AN ENHANCED TRANSMISSION LINE PROTECTION CONCEPT FOR NULTI – CIRCUIT LINES LINES

Increasing transmission requirements and public preassure to minimize new right-or-ways have forced utilities to maximize the transmission capability of existing right-of ways by multi-circuit transmission lines. This may result in initially high investments, if further circuits need to be added only later, and difficults in maintenance, as well as adding further circuits, while existing ones remain in service. The more Serious consequences of sympathetic tripping or relay and transmission channel failures required a further upgeaded security and dependability of the relay schemes and teleprotection channels. Single pole autoreclosure prevents a total loss of both lines in the casee of intercircuit faults. Only the fault-affected phase of each system is opened, while the line remains in service with about 50% of the transmission capability via the sound phases. This requires a strictly phase-selective fault clearance even with inter-circuit faults near the remote end. Reduced clearances between circuits and different voltage-level circuits on the same tower have resulted in more complex protection requiremelts, that can hardly be met by one measurent principle. Deficiencies in particular protection systems have been overcome by a dissimilar redundancy concept and improved numerical algorithms. Althcugh the Main Y distance- teleprotection scheme covers most possible fault types, the strictly phase-segregated current comparison protection has proven an ideal Main 2 protection scheme.