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

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.

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.