Travelling Wave Based DC Line Fault Location in VSC HVDC Systems

Transcription

1 M.Sc. Thesis Presentation Travelling Wave Based DC Line Fault Location in VSC HVDC Systems K.P.A.N. Pathirana Department of ECE University of Manitoba Canada.

2 Outline Introduction Surge detection method Modelling of Rogowski coil Line fault location performance Conclusion and future work

3 Background HVDC transmission lines and cables need repairs quickly as possible after a fault. Travelling wave based fault location is the common fault location method applied in HVDC transmission lines. IGBT based voltage source converter (VSC) HVDC systems are gradually gaining ground.

4 Problem definition No publications dealing with the fault location in VSC HVDC schemes with such long cable connections. The large DC capacitance at the converter terminal. Measurement bandwidth of the transducers.

5 Objectives Development of a method of measurement for detecting travelling wave arrival times in a VSC HVDC scheme. Testing and verification of the proposed measurement system through simulations. Investigate the effect of different parameters on the accuracy of fault location.

6 Line fault location methods Techniques based on impedance measurement Techniques based on high frequency spectrums of the currents and voltages Machine learning based approaches Techniques based on travelling waves

7 Line fault location methods Techniques based on impedance measurement Techniques based on high frequency spectrums of the currents and voltages Machine learning based approaches Techniques based on travelling waves

8 Travelling wave based fault location X F = l u. (t CC t CC ) 2

9 Current LFL technology Detection methods

10 Current LFL technology Detection methods Time stamping

11 Current LFL technology Detection methods Time stamping Typical accuracies

12 Line Termination in LCC and VSC Schemes LCC HVDC VSC HVDC

13 Travelling waves incident on junction

14 Travelling waves incident on junction v r x o, t = ρ. v x o, t v t x o, t = τ. v x o, t ρ = Z cc Z cc Z cc + Z cc τ = 2Z cc Z cc + Z cc

15 Travelling waves incident on junction Z cc = L C Z cc = Z ccccc ρ = Z cc Z cc Z cc + Z cc ρ 1 v o x o, t = 1 + ρ. v x o, t v x o, t = AA x o αα

16 Travelling waves incident on junction Z cc = L C Z cc = Z ccccc Voltage magnitude V(Xo,t) Vo(Xo,t) ρ = Z cc Z cc Z cc + Z cc ρ 1 v o x o, t = 1 + ρ. AA x o αα v x o, t = AA x o αα Time [S]

17 Travelling waves incident on junction Z cc = L C 0 Z cc = Z ccccc ρ = Z cc Z cc Z cc + Z cc ρ -1 v o x o, t = 1 + ρ. v x o, t v x o, t = AA x o αα

18 Travelling waves incident on junction Z cc = L C 0 Z cc = Z ccccc ρ = Z cc Z cc Z cc + Z cc ρ -1 Voltage magnitude V(Xo,t) Vo(Xo,t) v o x o, t = 1 + ρ. AA x o αα v x o, t = AA x o αα Time [S]

19 Test network

20 Terminal voltage Voltage [kv] No inductor Time [S] Solid P-G fault 70 km away from Converter-1

21 Terminal voltage Gradual Change Voltage [kv] No inductor Time [S] Solid P-G fault 70 km away from Converter-1

22 Terminal voltage Voltage [kv] No inductor 1 mh inductor Time [S] Solid P-G fault 70 km away from Converter-1

23 Terminal Current 0.6 No inductor 1 mh inductor Current [ka] Time [S] Solid P-G fault 70 km away from Converter-1

24 Terminal Current Less sharp terminal Current 0.6 No inductor 1 mh inductor Current [ka] Time [S] Solid P-G fault 70 km away from Converter-1

25 Problems with line voltage and current measurements Transducers need to be installed at very high potentials. Insulations requirements. Electrical isolation between sensor output and the data acquisition system. Bulky and expensive instrumentation.

26 Surge capacitor current Rate of change of terminal voltage 0.01 Current [ka] No inductor 1 mh inductor Time [S] Solid P-G fault 70 km away from Converter-1

27 Rate of change of the surge capacitor current Small effect on value of inductance Rate of change of surge capacitor current Time [s] No Inductor 1 mh 10 mh Solid P-G fault 70 km away from Converter-1

28 Proposed termination Converter side Inductor Rogowski Coil Cable Side Surge Capacitor vr

29 Experimental results Dorsey converter station LCC HVDC ± 500 kv 900 km Overhead line Inner radius Outer radius Resistance 260 mm 284 mm 468 Ω 0.5 H Self-Inductance 3.5 mh Converter side Cable Side 55 nf Capacitance pf Rogowski Coil vr Mutual-Inductance 0.55 µh

30 Experimental results 6 Rogowski coil voltage [V] (a) Time [ms] 2 x 10-3 Rogowski coil voltage [V] Rogowski coil voltage for a fault 356 km away from Dorsey converter station. (b) Time [ms]

31 Remarks If there is no series inductor voltage or surge cap cannot be used Current can be used With series inductor voltage or surge cap can be used The value of the series inductor is not that important as long as it is above 1 mh.

