Effect of Geomagnetically Induced Currents on Protection Systems

Transcription

1 Effect of Geomagnetically Induced Currents on Protection Systems Sture Lindahl Industrial Electrical Engineering and Automation

2 Effect of GIC on Protective Relays Activity of the Sun Propagation of the Solar Wind Magnetospheric Processes Ionospheric Processes Earth Surface Potential Geomagnetically Induced Currents Saturation of Power Transformers Performance of Protective Relays Sture Lindahl, LTH/IEA 2

3 Solar Flare Effects Sture Lindahl, LTH/IEA 3

4 Geomagnetically Induced Currents Electrojet GIC GIC GIC + Earth Surface Potential Gradient - GIC Sture Lindahl, LTH/IEA 4

5 Conclusions The risk is that protective relays operate unwantedly during a geomagnetic storm and causes a severe power system disturbance or even a nationwide blackout A less obvious risk is that the current transformers operates so far into saturation that the secondary current is too low for proper operation of the protection equipment at internal faults during geomagnetic storms. Sture Lindahl, LTH/IEA 5

6 Protective Relays at Risk The most important class of relays is the non-directional low set residual overcurrent relays commonly applied on shunt capacitors, power transformers, shunt reactors, and transmission lines Sture Lindahl, LTH/IEA 6

7 Shunt Capacitors International operational experience shows very clearly that low-set residual overcurrent relays for shunt capacitors with directly earthed neutral point are very vulnerable. So far, protective relays for shunt capacitors is Sweden have not maloperated during geomagnetic storms. It is recommended that the setting and the harmonic restraint of the (1) residual overcurrent and(2) neutral-point overcurrent relay are reviewed and tested. Sture Lindahl, LTH/IEA 7

8 Power Transformers Security of transformer protection There are some protective relays for power transformers that should be reviewed and tested. The candidates are: (1) the low-set residual overcurrent relay, (2) the low-set neutral-point overcurrent relay, and (3) the restricted earth-fault relay. The same holds true for similar protective relays applied on directly earthed shunt reactors. Sture Lindahl, LTH/IEA 8

9 Power Transformers Dependability of transformer protection Are the power transformers sufficiently protected in case of GIC? Power transformers and shunt reactors are in general equipped with mechanical and thermal fault detectors. These fault detectors operate independently of the instrument transformers and may keep up the dependability Sture Lindahl, LTH/IEA 9

10 Transformer Damage Sture Lindahl, LTH/IEA 10

11 and 130-kV Power Lines Operational experience shows that the lowset residual overcurrent relays are vulnerable to GICs. In 1986, all such relays on the 400- and 220- kv network were replaced by modern dependent time overcurrent relays with logarithmic characteristic and second harmonic restraint. There are, however, a number of residual over-current relays applied on power lines that have inadequate performance. Sture Lindahl, LTH/IEA 11

12 Residual Overcurrent Relays Future low-set residual overcurrent relays should preferably just measure the fundamental frequency component of the current. How to justify that the dependent time residual overcurrent relay must operate at 150 Hz? (SNDR-requirement) It should also be possible to restrain the relay not only from the second harmonic but also from other harmonics. Sture Lindahl, LTH/IEA 12

13 GIC Disturbance kV Hemsjö-Karlshamnsverket with the HVDC converter for SwePo Link 400 MW import from Poland interrupted The residual overcurrent dependent time relay operated unexpectedly. Sture Lindahl, LTH/IEA 13

14 GIC Disturbance Recordings Hemsjö RMS(Ires) RMS(3I0) Current [A] Time [ms] Sture Lindahl, LTH/IEA 14

15 GIC Disturbance Recordings Hemsjö , Harm(3I0) 1E+1 Relative Magnitude 1E+0 1E-1 1E-2 1E E-4 Fund 2nd 3rd 4th 5th 6th 7th 8th 9th Sture Lindahl, LTH/IEA 15

