Computer modelling of series-compensated EHV transmission systems

The use of series-compensated lines in long-distance AC transmission practice is well known. There are, however, problems encountered in the protection of such lines, and these arise primarily as a result of the rapid circuit-parameter changes due to the operation of the various capacitor spark gaps protecting the capacitor banks against overvoltages. Realistic simulation of such systems for both protection evaluation and as an aid to the design and development of protective gear is therefore of obvious importance. In the paper, digital methods are developed for accurately simulating the faulted response of series-compensated systems, and, in particular, details are given of methods for simulating changes in circuit state associated with capacitor-gap flashovers. The methods developed are verified using some recently performed field tests, and the paper concludes by establishing some of the factors which influence capacitor-gap flashover times, and their effect on system waveforms for a typical 500 kV long-line application