Digital simulation of fault autoreclosure sequences. With particular reference to the performance evaluation of protection for EHV transmission lines

The successful development of EHV transmission-line protection increasingly depends on a detailed simulation of power-system faulted responses. In consequence, increasing use is being made of programmable test equipment in which the primary-system responses are simulated digitally. Previous work on digitally simulating faulted-system responses has been concentrated very largely on the initial faulted period prior to the initiation of an autoreclosure sequence. The implications of incorrect operation of protection at any time throughout the process of fault clearance are, however, often serious, and the paper is therefore concerned with detailing methods of frequency-domain simulation which have been developed to greatly extend the capability of computer-based simulation methods in their application to protective-gear testing. Problems associated with the simulation of various network time nonlinearities are overcome, and the new methods enable both 3-phase and single-pole autoreclosure to be simulated. The paper concludes with a presentation of some simulation studies relating to a short 500kV interconnection which is subjected to various transient and sustained fault conditions