A New High Speed Distance Protection Scheme for Power Transmission Lines

This paper describes a new, high-speed protection for EHV transmission lines. The presented scheme also performs well on series compensated lines. The High speed distance protection (ZMFPDIS) function is a six zone full scheme protection with three fault loops for phase-to-phase faults and three fault loops for phase-to-earth faults for each of the independent zones, which makes the function suitable in applications with single-phase autoreclosing. The zones can operate independently of each other in directional (forward or reverse) or non-directional mode. A new built-in adaptive load compensation algorithm prevents overreaching of the distance zones in the load exporting end during phase-to-earth faults on heavily loaded power lines. It also reduces under-reach in the importing end. The ZMFPDIS function-block itself incorporates a phase-selection element and a directional element, where these elements are represented with separate function-blocks. Implementation of the new distance protection with fast tripping algorithms has been made in a modular line terminal platform. Comprehensive test results on various test systems show the benefits of the scheme. The results with a Real Time Digital Simulator (RTDS) are presented in this paper. The scheme is now in operation under trade name REL670 2.0.