TRAVELING-WAVE-BASED PROTECTION OF DOUBLE-CIRCUIT LINES

Double-circuit current comparison protection (DCCCP) is an algorithm f or travelling-wave-based protection of a double-circuit high-voltage l ine. It uses the balance between the two circuits to distingush betwee n 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 paramete rs is discussed, as well as its performance. The tripping time is betw een 100 and 200 mus for the majority of faults. For faults around volt age zero, the tripping time is between 1 and 3 ms, depending on the am plitude of the short-circuit current. Faults close to the remote line terminal are not detected at all. Some direct lightning strokes will l ead to an incorrect trip. To overcome the disadvantages of DCCCP, it i s combined with travelling-wave-based differential protection in a pro tective scheme. Differential protection is a somewhat slower but very reliable backup. Its parameter setting is discussed, as well as its pe rformance. The tripping time is between 1 and 3 ms. The protective sch eme further contains fast reclosure, breaker-failure detection and ada ptive setting for the backup relays.