92. rror to be calculated Percentage v 30 12 C Absolute Multiples of Iset I No Eror Calculation No Evaluation Figure 6 4 Screenshot from Overcurrent Relay Test Doble F6Test 3 12 0 Automated differential tests is another example of what a well equipped soft ware package is capable of performing A screenshot from Omicron s software differential test is shown in Figure 6 5 The procedure is similar to the overcur rent test the user inputs a number of test points selects type of fault and the relay runs the test and determines pass fail depending on the results 48 CHAPTER 6 RELAY TESTING ose ejs Ole elaj lalux ele E Bias Curve B Harmonic E General Operating Characteristic Diagram Ret e Actual 2 25 bias 6 40 Win Deviation Idiff Ibias tact inom 066 418 Nottested N T 1 06 251 Not tested 0 03 1 75 085 339 Nottested 0 03 r i IO 114 460 Nottested N T 158 595 Not tested 0 03 IO 153 640 Not tested N T N an Idif in Q 0 50 0 25 5 Ibias I In Figure 6 5 Screenshot from Differential Relay Test Omicron Test Universe 1 61 SR1 6 1 3 Event Recording Simulated Waveform Playback A relay tester is also capable of producing uploaded current and voltage wave forms COMTRADE and PL4 files are the most used file formats The waveforms can
93. rs it provides fast reliable and sensitive protection Transformers normally have two windings with a primary and secondary side requiring one set of CTs on each side In some cases one may encounter a three winding transformer which naturally would require three sets of CTs i e on the primary secondary and ter tiary Transformer differential protection is normally configured with a variable percentage characteristics In other words this means the slope of the gradient increases with increasing restraint current The change is either continuous or in discrete steps This characteristics is used to prevent mis operation due to CT saturation during external faults When designing a differential protection scheme for a transformer one faces some extra challenges which needs to be taken into account e Magnetizing Inrush Current e Overexcitation e Different Voltage Levels Different CT Types Ratios and Characteristics e Wye Delta Zigzag Winding Combinations Phase Shifts e Transformer Taps gt Varying Voltage Levels and or Phase Shifts 4 5 DIFFERENTIAL RELAY 33 Magnetizing Inrush Current During a rapid change in the voltage applied to a transformer a current tran sient known as magnetizing inrush current may occur This is caused by an exciting current trying to create flux in the transformer corresponding to the change applied voltage Magnetizing inrush current can in other words occur during energizing of the tr
94. rtz The currents and voltages also pass through anti aliasing filters These filters has a cut off frequency of a few hundred Hertz adjusted to the desired sampling rate of the A D The A D can also include several other signal processing functions e g DFT Discrete Fourier Transformation and Windowing 30 Details of advanced signal processing are not in the scope of the thesis therefore a study on this subject will not be made The sampling rate i e the interval between each sampling must be selected so that the error created by going from continuous to discrete values is negligible 8 The IEC61850 standard which will be studied later in this chapter defines two distinct sampling rates for current and voltage transformers 80 and 256 sam ples per cycle In a 50Hz system this equals a sampling rate of 4kHz and 12 8kHz respectively 26 However the relay manufacturer may choose to filter signals to a lower sampling rate for internal use in selected relay models if deemed advantageous 2 5 2 Digital Inputs and Outputs The digital inputs are binary signals normally used for indicating positions of contacts e g if a circuit breaker is open or closed The inputs are DC voltage signals with a low high 0 1 value indicating open closed An applied voltage in the range of e g 24 30 V will be interpreted by a corresponding transistor in the relay as high 1 while no applied voltage will equal low 0 2 These signals also pass throu
95. ry circuit never be left open 2 2 CURRENT TRANSFORMERS 5 a Complete Equivalent b Simplified Equivalent Figure 2 3 Equivalent Circuit for a Current Voltage Transformer Based on Figure 2 3 in 33 and Figure 5 6 in 15 Figure 2 3 above displays an equivalent circuit for a CT where Figure 2 3b is a simplified equivalent where the primary winding resistance Rp and the magnetiz ing resistance Rm are omitted The primary and secondary leakage inductances L Ls are also neglected The primary winding magnetizing inductance is also negligible and omitted in both representations The secondary winding resistance R is proportional to the number of secondary windings while the secondary lead resistance Rz is dependent on the metal cross section and length of the lead it self Under fault conditions the secondary lead resistance can be one way 1xRz or two way 2xR depending on the type of fault If it is a phase fault it is one way for ground faults it is two way Z represents the burden caused by the resistance of cables wiring and internal impedance of relays The burden is normally given in volt amperes with a corresponding ampere value VA From Figure 2 3b we can easily derive the expression for the secondary current I This is the output value of the CT that feeds the relay s N hale sL 2 2 P N As Equation 2 2 shows J will not be equal to the current from the primary side I x as long as the the exc
