Time domain distance protection based on polarity comparison for power transmission lines

1. A method for fault detection of a transmission line, the method comprising:

obtaining instantaneous measurements of local voltages and local currents of the transmission line;

obtaining filtered measurements of the local voltages and local currents by subjecting the measurements of the local voltages and local currents to low pass filtering;

obtaining a compensated voltage calculated by subjecting the filtered measurements to a differential equation based algorithm; and

performing fault detection by forming a ratio between the compensated voltage and a reference voltage, wherein an internal fault is determined when the ratio is below a threshold and an external fault is determined when ratio is above the threshold.

2. The method according to claim 1 , wherein the method is performed for each of three voltage phases.

3. The method according to claim 1 , wherein the method is performed for both phase-to-phase measurements and phase-to-ground measurements of the local voltages and currents.

4. The method according to claim 1 , further comprising providing a result of the fault detection to a distance protection arrangement for making a trip decision.

5. The method according to claim 4 , wherein the result causes a trip of a circuit breaker of the distance protection arrangement to be triggered only if the detected fault is an internal fault.

6. The method according to claim 1 , wherein the low pass filter used for the low pass filtering has a cutoff frequency between 1 and 5 kHz.

7. The method according to claim 1 , wherein the transmission line is represented by a resistor-inductor (RL) circuit and the differential equation based algorithm is an RL based differential equation based algorithm.

8. The method according to claim 1 , wherein the transmission line is represented by a resistor-inductor-capacitor in series for series capacitor compensated transmission lines (RLC) circuit and the differential equation based algorithm is an RLC based differential equation based algorithm.

9. The method according to claim 1 , wherein the ratio is determined as a normalized convolution between the compensated voltage and the reference voltage.

10. The method according to claim 1 , wherein the ratio is formed from measurements collected during a time window.

11. The method according to claim 1 , wherein the threshold is set to zero.

12. The method according to claim 1 , wherein the threshold is set to −0.2.

13. The method according to claim 1 , wherein the transmission line is an ultra high voltage (UHV) transmission line.

14. A method of operating a transmission line, the method comprising:

measuring local voltages and local currents of the transmission line to obtain instantaneous measurements of local voltages and local currents;

low pass filtering the measurements of the local voltages and local currents to obtain filtered measurements of the local voltages and local currents;

subjecting the filtered measurements to a differential equation based algorithm to obtain compensated voltage values;

performing fault detection by forming a ratio between the compensated voltage and a reference voltage, wherein an internal fault is determined when the ratio is below a threshold and an external fault is determined when the ratio is greater than the threshold; and

providing a result of the fault detection to a distance protection arrangement for making a trip decision.

15. The method according to claim 14 , wherein the result causes a trip of a circuit breaker of the distance protection arrangement to be triggered only if the detected fault is an internal fault.

16. A fault detection apparatus for a transmission line, the fault detection apparatus comprising:

processing circuitry;

a memory coupled to the processing circuitry, the memory storing a computer program comprising computer code that, when run on the processing circuitry, causes the fault detection apparatus to:

obtain instantaneous measurements of local voltages and local currents of the transmission line;

obtain filtered measurements of the local voltages and currents by subjecting the measurements of the local voltages and local currents to low pass filtering;

obtain a compensated voltage measurement by subjecting the filtered measurements to a differential equation based algorithm; and

perform fault detection by forming a ratio between the compensated voltage and a reference voltage, wherein an internal fault is determined when the ratio is below a threshold and an external fault is determined when the ratio is above the threshold.

17. The apparatus according to claim 16 , wherein the instantaneous measurements of the local voltages and local currents are performed for each of three voltage phases.

18. The apparatus according to claim 16 , wherein the instantaneous measurements of the local voltages and local currents are performed for both phase-to-phase measurements and phase-to-ground measurements of the local voltages and currents.

19. The apparatus according to claim 16 , wherein the computer code that, when run on the processing circuitry, causes the fault detection apparatus to provide a result of the fault detection to a distance protection arrangement for making a trip decision.

20. The apparatus according to claim 16 , wherein the transmission line is an ultra high voltage (UHV) transmission line.