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PAPPU-THESIS

1. 0 49 Line diagram showing point of connection of PMU cece eeeeeeeeeeereees 50 Flowchart description of the code nu lea 52 GUI deyeloped in MATLAB ana aa 53 Reactive Power consumption for both wind farms for wind speeds ranging from 3 6mM S essseseesesessssessessresresstssresressersresreeseseresees 55 Active Power transmission for wind speeds ranging from vii 6 3 6 4 6 5 6 6 6 7 6 8 6 9 6 10 6 11 6 12 7 1 71 2 1 3 7 4 7 5 8 1 8 2 8 3 Texas Tech University Santosh Pappu August 2012 Reactive Power consumption for both wind farms uersersnnesnneennnen nn 57 Voltage at 25kV bus for both wind farms ss sseesseesseesseeeesseesseessessseeeseee 58 Active power transmitted from both wind farms ue22er ser enneennnen nn 58 Reactive Power consumed for both wind farms uuessersnersnnesnneennnennn 60 Voltage at 25 kV for both wind farms 00 0 0 eeecceceseceeeeeeeeeneeeesteeeesneeeeaees 60 Active Power generated for wind speeds from 21 24m 8 cee eeeeeeseees 61 Reactive Power consumption for a three phase fault for OT SOC nenne raislekuirenn 62 Active Power Transmitted when 1 5MW is lost in both wind arms des dees ee tle aa aie ea eae 63 Active Power transmitted to the grid from both wind Electrical Torque of both generators when a three phase to ground fault oecurs aen eine lee 65 Active Power at point of interconnection uue
2. Delta Frequency o 3 00 12 40 00 22 pm mm m 12370 IE Fig 8 1 GUI display when there is an excursion in the parameters a 66 Texas Tech University Santosh Pappu August 2012 This information contains the plots of three phases of voltage frequency and delta frequency vs time All these graphs are plotted for the range of two minutes before the incident and two minutes after it three excel files on average These graphs will be saved to respective sub folders Each sub folder is named after the number of error and is under the folder which determines the type of error that has occurred For example if the voltage in phase A goes out of range for the first time a sub folder with the name of 1 is created under the folder with the name of VoltagePhaseAError Fig 8 2 shows the folder where the excel sheets which contain any excursion in data are saved E pmu 10 5 2011 5 33PM File folder di pmu9 10 5 2011 5 46PM File folder d pmuld 10 5 2011 6 17 PM File folder I PMUS6 10 14 2011 3 55 PM File folder d PMU100 10 5 2011 5 35PM File folde PMUFrequencytrror Program Files 10 26 2011 6 30 PM File folder I PTW32 9 9 2011 11 16PM File folder I SPB_Data 5 7 2011 11 04 PM File folder Fig 8 2 Folder where the erroneous files are saved Each sub folder also includes the excel file that contains the error All these folders are saved in the director
3. be equipped with any type of three phase generator Today the demand for grid compatible electric current can be met by connecting frequency converters even if the generator supplies alternating current AC of variable frequency or direct current DC Several generic types of generators may be used in wind turbines 1 e Asynchronous induction generator e squirrel cage induction generator SCIG e wound rotor induction generator WRIG e Doubly fed induction generator DFIG e Synchronous generator e wound rotor generator WRSG e Permanent magnet generator PMSG Texas Tech University Santosh Pappu August 2012 Fig 1 2 Generator of a Wind Turbine 3 Fig 1 2 shows the stator and rotor of a generator of a turbine The rotor of the wind turbine is connected to the rotor of the generator via a shaft or gear box The rotation of the blades of the wind turbine causes rotation of the rotor which in turn rotates the rotor of the generator This mechanical energy is converted to electrical energy which is supplied to the grid 1 2 Wind Energy Technologies Wind Turbine technologies can be classified according to type of speed control and power control Currently four different types of technologies exist They vary in terms of generators used and additional equipment used for speed and power control The four types are e Type 1 Induction Generator directly connected to the grid from the stator This is also known as fixed s
4. inputs 5 3 Synchrophasor Vector Processor SEL 3378 The SEL 3378 Synchrophasor Vector Processor uses synchronized phasor measurements for real time power system monitoring control and protection The SEL 3378 acquires and time correlates synchrophasor data from various Phasor 38 Texas Tech University Santosh Pappu August 2012 Measurement Units such as SEL 351 SEL 421 SEL 451 relays and from other devices that support the IEEE C37 118 2005 Standard for Synchrophasors for Power Systems The SEL 3378 receives synchrophasor messages through serial and Ethernet communications 17 The SEL 3378 was setup in Texas Tech and communication between the PMU and the Processor through Ethernet The SEL 3378 provides a mechanism for collecting and time correlating synchrophasor data from as many as 20PMUs at a maximum data rate of 60 messages per second with a message size of up to 354 bytes The SEL 3378 includes the Power Calculation Function Block Phase Angle Difference Function Block Modal Analysis Function Block and Substation and State Topology Processor Function A GPS clock is connected to the SEL 3378 to synchronize it with the PMUs for real time data collection and analysis The SEL 3378 allows the data from the PMU to be archived for analysis 16 Shown below in Fig 5 2 is an application of the SEL 3378 communicating through the Ethernet m gell wimi ki mk i ini ki J Hott Ley te A ef bt of aki ES
5. into the output of the stator The disadvantage of the WRIG is that it is more expensive than the SCIG and not as robust as the SCIG Texas Tech University Santosh Pappu August 2012 The DFIG consists of a WRIG with the stator windings directly connected to the constant frequency three phase grid and with the rotor windings mounted to a bidirectional back to back IGBT voltage source converter The term doubly fed refers to the fact that the voltage on the stator is applied from the grid and the voltage on the rotor is induced by the power converter This system allows a variable speed operation over a large but restricted range The converter compensates the difference between the mechanical and electrical frequency by injecting a rotor current with a variable frequency Both during normal operation and faults the behavior of the generator is thus governed by the power converter and its controllers The power converter consists of two converters the rotor side converter and grid side converter which are controlled independently of each other 1 rota connection poner electronic converters Power flow Fig 2 2 Rotor of the DFIG connected through the power electronics to the grid and the stator is connected directly to the grid 7 Fig 2 2 shows the schematic of a DFIG The rotor of the generator is connected to the grid through the power electronics The stator of the generator is connected directly to the grid Thi
6. of Power Quality from the Wind Turbine The data collected 69 Texas Tech University Santosh Pappu August 2012 would be analyzed using the code developed This would help maintain good Power Quality at the Facility 70 Texas Tech University Santosh Pappu August 2012 CHAPTER 10 FUTURE WORK The models built for comparison of wind farms for different ratings and evaluation of hub concept will be validated by simulating the models in software such as PSSE PSLF The code built for evaluating power quality will be made to evaluate more data like THD voltage sags dips swells The PMU will be installed once the wind turbine at XFAB has been installed and data will be recorded and evaluated 71 Texas Tech University Santosh Pappu August 2012 REFERENCES 1 Thomas Ackerman Wind Power in Power Systems Royal Institute of Technology Stockholm Sweden 2 http en wikipedia org wiki Wind_turbine 3 http planet energy org sustainable_energy Blog_17_page html 4 AGCTF 9 1 11 Meeting Materials 5 http en wikipedia org wiki Power_quality 6 Mathworks documentation Available http www mathworks com 7 http www ncl ac uk eee research project 974 8 http www almohandes org vb showthread php t 47664 9 http www donsion org calidad cc8 c8 11 pdf 10 AGCTF 9 6 11 Whitepaper 11 Kenneth E Okedu Transient Analysis of DFIG and IG during Grid Fault in The Pacific Journal of Scienc
7. source matching the system voltage in phase frequency and with amplitude which can be continuously and rapidly controlled for reactive power control The STATCOM can inject or absorb reactive power to from the bus where it is connected via a coupling transformer 13 Power System wen sc Fig 4 5 Schematic of STATCOM 13 30 Texas Tech University Santosh Pappu August 2012 The control system can be designed to maintain the magnitude of the bus voltage constant by controlling the magnitude and phase shift of the VSC output voltage With the VSC voltage and the bus voltage the output of the VSC can be expressed as 10 P 2 sind 4 3 _ Vile vf Q 2 cos 4 4 Where P and Q are the active and reactive power of the STATCOM respectively V and Vzare the bus voltage and VSC voltage respectively X is the reactance of the coupling transformer and 6 is the phase difference between the voltages V and V2 If the AC voltage generated by the VSC is higher lower than the system voltageV the STATCOM generates absorbs reactive power 8 The STATCOM is rated for 9 5MVA It is operated in voltage regulation mode The voltage reference Vref is set at 1 0 pu The STATCOM was set for a droop reactance of 0 003 pu The STATCOM provides reactive power for the wind farm as no fixed capacitor banks are used for this configuration 4 5 Topology of Wind Farms for Comparison of Wind Farms The wind turbines are connected to p
8. that have a poor power factor and often poor voltage regulation There are however other uses the most common use is for voltage stability A STATCOM is a voltage source converter VSC based device with the voltage source behind a reactor The voltage source is created from a DC capacitor and therefore a STATCOM has very little active power capability However its active power capability can be increased if a suitable 29 Texas Tech University Santosh Pappu August 2012 energy storage device is connected across the DC capacitor The reactive power at the terminals of the STATCOM depends on the amplitude of the voltage source For example if the terminal voltage of the VSC is higher than the AC voltage at the point of connection the STATCOM generates reactive current on the other hand when the amplitude of the voltage source is lower than the AC voltage it absorbs reactive power The response time of a STATCOM is shorter than that of an SVC mainly due to the fast switching times provided by the IGBTs of the voltage source converter The STATCOM also provides better reactive power support at low AC voltages than an SVC since the reactive power from a STATCOM decreases linearly with the AC voltage as the current can be maintained at the rated value even down to low AC voltage The STATCOM is designed using a power electronics voltage source converter VSC as shown in Fig 4 5 The function of the STATCOM is a fully controllable voltage
9. with DFIG Reactive Power MVAR N BEE EEE VE EEE VE EEE I 10 20 30 40 50 60 70 Time sec Fig 6 3 Reactive Power consumption for both wind farms 51 1 02 1 01 0 99 Voltage at 25kv bus pu 0 97 0 96 Active Power IVVV Texas Tech University Santosh Pappu August 2012 10 20 30 40 50 Time sec Fig 6 4 Voltage at 25kV bus for both wind farms 60 70 10 20 30 40 50 Time sec Fig 6 5 Active Power transmitted from both wind farms 52 70 Texas Tech University Santosh Pappu August 2012 6 3 Wind Speeds ranging from 21 24m s The wind farms were then simulated for wind speeds ranging from 21 24m s nearing cutoff wind speed Fig 6 6 shows the reactive power consumed for both wind farms The initial few seconds are the startup transients as the turbine starts rotating for a wind speed of 21m s The wind farm with FSIG trips after 5sec due to over speed and does not consume any reactive power after that The DFIG trips due to over speed when the wind speed is stepped up to 24m s and consumes reactive power until then Fig 6 7 shows the voltage at the 25kV bus Due to the initial wind speed of 21m s transients are present due to high reactive power consumption at that wind speed and settles once the turbine is tripped due to over speed in FSIG wind farm The voltage dips down to a certain value due to consumption of reactive power Once the turbin
