Practical Troubleshooting of Electrical Equipment and
Contents
1. eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeaaees 157 6 8 Installations ANd COMMISSIONING ccceceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeetees 160 6 9 Power supply connections and earthing requirement cccceeeeeeees 163 6 10 Precautions for start stop control of AC drives ccceeeeeeeeeeeeeeteeeeeeeees 166 6 11 Control wiringifor VSD Sitsccerdar ees ech aceaceen a eae ean else ae ua deletes 169 6 12 Commissioning VSDS oe aios sete oa sai ata ae ctelncaz sn odeae ete vaca een ec arate naan dem ease tee 170 7 Troubleshooting Control circuits aveeete eee eee ee te eee eee eg tke 173 7 1 Basic COMMO CMCUIS 31 30 ascent ecaers cere aac seeds ace a 173 7 2 Ladder LOGIC CNCUNS fests cdc n i e Lo es quae oes eel 177 7 3 TWO WIRE COMTO 2h bk ee i ee ee eee 178 7 4 Three wire control start Stop sssssseeeeeeesseeeeerrrrresstrrrnrrnnnrssrrrnnnrnneeseet 179 7 5 JOGA INCH SC IC LIES eS ornar er a e a a a a naasa 180 7 6 Sequence start and StODi csc aet Goins eaelulediod ie aealie Roh ee uel emt 181 7 7 Automatic sequence Starting sc ics iis shiscads i iaaein huss ea edna dene na 183 7 8 Reversing CIRC UN oso sc Fue te soras cus dedies ces a aucumdedeeces ia ai i 183 7 9 Plug stop and anti plug circuits ce cecccctecetenccececencdeneeedsceceeencdeeetenseeceeeecdeeeeens 187 7 10 Two speed motor control visck row eetascnert te ebe i eteeetera eee eareeistoeederieneds 189 7 11 Overload Protecto M sieaa eaae ea A nee2. Motor b Figure 1 11 Typical cross section and development of an electrical machine 1 2 6 Basic principles of electrical machines In an electrical machine the currents in all the windings combine to produce the resultant flux The field system produces flux Voltages are induced in the windings such as those of an armature When the armature carries current the interaction between the flux and the current produces torque 1 2 7 Basic principles 17 Types of electrical machine windings a Coil winding The winding consists of coils wound on all the poles of the machine and connected together to form a suitable series or parallel circuit The direction of the current in the alternate pole will be opposite so that when one pole is the North Pole the other adjacent pole will be a South Pole This produces the flux in the proper direction completing the magnetic circuit from the North Pole to the South Pole through the iron cores of both the stator and the rotor The coil may be wound on the stator or on the rotor forming the salient or non salient poles of the machine The DC supply is given to these windings and they produce a field proportional to the magnitude of the current through the windings If the poles are on the stator a stationary field is produced in the air gap b Commutator winding The commutator winding is on the rotor The armature has open slots and the conductors are located in these slots and connected to t
3. This however does not mean that you can apply a lower voltage and pass a higher current through the transformer The VA value is bounded individually by the rated voltage and rated current a Why is power transmitted at higher voltages When a particular amount of power has to be transmitted over a certain distance the following aspects need to be considered to decide the best voltage A lower voltage the need higher size conductors to withstand the high current involved There is a physical limitation to the size of conductor Also the percentage voltage drop may become excessive A higher voltage will make the conductor size manageable and reduce the voltage drop value but the cost of the line becomes high due to larger clearances needed The best voltage will be one in which the total operational cost which the sum of the annualized capital cost of the line and the running cost due to power loss in the line is the lowest In practice it is found that transmitting bulk power over long distances is economical if done in the HV range The actual voltage will vary based on the distance 12 Practical Troubleshooting of Electrical Equipment and Control Circuits 1 2 1 2 1 and quantum of power Distribution circuits where typically the amount of power and distance involved are both lower the best voltage is in the MV range 11 22 or 33 kV For the same reason low voltage circuits are found only in local sub distribution circuits Ba
4. always form circles around the current creating them Figure 1 7 Electric force line of a charge IN Current I 7 Figure 1 8 Magnetic field lines around a current carrying conductor Magnetic field produced by a current carrying conductor If a conductor carries a current it produces a magnetic field surrounding it The direction of the current and the direction of the field so produced have a definite relation that is given by the following rules The right hand rule Hold the conductor in the right hand with the fingers closed around the conductor and the thumb pointing towards in the direction of the current The fingers will point towards the direction of the magnetic lines of the flux produced around the conductor 14 Practical Troubleshooting of Electrical Equipment and Control Circuits 1 2 3 Flux produced by a current carrying coil Flux can be produced by causing the current to flow through a coil instead of a conductor Introduction of magnetic material in the core on which the coil is wound increases flux The direction of the magnetic flux in the coil is given by the right hand rule In the case of a motor the direction of the emf induced is such as to oppose the flow of current Whereas in a generator the emf induced is in such a direction as to establish a current Fleming s left hand rule This defines the relationship between the direction of the current the direction of field and the dir
