Practical Modeling of the Circuit Breaker ARC as a Short Line Fault Interrupter

The short-line fault interrupting ability of gas-blast circuit breakers is limited by arc energy balance processes very close to current zero. Practical calculation of the energy balance limit in a given circuit requires mathematical modeling of the arc as a circuit element. Using the combined Cassie-Mayr model, useful relations are derived for treating the limiting cases of the short-line fault both with and without capacitance shunting. Included are methods for approximate analysis and extrapolation of data from actual and simulated short-line fault tests with and without RRRV controlling resistance and capacitance shunts. In these analyses the arc is described by only two model parameters: a near-current-zero arc voltage Eo and an arc time constant 0, both definable as simple functions of the circuit di/dt. Examples are given of such analyses of high di/dt interrupting tests on actual and model SF6-blast interrupters.