Numerical and experimental design of three-electrode spark gap for synthetic test circuits

The development of a three-electrode spark gap used with a synthetic circuit for circuit breaker testing is considered in this paper. Two types of three-electrode gas insulated spark gaps have been tested: a spark gap with a third electrode being inside the main electrode, and a spark gap with a separate third electrode. Both types of spark gaps were theoretically sized in the optimal way. Several characteristic are determined experimentally: (1) the influence of the gas insulation parameters on the spark gap functioning, (2) the influence of the working and triggering voltages polarities on the spark gap functioning, (3) the influence of the triggering voltage rate-of-rise on the spark gap functioning and (4) the degree of spark gap erosion vs number of operations. Three types of gases were applied: SF/sub 6/ gas, N/sub 2/ gas and a mixture of 60% SF/sub 6/ with 40% N/sub 2/. Also, three electrode materials were used: copper, steel and tungsten. The spark gap switching time and delay time are measured. The statistical analysis of results is presented.