5. f Figure 1 9 A motor action The brushes will move on like this to achieve continuous coil rotation of the motor Similarly the AC motor also functions on the above principle except here the commutator contacts remain stationary because AC current direction continually changes during each half cycle every 180 1 2 4 1 2 5 Basic principles 15 Basic principle of generator We have discussed the basic working of a motor and through the diagrams we have seen a generator action as well In principle an AC generator s construction is similar to the construction of the motor Instead of putting current in current is taken out from the coil in an alternator A mechanical prime mover rotates the coil in between the poles of a permanent magnet and an AC potential is induced in the coil To further define if an AC current will make a coil turn then turning the coil will create an AC current As per Faraday s law when a wire is moved in to cut across magnetic field lines a force is exerted on the charge electrons in the wire by trying to move them along the wire This is how current will start flowing if a complete circuit is provided to it The magnetic field is provided not by magnets but by field coils The coil in which the voltage is induced is called armature winding while the coil that provides the magnetic field is called field winding In high voltage generators it is not good practice to have armatures
6. used for a MOtOFT lenen 106 4 12 Motor failures and methods to extend its life eee eeeeeeeeeeeeeeeeeeeeeeeneees 106 vi Contents 4 13 Motor control trouble remedy table cesceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 107 4 14 Motor starter check chart cacsccrvs siace ceat sree a deatidaSeetee lee death ede eee 109 5 Switches circuit breakers ANd SWitChbOards ccccseecceeeeeeeeeeeeeeeeeeeeeneeeeeaeaees 112 5 1 PPO CUCHOW ce tessticoers eects E A E te a A OA lakes EE aT 112 5 2 Switches and circuit breakers ccceeeeeeeeeceeeeeeeeeeeeeeeaeeeeeeeeeeeeenenaaaaes 112 5 3 Overloads and fault protection cceecsssecceeeeeeeeeeeesseaeeeeeeeeeeeeesenaaeaes 118 5 4 WIC DOAN OS r Fee des ecard sees ene wa al a carted ca be ac ee dae eee aca ae 119 5 5 Motor COMUOMECIMOR cet seerciurcice ca eiea Stes AS ase ee Ae ee ead 120 6 Troubleshooting variable Speed CIives ccccccccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 121 6 1 Theneed for VSDSs onda tercensaeg r a A a E ence 121 6 2 Ye Lo eh VS BE npn Pa a a ee AN 121 6 3 Power electronic COMPONENMS cccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeneneees 123 6 4 Electrical VSD Skrsi e ten eke ean eee 132 6 5 Power electronic rectifiers AC DC Converters cccceeeeeeeeeettteeeeeees 135 6 6 Gate commutated inverters DC AC converters cceeeeeeeeeeeeeeeteees 149 6 7 Overall protection and diagnostics
7. Practical Troubleshooting of Electrical Equipment and Control Circuits Mark Brown Pr Eng DipEE B Sc Elec Eng Senior Staff Engineer IDC Technologies Perth Australia Jawahar Rawtani M Sc Tech MBA Senior Electrical Engineer Nashik India Dinesh Patil BEng Patil and Associates Series editor Steve Mackay FIE Aust CPEng B Sc Elec Eng B Sc Hons MBA Gov Cert Comp Technical Director IDC Technologies AMSTERDAM e BOSTON e HEIDELBERG e LONDON NEW YORK e OXFORD e PARIS e SAN DIEGO Mm SAN FRANCISCO e SINGAPORE e SYDNEY e TOKYO ELSEVIER Newnes is an imprint of Elsevier Newnes Other titles in the series Practical Cleanrooms Technologies and Facilities David Conway Practical Data Acquisition for Instrumentation and Control Systems John Park Steve Mackay Practical Data Communications for Instrumentation and Control Steve Mackay Edwin Wright John Park Practical Digital Signal Processing for Engineers and Technicians Edmund Lai Practical Electrical Network Automation and Communication Systems Cobus Strauss Practical Embedded Controllers John Park Practical Fiber Optics David Bailey Edwin Wright Practical Industrial Data Networks Design Installation and Troubleshooting Steve Mackay Edwin Wright John Park Deon Reynders Practical Industrial Safety Risk Assessment and Shutdown Systems for Instrumentation and Control Dave Macdonald Practical Modern SCADA Protocols DNP3 60870 5
8. Software Services Pvt Ltd Pondicherry India www integra india com Printed and bound in The Netherlands Working together to grow libraries in developing countries www elsevier com www bookaid org www sabre org ELSEVIER BOOKAID Sabre Foundation Contents PGI ACC ccc EAE EEE AE acer AE es earn aa eee ates eae ares E vii 1 Basi RING IDLO i gme E cade sea E E E EEE EE a 1 1 1 DUE CIC OU sintia ey Be edn Py ee A ec 1 1 2 Basic principles of electrical MACHINES eee eternal 12 1 3 AC power systems cc oneness idee 19 1 4 Meters used in troubleshooting cecceeeeeeeeeeeeeeeeeeeeneeeeeeeneeeeeeeeeneeenees 22 2 Devices symbols and CiPCUItS cccccceeecc cece eeeeeeeeeeeeeeeeeeeaaeeaceeeeeeseeeseaanseeeeeeees 24 2 1 Devices ANG SYIMBONS siiis iekrita nans aranna ieee heidi cael 24 2 2 Electrical CIRCUS aoei eer erriei Suttons aeea rion aaga days ianea 24 2 3 Reading and understanding electrical drawings ssssssssseseeeseeseeeeeeeeeeee 28 2 4 Reading and understanding ladder logic ee eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee 36 2 5 Wires and terminal NUMbETPING ccccecceeeeeeeeeeeeeeeeeeeeeeneeeeeeeeeeeeeeeeeeees 39 3 Basic troubleshooting principles is c cciscats ieescid auneada dep saad debacads Hees ie eae ddd ee 42 3 1 TIM OQUIGCHON MeS eE ANS fos cestadas tude EEE tuts dadeusde odessa date de Gs sedies 42 3 2 Basic principles in using a drawing and meter in troub
