Study On The Synthesis Protection System In Underground Lv Feeder Switchgear

With the rapidly development of coal industry and the continuous improvement of mining automation, it is demanded that the underground power supply system must be of the higher reliability, security and continuity. Underground low voltage feeder switchgear plays center role in the coal mine low voltage power network. The capability of it directly affects the security and efficiencies in coal production. But the intelligence level of underground low voltage feeder switchgear mainly depends on the reliability and sensibility of protection system. Hence it is important to develop a new measurement and control system in underground low voltage feeder switchgear.On the basis of consulting internal and external documents, the synthesis protection system in underground low voltage feeder switchgear has been researched in detail based on PLC in this thesis as following:First of all, the characteristics of coal mine LV power supply system are analyzed, and the developing histories of underground low voltage feeder switchgear at home and aboard are reviewed. In addition, the disadvantages of traditional synthesis protection system are pointed out. Based on the rules of"Safety Regulation of Underground Coal Mines", the technical requirements are put forward in the thesis.According to the technical requirements of the protection system, the cause and fault characteristics of earth leakage, short circuit, over-load, over voltage and under voltage are theoretically analyzed, and the principle of fault detection are also introduced.Based on the introduction of PLC development and characteristic, PLC is used as the control core, and the hard circuits are designed also, including selective leakage protection circuit, phase-sensitive measurement circuit, negative sequence protection circuit and active power measurement circuit. It has been shown by the result that the circuits sample accurately, run steadily and detect the running state of power network.In the software construction, module programming design method is used, host monitor procedure and functional subprograms are compiled. It has been shown by the result that the programs compute accurately, run efficiently and operate steadily.The development process of man-machine interface is described in detail, including the choice of man-machine interface device, the introduction of software development environment and the program design. It has been shown by the result that the man-machine interface is friendly, accurate and easy to operate.According to the actual environment in the coal mine power network, the sources and features of interference signals are discussed. Based on the analyzed characteristics of interference sources in underground, the corresponding hardware and software measures of anti-interference are taken to increase the reliability of the monitoring system.The protection system has been tested in the laboratory. The results indicate that the system detect the running state of power network accurately, steadily and rapidly, and execute relevant operations. It has been proved by the mention above that the control scheme is correct and practical.