10. 2 gt gt gt D oo rR T T T T 1 L 1 1 Voltage at terminals of wind turbine pu gt nme T 1 fl le fed t 5 10 15 20 25 30 35 40 45 50 Time sec Fig 7 2 Voltage at the terminals of the wind turbine with three phase to ground fault Fig 7 3 shows that the fault on wind turbine in wind farm A has an effect on the wind farm B This is due to the fact that during the fault the wind turbine in wind farm A absorbs excessive reactive power from the grid to support the voltage This causes a dip in the voltage of wind farm B due to absorption of reactive power by the turbine subject to fault in wind farm A 62 Texas Tech University Santosh Pappu August 2012 1 02 amp 3s er T T 1 1 I 1 1 Voltage at 34 5kV bus of Wind farm B So so a T 1 0 95 0 5 10 15 20 25 30 35 40 45 50 Time sec Fig 7 3 Voltage at terminals of wind farm B Fig 7 4 shows the electrical torque of a wind turbine in the wind farm B When the fault occurs at 35sec in Wind Farm A pulsations occur in the rotor of the wind turbine in wind farm B and cause pulsations in the electrical torque 63 Texas Tech University Santosh Pappu August 2012 gt T 1 amp nm T x gt co 1 gt gt D n T T ri L 1 Electrical Torque Te of wind turbine of wind farm B gt gt m T T L 1 gt 5 0 6 a 5 X 5 4 amp 8 Timelsec Fig 7 4 Electrical Torque of wind turb
11. 2012 te gt i ai Asynchronous machine Stator currents Bl Grid side converter currents Vind mis Generator amp Converters Fig 4 4 Model of the DFIG in MATLAB Simulink 11 Fig 4 4 shows the inbuilt model of the DFIG in MATLAB Simulink The model as mentioned before is a phasor model The generator is modeled as a constant current source hence a resistor is placed in parallel to the generator The parameters used for the DFIG is listed below in Table 4 2 28 Texas Tech University Santosh Pappu August 2012 Table 4 2 PARAMETERS OF DFIG Parameter Value Nominal Power MW 1 5 Nominal Voltage V 575 Nominal Power Factor 0 9 Stator Resistance pu 0 0071 Stator Leakage Inductance pu 0 171 Rotor Resistance pu 0 005 Rotor Leakage Inductance pu 0 156 Magnetizing Inductance pu 2 9 Inertia Constant 5 0 Friction Factor 0 001 Pole Pairs 3 4 4 STATCOM A static synchronous compensator STATCOM also known as a static synchronous condenser STATCON is a regulating device used on alternating current electricity transmission networks It is based on a power electronics voltage source converter and can act as either a source or sink of reactive AC power to an electricity network If connected to a source of power it can also provide active AC power It is a member of the FACTS family of devices Usually a STATCOM is installed to support electricity networks
12. 30 40 50 60 10 Time Fig 6 10 Active Power transmitted when 1 5MW is lost in both wind farms 6 5 Equal Number of turbines Lost to Faults Situations in which three phase to ground faults were installed on the terminals of equal number of turbines on both the wind farm configurations Three phases to ground faults were installed on two wind turbines in each configuration In the wind farm consisting of the DFIG two additional turbines were tripped due to faults on two other turbines The reason for this trip was AC under voltage The voltages on both the turbines were less than 0 75pu for more than 5sec The fault on both the turbines caused high transient currents due to which the DC voltage increased beyond 1900V which caused the relay to trip both the turbines The reactive power consumed by the DFIG is less than that consumed by the FSIG The difference being in the order of IMVAR Fig 6 11 shows the active power transmitted in both cases For the wind 57 Texas Tech University Santosh Pappu August 2012 farm consisting of the DFIG the active power generated is 2 5MW as four turbines are totally tripped Whereas in the wind farm consisting of FSIG only two turbines are lost to faults and a total of 7 2MW real power is transmitted to the grid This way the FSIG generates more active power than the DFIG due to three phase faults on two turbines Fig 6 12 shows the Electrical Torque of DFIG and FSIG A three phase to ground fault is installed a
13. 30 times per second or 1800 times per minute This data is saved in the form of excel files in a specific directory Each excel file contains the information for two minutes of wind turbine function Due to issues such as transients it is necessary to check the data coming from PMU to see whether they meet the standard criteria or not Any sudden spike or inconsistency can seriously damage electronic devices In order to do this a MATLAB program was developed This MATLAB program checks the input frequency and three phase voltage It takes an average of two seconds for the code to process one excel file containing two minutes of data Fig 4 5 describes the working of the code in the form of a flowchart 45 Texas Tech University Santosh Pappu August 2012 Start GUI initialization Boundaries for Frequency nase B Read The Next Plot And Save The Error To the Respective Folder Fig 5 5 Flowchart description of the code In order to observe and analyze any interruption or possible error input frequency and voltages for all phases are checked through the code An upper bound and lower bound can be set for each variable These values are usually 3 Hz from 60 Hz for frequency and 5V from 120V for each phase in the three phase voltage 46 Texas Tech University Santosh Pappu August 2012 However users can set their own desired values for each boundary The Code uses a graphical user interface GUI to set these value
14. A B R vay L we Tu 5 4 1 where C A P is the characteristic curve which depends on the generator p is the air density R is the radius of the blades v is the wind speed is the blade angle and A is the tip speed ratio i e the ratio of the speed at the tip of the blades to the speed of the wind otherwise pease 4 2 Vw The wind farms have been simulated for three different wind profiles to analyze the active power transmitted from the wind farm to the grid and reactive power consumed for those wind profiles The three wind profiles are at cut in wind speed at rated wind speed where the turbines output maximum power and at cut off wind speed where the turbines trip due to over speed condition A PI controller has 23 Texas Tech University Santosh Pappu August 2012 been used to implement pitch angle control to limit the pitch angle of the blades of the turbine During high wind speeds an over speed condition of the generators initiates a trip which isolates the generator from the rest of the system 25 20 5 N n T oO T J Wind Speed m s 5 10 15 20 25 30 35 40 45 50 Time sec Fig 4 1 Various Wind Speeds used in the simulation for comparison of wind farms with different configurations Fig 4 1 shows the graph depicting the wind speeds with respect to time The models were simulated for the three wind speeds The t
15. DESIGN AND ANALYSIS OF WIND ENERGY SYSTEMS IN POWER APPLICATIONS by Santosh Pappu B E A Thesis In ELECTRICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCES IN ELECTRICAL ENGINEERING Approved Dr Stephen B Bayne Chair of Committee Dr Michael Giesselmann Peggy Gordon Miller Dean of the Graduate School August 2012 Copyright 2010 Santosh Pappu Texas Tech University Santosh Pappu August 2012 ACKNOWLEDGMENTS I am grateful to Dr Stephen Bayne for taking me as a graduate student early in my Masters He has been a guide in every senses His thoughts and insights to Electrical Engineering have only broadened my horizon in Electrical Engineering His ideas and guidance have been instrumental in publishing three IEEE conference papers during my time here His belief in my abilities and constant encouragement has made me work harder to achieve my goals I would like to thank Dr Michael Giesselmann for accepting to be the co chair on my committee for my thesis defense I thank Mr Jerry Lopez for being a great mentor He has been an inspiration throughout my Masters His work ethics and commitment has been a great influence on me Interacting with him has only made me a better person I thank my friends Chaitanya S K Purvi Patni and Sanjar Hussain for encouraging me throughout my Masters I thank Mr Sandee
16. acquisition Fig 4 2 Model of Induction Generator in MATLAB simulink 11 25 Texas Tech University Santosh Pappu August 2012 Fig 4 2 shows the model of the induction generator in MATLAB Simulink The model is readily available in MATLAB The model consists of a squirrel cage induction generator connected to a circuit breaker on the stator The model also consists of a wind turbine model The rotor of the turbine is connected to the rotor of the generator Wind speed is the input to the turbine A feedback loop is designed for the implementation of pitch angle control which is given as another input to the wind turbine Fig 4 3 shows the feedback control used for pitch angle control Bo Pref Pe Fig 4 3 Feedback loop for Pitch Angle control 12 In Fig 4 3 the nominal power is compared to the actual power from the generator and given to the PI controller The angle is fed to the controls of the turbine for pitch angle control This pitch angle helps in the control of active power of the wind turbine during high speeds The mechanical torque Tm of the wind turbine drives the rotor of the generator and is transferred as electrical torque T The circuit breaker connected to the stator of the generators receives trip signals from a relay The breaker trips the generator when the conditions such as over voltage over current over speed occur to shield the remaining power system from damage The relay sends a trip signal to th
17. c motors for instance elevators oscillating loads Consequences Most consequences are common to undervoltages The most perceptible consequence is the flickering of lighting and screens giving the impression of unsteadiness of visual perception fluctuation Noise Description Superimposing of high frequency signals on the waveform of the power system frequency Causes Electromagnetic interferences provoked by Hertzian waves such as microwaves television diffusion and radiation due to welding machines arc furnaces and electronic equipment Improper grounding may also be a cause Consequences Disturbances on sensitive electronic equipment usually not destructive Voltage Unbalance Description A voltage variation in a three phase system in which the three voltage magnitudes or the phaseangle differences between them are not equal Causes Large single phase loads induction furnaces traction loads incorrect distribution of all single phase loads by the three phases of the system this may be also due to a fault Consequences Unbalanced systems imply the existence of a negative sequence that is harmful to all three phase loads The most affected loads are three phase induction machines 5 2 SEL 421 The SEL 421 Relay is a high speed transmission line protection relay featuring single pole and three pole tripping and reclosing with synchronism check circuit breaker monitoring circuit breaker fail
18. chronous Generator Fig 2 4 Permanent Magnet Generator connected to the grid 11 Texas Tech University Santosh Pappu August 2012 Fig 2 4 shows the synchronous generator connected to the grid through the power electronics However the benefit is that power can be generated at any speed so as to fit the current conditions The stator of PMSGs is wound and the rotor is provided with a permanent magnet pole system and may have salient poles or may be cylindrical Salient poles are more common in slow speed machines and may be the most useful version for an application for wind generators Typical low speed synchronous machines are of the salient pole type and the type with many poles 2 3 Wind Turbine Technologies The electrical connection of wind turbines to the grid differs with the generator type used Currently four different technologies are prevalent for the four different types of the generators discussed in the previous section The four types will be discussed in this section 2 3 1 Type 1 This configuration denotes the fixed speed wind turbine with an asynchronous squirrel cage induction generator SCIG directly connected to the grid via a transformer Since the SCIG always draws reactive power from the grid this configuration uses a capacitor bank for reactive power compensation A smoother grid connection is achieved by using a soft starter 1 Capacitor bank Fig 2 5 Fixed Speed Wind Turbine Generator connec