16 GIC Disturbance Recordings Hemsjö , Harm(Ires) 1E+1 Relative Magnitude 1E+0 1E-1 1E-2 1E E-4 Fund 2nd 3rd 4th 5th 6th 7th 8th 9th Sture Lindahl, LTH/IEA 16

17 GIC Disturbance Recordings Hemsjö (3i0) Current [A] Time [ms] Sture Lindahl, LTH/IEA 17

18 GIC Disturbance Recordings Hemsjö , ires Current [A] Time [ms] Sture Lindahl, LTH/IEA 18

19 GIC Disturbance Recordings Hemsjö , Harm(Ures) 1E+1 Relative Magnitude 1E+0 1E-1 1E-2 1E E-4 Fund 2nd 3rd 4th 5th 6th 7th 8th 9th Sture Lindahl, LTH/IEA 19

20 GIC Disturbance Recordings Hemsjö , ures Voltage [kv] Time [ms] Sture Lindahl, LTH/IEA 20

21 GIC Disturbance The relay operation is caused by the 3 rd and 6 th harmonic current and not by the fundamental frequency current The stabilising 2 nd harmonic in the residual current is very low SNDR has requested that the residual current dependent time relay must operate for the 3 rd harmonic Sture Lindahl, LTH/IEA 21

22 Three-Phase System Model (Ch 5) AC Source DC Source Transformer Load Shunt Capacitor Sture Lindahl, LTH/IEA 22

23 Magnetising Inductance Relative Incremental Magnetising Inductance 1.5 Magnetising Inductance Saturated Region Non-Saturated Region Saturated Region (Magnetising Current)/Is Sture Lindahl, LTH/IEA 23

24 Magnetising Inductance Incremental Magnetising Reactance ms= 6 ms= 10 ms= Magnetising Reactance Relative Magnetising Current Sture Lindahl, LTH/IEA 24

25 Analytical or Dynamic Simulation RMS-Value of Magnetising Current (RMS-Value)/Is (DC Current)/Is Sture Lindahl, LTH/IEA 25

26 Analytical or Dynamic Simulation Peak-Value of Magnetising Current (Peak-Value)/Is (DC Current)/Is Sture Lindahl, LTH/IEA 26

27 Analytical or Dynamic Simulation Fundamental Frequency Current 500 (Fundamental)/Is (DC Current)/Is Sture Lindahl, LTH/IEA 27

28 Analytical or Dynamic Simulation Second Harmonic Current 60 (Second Harmonic)/Is (DC Current)/Is Sture Lindahl, LTH/IEA 28

29 Analytical or Dynamic Simulation Third Harmonic Current 60 (Third Harmonic)/Is (DC Current)/Is Sture Lindahl, LTH/IEA 29

30 Analytical or Dynamic Simulation Both methods give similar results Saturating power transformers cause a reduction of the busbar voltage Saturating power transformers cause both even and odd harmonics (k=1 to 9) Higher order harmonics not accurate The analytical method gives upper limit Sture Lindahl, LTH/IEA 30

31 Busbar Voltages (Ch 7) Busbar Voltage Voltage [kv] (Direct Current per Phase)/Is Sture Lindahl, LTH/IEA 31

32 Busbar Voltages Total Harmonic Distortion 5 4 THD [%] (Direct Current per Phase)/Is Sture Lindahl, LTH/IEA 32

33 Busbar Voltages Magnitude and Phase Angle of Second Harmonic Magnitude Phase Angle Magnitude V2/V Angle [degrees] (Direct Current per Phase)/Is -180 Sture Lindahl, LTH/IEA 33

34 Busbar Voltages Magnitude and Phase Angle of Third Harmonic Magnitude Phase Angle Magnitude V3/V Angle [degrees] (Direct Current per Phase)/Is -180 Sture Lindahl, LTH/IEA 34