9. a delta connection b Delta star connection c Star star connection d Star delta connection Basic principles 11 Line Line Phase Phase Connection Voltage Current Voltage Current a Delta delta Primary delta V I V I 1 132 Secondary delta V a Ia V a Ial1 132 b Delta star Primary delta V I V I 1 132 Secondary star 1 732 V a Ta 1 732 V a Ia 1 132 c Star star Primary star V I V 1 732 I Secondary star V a Ia V 1 732 a Ia d Star delta Primary star V I V 1 732 I Secondary delta V 1 132a 1 732 Ta V 1 132 a Ta Table 1 1 Voltage and current transformation for different three phase transformer connections Why is transformer rating defined in kVA A transformer unlike a motor has no mechanical output expressed in kW The current flowing through it can vary in power factor from zero PF lead pure capacitive load to zero PF lag pure inductive load and is decided by the load connected to the secondary The conductor of the winding is rated for a particular current beyond which it will exceed the temperature for which its insulation is rated irrespective of the load power factor Similarly the voltage that can be applied to a transformer primary winding has a limit Exceeding this rated value will cause magnetic saturation of the core leading to distorted output with higher iron losses It is therefore usual to express the rating of the transformer as a product of the rated voltage and the rated current VA or kVA
10. and Related Systems Gordon Clarke Deon Reynders Practical Radio Engineering and Telemetry for Industry David Bailey Practical SCADA for Industry David Bailey Edwin Wright Practical TCP IP and Ethernet Networking Deon Reynders Edwin Wright Practical Variable Speed Drives and Power Electronics Malcolm Barnes Practical Centrifugal Pumps Paresh Girdhar and Octo Moniz Practical Electrical Equipment and Installations in Hazardous Areas Geoffrey Bottrill and G Vijayaraghavan Practical E Manufacturing and Supply Chain Management Gerhard Greef and Ranjan Ghoshal Practical Grounding Bonding Shielding and Surge Protection G Vijayaraghavan Mark Brown and Malcolm Barnes Practical Hazops Trips and Alarms David Macdonald Practical Industrial Data Communications Best Practice Techniques Deon Reynders Steve Mackay and Edwin Wright Practical Machinery Safety David Macdonald Practical Machinery Vibration Analysis and Predictive Maintenance Cornelius Scheffer and Paresh Girdhar Practical Power Distribution for Industry Jan de Kock and Cobus Strauss Practical Process Control for Engineers and Technicians Wolfgang Altmann Practical Power Systems Protection Les Hewitson Mark Brown and Ben Ramesh Practical Telecommunications and Wireless Communications Edwin Wright and Deon Reynders Practical Hydraulics Ravi Doddannavar Andries Barnard Practical Batch Process Management Mike Barker Jawahar Rawtani P
11. avel with respect to each other at a definite speed In rotating machines both voltage and torque are produced Only the direction of power flow determines whether the machine is working as a generator or a motor For a generator e and i are in the same direction T 7 7 Where T mechanical torque T electrical torque T torque lost due to friction For a motor e and i are in opposite direction T T 1 1 2 2 Basic principles 13 In a generator the power is supplied by the prime mover Electrical power is produced by the action of the generator and the resultant power produced due to friction is lost Whereas in the case of a motor the power is supplied by the electrical power supply inputs and there is a Slight loss of the resultant mechanical power produced due to friction Basic principles of electromagnetism Magnetic and electric fields As you are aware each electric charge has its own electric field i e lines of force Electric field lines point away from the positive charges and towards negative charges Figure 1 7 Each charge exerts force on the other charge which is always tangential to the lines of force created by the other charge Similarly the magnetic field lines flow away from the N pole and towards the S pole Figure 1 8 A current moving the electric charges creates a magnetic field Every orbiting electron forms a current loop that creates its own magnetic field Magnetic field lines
12. ds EEE EEIE EEEE 189 7 12 Troubleshooting examples c 04 o4aneetevaten cee een 190 7 13 Troubleshooting strategies eceeeeceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 192 7 14 Ladder logic design exercise cccccceeeeeeeeeeeeeeeeeeeeneceeeeeeeeeeeeeneeeeeenes 194 Appendix A Units and abbreviations 2 2i cisceis ieedieds ethieds heed elses eid ee Ena 195 Appendix B TroubleSnOOling ccsaicccacteien ease 196 Appendix C Low voltage Networks cceeeeeeseceeeeeeeeeeeeeeeaeaeeeeeeeeeeaaaaaaaeeeeeeeeteseneaaeeeeeeees 213 UK ge aoe oc Sed aecet oes seus Seeds ced RAAE RAA nA Aiea ceue dena dati RAE EnA NEA seus sena A AARE RENA RSR AEA 232 Preface There is a large gap between the theory of electron flow magnetic fields and that of troubleshooting electrical equipment and control circuits in the plant In this book we try to avoid or at least minimize discussions on the theory and instead focus on showing you how to troubleshoot electrical equipment and control circuits The book helps to increase your knowledge and skills in improving equipment productivity whilst reducing maintenance costs Reading this book will help you identify prevent and fix common electrical equipment and control circuits The focus is outside the box The emphasis is on practical issues that go beyond typical electrical theory and focus on providing those that attend with the necessary toolbox of skills in solving electrical proble
