Study On The Measurement And Control System For Vacuum Magnetic Switchgear In 3.3kV Underground Distribution Networks Based On Several CPUs

The research project in this thesis is an important part of "Study on Measurement and Control System for Vacuum Magnetic Switchgear in 3.3kV Underground Distribution Networks Based on PLC"(NO.20031116) which is sponsored by Science and Technology Department of Shanxi Province. Building up the fully mechanized face with high production and efficiency supplied by 3.3kV distribution networks has been the trend to develop the coal industry in our country. However, because of slow development of related industry at home, the electrical switchgears in underground 3.3kV distribution networks are mainly imported from foreign countries. The long supply period of the fittings in switchgears and their high price are the key factors which badly hindered the development and popularization of 3.3kV power supply technique in underground distribution networks. So it is hence important to develop the measurement and control system of combined vacuum magnetic switchgear applied in 3.3kV underground distribution networks.The present developing situations of combined vacuum magnetic switchgear are firstly presented and the importance and necessity to develop the measurement and control system of 3.3kV vacuum magnetic switchgears are narrated. Besides, the function specifications, the control principle andtechnical requirements are established and the control strategies and methods are drawn up.According to the actual requirements of loads in underground mechanized face, the overall design scheme that three CPUs unite for controlling and protecting the motors is proposed and the real-time communication systems between PLCs, PLC and MCU and PLC and color liquid crystal display are developed. In terms of the safe requirements of electrical equipment in underground, an excellent intrinsically safe pilot circuit is designed, the fault characteristics of motor and distribution networks are analyzed, protection measurements are brought forward and the technical parameters corresponding to the fault protections for high capacity motors are also determined respectively.By analyzing the fault characteristics of earth leakage in underground 3.3kV distribution networks, relevant leakage protection methods and trip resistance value are put forward, at the same time, the technical scheme of high voltage insulation detection for 3.3kV cable and motors is given. CPLDs are first applied into underground flameproof electrical equipments and the interface circuit of BCD code with excellent performance is designed. The multifunction test circuits with easy operation and excellent performance are also developed, which do greatly heighten the operation reliability and safety of the measurement and control system.On the basis of the actual situations of underground 3.3kV distribution networks, the interference sources and features of interference signals in industrial environment are discussed. With the exception of this, anti-interference measures by use of hardware and software are taken to eliminate interference signals in this thesis. At the same time, module program design method, compiled monitoring program and function subprograms are emphatically described. Especially, more attention is paid to design philosophy, operation principle, hardware block diagrams and software flow charts.In the measurement and control system, three CPUs are used as maincontrol unit. Two PLCs are in charge of the control and protection of asynchronous motor with single speed and the motor with two speed respectively and MCU is responsible for phase sensitive protection and the reading of rated parameters. Several CPUs organically combined together to detect and process the signals of load system, as a result of this, the reliability and real time property of the measurement and control system are greatly improved.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 oth...