TRIGGERED VACUUM AND GAS SPARK GAPS

This paper present comparative analysis of the characteristics for the gas insulated three-electrode spark gaps and vacuum insulated three-e lectrode spark gaps. The experimental part of this paper includes the testing of spark gap models. Two spark gap types were studied: one hav ing the third electrode inside the main electrode and one having a sep arate third electrode, both being insulated by vacuum or gas (under pr essure, providing the same operating voltage as for a vacuum insulated spark gap). Both types of spark gaps were theoretically sized in the optimal way. Several characteristics are determined experimentally: 1) the influence of the gas and vacuum insulation parameters on the spar k gap functioning, 2) the influence of the rate of rise and injected e nergy of the triggering pulse on the spark gap functioning and 3) the degree of spark gap erosion vs. number of operations (long-time-stabil ity). Two types of gases were applied: SF6 gas, N-2 gas and three vacu um (residual) pressures: 10(-1) Pa, 10(-4) Pa, and 10(-6) Pa. Also, th ree electrode materials were used: copper, steel and tungsten. The spa rk gap switching time and delay time are measured. It was found that t he switching time decreases with application of pressure decrease, and the statistical dispersion of switching time raises with the pressure decrease. By comparison of results obtained for the vacuum insulated spark gap and the SF6 or N-2 gas insulated spark gap, it was found tha t the vacuum spark gap has a slightly shorter switching time and a sig nificantly higher corresponding statistical dispersion. Also, it was f ound that under a higher triggering time rate of rise - the switching time and its statistical dispersion increase with the triggering pulse rate of rise for the vacuum spark gap. The decrease of delay time and its statistical dispersion with rate of rise was observed. The influe nce of insulator or electrode materials type on delay time was not obs erved. For the vacuum spark gap the significant decrease of switching time and its statistical distribution with increase of injected trigge r pulse energy was observed. This phenomenon exists also for gas spark gap but less significant. The most striking irreversible changes appe ared in the vacuum spark gap with steel electrodes. The least irrevers ible changes appeared in the spark gap isolated by N-2 with tungsten e lectrodes.