Phase-controlled Technology Of Permanent Magnetic Actuator For Vacuum Circuit-breakers

The essence of phase-controlled breaking technology is to control the switch to complete opening action at the phase position with optimum current by applying intelligent control units, thus to enable arc current to cross zero after optimal arc time during breaking process. Phase-controlled breaking technology has many advantages including effectively reducing average arc time and peak arc current of contacts, increasing breaking capacity of circuit breakers and decreasing abrasion of contacts, by which power supply quality could be improved and switch life could be prolonged. In phase-controlled switching system, applying permanent magnetic actuator is the only way to solve the problems including the low reliability of current switching mechanism and difficulty in controlling dispersity. Currently, phase-controlled breaking technology of fault current is not mature, and there are still many problems to be resolved. This paper discusses the approaches for judging fault type, phase selection and short-circuit faults of phase-controlled breaking for vacuum circuit breaker(VCB) after short-circuit fault in the circuit.After short-circuit fault occurs in power system, fault type shall be judged to select fault phase and confirm initial time of failure occurrence. Short-circuit fault model is built by toolbox in relevant simulation software, fault phase is confirmed by fault component of the sum of phase currents, then fault current is sampled by means of wavelet analysis and results are obtained by wavelet toolbox, thus to confirm occurrence time of short-circuit fault and provide basis for following parameter calculations of fault current.Traditional half-wave Fourier algorithm has been improved by adding two sampling points on basis of sampled half cyclic wave, and data processing window has been transformed for two times to eliminate error, obtain characteristic parameters of short-circuit fault current and realize waveform recovery. Relevant parameters are set to conduct simulations, and algorithm is verified to prove its feasibility. After relevant parameters of fault current are calculated, zero-crossing point of fault current when arc extinction occurs during breaking process could be predicted to confirm optimal breaking time of contacts of the circuit breaker. Intelligent control units are designed on basis of DSP to sample and control the whole breaking process, thus to make the whole phase-controlled breaking process to be more accurate and prompt.