Synthetic testing of a.c. circuit breakers. Part 1: Methods of testing and relative severity

The paper describes the first phase of a collaborative investigation into the practicability of the synthetic testing of circuit breakers in which current and voltage are supplied from independent sources. Two basic forms, current injection and voltage injection, are discussed, and reasons given for the choice of the method of current injection suggested by the ERA. A statistical approach has been made to the investigation, and the results of a very large number of tests using air-blast circuit breakers on a single-phase circuit, with one loop of current, are given. The tests, which cover a range of powers from 33 to 1200MVA, have been made with the objects of establishing the validity of the method and determining the relative severity of the direct and synthetic tests. Analysis of the results shows that, provided particular attention is given to the voltage and current waveforms around the current-zero period, the method is valid, and there is no significant difference between the seventies of the direct and synthetic tests. Mention is made of both practical and analytical studies of the application of the basic synthetic circuit to the various circuit arrangements and test duties normally associated with direct testing, and it is concluded that the proving of circuit breakers with low-arcing-voltage characteristics is a practical proposition, and that validity will also hold for powers above the limit of 1200MVA so far investigated.