13. e distribution of the currents around the core surfaces and the voltages applied to the windings In various types of electrical machines the arrangement differs in the distribution of the conductors windings and in core constructions depending on whether it is a continuous or a Salient pole type The magnetic flux permeates the iron cores in a complex manner However as the iron has a high permeability the accurate working of a machine can be determined by considering the flux distribution in the air gap The conductors are actually located in slots formed in the laminations of the core A typical cross section and the corresponding development diagram of an electrical machine with four poles perpendicular to the axis of the cores is shown in Figure 1 11 As shown in the diagram the distribution of flux and current repeats itself at every pair of poles On the poles the windings are so wound that the current flows in the opposite direction and produces a field corresponding to the north and south polarities Maximum flux is along the center of the pole and reduces to zero between the interpole gaps 16 Practical Troubleshooting of Electrical Equipment and Control Circuits Rotor core ae Frame Stator core Stator winding ST WFAN Rotor winding Shaft Bearing Figure 1 10 Common features of an ideal electric machine Ae E e a SE TN OOO POODOSD OOOOOOOl GBOODOO OOA Generator lt
14. e risks involved must be properly evaluated Three phase transformers Large scale generation of electric power is generally three phasic with voltages in 11 or 32 kV Such high three phasic voltage transmission and distribution requires use of the three phase step up and step down transformers Previously it was common practice to use three single phase transformers in place of a single three phase transformer However the consequent evolution of the three phase transformer proved space saving and economical as well Still construction wise a three phase transformer is a combination of three single phase transformers with three primary and three secondary windings mounted on a core having three legs Commonly used three phases are e Three phase three wire delta e Three phase four wire star 1 Delta connection It consists of three phase windings Figure 1 4 connected end to end and are 120 apart from each other electrically Generally the delta three wire system is used for an unbalanced load system The three phase voltages remain constant regardless of load imbalance V Vin Where V line voltage V phase voltage Relationship between line and phase currents I V3 I ph Where I line current I phase current 2 Three phase four wire star connections The star type of construction Figure 1 5 allows a minimum number of turns per phase since phase voltage is 1 V3 of line voltage but the cross
15. ection of the motion If the forefinger of the left hand points in the direction of the field the middle finger points in the direction of the current and the thumb points in the direction of the motion The basic principle of motor The basic working of a motor is based on the fact that when a current carrying conductor is placed in a magnetic field it experiences a force If you take a simple DC motor it has a current carrying coil supported in between two permanent magnets opposite pole facing so that the coil can rotate freely inside When the coil ends are connected to a DC source then the current will flow through it and it behaves like a bar magnet as shown in Figure 1 9 As the current starts flowing the magnetic flux lines of the coil will interact with the flux lines of the permanent magnet This will cause a movement of the coil Figures 1 9 a b c d due to the force of attraction and repulsion between two fields The coil will rotate until it achieves the 180 position because now the opposite poles will be in front of each other Figure 1 9 e and the force of attraction or repulsion will not exist The role of the commutator The commutator brushes just reverse the polarity of DC supply connected to the coil This will cause a change in the direction of the current of the magnetic field and start rotating the coil by another 180 Figure 1 9 f n nC Js s ce Se NS z LS NY st a d
16. gh torque characteristics of a series motor and the speed regulation of a shunt motor 2 AC machines a Squirrel cage induction motor AC machines are simple and sturdy The most common machine of this type is the Squirrel cage induction motor the name was derived from its construction type The basic working of this was dealt with in the previous sections The following relation gives the speed of this motor 12 vons E Pp Where f frequency p number of poles For example if the motor has two poles then at 50 Hz frequency the motor rpm will be 3000 rpm However you will not find 3000 or 1500 rpm on the motor nameplate because the motor rpm will not be 3000 rpm at full load This is because of a slip associated with an induction motor The RPM of the motor is controlled by controlling the frequency f as frequency increases motor speed will also increase High starting current is limited using a star delta starter or reduced voltage starters b Wound rotor motor This is similar in construction to the squirrel cage and works similarly too except that slip rings are provided The main feature of the slip ring motor is that resistors which are connected in series with the rotor circuit limit the starting current
