Experimental Investigation of Limiting Curves for Current Interruption of Gas Blast Breakers

Summary

This contribution reviews recent measurements of initial or thermal recovery speed of gas blast interrupters and addresses thus a problem which is critically important for transmission line circuit breakers (short line fault, itrv).

Most measurements were made on gas blast interrupter models of reduced size and with frequencies of the power current significantly higher than 60 Hz. Theoretical arguments and some experimental evidence are presented in support of such a model testing procedure.

Rate of rise of recovery voltage was investigated in its dependence on several important design and circuit parameters: the rate of fall of current dI/dt before current zero, which is representative of the current level, the kind of gas used, the gas pressure and to some extent the electrode nozzle geometry. The variable found to be affecting rrry most sensitively is dI/dt, especially for SF₆ at moderate currents below 30 kA. Also different gases, such as SF₆, CF₄, N₂, etc. show great differences in recovery speed. The dependence of rrry on pressure is linear or somewhat steeper. These results agree in general well with predictions of theory. There are, to be sure, still some discrepancies between the experimenters and also between theory and experiment. It is suggested that future experiments with increased attention to both the detailed structure of the flow field and to the wave shapes of current and voltage very close to current zero (microstructure) will assist in resolving these uncertainties.

Work supported in part by Electric Power Research Institute under Contract RP 246–1.