Testing of the relay protection for overcompensated lines

The paper presents differential and distance relay tests for protecting an overcompensated line (the compensation degree of 140 %) and its adjacent lines. A substation installed in the middle of a 400 kV series compensated line will increase the compensation to 140 %. The meshed network near the overcompensated line has several series compensated lines, too. The relay tests included 1-phase, 2-phase, and 3-phase faults along both on the overcompensated line and other lines. The performance of the relays from two manufacturers was tested with a real time digital simulator (RTDS) in order to confirm the correct operation of the protection during the faults on the protected line and other lines. Comprehensive test results on various tests show the performance of the protection schemes. In the tests, the relays did not erroneously trip external faults and tripped all the simulated internal faults when the fault resistance was not too high. When the fault resistance exceeded 200 Ω the differential relays did not trip for a few tested internal faults.