Behaviour of SF ₆ high-voltagecircuit breakers with different arc-extinguishing systems at short-line fault switching

A series of tests on thermal arc-extinguishing capability has been carried out on two different types of SF6 high-voltage power circuit breakers, namely a double-nozzle breaker (ratings 145 kV, 31.5 kA) and a self-compression insulating-nozzle breaker (ratings 123 kV, 31.5 kA). In addition to the routine measurements taken in accordance with IEC-tests, another series of measurements of current and voltage to a high-resolution timescale was taken in the vicinity of current zero. These latter measurements made it possible to ascertain maximum fault current interrupting capability and to apply this to various types of circuit breakers and to discuss and assess the results. The measurements were also used to ascertain direct values that can be employed as criteria for the assessment of breakers. These could be, for example, values of arc resistance in a time range immediately before or at current zero, the course of arc voltage or the rate of current rise at current zero. Comparisons of the results obtained for the various breaker types allow the explanation of differences in arc-extinguishing mechanisms.