Harmonic Design Considerations for Wind Farms

Transcription

1 Harmonic Design Considerations for Wind Farms To Ensure Grid Code Compliance Liam Breathnach Power System Studies Group ESB International

2 Agenda Introduction Harmonic Theory and Concepts Grid Code Requirements Modelling and Simulation Case Studies Mitigation Measures

3 Introduction AC Power systems sinusoidal voltages / currents Non-linear devices Power electronic equipment Saturable devices May cause distortion Unwanted effects on equipment and system

4 Introduction Grid Transformer System Picture Area Picture Area Cable Wind Turbine & Step-up Transformer Grid Voltage

5 Introduction Examples of Unwanted Effects: Conductors Increased losses Transformer Increased losses and excessive heating Circuit Breakers Nuisance tripping Capacitors Permanent failure

6 Introduction Doubly Squirrel Fed Cage Induction Generator No Harmonics currents Synchronous Induction generator / Induction with variable Generator resistance with Full Converter No Harmonics currents

7 Harmonic Theory and Concepts 50 Hz Harmonics occur at multiples of the fundamental Hz frequency (50Hz) Hz Distorted waveform can be expressed in terms of it s Hz component waveforms

8 Harmonic Theory and Concepts Harmonic currents produced by a wind turbine Fundamental 50Hz MC's PlotXY - Fourier chart(s). Copying date: 26/05/2010 File WF_Harmonics_Paper_rev0p0_BaseCase_TurbineHarmonics.pl4 Variable c:x0016a-x0031a [peak] MC's Initial Time: PlotXY Fourier Final Time: chart(s). 2 Copying date: 27/05/2010 File WF_Harmonics_Paper_rev0p0_BaseCase_TurbineHarmonics.pl4 Fifth Harmonic = 250Hz Variable c:x0016a-x0031a 70 Initial Time: 1.98 Final Time: Current Harmonics >50Hz harmonic order order Frequency [Hz]

9 Harmonic Theory and Concepts Voltage Distortion: System Impedance Vh Zh* Ih Impedances varies with frequency X L 2 fl May result in harmonic voltages Total Harmonic Distortion (THD) X C 1 2 fc

10 Harmonic Theory and Concepts Impedance 1.2 * System Harmonic Impedance Resonance (file WF_Harmonics_Paper_rev0p0_Cable_SeriesReactor.pl4; x-var f) v:pcca M C's PlotXY - Fourier chart(s). Copying date: 26/05/2010 File WF_Harmonics_Paper_rev0p0_BaseCase_TurbineHarmonics.pl4 Frequency Variable [Hz] c:x0016a-x00 Initial Time: 1.98 Final Time: Harmonic Current Current harmonic order

11 Harmonic Theory and Concepts System Short Circuit Level System Harmonic Impedance affected by: Short Circuit Level Capacitor Cable/Overhead Banks Line Q A Capacitor banks lower the resonant frequencies I h Connection Cable/ Overhead Line Transformers/ Reactors

12 Grid Code Requirements Distortion limits outlined in IEC High Voltage THD planning level is 3% Limits for individual harmonic magnitudes

13 Percent [%] Grid Code Requirements Individual Harmonic Planning Limits th Harmonic, 250Hz, 2% limit Harmonic Order

14 Modelling & Simulation Build model Represent harmonic sources as current injectors Wind Test Report (IEC ) Frequency scan analysis Identify potential resonances Processing techniques individual harmonic distortions THD 1.2 * (file WF_Harmonics_Paper_rev0p0_Cable_SeriesReactor.pl4; x-var f) v:pcca

15 Modelling & Simulation Loads not producing harmonics Damping Phase angles of sources Transformer connections R L Modelling of lines and cables PI equivalent model (multiple sections) System representation C How far back? Capacitor banks Short circuit capacity

16 Case Studies Short Circuit Capacity High Short Circuit Level Typically lower harmonics Lower Short Circuit Level Weaker system More pronounced resonance peaks

17 Case Studies - Cable vs Overhead Line *10 * Overhead 0.8 Line 3 Impedance System Relatively small capacitance Cable 1 Impedance 0.2 Voltage Greater capacitance 0.0 M0 C's PlotXY - Fourier chart(s). Copying date: 26/05/2010 File 00 WF_Harmonics_Paper_rev0p0_BaseCase_TurbineHarmonics.pl Variable Frequency [Hz] c:x0016a-x0031 Initial Time: 1.98 Final Time: 2 Lowers resonant frequencies (f ile (f ile WF_Harmonics_Paper_rev wf _harmonics_paper_rev0p0_basecase_ohl.pl4; 0p0_basecase_cable.pl4; x-v ar f f )) v :PCCA 70 Frequency [Hz] Current harmonic order

18 Case Studies Distance Along Cable 1.2 * Point along Cable End of Cable 0.8 Impedance (file wf_harmonics_paper_rev0p0_basecase_cable.pl4; x-var f) v:sect3a v:pcca Cable capacitance distributed along its length Point to connection important Frequency [Hz]

19 Harmonic Mitigation Active Filters Mitigate multiple harmonics Complex and costly Passive Filters Simple and reliable Relatively inexpensive Cannot mitigate multiple harmonics

20 Network Impedance p.u. Harmonic Mitigation Impedance Frequency (Hz) Without Filter With Filter Frequency [Hz]

21 Summary Wind turbines may be source of harmonics May interact with system impedance Resulting distortion may: Damage equipment Increase losses Mitigation measures May prove costly Identify potential issues early