17. he commutator segments in a continuous sequence c Polyphase winding Polyphase winding is a distributed winding Individual conductors are distributed in slots in a suitable way and connected into a number of separate circuits one for each phase The group of conductors forming the phase bands is distributed in a regular sequence over the successive pole pitches so that there is balanced winding that produces an equal voltage per phase This type of winding is mainly used for the stator When supplied with three phase currents it produces a rotating field in the air gap This is of a constant magnitude but rotating at a constant synchronous speed Types of electrical machines Depending on the type of combinations of windings used on the stator and the rotor electrical machines are classified in different types as follows 1 DC machines The DC machines have an edge over AC machines when it comes to the speed control of a motor It is easier and cheaper a Shunt motor This machine has field winding mounted in yoke and the armature winding is mounted on rotor The shunt motor is used where speed regulation is important Self excited Field winding is connected in parallel shunt with the armature winding on the same supply Changing the field current can vary the speed Torque is proportional to armature current This machine can also act as a generator To limit the high starting current of the motor drive release the voltage in
18. leakage e Hence there are no J R losses and core losses e The permeability of the core is high so that the magnetizing current required to produce the flux and to establish it in the core is negligible e Eddy current and hysteresis losses are negligible Types of transformers 1 As per the type of construction a Core type Windings surround a considerable part of the core b Shell type Core surrounds a considerable portion of the windings 2 As per cooling type a Oil filled self cooled Small and medium sized distribution transformers b Oil filled water cooled High voltage transmission line outdoor transformers c Air Cooled type Used for low ratings and can be either of natural air circulation AN or forced circulation AF type 3 As per application a Power transformer These are large transformers used to change voltage levels and current levels as per requirement Power transformers are usually used in either a distribution or a transmission line b Potential transformer PT These are precision voltage step down trans formers used along with low range voltmeters to measure high voltages c Current transformer CT These transformers are used for the measurement of current where the current carrying conductor is treated as a primary transformer This transformer isolates the instrument from high voltage line as well as steps down the current in a known ratio d Isolation transformer These are
19. leshooting circuits 43 3 3 Checks for circuit continuity with disconnected supplly cccceeeeeeeee 44 3 4 Checks for circuit continuity with live Supply cece eee eeeettteeeeeeeeeeeeeee 47 3 5 POSTS AMSG OS oss ee ence die aa aa ai ie dene 48 3 6 TeSUNG dEVICOS iiie ee eee aceite ean eee 49 3 7 NCGS a ha ia gn lace heel ae aoe crea dat ieee Neda a ue Maia ata eo 61 3 8 Accurate wiring of circuits ANd CONNECTIONS cc eeeeeeeeetetetttteeeeeeeeeeeeeeeeeees 62 3 9 Tests for installation and troubleshooting seeeeeseeeeeeeeeeeeeeeeeeeeeseeeeeeeseeeeee 66 4 Troubleshooting AC motors and starters c cece eeceeneee teeter eeeeeeceeeeeeeeeeeeeeeeeaaees 68 4 1 HAO CUCUOM xe 3a ce ae oe Soe AAT at nated ee a tet 68 4 2 Fundamentals of three phase AC Motors ccccecceceeeeeeeeeeeeeeeeeenneeeeeeees 68 4 3 Fundamental of single phase AC MOtors cccceeeccceesceeeeeeeeeeeeeesnneeeeeeees 78 4 4 DO MOTOTS a a iianeh teense delanetst xe tess anes acids aE 81 4 5 Motor ONGIOSUTSS arreire se dare de inaia a enseia o ripidi denned cotedas depaadadeuatde 85 4 6 Motor terminal identification and connection diagram ceeeeeeeees 86 4 7 Motor rating and insulation types neal 88 4 8 Operating a motor for forward and reverse operation cccceeeeeeeeeeeeees 90 4 9 Motor braking Meth S erasana eea ae a eee eee ee 91 4 10 ONOI 1OSUING E E EEE E ae ee ek 100 4 11 Measurements
20. ms 2 Practical Troubleshooting of Electrical Equipment and Control Circuits Voltage is defined as the electrical potential difference that causes electrons to flow Current is defined as the flow of electrons and is measured in amperes Resistance is defined as the opposition to the flow of electrons and is measured in ohms All three are bound together with Ohm s law which gives the following relation between the three V IxR Where V Voltage I Current R Resistance a Power In DC circuits power watts is simply a product of voltage and current P VxI For AC circuits the formula holds true for purely resistive circuits however for the following types of AC circuits power is not just a product of voltage and current Apparent power is the product of voltage and ampere i e VA or KVA is known as apparent power Apparent power is total power supplied to a circuit inclusive of the true and reactive power Real power or true power is the power that can be converted into work and is measured in watts Reactive power If the circuit is of an inductive or capacitive type then the reactive component consumes power and cannot be converted into work This is known as reactive power and is denoted by the unit VAR b Relationship between powers Apparent power VA V XA True power Watts VA xcos Reactive power VAR VA x sing c Power factor Power factor is defined as the ratio of real power to apparent powe
21. ms ranging from control circuits to motors and variable speed drives This book focuses on the main issues of troubleshooting electrical equipment and control circuits of today to enable you to walk onto your plant or facility to troubleshoot and fix problems as quickly as possible This is not an advanced book but one aimed at the fundamentals of troubleshooting systems The book is very practical in its approach to troubleshooting and the examples you will be shown are applicable to any facility We would hope that you will gain the following knowledge from this book Diagnose electrical problems right first time Minimize the expensive trial and error troubleshooting approach Reduce unexpected downtime on electrical motors and other equipment Improve plant safety Learn specific techniques to troubleshoot equipment and control circuits Analyze equipment problems Determine causes of equipment failure Troubleshoot electrical equipment and control circuits Typical people who will find this book useful include Plant Electricians Mechanical Engineers Production Operators and Supervisors Utilities Maintenance Personnel Plant Engineers Pre requisites A basic understanding of electrical theory and problems you have encountered in the past would be helpful but a basic review is undertaken at the beginning of the book 1 1 Basic principles Objectives e To refresh basic electrical concepts e To define basic concep
