Study On Synthetic Protection System For High-Voltage Flameproof Switchgear Based On Microcomputer Control

The high-voltage flameproof switchgear is a key apparatus for 6kV-power supply system in underground mines. The switchgear is used for supplying power energy to HV working machinery or next LV distribution station in coalface. However, there have been many disadvantages with the HV flameproof switchgear widely used in underground for long time, such as smaller breaking capacity, simpler protection system and higher fault probability, which impairs the reliability, safety and continuity of underground power distribution system. It is hence important to develop a kind of new intelligent protection system with wonderful performances used in flameproof switchgear which can not only improve the supply quality of underground HV distribution system but also perfect its protective properties, Especially can prevent the underground from gas explosion and guarantee the operating safety for underground worker.According to the present actual underground power system which neutral point is grounded through arc suppression coil in many supper big shaft, the development history and present situation of synthetic protection system used in HV flameproof switchgear are reviewed, and on the basis of analyzing the problems existed in high voltage flameproof switchgear, the selective leakage protective method based on the detecting harmonic direction of zero sequence current as well as the value of zero sequence voltage is proposed in this paper, and at the same time, harmonics extracting schematic and transforming circuit are also designed. It has been proved by test results that this protective method is suitable not only for neutral point insulated system, but also for neutral point grounded system through arc suppression coil.A protective method based on Voltage-Frequency-Converter and additional DC measuring the insulation between monitor wire and ground lines of HV double screen cable is developed and realized by analog and digitalcircuits. It has been proved that this protective system is able to detect effectively monitoring insulation, and is of rapid responding characteristics.A novel measurement and control system (MCS) used in HV flameproof switchgear has been established based on the 80C196KB single-chip microprocessor, by which electrical faults such as short circuit, over-load, over-voltage, open circuit, earth leakage and so on can be automatically distinguished and processed, and with the exception of this, the insulation degree of the double screen cables is monitored on-line. The operating condition and fault parameters can be displayed in turn with liquid crystal display. Every system parameters is put into MCS by BCD dial switches.The original signals are detected by AC sampling algorithm in the protection system, at the same time, power system parameters, such as voltage value, current value are obtained through Fourier transform, which accelerates the reaction speed of MCS and improve the reliability of MCS.The interferences sources and the features of interference signals in underground environment are discussed; Excepting this, anti-interference measures by use of hardware and software are taken to eliminate interference signals from MCS in this paper.It has been proved by tests in our laboratory that all performance and feature parameters are all satisfied the technical requirements proposed by research application, and the measurement and control system is more utilizable and reliable than other traditional protective system.