Guest editorial special issue on Electrical discharges in vacuum

The 27 papers in this special issue are expanded versions of selected papers presented at the 23rd International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), held in Bucharest, Romania, on September 15-19, 2008

Evaluation of high-voltage circuit breaker performance with a validated arc model

A digital current-zero measuring system was used to monitor about 200 zero crossings of short-line fault currents in three designs of commercial high-voltage circuit breakers. The breakers were subjected to standard IEC 60056 tests in a high-power laboratory. With these results, an empirical arc model was derived, based on the series connection of three classical modified Mayr models. It was found that only three `free' parameters, extracted from the arc voltage and current during the pre-zero period can describe the state of the breaker after each test. With this model, the margin of the interrupting capability could be directly obtained. A strong relation between this margin and the arc conductivity at current zero can be established. Independent of arcing time, arcing current and state of the breaker, it was found that the current zero conductivity must decrease to 1-2 ms (only depending on the design of the breaker) to make a successful interruption possibl

The testing of generator circuit-breakers

Generator circuit-breakers face much higher current and voltage stress than distribution switchgear. This has led to a special standard (ANSI C37.013). Strictly in accordance with this standard's requirements, test circuits and parameters for a 100 kA and 120 kA (25.3 kV) SF6 generator circuit-breaker have been defined. The circuit-breaker is equipped with capacitors at both sides of the extinction chambers. The effect of these is to reduce the TRV severity and this is quantified for the relevant switching duties. Adequate test-circuits are described. Also, the optional verification of interruption of generator-fed faults with very large DC components has been demonstrated. Herein, delayed current zero can extend arcing time. The importance of arc voltage in reducing the longer arcing time is illustrated in a calculated exampl

Current-zero measurements of vacuum circuit breakers interrupting short-line faults

Current zero measurements are performed during short-line fault interruption tests of vacuum circuit breakers. This switching cycle is characterized by a very steep transient recovery voltage. High-resolution measurements of near current-zero arc current and voltage were carried out. Various reignition modes (occurring between 0 and 75 ms after current zero) were observed due to insufficient arcing time or current in excess of the rated short-circuit breaking current. The relationship between post-arc current/charge, reignition mode, and transient recovery voltage is discussed in this paper. In addition to the "classical" post-arc current, already described in the literature, another "late" post-arc current was observed reaching values up to several tens of amperes after severe thermal arcing stress. All interrupters interrupted at the first or second current zero under the "rated" conditions of short-line fault current and transient recovery voltage