22. phase transformers or a three phase transformer can be connected in the following ways e Primary in delta secondary in delta e Primary in delta secondary in star e Primary in star secondary in star e Primary in star secondary in delta Figure 1 6 shows the various types of connections of three phase transformers On the primary side V is the line voltage and the line current The secondary sideline voltages and currents are determined by considering the ratio of the number of turns per phase a N N gt and the type of connection Table 1 1 gives a quick view of primary line voltages and line currents and secondary phase voltages and currents The power delivered by the transformer in an ideal condition irrespective of the type of connection 1 732 V i assuming cos 1 Testing transformers The following tests are carried out on transformers Measurement of winding resistance Measurement of Voltage ratio Test phasor voltage relationship Measurement of impedance voltage short circuit impedance and load loss Measurement of no load loss and no load current Measurement of insulation resistance Dielectric test Temperature rise 10 Practical Troubleshooting of Electrical Equipment and Control Circuits I al V IN3 V a a I al V3 va V3 V a b I al i 7 VIN3 Viav3 V 4 4 Via c al V3 VIN 3a lt S k a d Figure 1 6 Types of connections for three phase transformers a Delt
23. r The maximum value it can carry is either 1 or 100 which would be obtained in a purely resistive circuit True power Power factor ___ Apparent power Watts kVA d Percentage voltage regulation No load voltage Full load voltage Regulation 100 Full load voltage Basic principles 3 e Electrical energy This is calculated as the amount of electrical energy used in an hour and is expressed as follows Kilowatthour kW xh Where kW kilowatt h hour f Types of circuits There are only two types of electrical circuits series and parallel A series circuit is defined as a circuit in which the elements in a series carry the same current while voltage drop across each may be different A parallel circuit is defined as a circuit in which the elements in parallel have the same voltage but the currents may be different Transformer A transformer is a device that transforms voltage from one level to another They are widely used in power systems With the help of transformers it is possible to transmit power at an economical transmission voltage and to utilize power at an economic effective voltage Basic principle Transformer working is based on mutual emf induction between two coils which are magnetically coupled When an AC voltage is applied to one of the windings called as the primary it produces alternating magnetic flux in the core made of magnetic material us
24. ractical Troubleshooting of Electrical Equipment and Control Circuits Newnes An imprint of Elsevier Linacre House Jordan Hill Oxford OX2 8DP 30 Corporate Drive Burlington MA 01803 First published 2005 Copyright 2005 IDC Technologies All rights reserved No part of this publication may be reproduced in any material form including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication without the written permission of the copyright holder except in accordance with the provisions of the Copyright Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd 90 Tottenham Court Road London England W1T 4LP Applications for the copyright holder s written permission to reproduce any part of this publication should be addressed to the publisher British Library Cataloguing in Publication Data Brown Mark Practical troubleshooting electrical equipment 1 Electrical fault location 2 Electric machinery maintenance and repair 3 Electric engineering materials testing Title Il Rawtani Jawahar III Patil Dinesh 621 3 192 Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress ISBN 07506 6278 6 For information on all Newnes Publications visit our website at www newnespress com Typeset and edited by Integra
25. rotating because current collecting brushes of high ratings are required Rather the armature is kept stationary and the field is kept rotating Alternators of low capacity use a permanent magnet as a field while in high capacity alternators field winding supply is derived from the exciter assembly An exciter assembly is a small alternator connected on the same shaft Idealized machines There is a stationary member called a stator and a rotating member called a rotor The rotating member is mounted on bearings fixed to the stationary member The stator and the rotor have cylindrical iron cores separated by an air gap Windings are wound on the stator and the rotor core A common magnetic flux passes across the air gap from one core to another forming a combined magnetic circuit Two cylindrical iron surfaces with an air gap between them move relative to each other The cylindrical surface may be divided by an even number of salient poles with spaces in between or it may be continuous with slot openings uniformly spaced around the circle This structure may be for either of the stator or the rotor The common features of an ideal electrical machine are shown in the Figure 1 10 For windings conductors run parallel to the axis of the cylinders near the surface The conductors are connected into coils by the end connections outside the core and the coils are connected to form the windings of the machine The operation of the machine depends on th