96. s also used between relays and non conventional transducers This is contrary to traditional transducers which are hard wired to the relays Early generation digital relays had simple communication outputs through se rial and or parallel ports With the technology advancing the latest relay gen erations has fiber optic Ethernet communication Fiber optic communication technology is fast reliable and provides high transfer capacity There are mainly two ways a set of relays can be connected to each other direct fiber optic connection or fiber optic connection via a central network system One of the main differences between these two options is the time delay If the there is a direct connection between the relays there will be no time delay This allows the time stamped sampled values to be used by both relays without any problems However if they are connected via a central network system the data packets will pass through a rugged switch environment Rugged switches are used since they can handle the level of interference which may occur in substation data network systems The cost of this is an extra varying time delay The sampled data can now not be used by both relays since there is no guarantee that the time stamp is valid The solution for this is to make sure that the internal clocks of both relays are synchronized at all times This can be accomplished by synchronizing the clocks with GPS signals This is more closely described in A
97. ssentials of relay testing is described in the paper The different methods available for the testing of relays scaled physical networks relay testers and fault simulators are mentioned Focus has been put on use of relay testers as it is most relevant for the lab A description of common test procedures is also included Selected relevant software has been studied to find a software which can be used in the lab exercises Discussion of practicalities regarding the lab i e the design and set up of the lab is also made in the thesis Opportunities for and use of the lab have been discussed The basics of relay configuration is explained Proposals for lab exer cises that can be performed in the new relay lab are presented near the end A list covering proposals for further work for the relay lab is the final part of the thesis II Sammendrag Denne rapporten inneholder teoretisk bakgrunn om beskyttelse av kraftsystemer rel vernsfunksjoner moderne rel vernsteknologi og testing av rel vern Den teo retiske delen st tter det praktiske arbeidet med design montering og forslag til bruk av en ny rel vernlab ved NTNU Teoridelen inkluderer beskrivelse av de forskjellige komponentene i ett rel vern system inkludert deres funksjonalitet og egenskaper Ett kapittel som forklarer beregninger av kortslutningsstrommer er med for a illustrere st rrelsen pa disse str mmene og viktigheten av rel vern De mest brukte rel vernsprinsippen
98. standards for the characteristics of these time current curves TCCs which are commonly used however the user may choose create tailored characteristics 2 4 2 OVERCURRENT RELAY 23 tA Definite Time Inverse Time Pick up Multiple of Pick up Current Instantaneous Current I I Trip Current Figure 4 3 Inverse Time and Instantaneous Characteristics Overcurrent Protection The setting of the pick up current is the key element for overcurrent protection This setting is crucial for the reliability of the protection system Put differently the relay should trip when it is supposed to and should not trip when it is not supposed to The relay should operate when there is a fault in its protection zone or as remote back up for downstream protection It should not operate for high load currents or before downstream protection To achieve this relay coordination is very important Relays should be set so that they do not operate before downstream protection has time to operate but still be able to operate with a certain delay if the downstream protection fails The setting for overcur rent relays may vary between situations however a rule of thumb is to set the pick up current as follows 14 LOT Wasted lt I lt 0 81 MinFault 4 1 This provides a sufficient safety margin for fault and load current calculation errors The drawback of overcurrent relays is that they are not very good at pinpoint ing the fault l
99. t A well developed software will have a comprehensive database with characteristics of different relay models The basic software pack ages will include automated testing tools for the most used protection schemes i e overcurrent distance and differential protection For instance can the characteristics of a relays overcurrent function be imported from the database to the overcurrent testing tool The user then inputs the pick up current selects the different testing points i e multiples of the pick up current and the types of faults three phase phase to ground etc to be tested as shown in the screenshot in Figure 6 4 The relay tester will then apply the corresponding currents and voltages in an automatic order while noting the different trip times and calculating the error for each case a elec a w 7j w B Test Test Points Test Configuration Test Elements Reports Notebook Test Points and Results an BN cn a Y ec Y ca asc 30 2 xlset ltest A Texp Tmax Tmin Tact a 1 5 1 714 10 286 5 8481 6 1955 5 5185 1 929 11 571 4 2624 4 488 4 0459 2143 12 857 3 3058 3 467 3 15 2 357 14143 2 6747 2 7973 0 15 2 571 15 429 0 2 2 3297 0 15 2 786 16 714 0 2 0 25 0 15 3 000 18 000 0 2 0 25 0 15 X 2m Oscillograph Run Tests Mult point Shots Show Phasors C Selected Point Only Current Scale T Voltage Output Multiples C Ampere Fault Type 7 AN 7 BN V CN E
