MULTI-BREAK ARC INTERACTION IN THE ENERGY BALANCE REGION

The interaction between the arcs in a multi-break circuit breaker during fault interruption was investigated experimentally and theoretically. A short line fault situation was used to study the interaction, providing the most severe stresses in the energy balance region a few microseconds after current zero.;The experimental results showed that the single-break interrupter failed thermally but that the two-break unit did not. The two-break unit, under comparative conditions, went on to fail in the dielectric region. This indicated that the two-break interrupter was able to traverse the energy balance region whereas the single-break unit did not.;Mayr's differential equation, which is most applicable to the energy balance time period immediately following current zero, was utilized to model arc behavior. This non-linear equation, together with equations representing the electrical network and fault condition, were solved for variations in certain parameters and expected unbalances in the voltage distribution of the arcs.;The simulations were programmed on the University of Pittsburgh DEC System-10 computer incorporating a software code for the numerical solution of ordinary differential equations.;Experimental tests were performed on fixed gap interrupters having small axial air flows. The tests on single and two-break interrupters were conducted in an effort to demonstrate that the former will fail while the latter may not. Several researchers have postulated that the performance of a multi-break interrupter, in the energy balance region, is better than that expected from a proportional extrapolation of the test results of a single-break unit.;The related parameters varied were the time constant of the arc, (theta), and the arc dissipation constant, N(,0), of the Mayr equation. The recovery voltage distribution is a function of the circuit breaker design and inherent and voltage dividing capacitances. Results of the simulations show the effect of these variations in the critical operation of circuit breakers.;Comparisons were made between the operation of a circuit breaker with two breaks and one with a single break having the same voltage stress. It was shown that in the neighborhood of criticality the two-break configuration interrupted the fault current whereas the single-break did not. In the case of the two-break interrupter a feedback effect between the breaks tended to equalize the voltage stresses. As the conductance of one break started to decrease, with the post-arc plasma being cooled, it assumed an increasing share of the applied voltage. In contrast, the second break began to experience a reduced voltage stress as its conductance started to increase.;This interaction between the breaks had the effect of equalizing their respective conductances. In so doing, recombination of the ionized plasma in each break was able to occur, reducing the conductances, and leading to successful interruption of the fault current. The single-break interrupter was initially stressed to the same level as the more highly stressed source-side break of the two-break unit. Given this situation, and without the interactive effect of a companion break, the single-break unit failed to interrupt.