Research On Three-Phase Synthetic Test Synchro Control Method Of High Voltage Circuit-Breaker

Synthetic test (ST) is regarded as a very important method for testing the breaking capability of high voltage circuit breakers, and the only method for testing the breaking capability of ultra-high voltage circuit breakers. The equivalence property of ST had been recognized by IEC standard. With the development of gas-insulated metal-enclosed switchgear (GIS), the capability of circuit-breaker is improved increasingly, but the single-phase synthetic test can't assure the capability of three-phase circuit-breaker, so three-phase synthetic test must be used to test the capability of three-phase circuit-breaker.ST demands strict synchronal control, especially three-phase ST, it needs two high voltage circuit (HVC) synchronal impulses and three synchronal impulses arc prolonging circuit (APC), which means test will fail even little mismatch. According to the fundamental and the IEC standard of ST, the synchronal control requirement of the high voltage circuit (HVC) and the arc prolonging circuit (APC) are analyzed, and then the injection moment and the permissible deviations of HVC and APC are determined. Furthermore, the synchronal control method and its problems of HVC and APC for synthetic testing are discussed. Base on the above, an approach is presented in this dissertation that the short circuit current (SCC) is measured and analyzed by means of digital measurement technique and digital signal processing arithmetic in order to forecast SCC zero and self-adaptive control the injection moment of HVC and APC .The SCC of three-phase insulated neutral system breaking process and the rule of firstly and secondly phase breaking orders are analyzed. The typical waveform analysis methods improved fast Fourier transform (IFFT) is analyzed, and the mathematical models are built for analyzing SCC and forecasting its zero. In order to determine the numbers of significant digits of the analog to digital (A/D) converter and the sampling rate as well as the sampling time window, the discrimination, the quantization sample functions and the actual measured SCCs are analyzed using IFFT. The simulation results show that, it should be necessary for IFFT arithmetic to have enough numbers of significant digits of A/D converter and sampling time window, and that if the SCC contains direct current decay component, A/D converter with 12 and over numbers of significant digits is needed. Moreover, the estimated values of arithmetic would be inaccuracy in case of frequency offset.The paper designed a computer software control system with LabVIEW language, which used for three-phase ST, besides, the correlative of synchronal control system hardware interfaces are designed, such as SCC measuring and conditioning circuit, communication circuit and signal transmission and isolation circuit. LabVIEW is adopted to compile special user control console, in which user can set and calculate sequential control and synchronal control parameters, control three-phase ST in operation, select test type and test voltage level, determine channels whether active or not to output trigger pulse. Serial port communication function is also included.