100. t engineering projects one of the most if not the most important aspects is the cost benefit relationship A protection system will have a high investment cost and may lead to increased complexity and maintenance costs of the overall power system The benefits of a protection system should if designed correctly be higher than the cost A protection system that is able to clear a fault quickly i e minimizing the total outage time and damage to vital components will without a doubt make up the investment cost 3 Short Circuits and Abnormal Conditions Unwanted connections between points of different potential in a power system is called a short circuit or a fault Such an event will lead to high currents and lowered voltage levels at the fault location A short circuit does not necessarily imply that the impedance between the points are zero For instance if an arc occurs at the fault location there will be some resistance in the arc itself In other words depending on the cause of the fault the fault impedance may vary The fault impedance is decisive for the magnitude of the fault current ref Ohm s law a negligible to low fault impedance can cause a high fault current while a high fault impedance will contribute to a lower fault current for the same fault Bolted faults e g caused by a downed pole have negligible fault impedance and can lead to fault currents in the order of 1 100 kA depending on the location If the fault is
101. t is not supposed to This is illustrated in Figure 4 6 Zone 1 To provide remote back up for the relays protecting adjacent lines the relay has another setting which over reaches into the adjacent line Zone 2 Typically the setting is 125 130 of the impedance of Line 1 This setting has an added intentional time delay to make sure the primary protection has a chance to operate first A third protection zone is also common and it will function as remote back up for an even greater portion of adjacent lines An extra longer time delay is added here 21 The distance relays will have protection zones in both directions however this is not illustrated in Figure 4 6 Traditionally relay settings have been in secondary values However with the introduction of modern transducers e g optical CTs which have no ratio and therefore no secondary value it is common that modern relay have settings in primary values 2 4 4 DISTANCE RELAY 27 On the other hand if a distance relay were to use secondary values the impedance settings must be converted CTR VTR Where CTR and VTR are the ratios of the current and voltage transformer Zsec Zpri 4 2 gt z U gt Zy Sioad a Quadrilateral Zone Settings b Circular Mho Zone Settings Figure 4 8 Corresponding RX diagrams with Zone Settings Line Load and Fault Impedances for Line 1 in Figure 4 7 The impedance settings for the different z
102. timer to stop when the digital input make sure correct input is assigned receives a trip signal from the relay e Set the current output of one phase to be 5 10 over instantaneous pickup and enable outputs e Wait for trip signal If there is no trip signal within reasonable time double check pick up and relay output settings and re run test If settings are correct the relay failed the test e Note the trip time and compare with expected value e Conclude whether the relay passed failed the test The timing test should be performed again while decreasing pickup values until the relay no longer trips and then increasing it until it trips again to determine the error of the instantaneous pick up Equation 6 1 as described in Chapter 6 5 The control panel also has step ramp options where the user can step ramp amplitude phase angle or frequency manually or with fixed time intervals The stepping ramping can be stopped automatically with an external signal to one of the digital inputs This can be used to test or verify relay settings by in creasing decreasing current voltage amplitude frequency or phase angle until the relay trips and record how much the increasing decreasing value changed e g for testing of an undervoltage or overvoltage function 6 1 TESTING RELAY TESTER 47 6 1 2 Software Routine Testing The software packages of relay testers normally include aids to make relay testing faster and more efficien