19. co re a za ES E E m gt F x L r 5 ll Fig 5 2 System Configuration of SEL 3378 communicating through the Ethernet 17 Texas Tech University Santosh Pappu August 2012 The connection to the computer can be through serial port or Ethernet Here the PMUs and other Phasor Data Concentrators send data to the SEL 3378 through Ethernet The SEL 3378 processes the data from the PMUs and sends it to the computer for applications such as archiving and real time data plots 5 4 SVP Configurator The SVP Configurator allows you to build projects based on your required applications The Run Time System RTS turns the SEL 3378 into an IEC 61131 3 programmable logic controller PLC The programming languages that the SVP Configurator offers conform to the requirements of IEC 61131 3 an international standard for programming languages of PLCs 17 The code for initialization of the processor was written in the SVP Congfigurator The SVP Configurator supports all the languages that the IEC 61131 3 standard describes These languages can be characterized as textual and graphical languages The SVP Configurator code involves creating project files for Time Alignment Client Server TCS that provides time aligned IEEE C37 118 2005 Standard for Synchrophasors for Power Systems synchrophasor messages to internal and external client
20. cy outside the normal tolerances with duration of more than one cycle and typically less than a few seconds Causes Start stop of heavy loads badly dimensioned power sources badly regulated transformers mainly during off peak hours Consequences Harmonic distortion Description Voltage or current waveforms assume non sinusoidal shape The waveform corresponds to the sum of different sine waves with different magnitude and phase having frequencies that are multiples of power system frequency Causes Classic sources electric machines working above the knee of the magnetization curve magnetic saturation arc furnaces welding machines rectifiers and DC brush motors Modern sources all non linear loads such as power electronics equipment including ASDs switched mode power supplies data processing equipment high efficiency lighting Consequences Increased probability in occurrence of resonance neutral overload in 3 phase systems overheating of all cables and equipment loss of efficiency in electric machines electromagnetic interference with communication systems errors in measures when using average reading meters nuisance tripping of thermal protections 36 Texas Tech University Santosh Pappu August 2012 Table 5 1 Continued Voltage Description Oscillation of voltage value amplitude modulated by a signal with frequency of 0 to 30 Hz Causes Arc furnaces frequent start stop of electri
21. e trips due to over speed the voltage level increases to lpu Fig 6 8 shows active power generated from the two wind farms The DFIG generates active power till the wind speed reaches 24m s The relay trips the generator due to over speed condition The wind farm consisting of FSIG does not generate any power for both wind speeds The first few seconds display the initial transients of the wind farm experienced at startup due to the high wind speed 53 Voltage at 25kV bus pu Reactive Power MVAR uo 20 10 10 15 Texas Tech University Santosh Pappu August 2012 0 10 20 1 05 0 95 0 9 0 85 Fig 6 6 Reactive Power consumed for both wind farms 30 Time sec 40 50 70 T 0 10 20 Fig 6 7 Voltage at 25kV bus for both wind farms 30 Time sec 54 40 50 60 70 Texas Tech University Santosh Pappu August 2012 _ oO So Eat 1 Active Power MYY co for 30 40 50 60 70 Time sec Fig 6 8 Active Power generated for wind speeds from 21 24m s 6 4 Equal Power Lost Equal amount of power was taken out from the two configurations to check the active power transmitted reactive power consumed and the voltage at the bus at point of common coupling A three phase fault was installed on three turbines in the wind farm with 500kW and on one turbine in the wind farm consisting of 1 5MW DFIG turbines The wind far
22. e Tg is the torque of the generator and w is the generator speed 2 2 Generators Used in the Wind Industry Presently in the Wind Industry four different types of generators are being for power generation All the four types have been discussed below 2 2 1 Singly Fed Induction Generator The most common generator used in wind turbines is the induction generator It has several advantages such as robustness and mechanical simplicity and as it is produced in large series it also has a low price The major disadvantage is that the stator needs a reactive magnetizing current The asynchronous generator does not contain permanent magnets and is not separately excited Therefore it has to receive its exciting current from another source and consumes reactive power The reactive power may be supplied by the grid or by a power electronic system The generator s magnetic field is established only if it is connected to the grid In the case of AC excitation the created magnetic field rotates at a speed determined jointly by the number of poles in the winding and the frequency of the current the synchronous speed Thus if the rotor rotates at a speed that exceeds the synchronous speed an electric field is induced between the rotor and the rotating stator field by a relative motion slip which causes a current in the rotor windings The interaction of the associated magnetic field of the rotor with the stator field results in the torque acting on
23. e and Technology 12 MATLAB Simulink Documentation Available http www mathworks com 13 V Ramakrishnan and S K Srivatsa Pitch Control of Wind Turbine Generator by using New Mechanism 14 Omar Noureldeen Low Voltage Ride through Strategies for SCIG Wind Turbines Interconnected Grid in International Journal of Electrical amp Computer Sciences IJECS IJENS Vol 11 No 02 15 A de Almeida L Moreira J Delgado Power Quality Problems and New Solutions 16 Power Quality Problems and New Solutions A de Almeida L Moreira J Delgado 17 SEL 421 Relay Protection and Automation System Instruction Manual Schweitzer Engineering Laboratories INC 18 SEL 3378 Synchrophasor Vector Processor Instruction Manual Schweitzer Engineering Laboratories INC 19 SEL 5078 SynchroWave console User Manual Schweitzer Engineering Laboratories INC 72 Texas Tech University Santosh Pappu August 2012 20 SEL 5076 SynchroWave Archiver User Manual Schweitzer Engineering Laboratories INC 13 Texas Tech University Santosh Pappu August 2012 PUBLICATIONS 1 Santosh Pappu and Stephen Bayne Evaluation of Hub Concept for Wind Turbines JEEE Power and Energy Conference at Illinois 2012 2 Santosh R Pappu Arash Rahnama Mathew Tovar Stephen Bayne Boby Little Sid Friend and Marcus Borhani Power Quality Analysis at a Sensitive Load using a Phasor Measurement Unit IEEE Green Technol
24. e circuit breaker when it detects any of the conditions mentioned before Since the induction generator is modeled as a constant 26 Texas Tech University Santosh Pappu August 2012 current source a resistance is placed in parallel The active power and reactive power from the generator are measured from the voltage and current values measured using the measurement blocks The parameters used for the induction generator is shown below in Table 4 1 Table 4 1 PARAMETERS OF INDUCTION GENERATOR Parameters Values Nominal Power kW S00kW Nominal Voltage V 575 Nominal Frequency Hz 60 Nominal Power factor 0 9 Stator Resistance pu 0 0065 Rotor Resistance pu 0 0093 Stator Leakage inductance pu 0 0894 Rotor Leakage inductance pu 0 1106 Magnetizing Inductance pu 3 887 Inertia constant 5 04 Friction factor 0 01 Pole pairs 3 4 3 Doubly Fed Induction Generator Model in MATLAB In MATLAB the DFIG is represented using a phasor model This model is adapted to simulate the low frequency electromechanical oscillations over long periods of time In phasor simulation method the sinusoidal voltages and currents are replaced by phasor quantities at the system nominal frequency 60Hz This model is mostly used for transient stability studies of wind turbines Shown in Fig 4 4 is the model of the Double Fed Induction Generator used in MATLAB 27 Texas Tech University Santosh Pappu August
25. e oe tes PER E oe tana ecrawy nce veu shed E 37 5 3 Synchrophasor Vector Processor SEL 3378 uussessssesesssneesnnnnennnennnnn 38 3 4 SVP Configurator sauna Le 39 5 5 SEL SynchroWave Archiver sacccysisarealcoreteuleetomeneeaai sca ceoaseacttaseam ee 41 3 0 SEb Synehro Wave Consele 2 2 Reese 41 5 7 Point of Connection of PMU uaennieeteseingn n 43 5 8 Baseline of Parameters of Power Flowing into the Facility 43 5 9 Description of Code for Power Quality Analysis _ eeesesessnennsnnenn 44 VI RESULTS FOR COMPARITIVE STUDY OF WIND TURBINES 0cscessseseseseeeee 47 6 1 Wind Speeds ranging from 3 6m S 0 eeeeceeeeeceeesececeseeeceeeeeeneeeeneeeenaeeees 47 6 2 Wind Speeds ranging from 9 12M S eee eeeeecesececeeeceeseeceeseeeeneeeenaeeees 49 6 3 Wind Speeds ranging from 21 24m S 000 0 eeeeeeeeececeeeceeeeeeeeteeeesteeeesaeeees 52 6 4 Equal Power Lost oein niria aa E R E ein 54 6 5 Equal Number of Turbines Lost to Faults ceeeeeecceesseceesneeeesteeeeneeees 56 VII RESULTS FOR EVALUATION OF HUB CONCEPT essessesessossesossossesoosoesessossssose 59 7 1 Rated Conditions enren a a E r EEA 59 7 2 Fault on One Wind Turbine in Wind Farm seseeeeseeesseesseesserssesssssesssees 60 7 3 Paul Ga Wind Farm Arne e a e RE 63 VIII RESULTS FOR POWER QUALITY ANALYSIS USING A PMU ccccccsssssceseee 65 IX CONCLUSION scsdscsessesstduissidoscedseiscscveadectassetstdovddescedesisceutsadsesestensOcub
26. ent of a new Hub may be proposed by SPP either through the Integrated Transmission Planning ITP process or the Generation Interconnection process once two or more generators are proposing to interconnect to the same transmission line in close proximity to each other An existing substation may be designated as a Hub for any new generation interconnection requests in that vicinity The designation of a Hub will result in more certainty of the location of such generation collection substations The decision to propose the designation of a hub will be based on two different analyses The technical analysis will be based on a review of the transmission system by SPP and the appropriate Transmission Owner and subsequent study to review switching transients and whether switching transients are a concern If the technical studies determine that the addition of a new substation does not result in switching transients that need to be controlled then the second analysis based on economics will be used Here only the technical aspect of allocation of Hubs will be discussed 3 2 Technical Analysis for Designation of Hubs The AGCTF recommends that multiple generators connect at one point on a line rather than at multiple points because it is more efficient reliable and cost effective Extremely long over 75 miles transmission lines that are tapped by multiple generation interconnection substations may require the addition of line reactors at each substati
27. ept Currently the interconnection of multiple wind farms on the same transmission line is being debated by some of the Regional Transmission Organizations RTO such as Southwest Power Pool SPP The point of interconnection is being designated as the Hub The Generation Interconnection process in the tariff allows each Generation Interconnection Customer to identify a transmission line or station on the transmission system to interconnect with It was recommended that multiple generators connect at one point on a line rather than at multiple points because it is more efficient reliable and cost effective 4 Research was conducted to analyze the impact of transients on wind farms simulated modeled around the Hub concept A description about the Hub concept has been included in Chapter 3 The wind farms were simulated for faults at various locations and active power reactive power and voltage at the bus were monitored for their respective cases 1 5 Introduction to Power Quality Power Quality is the set of limits of electrical properties that allows electrical systems to function in their intended manner without significant loss of performance or life The term is used to describe electric power that drives an electrical load and the Texas Tech University Santosh Pappu August 2012 load s ability to function properly with that electric power Without the proper power an electrical device or load may malfunction fail prematurely or n
28. escribe the active and reactive power flow in a line in terms of Vi and Vs the transformer impedance which can be assumed as ideal and the angle difference between both bars we can defined Pand Q The angle between the Vs and Vi in the system is d When the STATCOM operates with d 0 we can see how the active power to the system device becomes zero while the reactive power will mainly depend on the voltage module This operation condition means that the current that goes through the transformer must have a 90 phase difference to Vs In other words if Vi is bigger than Vs the reactive will be sent to the STATCOM of the system capacitive operation originating a current flow in this direction In the contrary case the reactive will be absorbed from the system through the STATCOM inductive operation and the current will flow in the opposite direction Finally if the modules of Vs and Vi are equal there won t be nor current nor reactive flow in the system PT VEN No load Capacitive Operation Inductive Operation Lagging Fig 2 11 Waveforms of Current and Voltage for lagging and leading power factor 9 18 Texas Tech University Santosh Pappu August 2012 Thus we can say that in a stationary state Q only depends on the module difference between Vs and Vi voltages The amount of the reactive power is proportional to the voltage difference between Vs and Vi There can be a little active power exchange be