26. s Figure 1 1 Schematic diagram of a single phase transformer Potential induced There is a very simple and straight relationship between the potential across the primary coil and the potential induced in the secondary coil The ratio of the primary potential to the secondary potential is the ratio of the number of turns in each and is represented as follows 2 2 ll Sis The concepts of step up and step down transformers function on similar relation A step up transformer increases the output voltage by taking N gt N and a step down transformer decreases the output voltage by taking N gt N Current induced When the transformer is loaded then the current is inversely proportional to the voltages and is represented as follows ees a Mie 1 N I as EMF equation of a transformer rms value of the induced emf in the primary winding is E 4 44x f XN xo rms value of the induced emf in the secondary winding is E 4 44x f x N X n Where N Number of turns in primary N Number of turns in secondary Maximum flux in core and f Frequency of AC input in Hz 1 1 3 Basic principles 5 Ideal transformer The following assumptions are made in the case of an ideal transformer e No loss or gain of energy takes place e Winding has no ohm resistances e The flux produced is confined to the core of the transformer which links fully both the windings i e there is no flux
27. section of the conductor will have to be increased as the current is higher compared to a delta winding by a factor of V3 Each winding at one end is connected to a common end like a neutral point therefore as a whole there are four wires 8 Practical Troubleshooting of Electrical Equipment and Control Circuits B O B R Y B YO OY Pri side Sec side R O O R Figure 1 4 Three phase transformer delta connection on primary side A three wire source as obtained from a delta winding may cause problems when feeding to a star connected unbalanced load Because of the unbalance the load neutral will shift and cause change of voltage in the individual phases of the load It is better to use a star connected four wire source in such cases Three wire sources are best suited for balanced loads such as motors B O O B y R 1 B YO OY N Pri side Sec side RO OR NO e O N Figure 1 5 Three phase four wire transformer star connection Basic principles 9 Relationship between line and phase voltages V V3 Von Where V line voltage V phase voltage Relationship between line and phase currents I la Where I line current I phase current Output power of a transformer in kW P V3 xV xI xcos kW Where V line voltage I line current cos power factor 3 Possible combinations of star and delta The primary and secondary windings of three single
28. sic principles of electrical machines Electromechanical energy conversion The electromechanical energy conversion device is a link between electrical and mechanical systems When the mechanical system delivers energy through the device to the electrical system the device is called a generator Generator Mechanical gt Electrical system system When an electrical system delivers energy through the device to the mechanical system the device is called a motor Motor Mechanical E Electrical system system The process is reversible however the part of energy converted to heat is lost and is irreversible An electric machine can be made to work either as a generator or as a motor The electromechanical conversion depends on the interrelation between e Electric and magnetic fields e Mechanical forces and motion In rotating machines power is generated by the relative motion of the coils In the case of a generator the winding is rotated mechanically in the magnetic field This causes the flux linkages with the windings to change causing induced voltages In the case of a motor the current carrying conductor is allowed inside a magnetic field Mechanical force is exerted on a current carrying conductor in a magnetic field and hence a resultant torque is produced to act on the rotor In both a generator as well as a motor the current carrying conductor is in the magnetic field The conductors and flux tr
29. the polarity In the above example primary total turns to secondary total turns are in the 2 1 ratio leading to half voltage H1 480 V AC H4 H 200 turns 200 turns Xmer 1 Xmer 2 400 turns Pri side Sec side 100 turns 200 turns 100 turns X4 240V AC X1 Figure 1 2 Series connection of two single phase transformers b Parallel connection of two single phase transformers As shown in Figure 1 3 two transformers are connected in series on the primary side while the secondary sides are connected in parallel H1 480 V AC H4 H 1 H2 H3 200 turns 200 turns Xmer Xmer 2 400 turns Pri side Sec side 100 turns x3 X2 x1 X4 120V AC Figure 1 3 Parallel connection of two single phase Transformers Basic principles 7 On the primary side the number of turns is added while on the secondary side they remain as it is due to their parallel condition LVDT linear voltage differential transformer is the best practical example of the basic transformer and its series connection Use of transformers with such connections can pose problems of safety and load sharing and are hardly used in practical power circuits It is possible to deploy these connections while designing control transformers if such use will have any specific advantage Parallel operation of two separate transformers is possible under specific conditions to meet an increased load requirement but th
