A novel non-unit protection for series compensated EHV transmission lines based on fault generated high frequency voltage signals

A new high-speed protection technique based on fault generated high frequency (HF) voltage signals is developed and applied to the protection of series compensated lines. It is a non-unit protection technique as it relies totally on locally derived information, but it has the discriminative properties normally associated with unit protection schemes. The protection scheme has been designed using computer-aided-design (CAD) techniques including emulation of analogue interface and hardware. It is shown that the new relay scheme is able to overcome many difficult protection problems encountered on such lines using conventional methods, and discriminates clearly between internal and external faults, producing a fast trip output.