29. farms are connected at the same point on the transmission line at 345kV 32 Texas Tech University Santosh Pappu August 2012 Hub or Point of Interconnection of Wind Farms 20 km lines g J ithe A Forms gt A amam NT 120 2500 MVA B120 Note HD STATCOM Phasor Type km lines yagay z y Transformer X0 4 7 Ohmst Tel 0 o A Notip Lie o sl Bohm 1 STATCOM Phasor Type REN B25 20 km line6 amp ang Bp eae X0 4 7 Ohms3 E 20 km ling g No trip2 1 al Manual Swit 3 ohms d Trip2 STATCOM Phasor Type 2 Fig 4 7 Schematic of wind farms for HUB concept Fig 4 7 shows the schematic of the interconnection of wind farms for Hub concept The three wind farms here share a common point of interconnection to the grid This common point of interconnection is termed as the Hub A STATCOM is connected to the wind farms for reactive power and voltage support during transient conditions The STATCOM can be disconnected from the wind farm by connecting the STATCOM to a logic one The wind farm is connected to a 25km transmission line at 34 5kV The voltage is then stepped up to 345kV and connected to a transmission line of length 25km At this point the three wind farms are interconnected to form a Hub This is then connected to the grid which is at 345kV 33 Texa
30. full scale frequency converter The frequency converter performs the reactive power compensation and the smoother grid connection The generator can be excited electrically or by a permanent magnet permanent magnet synchronous generator 1 Full scale frequency converter coe OE u PMSG WRSG WRIG Fig 2 8 Type 4 Wind Turbine 15 Texas Tech University Santosh Pappu August 2012 Fig 2 8 shows the schematic of a type 4 wind turbine The stator is isolated from the grid in this configuration The stator is connected to the grid through the power electronics Since the nominal power of the generator is transferred through the power electronics the switches need to be rated for full rating This would increase the cost of the power electronics thereby increasing the total cost of the whole setup The power electronics enables the generator to run at variable frequency 2 4 STATCOM A STATCOM is a device connected in derivation composed of a coupling transformer that serves of as a link between the electrical power systems EPS and the voltage synchronous controller VSC The VSC generates the voltage wave comparing it to the one of the electric system to realize the exchange of reactive power The control system of the STATCOM adjusts at each moment the inverse voltage so that the current injected in the network is in cuadrature to the network voltage in these conditions P 0 and Q 0 In its most general way the STATCOM can be m
31. g 4 1 The step change causes a change in reactive power and active power Fig 6 1 shows the reactive power consumed for both the topologies The wind farm consisting of DFIG consumes reactive power from 40sec This is because the DFIG transmits power at low wind speeds As the wind speed steps up to 6m s the DFIG starts generating active power and hence consuming reactive power while the wind farm consisting of FSIG does not consume any reactive power as it does not generate any active power at low wind speeds The voltage on the 25kV bus is stable for both the configurations as consumption of reactive power consumption is very less for low wind speeds Fig 6 2 shows the active power transmission to the grid of both wind farms for this particular wind profile The first few seconds show the initial transients on both the configurations The wind farm consisting of FSIG does not generate any power for both the wind speeds The wind farm consisting of DFIG starts generating active power as the wind speed steps at 20sec 48 Texas Tech University Santosh Pappu August 2012 04 ee FSIG ri FIG 0 gt Reactive Power MV AR gt gt gt gt f t t I l 4 4 t I I j ji t I I I 1 5 10 15 20 25 30 35 Time sec Fig 6 1 Reactive power consumption for both wind fa
32. he excel files from the specific directory that was set by the user and PMU is saving the data into Frequency and three phase Voltage are compared to the boundaries set by the user In case of sudden jump if the magnitude of any phase in the input 3 phase voltage or the frequency is out of range code will consider the error and alert the user Code will plot three graphs to provide enough information for analyzing the error Fig 8 1 displays the GUI when a excursion is found in the values of the excel sheet given as input It shows the frequency delta frequency and voltage in all three phases which contain data which is not within the limits PMU Analyzer Bries File Edit View Insert Tools Desktop Window Help Aei CEER T r 0B ad Frequency Upper Bound 60 035 60 035 Frequency Lower Bound 60 phase A voltage il Wh Il phase B voltage 1 AMATI phase C vottage NM i Wi Voltage Phase A Upper Bound 123 419 495 Voltage Phase A Lower Bound f Figure 4 File Edit View Insert Tools Desktop Window Help BETTIDEERELTELT EIN I Mh a Voltage Phase B Upper Bound Voltage Phase B Lower Bound 60 04 Dies File Edit View Insert Tools Desktop Window Help 60 035 Voltage Phase C Upper Bound OGMsl k AAO924 8 0B a0 Voltage Phase C Lower Bound wm AM gt 60 025 5 0 036 Fa am 0 03 2 gt s 4 60 01 4
33. hing and knowing this baseline for the power quality is imperative when deciding which form of green energy to choose or which manufacture to negotiate with When understanding this the wind turbine manufactures that are providing and installing the turbines have to guarantee a power quality that will match the current utility power Shown in Table 5 1 are the variations of the parameters of the data that was recorded from the PMU at the Facility TABLE 5 1 VARIATION OF PARAMETERS OF THE DATA RECORDED Parameters Nominal Voltage Variation max Voltage Va Vb Vc 120 V 0 6V 44 Texas Tech University Santosh Pappu August 2012 Frequency 60Hz 0 2Hz The voltage on all three phases varied a maximum of 0 6V from the nominal value The frequency varied a maximum of 0 2Hz from its nominal voltage 5 9 Description of Code for Power Quality Analysis The data that the PMU samples and saves it s information on are all three voltage and current phases with their respective real and imaginary parts power factor frequency the change in frequency and the real imaginary and magnitude parts of the power The PMU saves millions of data points into thousands of excel files For this data mining to be useful a program needs to be implemented to systematically analyze this raw information and present it in a clear concise and accurate format for a person to comprehend The PMU samples the data
34. hree wind speeds are 3 6m s 9 12 m s 21 24 m s The wind speeds step up from the minimum value to the maximum value at time 20sec The two wind farms have been simulated for cut in rated and cut off wind speeds to compare the performance in aspects of e Reactive power consumed for different wind profiles e Power transmitted to the grid taking transmission losses into account e Steady state and dynamic performance of both the wind farm configurations with equal number of turbines lost e Steady state and dynamic performance of both the wind farm configurations with equal power lost 24 Texas Tech University Santosh Pappu August 2012 The simulation time considered is 50 seconds The step change in wind speed is considered to observe the response of the wind turbine to step changes in wind speed 4 2 Induction Generator Model in MATLAB In MATLAB the Induction Generator is represented using a wind torque model applied to the shaft of the Induction generator as shown in Fig 4 2 It also contains a pitch angle control block which controls the pitch angle of the blades in case of high wind speeds to limit the output power to the power rating of the machine The machine is initiated to a negative 1 slip to make it run in super synchronous mode to generate power thereby not considering the sub transients in the simulation Wind m s Wind Turbine g Rotor speed wm gt Pnom 1000 Data
35. ine in wind farm B 7 3 Fault on Wind Farm A A three phase to ground fault was installed on the terminals of the wind farm A The response of the neighboring wind farms to the fault was analyzed The voltage at the terminals of the wind farm B was analyzed for impact of the fault on the neighboring wind farm Fig 7 5 shows the voltage at wind farm A At 35sec a three phase to ground fault is installed The fault lasts for O 1sec 64 Texas Tech University Santosh Pappu August 2012 MT IT TI I I 0 98 0 96 0 92 4 0 9 Voltage at terminals of Wind farm A pu 0 84 4 082 0 5 10 15 20 25 30 35 40 45 50 Time sec Fig 7 5 Terminal Voltage of Wind farm A Fig 7 5 shows the voltage at the terminals of the wind farm B At 35sec the voltage reduces by 0 2pu for about 0 1 sec This implies that a fault on the wind farm A causes an impact on the voltage and reactive power of wind B and C This is due the excessive reactive power drawn from the grid by wind farm A to support the voltage dip This excessive consumption of reactive power from the grid causes dip in the reactive power consumed by wind farm B and causes a reduction in the voltage 65 Texas Tech University Santosh Pappu August 2012 CHAPTER 8 RESULTS FOR POWER QUALITY ANALYSIS USING A PMU The data recorded from the PMU set up at the semiconductor facility was archived A code developed in MATLAB reads t
36. ing the IDCODE of the corresponding PMU The data to be archived can be chosen to be stored in a 41 Texas Tech University Santosh Pappu August 2012 specific location as specified by the user The communication for the PMU should be setup by mentioning the IP address of the PMU and scheme of transportation of data The data recording will start once Activate Archiver is selected The data will be stored in the selected folder The archiver will record the data points of the parameters selected Since only one input was connected each on the current and voltage terminals the number of parameters that were recorded was seventeen which included frequency and delta frequency Continuous data storage mode was used for this project to collect large data for analysis of Power Quality 5 6 SEL SyncrhoWave Console The SynchroWave Console is wide area visualization software for synchrophasors that offers flexibility for operators and engineers to view multiple displays in multiple dockable windows and customize the visualizations to optimize the ability to monitor the power system The Console displays a graphical interpretation of real time data It can plot magnitudes of phase voltages and currents phase angles of the three phases frequency and delta frequency To connect the Console to the PMU concerned the communication parameters such as IP address and transportation scheme need to set up Here the IP address refers to the IP address of the P
37. m is simulated for wind speeds from 9 12m s which steps up from 9m s to 12m s at 20sec A fault lasting for O lsec occurring on the terminals of the wind turbine was simulated on both the wind farms Fig 5 9 shows the reactive power consumption for this scenario The reactive power consumed is less for DFIG as shown The DFIG takes more reactive VARs during the fault and settles down after the fault The DFIG takes longer time to reach steady state than the FSIG which also consumes more VARs than the DFIG during steady state Fig 6 10 shows the active 55 Texas Tech University Santosh Pappu August 2012 power transmitted to the grid The DFIG takes power from the grid when the fault occurs and returns to generating mode once the fault is cleared For speeds up to 9m s the DFIG generates more active power than the FSIG As the wind speed steps up to 12m s the power generated increases on both configurations But the DFIG takes longer time to achieve steady state than the FSIG due to machine dynamics Both the configurations generate the same power once they reach steady state 20 DFIG a FSIG 15 gt 10 5 3 fe L 0 25 3 x 0 10 20 30 40 50 60 70 Time Fig 6 9 Reactive power consumption when a three phase to ground fault occurs at 40sec to last for 0 1sec 56 Texas Tech University Santosh Pappu August 2012 Active Power MYY 4 10 20
