The problem of defining a test circuit for circuit breakers in terms of the prospective voltage

The present IEC requirements for testing high-voltage circuit breakers impose certain conditions on the prospective voltage of the test circuit. This approach seems justified by the fact that the prospective voltage in theory describes exactly the test circuit in its elements and its topology. As in practice the prospective voltage is known only with certain tolerances, this method needs to assume that slight variations in the test circuit mean only slight variations in the circuit-breaker behaviour. By using the Urbanek equation to describe the circuit breaker, it is shown that, in direct test circuits which yield undistinguishable prospective voltages, differences of 9.7% in the breaking capacity of an otherwise identical breaker are possible. An explanation of this phenomenon is given and the limits are shown. In more realistic circuits, the result is verified in its trend.