30. the ramp For this motor a variable resistor is connected in series with the field circuit to change the flux value and the speed by a small amount Separately excited Field winding is connected in parallel shunt with the armature winding with separate excitation 18 Practical Troubleshooting of Electrical Equipment and Control Circuits Torque is proportional to armature current In a separately excited shunt motor speed can be varied up to a certain limit by changing armature voltage After that using field weakening reducing field current it is possible to increase the speed of motor above base speed Other features remain same as that of the self excited one b Series motor As the name suggests in this type of motors field winding is connected in series with the armature winding Naturally heavy current will pass through it hence field winding of a thicker gage is used A series motor is used where speed regulation is not important The main advantage of this motor is that a high torque can be obtained which makes it useful for applications such as diesel locomotives cranes etc The relationship between Torque and current is as follows T a la It is important to start this motor in a loaded condition else it could lead to damage of the motor and its surroundings c Compound motor If we combine both series and shunt motors then we will have a compound motor This combines the good features of both types such as hi
31. ts of transformer e To refresh single phase power concepts e To refresh three phase power concepts Introduction A significant proportion of industrial electricity is about single phase and three phase transformers AC and DC machines In this context we will study the electrical circuits and their construction design testing operation and maintenance For troubleshooting electrical equipment and control circuits it is important to understand the basic principles on which the electrical equipment works The following sections will outline the basic electrical concepts Basic electrical concepts In each plant the mechanical movement of different equipments is caused by an electric prime mover motor Electrical power is derived from either utilities or internal generators and is distributed through transformers to deliver usable voltage levels Electricity is found in two common forms e AC alternating current e DC direct current Electrical equipments can run on either of the AC DC forms of electrical energies The selection of energy source for equipment depends on its application requirements Each energy source has its own merits and demerits Industrial AC voltage levels are roughly defined as LV low voltage and HV high voltage with frequency of 50 60 Hz An electrical circuit has the following three basic components irrespective of its electrical energy form e Voltage volts e Ampere amps e Resistance oh
32. ually some form of steel The flux is produced by a small magnetizing current which flows through the winding The alternating magnetic flux induces an electromotive force EMF in the secondary winding magnetically linked with the same core and appears as a voltage across the terminals of this winding Cold rolled grain oriented CRGO steel is used as the core material to provide a low reluctance low loss flux path The steel is in the form of varnished laminations to reduce eddy current flow and losses on account of this Typically the coil connected to the source is known as the primary coil and the coil applied to the load is the secondary coil A schematic diagram of a single phase transformer is shown in the Figure 1 1 A single phase transformer consists mainly of a magnetic core on which two windings primary and secondary are wound The primary winding is supplied with an AC source of supply voltage V The current J flowing in the primary winding produces flux which varies with time This flux links with both the windings and produces induced emfs The emf produced in the primary winding is equal and opposite of the applied voltage neglecting losses The emf is also induced in the secondary winding due to this mutual flux The magnitude of the induced emf depends on the ratio of the number of turns in the primary and the secondary windings of the transformer 4 Practical Troubleshooting of Electrical Equipment and Control Circuit
33. used to isolate two different circuits without changing the voltage level or current level A few important points about transformers e Used to transfer energy from one AC circuit to another e Frequency remains the same in both the circuits e No ideal transformer exists e Also used in metering applications current transformer i e CT potential transformers i e PT e Used for isolation of two different circuits isolation transformers e Transformer power is expressed in VA volt amperes e Transformer polarity is indicated by using dots If primary and secondary windings have dots at the top and bottom positions or vice versa in diagram then it means that the phases are in inverse relationship 6 Practical Troubleshooting of Electrical Equipment and Control Circuits 1 1 5 Connections of single phase transformer Depending on the application s requirement two or more transformers have to be connected in a series or parallel circuits Such connections can be undertaken as depicted in the following diagram examples a Series connection of two single phase transformers As shown in Figure 1 2 two transformers can be connected in a series connection If both are connected as in Figure 1 2 then voltage twice that of voltage rating of the individual transformer can be applied Their current rating must be equal and high enough to carry load current Precaution should be taken to connect transformers windings keeping in mind
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