38. nssrnssrnnsrnssrnnt 7 2 2 2 Doubly Fed Induction Generator urs44srsnsunnnennnnnnennnnnnnnnnnnnnnnnnennnnnnn 8 2 2 3 Synchronous Generator u r200unsnennnnnnennnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn en 10 2 2 4 Permanent Magnet Generator 40srs4susrsnennnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn 11 2 3 Wind Turbine Technologies ins een 12 2 3 1 TYPel tes ok tvs ve nes len Hessen 12 292 TYPE 2 arrena iaie bs HIDDEN 13 22313 PYDO S en sn Kal E E E E 14 23a WP A en en nee tet E ehe 15 ZAS TAI COM are ee 16 iii Texas Tech University Santosh Pappu August 2012 III EVALUATION OF HUB CONCEPT FOR WIND TURBINES ccscessessssessoeseeeee 20 3 1 DESIEnAUEn OF Hubs A en a a a ia 21 3 2 Technical Analysis for Designation of Hubs 2200220 rs 21 IV MODEL DEVELOPMENT PROCEDURE 2c0srs00sesonsssnnssnnnsnnnsssnnsnnnssnnnsnnnsssnnnnnnne 23 4 1 Wind Profileren eee ae ier E Sus taceaaetgeas Eea 23 4 2 Induction Generator Model in MATLAB uussssssneennnennn 25 4 3 Doubly Fed Induction Generator Model in MATLAB 27 LASTATCOM naar En ns ea 29 4 5 Topology of Wind Farms For Comparison of Wind Farms 31 4 6 Topology of Wind Farms for Hub Concept cee eeecceceseceeeteceeeteeeeneeees 32 V POWER QUALITY ANALYSIS USING PHASOR MEASUREMENT UNIT c00000 34 Sal Power Quality ISSUGs learn ea 34 VAI DI ET P E EEE Van
39. ntrolled startup and emergency stopping Its major drawback is that at high wind speeds even small variations in wind speed result in large variations in output power The pitch mechanism is not fast enough to avoid such power fluctuations By pitching the blade slow variations in the wind can be compensated but this is not possible in the case of gusts 2 3 2 Type 2 This configuration corresponds to the limited variable speed wind turbine with variable generator rotor resistance It uses a wound rotor induction generator WRIG The generator is directly connected to the grid A capacitor bank performs the reactive 13 Texas Tech University Santosh Pappu August 2012 power compensation A smoother grid connection is achieved by using a soft starter 1 Variable resistance Capacitor bank Fig 2 6 Type 2 Wind turbine directly connected to the grid Fig 2 6 shows the schematic of a type 2 wind turbine It has variable additional rotor resistance which can be changed by an optically controlled converter mounted on the rotor shaft Thus the total rotor resistance is controllable This optical coupling eliminates the need for costly slip rings that need brushes and maintenance The rotor resistance can be changed and thus controls the slip This way the power output in the system is controlled The range of the dynamic speed control depends on the size of the variable rotor resistance Typically the speed range is O 10 above
40. odeled as a regulated voltage source Vi connected to a voltage bar Vs through a transformer 9 Fig 2 9 STATCOM connected to a transmission line 9 16 Texas Tech University Santosh Pappu August 2012 The STATic COMpensator STATCOM uses a VSC interfaced in shunt to a transmission line In most cases the DC voltage support for the VSC will be provided by the DC capacitor of relatively small energy storage capability hence in steady state operation active power exchanged with the line has to be maintained at zero as shown symbolically in Fig 2 9 With the active power constraint imposed the control of the STATCOM is reduced to one degree of freedom which is used to control the amount of reactive power exchanged with the line Accordingly a STATCOM is operated as a functional equivalent of a static VAR compensator it provides faster control than an SVC and improved control range 9 Power System GTO Inverter y Ww DC Capacitor lt l VS of A t tl Mis et ca Output l System Voltage Voltage Fig 2 10 Equivalent Circuit of STATCOM 9 17 Texas Tech University Santosh Pappu August 2012 Fig 2 10 shows the equivalent circuit of a STATCOM system The GTO converter with a dc voltage source and the power system are illustrated as variable ac voltages in this figure These two voltages are connected by a reactance representing the transformer leakage inductance Using the classical equations that d
41. ogies Conference 2012 3 Santosh Pappu Sandeep Nimmagadda and Stephen Bayne Analysis and Comparison between two wind farms consisting of 500kW midsize turbines and 1 5MW turbines IEEE Power Electronics and Machines in Wind Applications PEMWA 2012 accepted to be presented on July 17 2012 74
42. on where the transmission line terminates Line reactors are required to limit transient switching voltages to a level that will not cause damage to line switching equipment circuit breakers 10 Destructive transients can be generated during normal switching operations thus requiring fixed line reactors to control these switching transients to a safe level Identifying the circumstances when these switching transients could occur requires complex analysis and the situation does not occur for all lines For lines where 21 Texas Tech University Santosh Pappu August 2012 destructive switching surges are expected to occur a transient analysis is necessary to be performed to determine among other things the hub spacing taking into consideration the equipment needed to control switching surges the increased cost of the stations and the effect fixed line reactors will have on line loadability 10 Normally line reactors are installed on transmission lines to maintain voltages on long lines during light loading conditions When the line reactors are installed for this reason they can be remotely disconnected from the transmission system during times of heavy flows If a reactor cannot be disconnected during times of heavy loading it can cause voltage depression and ultimately decrease safe line loading capability 10 In addition each time a fixed shunt reactor is added to a line the impedance of the line increases If enough fixed sh
43. ot operate at all There are many ways in which electric power can be of poor quality and many more causes of such poor quality power While power quality is a convenient term for many it is the quality of the voltage rather than power or electric current that is actually described by the term Today wind generating system is connected into the power system to meet the consumer s demand The addition of wind power into the electric grid affect s the power quality Due to the increase awareness of power quality particularly in highly sensitive industry like continuous process industry complex machine part producing industry and security related industry where standardization and evaluation of performance is an important aspect 5 1 6 MATLAB Though different software were used for this research primarily the modeling for the wind turbines for comparative study and evaluation of hub concept were done in MATLAB The modes were built and simulated in MATLAB Simulink and Sim Power Systems For archiving the data being recorded from the Phasor Measurement Unit PMU Synchrowave Archiver was used SVP configurator was used to initialize the PMU Synchrowave Console was used to capture the instantaneous values of voltage current and frequency as a plot with respect to time Texas Tech University Santosh Pappu August 2012 CHAPTER 2 THEORETICAL BACKGROUND There are four different types of generators used in the wind industry out of
44. p Nimmagadda for helping me with my research and internship I thank Srividya for being my pillar of strength throughout my Masters Without her it wouldn t have been possible to survive the day to day hardships of life in USA Lastly I would like to thank my parents and Almighty from the bottom of my heart for giving me the opportunity to study in the United States Without their blessings none of this would have been possible ii Texas Tech University Santosh Pappu August 2012 TABLE OF CONTENTS ACKNOWLEDGMENTS Sun ige dcaseesveaganscsctadedsoeieaudasbeasec ll ABSTRACT ee nee a a EN EISTOFTABLES sa een VA LISTOR FIGURES u a cues consaspeaest tcsssepsadnieebeunpsossdsunseubiassnaesinie VIL CHAPTER 1 1 Introduction to Wind Erersya na sade oes ccatenseaveosmae tages 1 VAST Wind Turbinesa Se 0er need nee 1 IAD GONCFALONS i E ns devas E E A E A E E Shenae 2 1 2 Wind Energy Technologies unse 3 1 3 Introduction to Comparison of Wind Turbines with Different Power Ratings LA Introduction to Hub Concept u susanne 4 1 5 Introduction to Power Obi BR 4 GMT TIGA o ehe een e aes igini 5 II THEORETICAL BACKGROUND ssseessessoesoossessoesoosseesoesoossoesoesoossoesoesoossoesoessossosssees Zak meray COnyersion nee E E E a eE tenses 6 2 2 Generators Used in the Wind Industry e eee eeececeeeeeceseceeseeeeeseeeeneeeeaas 7 2 2 1 Singly Fed Induction Generator ssessseseeesirssrrssrrssrrssrnssrnssrnssr
45. peed generator since the frequency of the stator is same as the grid frequency e Type 2 Variable speed turbine connected to the grid directly The speed can be varied by varying the rotor resistance e Type 3 These are Doubly Fed Induction Generators which are variable speed The rotor is connected to the grid via power electronics This makes both the stator and rotor feed power to the grid e Type 4 These types of generators are connected to the grid via the power electronics The stator of the generator is connected to the power electronics which in turn is connected to the grid These are variable speed wind turbines 1 Texas Tech University Santosh Pappu August 2012 In this research we have considered two types of generators Those are type 1 and type 3 wind turbines 1 3 Introduction to Comparison of Wind Turbines with Different Power Ratings In this research two wind farms consisting of 9MW each are compared The two wind farms differ in the turbine being used One wind farm has eighteen singly fed induction generators each rated at 500 kW and the other wind farm consists of six doubly fed induction generators each rated at 1 5 MW The two wind farms have been simulated for various wind speeds and transient stability The performances of both the wind farms have been analyzed for the above said conditions and parameters such as voltage active power and reactive power have been monitored 1 4 Introduction to Hub Conc
46. peeds the DFIG is superior than FSIG in the terms of active power transmitted voltage stability The reactive power consumed also is less than the FSIG The performance of both the topologies is same when equal amount of power was taken out due to faults Hence all the above factors should be considered while deciding which topology of wind farms would be used for generation of wind energy The Hub concept was discussed and modeled on the same lines in MATLAB Simulink A transient analysis was conducted on the wind farm in different scenarios It was concluded that the installations of faults in one wind turbine caused an impact on the neighboring wind farms This is due to excessive reactive power consumption from the grid for voltage support The installation of FACTS devices such as STATCOM reduces the impact of the fault on neighboring wind farms A unique method for analyzing Power Quality was developed in MATLAB A set of limits was established for parameters such as voltage and frequency for data analysis of Power Quality The power coming from the utility had no aberrations from the normal as expected The data analyzed before the installation of the wind turbine at the Facility forms an important basis for analysis after the installation of the wind turbine After the installation of the turbine continuous data monitoring would be taking place with the help of the PMU The PMUs should be placed at various critical locations for monitoring
47. pper volage Phase CEnor 0 Vinimum Votage Phase A Reached 118 88 Bound 123 1190 Voltage Phase C Lo 117 In case of a rer formalen is saved in the following addresses Yortane Phase G Lower Nax mum Votaye Phase 8 Reached Round an i 119 31 C PMUFrequenoy Emon CAPMUVolageAE morn Mnmum Votage Phase B Reached 190 a m3 CPMUVotageBError Lae CiPMUVOlageCla Maximum Voltage Phase C Reached 11972 Minoru Voltage Phase C Reached 1119 47 u Fig 5 6 GUI developed in MATLAB 47 Texas Tech University Santosh Pappu August 2012 CHAPTER 6 RESULTS FOR COMPARATIVE STUDY OF WIND TURBINES The analysis was carried out on MATLAB Simulink simulation environment Both the configurations were simulated for the same length of time to make the analysis comparable The same base values were used for both the configurations The configurations were simulated for various wind conditions and fault conditions to check parameters like reactive power consumption voltage stability and active power transmission The various conditions for both wind farms are simulated and demonstrated below The voltage values are displayed in pu system and reactive power and active power are displayed in MW and MVAR respectively The measurements are recorded at the terminals of the wind farm and at the 25kV bus for both the wind farms 6 1 Wind Speeds ranging from 3 6m s Both the configurations have been simulated for wind speeds ranging from 3 6m s as shown in Fi
