Distributed moving-boundary circuit-breaker model

Abstract
The behaviour of the arc in the throat of an air-blast circuit breaker around a current zero is analysed by applying a simplified energy-balance equation to a constant-pressure model having a flexible radial temperature distribution and a variable conducting radius, as determined by a boundary-loss empirical formula derived from the steady v/i characteristic. Such a model, in a single-frequency-fault circuit, is examined on a computer, and clear/fail conditions are determined. Results may be simply displayed by a single curve using co-ordinates of suitably normalised combinations of arc and circuit parameters and initial conditions, if linear gas properties between σ, S and ∫ ρ dh are assumed. Alternatively, arcs with nonlinear gas properties may readily be examined in specific cases. The radial S distributions show considerable deviations from steady-state profiles; there are marked variations of instantaneous arc time constants, and the total loss varies widely. This model is therefore able to more faithfully follow real life than could simpler models used previously, and gives encouraging agreement with real test results of, say, voltage and current against time and (dG/dt)/G against power.

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