32 Modelling of Rogowski Coil H(t). cos α. dd = i p (t) N s. i s (t) dd = A. N s l dd. μ 0. H(t). cos(α)

33 Modelling of Rogowski Coil φ(t) = μ 0. A. n. i p (t) e(t) = dd(t) dd = μ 0. A. N s l. di p(t) dd

34 Equivalent Circuit of Rogowski Coil v r t = e(t) L. i t = C. dv r t dd dd t dd + v r t Z b i t. R

35 Parameters of the designed Rogowski coil Inner radius Outer radius mm mm Number of Turns 870 measured calculated Resistance 4 Ω 3.9 Ω Self-Inductance 81 µh 81 µh Capacitance * - 13 pf Mutual-Inductance µh µh * Capacitance is too small to measure

36 Test setup

37 Verification of the Rogowski coil model Current [A] 0-20 Current Through the Rogowski coil Time [ms] 3 Voltage [V] 1-1 Simulated Experimental Time [ms]

38 Verification of the Rogowski coil model Current [A] 0-20 Current Through the Rogowski coil Time [ms] 3 Voltage [V] 1-1 Simulated Experimental Time [ms]

39 Line Fault Location Performance

40 Line Fault Location Performance

41 Terminal voltages and Currents Positive pole Negative pole Voltage [kv] Con. 1 Con (a) Time [ms] Voltage[kV] Con. 1 Con (b) Time [ms] Current[kA] Con Con (c) Time [ms] -0.5 Con. 1-1 Con (d) Time [ms] solid pole-to-ground fault on positive pole 130 km from Converter-1 Current[kA]

42 Current[kA] Voltage[V] Surge Capacitor currents and Positive pole Rogowski coil Voltages Con. 1 Con (e) Time [ms] Con Con (g) Time [ms] Negative pole (f) Time [ms] solid pole-to-ground fault on positive pole 130 km from Converter-1 Current[kA] Voltage[V] Con. 1 Con. 2 Con. 1 Con (h) Time [ms]

43 Threshold setting

44 Threshold setting Actual fault location (km) Fault location errors (km) visual inspection Threshold 1 Threshold 10 Threshold

45 Threshold setting and fault resistance Error[km] ohm 50 ohm 100 ohm Threshold Solid fault 30km the Converter -1

46 Threshold setting and fault resistance Error[km] ohm 50 ohm 100 ohm Threshold Solid fault 50km the Converter -1

47 Threshold setting and fault resistance Error[km] ohm 50 ohm 100 ohm Threshold Solid fault 220km the Converter -1

48 Threshold setting and fault resistance/low Thresholds Error[km] ohm 50 ohm 100 ohm Threshold Solid fault 220km the Converter -1

49 Possibilities of improving the accuracy Modal Transform Remove the coupling between conductors. Filtering Selecting frequency band.

50 Modal transform u mm u mm = T. u N up i mm i mm = T. i N ip T = ku mm ku mm = ku N ku P v rrr v rrr = v rr v rr

51 Fault Location errors /Modal transform Actual fault location (km) Fault location error (km) No M.Trans. Mode 0 Mode Solid-Fault

52 Fault Location errors /Modal transform Actual fault location (km) Fault location error (km) No M.Trans. Mode 0 Mode Ω Fault resistance

53 filtered and unfiltered Rogowski coil voltages Voltage [V] No filter 100 khz L.P Time [ms] Solid P-G fault 130 km away from the Converter-1.

54 Line Fault Location Performance No filter 100 khz L.P. Voltage [V] x 10-3 No filter 100 khz L.P Time [ms] 0 Voltage [V] Time [ms] Solid P-G fault 130 km away from the Converter-1.

55 Fault location with filtered signals (Threshold-1/Solid fault) Actual fault location (km) Fault location error (km) No filter 1MHz 500 khz 100kHz 50kHz 10kHz

56 Fault location with filtered signals (Threshold-1/100 Ω) Actual location (km) fault Fault location error (km) No filter 1MHz 500 khz 100kHz 50kHz 10kHz

57 Fault location with filtered signals (Threshold-10/Solid fault) Actual fault location (km) Fault location error (km) No filter 1MHz 500 khz 100kHz 50kHz 10kHz

58 Fault location with filtered signals (Threshold-10/100 Ω) Actual fault location (km) Fault location error (km) No filter 1MHz 500 khz 100kHz 50kHz 10kHz

59 Fault location errors with cable connection 0.1 Threshold 10/ 100kHz L.P Error[km] Solid fault Distance to Fault fron Con Threshold 10/ 100kHz L.P Error[km] Ω fault resistance Distance to Fault fron Con.1

60 VSC HVDC scheme with overhead lines ohm 100 ohm Error [km] Threshold Solid fault 300km the Converter -1

61 VSC HVDC scheme with overhead lines ohm 100 ohm Error [km] Threshold Solid fault 600km the Converter -1

62 VSC HVDC scheme with overhead lines ohm 100 ohm Error [km] Threshold Solid fault 100km the Converter -1

63 Fault location errors with overhead line ohm 0.07 Error [km] Actual fault location [km]

64 Fault location errors with overhead line ohm 0.03 Error [km] Actual fault location [km]

65 Remarks Simulation results indicated that there is an optimum range of threshold settings. Accuracy improved by filtering the signal from Rogowski coil with a low pass filter with a cut-off frequency of khz.

66 Conclusions Proposed termination enables successful detection of travelling waves in VSC HVDC schemes. Fault location accuracy can be improved by filtering and selecting a optimum threshold setting. Fault location accuracy of ±250 m for a 1000 km overhead line or 300 km long cable in a VSC HVDC system with the proposed method.