Synthetic testing of a.c. circuit breakers. Part 2: Requirements for circuit-breaker proving

The paper forms the second part of a collaborative investigation into the practicability of synthetic testing. It gives further experimental evidence in support of the validity of the parallel-current-injection method for air-blast circuit breakers, but it is mainly concerned with the results of studies of the problems involved in adapting synthetic testing to circuit-breaker proving. Detailed attention is given to various test conditions, both from the circuit and circuit-breaker points of view, and the limitations of the basic synthetic circuit are pointed out. The addition of an alternating recovery voltage is shown to be necessary for certain test duties, and, in a detailed discussion of its application, it is shown that a particular method in which the alternating voltage is connected directly across the test circuit breaker is to be preferred. The question of multiloop testing is also raised, and a suggestion is put forward for a testing sequence which closely represents that of a direct test. The problems associated with the synthetic testing of oil circuit breakers are discussed, and the various factors which must be taken into account when assessing validity are indicated. The advantages and disadvantages of the current- and voltage-injection methods are briefly reviewed, and their suitability for particular applications pointed out.