48. r two seconds Causes Mainly due to the opening and automatic reclosure of protection devices to decommission a faulty section of the network The main fault causes are insulation failure lightning and insulator flashover Consequences Tripping of protection devices loss of information and malfunction of data processing equipment Stoppage of sensitive equipment such as ASDs PCs PLCs if they re not prepared to deal with this situation Long interruptions Description Total interruption of electrical supply for duration greater than 1 to 2 seconds Causes Equipment failure in the power system network storms and objects trees cars etc striking lines or poles fire human error bad coordination or failure of protection devices Consequences Stoppage of all equipment Voltage spike Description Very fast variation of the voltage value for durations from a several microseconds to few milliseconds These variations may reach thousands of volts even in low voltage Causes Lightning switching of lines or power factor correction capacitors disconnection of heavy loads Consequences Destruction of components particularly electronic components and of insulation materials data processing errors or data loss electromagnetic interference 35 Texas Tech University Santosh Pappu August 2012 Table 5 1 Continued Voltage swell Description Momentary increase of the voltage at the power frequen
49. rms for wind speeds ranging from 3 6m s 49 Texas Tech University Santosh Pappu August 2012 Active Power MYY 0 10 20 30 40 50 60 10 Time Sec Fig 6 2 Active Power transmission for wind speeds ranging from 3 6m s 6 2 Wind speeds ranging from 9 12m s The wind farms were then simulated for wind speeds ranging from 9 12m s The wind speed 12m s is the rated wind speed for both wind farm configurations Fig 6 3 shows the reactive power consumption of both wind farms The reactive power consumption rises as the wind speed steps up from 9m s to 12m s due to increase in generation of active power up to rated capacity The response of the wind farm with FSIG is immediate whereas the consumption of reactive power attains steady state after a few seconds for the wind farm with DFIG Fig 6 4 shows the voltage at the 25kV bus for both wind farms The voltage at the bus rapidly reduces for wind farm consisting of FSIG as the wind speed increases from 9m s to 12m s due to increase in 50 Texas Tech University Santosh Pappu August 2012 reactive power consumption It gradually decreases for the DFIG wind farm Fig 6 5 shows the active power generation of both wind farms for this wind profile Both wind farms reach rated capacity of generation when the wind speed is stepped up to 12m s As shown in Fig 6 5 the wind farm with FSIG responds faster than wind farm with DFIG thereby capturing more power for longer than the configuration
50. rocessor as the PMU sends data to the Processors which in turn process the data from the PMU 18 Once the communication parameters are set up the Console can connect to the Processor and the real time data can be seen on the screen of the console The data by default is recorded for duration of five minutes This duration can be changed to a maximum of twenty four hours Shown in Fig 5 3 is a plot of Current in Phase C This data has been recorded for duration of one hour The data is being recorded from the PMU located at the Semiconductor Foundry Fabrication Facility The plot included some interruption which was due to loss of communication between the Processor and PMU 42 Texas Tech University Santosh Pappu August 2012 Fig 5 3 Plot from the SynchroWave Console of the Current in Phase C 5 7 Point of Connection of the PMU The point of connection of the PMU in the Facility is shown below in Fig 5 4 The voltage was stepped down to 120V using a potential transformer and connected to the PMU 43 Texas Tech University Santosh Pappu August 2012 15KVA MAIN SWGR Sr _ PMU INSTALLED HERE ze gt gt ous ces Fig 5 4 A part of the line diagram which shows the point of connection of the PMU 5 8 Baseline of Parameters of Power Flowing into the Facility It is important to establish a baseline for the values of the parameters such as voltage and frequency coming into the Facility from the utility Establis
51. roduce 9MW of real power excluding losses The above mentioned models were used in MATLAB Fig 4 6 shows the topology of the wind turbines in the wind farm The same topology has been implemented for both the configurations 31 Texas Tech University Santosh Pappu August 2012 25 KVI575 V 1kmcable 4MVA Wind Turbine 1 Wind Farm Terminal a 20 I Pe a EEE 120 KV 25 kV 25 km line 47 MVA Wind Turbine 18 1km cable 25 kV 575 V 4MVA STATCOM Fig 4 6 Topology of the wind turbines connected in a wind farm In Fig 4 6 the wind turbines are labeled from 1 to 18 Each turbine is connected to a step up transformer which steps up the voltage to 25 kV from 575V This transformer is generally known as the padamount transformer and is fixed in the hub of the turbine The high side of the padamount transformer is connected to a cable which extends up to roughly Ikm All the cables from the turbines route to the substation which steps up the voltage to 120 kV and connect it via a transmission line to the grid The STATCOM is placed at the terminals of the wind farm to provide reactive power support 4 6 Topology of Wind Farms for HUB concept Each wind farm comprises of the topology as shown in Fig 4 6 The three wind farms tap in from the same point on the transmission line This point is a collector system for the wind farms or also known as the Hub Fig 4 7 shows the model simulated The wind
52. rrel Cage Induction Generator Connected to grid uersenennenneennn 15 Doubly Fed Induction Generator Connected to grid uersersnnesnneennnennn 16 Schematic of Syncrhonous Generator 0 0 0 eee esseceseceseeeeseeceneeneeeeeeeeneees 17 Permanent Magent Generator Connected to grid eeeesesereerrerrererrererse 18 Fixed Speed Wind Turbine Generator Connected to grid eee 19 Type 2 Wind Turbine Connected to grid esssssseseseeseesrsereererserereerersersreses 21 Type 3 Wind Turbine ssa aera ra eens ani aa gruen 22 Type Wind Turbine Seas ne 22 STATCOM connected to a transmission line esseeeeeeseseeeeeserereererserersees 23 Equivalent Circuit of STATCOM uuuuuusunesunisie aannsakens 24 Waveforms of Current and Voltage nalen 25 Various Wind Speeds used in Simulation uusssssessssenseneseeneeennn nen 31 Model of Induction Generator in MATLAB Simulink 32 Feedback loop for Pitch Angle Control 2 0 eeeceeeecceceseceeeteceeseeeeenteeeeaees 33 Model of the DFIG in MATLAB 222 22 er 35 Schematic of STATGOM 22 2 na aaa lie 37 Topology of Wind Turbines connected in a Wind Farm 39 Schematic of wind farms for Hub Concept eeeceeeeeeeeseeeceseeeenteeeeseeees 40 Schematic of SEL 421 connected using CT s and PT S 45 System Configuration of SELE33 8 aaa 46 Plot from Synchrowave Console of Current in Phase C
53. rssersnnesnnernneennnersnnesnnennnennne nn 67 Voltage at terminals of wind turbine with three phase to ground Tausend 68 Voltage at terminals of wind farm B 2u0rs0ursnnesnneennnersnnesnnennnennnen en 69 Electrical Torque of wind turbine in wind farm B uuersersnnsnnennnennn 70 Terminal Voltage of Wind Farm A e cc ceeccecesccecesececeeeeeceseeeesceeesaeeesaaees 41 GUI display when there is an excursion in the parameters 72 Folder where the erroneous files are saved uu 2220222002000r ser snnennnennnnneen 73 Sub folder where the waveforms and excel sheet c ntamine the dataaresayedasni else Reel 74 viii Texas Tech University Santosh Pappu August 2012 CHAPTER 1 INTRODUCTION 1 1 Introduction to Wind Energy Wind energy is gaining increasing importance throughout the world This fast development of wind energy technology and of the market has large implications for a number of people and institutions electrical engineers at universities For wind turbine manufacturers and for developers of wind energy projects who also need that understanding in order to be able to develop feasible modern and cost effective wind energy projects 1 1 1 1 Wind Turbines A wind turbineis a device that converts kinetic energy from the wind into mechanical energy If the mechanical energy is used to produce electricity the device may be called a wind generator Wind turbines are de
54. s User can set the desired values and start the analysis The GUI also shows the frequency magnitudes and phase angles of voltages for each phase in real time Number of errors and disruptions are also shown on the GUI As the code processes the excel files the phase angles for all three phases of voltage is graphed on GUI to show whether voltages are 120 out of phase with each other or not The GUI also shows the lowest and the highest values that each frequency and voltages in all three phases that have been recorded during the analysis Fig 4 5 describes the working of the code in the form of a flowchart Fig 4 6 shows the GUI developed in MATLAB The GUI displays the voltages in three phases frequency delta frequency phase angles graphical display of phase angles and information of the files having abnormal data The code will start processing data when the start button is clicked and stops when the stop button is clicked Bp tars ctu _ 7 Bor PMU Analyzer Frequency Upper Bound 6 60 002 Voltage Phase A 1677 Frequency Lower Bound 5 Ange Votage Phase B 482 Angle Voltage Phase A Upper t P r ape hye 14906 Votage Phase 72 00 Votage Phase A Lower m Ange Bound Nairn Frequeney Reached 160 007 Voltage Phase B Upper Frequency Error 0 Animum Frequency Reached 30902 Bound 123 119 22 Voltage Phase A Eror 9 Votage Phase B Lower 1 Bound Votage Phase 8 Emor 0 Maximum Vohage Phase A Reached 119 22 Votage Phase U
55. s Tech University Santosh Pappu August 2012 CHAPTER 5 POWER QUALITY ANALYSIS USING PHASOR MEASUREMENT UNIT This chapter focuses on research conducted on Power Quality Analysis at a Semiconductor Fabrication Facility using a Phasor Measurement Unit PMU The PMU used in this research is the SEL 421 The data collected using the PMU at the facility was transmitted to the lab in Texas Tech via Ethernet The data received was processed by the SEL 3378 which is a data processor The purpose of this research was to analyze the quality of power coming into the facility The facility intends to install a wind turbine which will supply power to the facility Since the facility has sensitive equipment any excursion in voltage frequency will cause damage to equipments in the facility This could result in millions of dollars loss Recording the data of voltage current and frequency coming into the facility in the absence of a wind turbine can set standards of power quality once the turbine is installed for power delivery to the facility The following sections describe the SEL 421 3378 and the methodology associated with data recording and associated software 5 1 Power Quality Issues Power Quality PQ related issues are of most concern nowadays The widespread use of electronic equipment such as information technology equipment power electronics such as adjustable speed drives ASD programmable logic controllers PLC energy efficient ligh
56. s and provides an interface for transmitting control commands The Configurator also involves providing an interface for accessing PMCU data for user applications Power Calculation which calculates real and reactive power based on user assigned phasors Phase angle Difference Monitor Modal Analysis and Substation and Topology Processor For this project involving Power Quality Analysis the Time Alignment Client Server Power Calculation and Phasor Measurement and control Unit Input interfaces were used The code in the Time Alignment Client Server includes the IDCODE for the PMU type of connection status and transport scheme IP address of the Processer PMU and the computer where the data archived would be stored Each PMU has a unique IDCODE provided by the manufacturer The connection between the Processor and PMU can be serial communication or as in this case Ethernet The data ports and 40 Texas Tech University Santosh Pappu August 2012 command ports of the Processor are given different port numbers to avoid conflict The Processor allows four different transportation schemes for data which can be UDP UDP_T UDP_F and TCP The Message rate of the PMU was set at 30 samples per second When the PMU is stationed in a different network than that of the Processor it is necessary to make sure that the subnet and the gateway of the devices entered are correct The subnet mask and the gateway are important parameters when both the equipment