103. tion Lab with PMUs e As mentioned in Chapter 5 6 Wide Area Protection is considered to be a part of the future for power system protection Therefore the lab should be developed to include PMUs and other devices used for WAP in a few years time A relay lab with this capability allows students to do research on WAP which is important for the future These are just proposals for future expansions of the lab and they should be continuously revised as work progresses to ensure optimal development of the lab 8 3 PRACTICAL SET UP OF LAB 63 8 3 Practical Set Up of Lab This thesis focuses on the first step of the relay lab as described in the previous section a lab with autonomous relays Practically this means mounting the relays in a rack together with power supply and necessary wiring cabling In addition as discussed later in Chapter 8 3 1 a test switch test handle solution will be used in the lab as it among other things gives easy access to relay inputs and outputs The lab system proposed is shown in Figure 8 1 582 3 i 492 2 HE RED670 RED670 36 HE 582 3 i 492 2 HE REG670 RET670 36 HE Figure 8 1 Conceptual Illustration of Relays in Mobile Rack 64 CHAPTER 8 RELAY LAB The vital components of the relay lab consists of the following a more detailed equipment list can be found in Appendix D e Relays 2x ABB RED670V2 0 Line Differential and Line Dist
104. tive Active and Reactive Power Consumption e Z Line Impedance e Line Part 1 From Bus B to Fault Location e Line Part 2 From Fault Location to Bus B 3 1 Three Phase to Ground Faults B B I Pa MAE DES Topea Figure 3 2 Three Phase to Ground Fault A Three Phase fault is a condition where all three phases in a network is short circuited This is characterized as a symmetrical fault given that the system was symmetrical pre fault There can also be connection between the three phases and ground however assuming the system is symmetrical Kirchoff s current law yields that the sum of the three phase current is equal i e no current will be flowing to ground 3 1 THREE PHASE TO GROUND FAULTS 15 J J ia zd Z laa la Zi lt Figure 3 3 Reduced Sequence Networks Interconnection for Three Phase Fault No Negative or Zero Sequence Network Component e Zi Z Zo Positive Negative and Zero Sequence Impedance of Generator at bus B and Line Part 1 e Zl Z Zo Positive Negative and Zero Sequence Impedance of Generator at bus B Line Part 2 From Equation A 1 in Appendix A it can be seen that the positive sequence current 1 is equal to the fault current Ip This is illustrated in Figure 3 3 In other words the original three phase system can be represented with just the positive sequence components of the symmetrical components which is the same as the original ph
105. to todays micro processor based relays which are significantly faster Modern relays are also capable of providing several protective functions in one unit i e one modern relay can replace several traditional units The communication possibilities of modern relays are also a major advantage over traditional devices 32 31 Power Supply The power supply of a protection system should be independent of the AC voltage of the grid This is due to the fact that a fault may lead to the AC supply becoming unreliable at a point of time when a reliable supply of power to the protection system is at its most critical Therefore batteries are used as a main power supply The batteries are connected to the AC voltage via a charger and during normal operating conditions the batteries will float on the charger 32 Circuit Breakers Circuit breakers CBs have two distinct tasks operating as a part of the power system under normal conditions and providing the protection system with the ability to clear a fault Under normal conditions the CBs can receive manual and automatic commands from the control center to open or close If the relay detects a fault it will send a trip signal to the CB for it to break the current and isolate the faulted network area Since a normal load current is much lower than the maximum fault current the rating of the CB must be according to the higher fault current 32 28 4 CHAPTER 2 POWER SYSTEM PROTECTION 2 2 Cur
106. ttp www05 abb com global scot scot301 nsf veritydisplay 1154cc88eea72c0ac1257cd1002c52ab f ile 1MRK001024 CA_U_en_Test_switch_RTXP_24 Symbol_catalogue pdf 2014 Inc Advanced Systems for Power Engineering ASPEN One Liner http www aspeninc com web index2256 html option com_ content amp view article amp id 91 amp Itemid 64 Siemens AG PSS E http www energy siemens com hq en services power transmission distribution power technologies international software solutions pss e htm James S Thorp Arun G Phadke Computer Relaying for Power Systems Wiley Second edition 2009 DIgSILENT PowerFactory http www digsilent de index php products powerfactory html Open Electrical http www openelectrical org wiki index php title Power Systems Analysis Software March 4th 2014 Alstom Grid OTCF Capacitor Voltage Transformers 72 5 to 765 kV http www alstom com Global Grid Resources Documents Products High 20voltage 20products OCTF 20Capacitor 20Voltagey 20transformers 2072 5 20t0 20765 20kV 20 7 20Brochure 20ENG pdf November 2011 93 12 15 16 17 20 21 22 23 J Holbach Modern Solutions to Stabilize Numerical Differential Relays for Current Transformer Saturation during External Faults In Power Systems Conference Advanced Metering Protection Control Communication and Distributed Resources 2006 PS 06 pages 257 265 March 2006 Hans Kr Hgidalen ATPD
