Self-magnetic effects in a model gas-blast circuit breaker at very high currents

Substantial self-magnetic effects are anticipated within the arc columns of gas-blast circuit breakers at very high currents (10¿¿100kA). The paper reports measurements of gas pressure within the arc column, at the tip of the upstream electrode in a model gas-blast circuit breaker, which, along with a knowledge of the ambient gas pressure, yields values for the pressure elevation due to self-magnetic effects. The results of the investigation confirm the exitence of such self-magnetic effects but indicate that for peak currents in excess of typically 20kA the self-magnetic pressure elevation is less pronounced than predicted by simple theory. There is evidence that these abnormally low magnetic pressures are due to increased swirl of the arc plasma at high-current levels. Possible consequences of such a plasma swirl in relation to current-zero arc behaviour are considered.