57. s are not on the same device 17 The Power Calculation block calculates the real and reactive power based on user selected voltage and current phasors PWRC outputs the instantaneous values of the real power kW and reactive power kVAR with their corresponding timestamps The equations below show the implementation of the function block 17 P RE_V RE_I IM_V IM_T J 1000 5 1 Q IM_V RE_I RE_V IM_D 1000 5 2 The Real Power P is in kW and Reactive Power Q is in KVAR In the above equations IM stands for imaginary and RE stands for real 5 5 SEL SynchroWave Archiver The SEL 5076 SynchroWave Archiver Software provides continuous or triggered storage of power system data Data can be archived over a wide geographic area by using the accurate time stamps The archiver was set up to record the data from the PMU connected at the Facility The archiver receives data from the Processor which in turn receives data from the PMU The archiver plots the values of the voltages currents of the inputs along with frequency delta frequency real and reactive power in each individual phase and also the total three phase power It samples data at the rate of 30 samples per second The data archived is stored in the form of CSV or Comtrade 18 The Main Menu of the archiver consists of a GUI for means to add or remove PMUs to modify the archiver configuration and communication A new source or PMU can be added by clicking on New Source and by add
58. s cdocdedeasaesatl 68 X EUTURE WORK ans cesnsevescscdccnsscucstasssedess Soe Eet tioa Seeus SEE Esos EiS 71 REFERENCES EAEE TE E E 72 PUBLICATIONS isescccscscnssacestescscessuscssescesescssecsssstencsescosessvesseuccsssesseedsabecesonsessesesssaned 74 iv Texas Tech University Santosh Pappu August 2012 ABSTRACT Advance Research was conducted in Wind Energy It was divided into various categories of wind energy The areas of research are comparison between mid size and large size wind turbines power quality analysis and the evaluation of hub concept for wind turbines The characteristics of two wind farms of the same power capacity having two different size generators were compared The research compared the performance of mid size turbines to large turbines The systems were modeled in MATLAB Simulink A 9MW wind farm consisting of eighteen Fixed Speed Induction Generators FSIG with STATCOM at the terminals of the wind farm was compared to a 9MW wind farm consisting of six Doubly Fed Induction Generators DFIG An analysis on total power available for transmission reactive power consumption at different wind speeds cut in rated cut off power loss due to loss of turbines was done The next part of the research involved transient response of three wind farms interconnected to the grid at the same point designated as Hub rated 9MW each was modeled and simulated Each wind farm consists of six Doubly Fed Induction generator turbine
59. s implies that the stator needs to operate at grid frequency and the rotor can operate at variable frequency due to the power electronics interface Texas Tech University Santosh Pappu August 2012 2 2 3 Synchronous Generator The synchronous generator is much more expensive and mechanically more complicated than an induction generator of a similar size However it has one clear advantage compared with the induction generator namely that it does not need a reactive magnetizing current The magnetic field in the synchronous generator can be created by using permanent magnets or with a conventional field winding If the synchronous generator has a suitable number of poles it can be used for direct drive applications without any gearbox As a synchronous machine it is probably most suited for full power control as it is connected to the grid through a power electronic converter The converter has two primary goals 1 to act as an energy buffer for the power fluctuations caused by an inherently gusting wind energy and for the transients coming from the net side and 2 to control the magnetization and to avoid problems by remaining synchronous with the grid frequency Applying such a generator allows a variable speed operation of wind turbines 1 ac dc ac converter n variable speed with or synchronus without generator Fig 2 3 Schematic of Synchronous Generator 8 10 Texas Tech University Santosh Pappu Augu
60. s rated at 1 5MW each interfaced with power electronics on the rotor side The model was modeled in MATLAB Simulink Analysis on voltage stability of wind farms due to faults on the neighboring wind farm was done A novel approach to record and analyze the power coming from the utility was devised A Phasor Measurement Unit PMU was set up located at a Semiconductor Foundry Fabrication Facility sensitive load for analysis of the Power Quality of the Facility A code was developed for filtering the data collected from the PMU in MATLAB A GUI developed in MATLAB analyzed the data from the PMU and highlights aberrations in the values of Voltages and Frequency from the Power Quality limits for sensitive loads A unique method for analysis of Power Quality before the installation of a wind turbine directly feeding the Facility so as to set a standard after the wind turbine is installed 4 1 4 2 5 1 Texas Tech University Santosh Pappu August 2012 LIST OF TABLES Parameters of Induction Generator eeececeeseeceeececeseeeeeseeeeseeeesaeeeeaees 34 Parameters Of DRIG an 2a ae 36 Common Power Quality ISssuss au sense eher 42 vi 1 1 1 2 2 1 22 2 3 2 4 2 5 2 6 2 7 2 8 2 9 2 10 2 11 4 1 4 2 4 3 4 4 4 5 4 6 4 7 5 1 5 2 5 3 5 4 5 5 5 6 6 1 6 2 Texas Tech University Santosh Pappu August 2012 LIST OF FIGURES Offshore Wind Turbine 12 22 2 Cee CE ee Se 8 Generator of a Wind Turbine 2 usa 10 Squi
61. signed to exploit the wind energy that exists at a location Aerodynamic modeling is used to determine the optimum tower height control systems number of blades and blade shape 2 Fig 1 1 shows an offshore wind turbine Fig 1 1 Offshore Wind Turbine 2 Wind turbines convert wind energy to electricity for distribution Conventional horizontal axis turbines can be divided into three components 2 Texas Tech University Santosh Pappu August 2012 e The rotor component which is approximately 20 of the wind turbine cost includes the blades for converting wind energy to low speed rotational energy e The generator component which is approximately 34 of the wind turbine cost includes the electrical generator the control electronics and most likely a gearbox e g planetary gearbox adjustable speed drive or continuously variable transmission component for converting the low speed incoming rotation to high speed rotation suitable for generating electricity e The structural support component which is approximately 15 of the wind turbine cost includes the tower and rotor yaw mechanism 2 Small wind turbines may be used for a variety of applications including on or off grid residences telecom towers offshore platforms rural schools and clinics remote monitoring and other purposes that require energy where there is no electric grid or where the grid is unstable 1 1 2 Generators Basically a wind turbine can
62. st 2012 Fig 2 3 shows the schematic of the synchronous generator The stator is connected to the grid through the power electronics The rotor is energized by DC excitation The rotor is connected to a rectifier for DC excitation The stator windings of WRSGs are connected directly to the grid and hence the rotational speed is strictly fixed by the frequency of the supply grid The rotor winding is excited with direct current using slip rings and brushes or with a brushless exciter with a rotating rectifier Unlike the induction generator the synchronous generator does not need any further reactive power compensation system The rotor winding through which direct current flows generates the exciter field which rotates with synchronous speed The speed of the synchronous generator is determined by the frequency of the rotating field and by the number of pole pairs of the rotor 2 2 4 Permanent Magnet Generator In the permanent magnet PM machine the efficiency is higher than in the induction machine as the excitation is provided without any energy supply However the materials used for producing permanent magnets are expensive and they are difficult to work during manufacturing Additionally the use of PM excitation requires the use of a full scale power converter in order to adjust the voltage and frequency of generation to the voltage and the frequency of transmission respectively This is an added expense 1 Permanent Magnet Syn
63. synchronous speed The energy coming from the external power conversion unit is dumped as heat loss 2 3 3 Type 3 This configuration known as the doubly fed induction generator DFIG concept corresponds to the limited variable speed wind turbine with a wound rotor induction generator WRIG and partial scale frequency converter rated at approximately 30 of nominal generator power on the rotor circuit The partial scale frequency converter performs the reactive power compensation and the smoother grid connection Typically the speed range comprises 40 to 30 of synchronous speed 14 Texas Tech University Santosh Pappu August 2012 1 The smaller frequency converter makes this concept attractive from an economical point of view Its main drawbacks are the use of slip rings and protection in the case of grid faults Partial scale frequency converter Fig 2 7 Type 3 Wind Turbine Fig 2 7 shows the schematic of a type 3 wind turbine The stator is directly connected to the grid The rotor is connected via the power electronics This enables the rotor to operate at variable speed This also minimizes the voltage oscillations due to mechanical oscillations on the rotor The power electronics are rated for 30 of the nominal power This reduces the cost of power electronics 2 3 4 Type 4 This configuration corresponds to the full variable speed wind turbine with the generator connected to the grid through a
64. t 40sec The torque increases gradually and then settles down at zero after the fault has occurred Active Power MVV 8 0 10 20 30 40 50 60 70 Time sec Fig 6 11 Active Power transmitted to the grid from both the wind farms 58 Texas Tech University Santosh Pappu August 2012 Electrical Torque pu a co FSIG ol DFIG 1 o 4 A Ep fi fl ge el el u 0 10 20 30 40 50 60 70 Time Fig 6 12 Electrical Torque of both the generators when a three phase fault occurs 59 Texas Tech University Santosh Pappu August 2012 CHAPTER 7 RESULTS FOR EVALUATION OF HUB CONCEPT The simulation was carried out in MATLAB Simulink simulation environment The simulation time was 50secs The model was simulated for a constant wind speed of 12m s to attain steady state fast The model has been simulated for various transient conditions The voltage and torque values are recorded in pu system The active power and reactive power values are recorded in MW and MVAR respectively The measurements are recorded at the 34 5kV bus for the wind farms and 345kV bus at the point of interconnection This section demonstrates the working of the model for rated conditions and for faults at various locations 7 1 Rated Conditions The wind farms are simulated for rated conditions A wind speed of 12m s is given as input to the wind turbines in all three wind farms The active power voltage and reacti
65. ted directly to a grid 12 Texas Tech University Santosh Pappu August 2012 Fig 2 5 shows the schematic of a type 1 technology wind turbine The generator is directly connected to the grid For the purpose of synchronization the generator is forced to run at a frequency of 60Hz The capacitor bank is provided for reactive power compensation Regardless of the power control principle in a fixed speed wind turbine the wind fluctuations are converted into mechanical fluctuations and consequently into electrical power fluctuations In the case of a weak grid these can yield voltage fluctuations at the point of connection Because of these voltage fluctuations the fixed speed wind turbine draws varying amounts of reactive power from the utility grid unless there is a capacitor bank which increases both the voltage fluctuations and the line losses Thus the main drawbacks of this concept are that it does not support any speed control it requires a stiff grid and its mechanical construction must be able to tolerate high mechanical stress Type 1 wind turbines also consist of active pitch control type and stall control type Stall controlled wind turbines cannot carry out assisted startups which imply that the power of the turbine cannot be controlled during the connection sequence They are popular because of its low price and simplicity The main advantages of active pitch control wind turbines are that it facilitates power controllability co