107. ustry ABB Siemens it be came quite clear that there is a gap between their respective protection system strategies The relay engineers in the utility companies are fairly conservative in their strategy They use methods equipment and devices they are familiar with instead of exploring the opportunities that lies in modern relay technology and its communication possibilities This is justifiable to some extent as the risk of making an error increases with new and more complex systems The consequence of such an error can also be major in a worst case scenario it may lead to black outs of major areas The industry is the driving force behind the development of relay technol ogy and the protection of power systems This is understandable as they want to develop better devices and solutions to be competitive and to meet further protection challenges with a shift to more complex power systems and Smart Grids The type of skills and knowledge the utility companies and industry would pre fer students to graduate with is naturally reflected in their protection strategies Utility companies prefer students to have knowledge about past and present tech nologies with a practical feel for the entire protection chain while the industry is more future oriented and focused on how modern relay technology can supply the protection needs of smart grids and more complex power systems A new relay lab in combination with a future power system protection
108. verview over the output The settings can be adjusted off line or when the outputs are live in real time CMC 56 Voltage i 110 000 0 00 2 110 000 120 00 3 110 000 120 00 CMC 56 Current 1 10 000 A 30 00 2 10 000 A 90 00 No Amplifier Configured 1 n a n a 2 n a n a a n a n a No Amplifier Configured 1 n a n a 2 n a n a 3 10 000 A 150 00 3 n a na Frequency Binary Outputs Analog Inputs ui a 50 000 Hz fF DC Eremi Vde 2 7927 V Ide 1 1853 m Step Binary Inputs Triple A Siz 0 000 Hz J 123 4 5 6 8 3 10 f wy S919 9 9 oto io ig Quantity Frequency Time 100s g uals im et dt ee Do M Auto Step z Trigger n a Figure 6 3 Screenshot from Omicron Test Universe 1 61 SR1 QuickCMC Con trol Panel The control panel also allows the user to define the use of the digital output and input contacts A timer function which can be set to start and stop at a given events is useful e g for simple relay tests 46 CHAPTER 6 RELAY TESTING Instantenous Overcurrent Test A simple instantaneous overcurrent function test can be performed in a manual way using the control panel e Check that relay tester outputs are off e Verify relay settings and trip circuit settings e Connect relay tester to relay Example shown in Figure 6 2 e Set the timer to start when the current in phase a becomes non zero e Set the
109. where increasing burden limits the distance 26 32 Wide Area Measurement Systems ref Appendix B is an emerging trend in power systems PMUs and other IEDs carefully placed at important locations in the power system provide real time data of the status of the power system Comparing data from different locations will give information about the health of the power system which can be used to predict potential unwanted scenarios at an early stage Applying intelligent load shedding and power system control it can be used to prevent unwanted conditions before they arise in other words it can provide Wide Area Protection WAP 6 Relay Testing Modern relays are becoming more advanced with the number of built in features and capabilities increasing Most relays will not only have one protective relay ing function it will have several The relay functions will be dependent on the software firmware of the relay and only be limited by the number of inputs and outputs the physical relay has For instance will a comprehensive line differential function require several current inputs one per phase times number of lines At the same time the relay testing methods and equipment are become more powerful The need for relay testing can be divided into five categories 32 e Type Testing Type testing is performed by the relay manufacturer or the end user It is an extensive process where the manufacturer controls the quality of a newly fab
110. y is desirable It is therefore important to have a vision for the future expansions and use of the lab The final outlook for the relay lab may change as it is developed but having a next step defined is vital for ensuring a steady development Ideas for future expansion steps are outlined on the next page 1 Autonomous System e A system with autonomous devices and testing of the basic protection functions overcurrent distance and differential protection is a good start This first part is the focus of this thesis 2 Simple Communication e The next step should be setting up communication between relays It can consist of simple boolean communication used between relays at both ends of a line as described in Chapter 4 4 Or it can be communication capable of transmitting time stamped currents for instance between two relays providing differential protection of a line 3 Advanced IEC61850 Communication e To demonstrate the many capabilities of an IEC61850 compliant protection system the relay lab should be further developed to meet the require ments of this standard The relays provided by ABB are IEC61850 compatible however switches fiber optic cables and configurations are needed before communication is up and running At this stage it could be very interesting to incorporate relays from other manufacturers es pecially other IEC61850 compatible relays to study interoperability opportunities and challenges 4 WAP Protec

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