Travelling-wave-based protection of double-circuit lines

Double-circuit current comparison protection (DCCCP) is an algorithm for travelling-wave-based protection of a double-circuit high-voltage line. It uses the balance between the two circuits to distinguish between an internal fault and an external disturbance. To prevent incorrect trips superimposed currents are used, and the relay has to be blocked after detecting an external disturbance. The setting of relay parameters is discussed, as well as its performance. The tripping time is between 100 and 200 μs for the majority of faults. For faults around voltage zero, the tripping time is between 1 and 3 ms, depending on the amplitude of the short-circuit current. Faults close to the remote line terminal are not detected at all. Some direct lightning strokes will lead to an incorrect trip. To overcome the disadvantages of DCCCP, it is combined with travelling-weave-based differential protection in a protective scheme. Differential protection is a somewhat slower but very reliable backup. Its parameter setting is discussed, as well as its performance. The tripping time is between 1 and 3 ms. The protective scheme further contains fast reclosure, breaker-failure detection and adaptive setting for the backup relays