35 Busbar Voltages Saturating transformers cause harmonic distortion of the busbar voltages Busbar voltage drops by about 3% Total harmonic distortion is about 3% Individual harmonics is lower than 3% Sture Lindahl, LTH/IEA 35

36 GIC Disturbance Recordings Hemsjö , Harm(Ures) 1E+1 Relative Magnitude 1E+0 1E-1 1E-2 1E E-4 Fund 2nd 3rd 4th 5th 6th 7th 8th 9th Sture Lindahl, LTH/IEA 36

37 Earthed Shunt Capacitors (Ch 9) Phase Currents at 200 Mvar (Idc/Is=5.94) Phase a Phase b Phase c Current [A] Time [ms] Sture Lindahl, LTH/IEA 37

38 Earthed Shunt Capacitors Total Harmonic Distortion of the Phase Currents THD [%] (Direct Current per Phase)/Is Sture Lindahl, LTH/IEA 38

39 Earthed Shunt Capacitors Magnitude and Phase Angle of Third Harmonic Magnitude Phase Angle Magnitude I3/I Angle [degrees] (Direct Current per Phase)/Is -180 Sture Lindahl, LTH/IEA 39

40 Earthed Shunt Capacitors Magnitude and Phase Angle of 6th Harmonic Magnitude Phase Angle Magnitude I6/I Angle [degrees] (Direct Current per Phase)/Is -180 Sture Lindahl, LTH/IEA 40

41 Earthed Shunt Capacitors RMS-value of Residual Current 0.5 (Residual Current)/In (Direct Current per Phase)/Is Sture Lindahl, LTH/IEA 41

42 Earthed Shunt Capacitors Magnitude and Phase Angle of Second Harmonic Magnitude Phase Angle I2/In Angle [degrees] (Direct Current per Phase)/Is -180 Sture Lindahl, LTH/IEA 42

43 Earthed Shunt Capacitors Magnitude and Phase Angle of Third Harmonic Magnitude Phase Angle I3/In Angle [degrees] (Direct Current per Phase)/Is -180 Sture Lindahl, LTH/IEA 43

44 Earthed Shunt Capacitors Magnitude and Phase Angle of 6th Harmonic Magnitude Phase Angle I6/In Angle [degrees] (Direct Current per Phase)/Is -180 Sture Lindahl, LTH/IEA 44

45 Earthed Shunt Capacitors The fundamental frequency phase current decreases because of the busbar voltage The total harmonic distortion in the phase current is higher than 10% The 3rd harmonic of the phase current is higher than 6% of the phase current while the 6th harmonic is higher than 10% The RMS value of the residual current is about 40% while the 6 th harmonic is higher than 20%. Sture Lindahl, LTH/IEA 45

46 Current Transformers (Ch 12) I : I :1 pn sn L λ R w Lb i p i p e s i s R b Ψ s Sture Lindahl, LTH/IEA 46

47 Instrument Transformers (Ch 10) How to determine the B-H characteristic from the V-I characteristic? Sture Lindahl, LTH/IEA 47

48 Experimental Data Magnetising Curve U [V] U [V] I [ma] Sture Lindahl, LTH/IEA 48

49 Instrument Transformers RMS Characteristics of a Saturating CT Sinusoidal Current Sinusoidal Voltage 2.0 Voltage [pu] Current [pu] Sture Lindahl, LTH/IEA 49

50 Instrument Transformers It seems reasonable to use the RMS value of the magnetising current at the knee point and use that value to determine when the magnetising inductance drops from the nonsaturated value to the saturated value Sture Lindahl, LTH/IEA 50

51 Current Transformers Harmonic Content of Secondary Current Fundamental 2nd 3rd 4th 5th 6th Amplitude [A] Magnitude of Direct Current, IDC [A] Sture Lindahl, LTH/IEA 51

52 Future Work Requirements on the dependent time residual overcurrent relay for power lines and power transformers Protection for earthed shunt capacitors How to protect power transformers against GIC? Sture Lindahl, LTH/IEA 52