66. the rotor So far the Squirrel Cage Induction Generator SCIG has been the prevalent choice because of its mechanical simplicity high efficiency and low maintenance requirements The SCIG is directly coupled to grid Hence this is normally used in Fixed Speed configuration as the generator frequency and grid frequency should match for synchronism 1 Texas Tech University Santosh Pappu August 2012 Fitch Control Fig 2 1 Squirrel cage Induction Generator connected to the grid on the stator and wind turbine on the rotor 6 Fig 2 1 shows the schematic of the singly fed induction generator The rotor of the generator is connected to the rotor of the turbine The stator is directly coupled to the grid 2 2 2 Doubly Fed Induction Generator The Doubly Fed Induction Generator DFIG comes under the category of Wound Rotor Induction Generators WRIG In the case of a WRIG the electrical characteristics of the rotor can be controlled from the outside and thereby a rotor voltage can be impressed The windings of the wound rotor can be externally connected through slip rings and brushes or by means of power electronic equipment which may or may not require slip rings and brushes By using power electronics the power can be extracted or impressed to the rotor circuit and the generator can be magnetized from either the stator circuit or the rotor circuit It is thus also possible to recover slip energy from the rotor circuit and feed it
67. ting led to a complete change of electric loads nature These loads are simultaneously the major causers and the major victims of power quality problems Due to their non linearity all these loads cause disturbances in the voltage waveform 14 Although many efforts have been taken by utilities some consumers require a level of PQ higher than the level provided by modern electric networks This implies that some measures must be taken in order to achieve higher levels of Power Quality The most common type of power quality issues are listed in the table below 34 Texas Tech University Santosh Pappu August 2012 Table 5 1 Common Power Quality Issues 15 Voltage sag or dip Description A decrease of the normal voltage level between 10 and 90 of the nominal rms voltage at the power frequency for durations of 0 5 cycle to 1 minute Causes Faults on the transmission or distribution network most of the times on parallel feeders Faults in consumer s installation Connection of heavy loads and start up of large motors Consequences Malfunction of information technology equipment namely microprocessor based control Systems PCs PLCs ASDs etc that may lead to a process stoppage Tripping of contactors and electromechanical relays Disconnection and loss of efficiency in electric rotating machines Very short interruptions Description Total interruption of electrical supply for duration from few milliseconds to one o
68. trical reliability and aesthetics 10 The Generation Interconnection process in the Tariff allows each Generation Interconnection Customer GIC to identify a transmission line or station on the transmission system to interconnect with When a GIC elects to interconnect with a transmission line a new station must be built GICs request that these new stations be located at a point on the transmission line which minimizes the distance to their generator In addition the inability of a subsequent generator developer to obtain right of way across land that is already leased to an earlier developer may inhibit the ability of the subsequent GIC to gain access to a transmission line or specific substation This leads the GIC to request an exclusive interconnection station at a location which minimizes the length of the generator lead it needs to build utilizing the right of way it can obtain For solitary interconnection requests this is not an issue But in those areas where SPP has seen high concentration of interconnection requests there can be many GIC s requesting interconnection in the same geographical area each expecting its own new interconnection station 10 20 Texas Tech University Santosh Pappu August 2012 3 1 Designation of Hubs The AGCTF designates a specific new substation Hub in an area where multiple generators are located as a single interconnection point Hubs will only be designated at 300kV or above The establishm
69. tween the STATCOM and the EPS The exchange between the inverter and the AC system can be controlled adjusting the output voltage angle from the inverter to the voltage angle of the AC system This means that the inverter cannot provide active power to the AC system form the DC accumulated energy if the output voltage of the inverter goes before the voltage of the AC system On the other hand the inverter can absorb the active power ofthe AC system if its voltage is delayed in respect to the AC system voltage 19 Texas Tech University Santosh Pappu August 2012 CHAPTER 3 EVALUATION OF HUB CONCEPT FOR WIND TURBINES Research was conducted for analysis of Hub Concept by building models of wind farms in MATLAB based on the Hub Concept The Southwest Power Pool SPP is currently dealing with the Hub Concept The committee responsible for the allocation designation of Hubs is the Area Generation Task Force The Area Generation Connection Task Force AGCTF is responsible for developing and recommending policy to guide SPP Staff to determine the optimum method of interconnecting generation given the complex situations generally prevalent 10 The Hub Concept was initiated as Generation Developers are requesting multiple interconnections on the same transmission line in close proximity to each other In addition to adding costs having multiple interconnection substations in the same geographical area can create many issues some of which are elec
70. unt reactors are added to a line the increased impedance can also reduce the amount of power that can flow down the line thereby reducing the amount of capacity available on the line for the normal movement of power It is evident that interconnecting multiple generators at different points along a single transmission line segment may degrade the reliability of the transmission system 10 22 Texas Tech University Santosh Pappu August 2012 CHAPTER 4 MODEL DEVELOPMENT PROCEDURE In this chapter two wind farm topologies will be presented a singly fed generator and a doubly fed induction generator along with the wind profiles for which they have been simulated The fixed speed wind farm has been compared to the DFIG wind farm in various aspects The development of wind farm transient models provides an interesting insight into the performance of the topologies for disturbances and fault conditions The model used for Evaluation of Hub Concept has also been discussed First the models for the comparison of wind farms with different configurations are discussed and then models of the evaluation of Hub Concept are discussed 4 1 Wind Profile In this section the wind profile used in the model is discussed For determining the effect of wind generation on the electrical characteristics it is only necessary to translate the input wind speed into a mechanical torque which is then applied to the blades of the generator 11 _ npCy
71. ure protection and series compensated line protection logic The relay features extensive metering and data recording including high resolution data capture and reporting Synchrophasor measurements are available 37 Texas Tech University Santosh Pappu August 2012 when a high accuracy time source is connected to the relay The SEL 421 supports the IEEE C37 118 Standard for Synchrophasors for Power Systems The SEL 421 can be used as a relay and Phasor Measurement unit In this application it has been used as a Phasor Measurement Unit to capture the data and use it for applications such as archiving and analysis for Power Quality The PMU captures data at 30 samples per second It has two sets of inputs for three phase Voltages and currents The input Current terminals are rated at 5A and Voltage terminals are rated at 120V phase to ground The current and voltage from the line are stepped down using Current Transformers and Potential Transformers respectively and then fed to the PMU The three phase voltages and currents can be given to either one of the inputs 16 Shown below in Fig 5 1 is the schematic of connection of the PMU Fig 5 1 Schematic of SEL 421 connected using current transformers and potential transformers 16 Fig 5 1 shows the SEL 421 connected to the line via current transformers and potential transformers The CT s step the current down to 5A and PT s step the voltage down to 120V and feed it to the PMU as
72. ve power at the point of interconnection are recorded The active power at this point is the total power generated from all three wind farms including transmission losses The wind turbines are set to generate 0 95pu of the mechanical power at this wind speed Fig 7 1 shows the active power recorded at the 345kV bus This power is the total power generated by all the three wind farms The output reaches steady state after certain time The time taken is due to start up transients The power recorded at the point of interconnection is about 25MW The three wind farms are rated for 27MW 60 Texas Tech University Santosh Pappu August 2012 30 Active Power MVV 5 0 5 10 15 20 25 30 35 40 45 50 Time sec Fig 7 1 Active Power at the point of Interconnection 7 2 Fault on One Wind Turbine in Wind Farm A three phase to ground fault was installed on one wind turbine in wind farm A The response of the wind turbines in wind farm A and B to the fault were recorded The fault was installed to trigger at time 35sec for duration of 0 1sec When the fault acts on the wind turbine the voltage of the wind turbine reduces to 0 1pu The relay senses the dip in voltage and trips the wind turbine The effect of this fault on the wind turbine in the neighboring wind farm is analyzed Fig 7 2 Shows the voltage at the turbine which has been shorted in wind farm A 61 Texas Tech University Santosh Pappu August 201
73. which two have been used in this research A brief description about all the four types of generators and the technologies they are associated is also discussed The theory behind the conversion of energy from mechanical to electrical is also discussed to give a better understanding 2 1 Energy Conversion The aerodynamic blades on the rotor convert the kinetic energy of the wind into mechanical energy effectively providing the torque Tr on the rotor ate 2 1 Or Where w angular speed of rotor and power is Pr and is given by the following relation P m1pR v3 cp 4 8 2 2 p is the air density R the wing radius and v the effective wind speed c is the efficiency coefficient which is a function of the blade pitch angle 0 and the tip speed ratio A In the context of this project A is the ratio between the blade tip speed and the wind speed v v A 2 3 Vtip Rwy Where Vtip is the speed at the tip of the blade However the inverse ratio is also commonly met in the literature The performance coefficients cp for wind turbines are obtained through numerical calculations and look up tables Assuming the generator is lossless the total power is transferred from the rotor of the wind turbine to the generator Hence rotor power would be equal to electrical power generated P P 2 4 Texas Tech University Santosh Pappu August 2012 where P is the electrical power of the generator R T g 2 5 wher
74. y determined by the user Code will continue analyzing the data for all the excel files Fig 8 3 shows the subfolder containing the waveforms of the parameters and the excel sheet containing data 67 Texas Tech University Santosh Pappu August 2012 m gt Computer Local Disk C PMUFrequencyError 2 E m Organize v Includeinlibray v Sharewithv Slideshow Burn New folder a jE Computer x u Bi Local Disk C N iy J crystalreportvie a A Hy MR d Dri d d rivers ZEA s Intel 110915 123709667 Deltafrequencyer Frequencyerror2 Voltageerror2 Mus 0 station device ror2 sic company type g National Instru d PerfLogs J pmu M pmu2 Ji pmut J pm Ji pmu6 i pmu7 Ji pm Fig 8 3 Sub folder where the waveforms and excel sheet containing the data are saved J 68 Texas Tech University Santosh Pappu August 2012 CHAPTER 9 CONCLUSION The transient models of FSIG and DFIG were developed and simulated in MATLAB Simulink It is becoming increasingly important to decide which topology of wind farm should be implemented when starting a wind farm This model is simulated for all wind conditions to demonstrate the response of the two topologies to all wind conditions and fault conditions and show the reactive power consumed voltage stability at the point of common coupling and active power transmitted to the grid during all wind conditions At cut in rated and cut off wind s

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