| The research project in this thesis is the protection part of "Study on the measurement and control system of 8 combined magnetic switchgear based on PLC in the 3.3kV underground distribution networks"(No.031116), which is supported by Science and Technology department of Shanxi province. The efficiency of coal production has been greatly improved since 3.3kV distribution networks was introduced from developed countries in the 1990s, and a new production mode has been formed, i.e. there is only one well and one working face in one colliery, which is the developing direction of coal production in our country in the future. However, it is still backward in the research field of 3.3kV power supply equipment in our country so that all of the electrical equipment in 3.3kV underground distribution networks are mainly imported from developed countries. It is quite evident that it is very important and urgent to develop the measurement and control system of the combined magnetic switchgears used in 3.3kV underground distribution networks.The research of protection system in 3.3kV combined magnetic switchgears is deeply carried out in this paper as following:First of all, the development and the application of 3.3kV distribution networks in underground at home and abroad are reviewed, the necessity and exigency to develop the measurement and control system are also introduced. It has been proved by the investigation and analysis in the field that it is feasible to develop the 3.3kV flameproof combined vacuum switchgear in technology and engineering. The protective functions and technical specifications of the measurement and control system are put forward, and the control strategies and methods by MCU are also drawn up according to the field requirements.The possible causes and the corresponding characteristics of electricalfaults occurred in underground power system networks are analyzed according to the specifications of 3.3kV distribution networks and the start requirements of asynchronous motors. The protection circuits are designed and the technical specifications are established based on different electrical characteristics. The main protective functions in the measurement and control system include: earth leakage lockout, earth leakage, symmetric short circuit, overload, asymmetric short circuit, one phase open, over-voltage and under-voltage. All the protective circuits designed in this paper have been tested and the results show that the protective circuits are feasible in theory, stable in performance, reliable in action and sensitive to electrical faults.The real-time property of the measurement and control system is efficiently improved under the mode of multi-CPU working in coordination. Serial communication is adopted between CPUs and the communication circuit is also designed in this paper. Favorable interface has been established between operators and the measurement and control system. Advanced CPLD devices are applied in the rated parameter input circuits. The experimental results show that the measurement and control system can examine any fault immediately, the communication circuits work reliably and the parameters can be changed freely and exactly.On the basis of actual situations of underground 3.3kV distribution networks, the interference sources and the characteristics 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 protect the measurement and control system from the interference signals. As a result the reliability and stability of the system has been greatly improved.The protection system has been tested in the intelligent electrical equipment laboratory in TYUT. It has been proved by the tests that the system can not only control and protect 8 motors at the same time, but also work stably, act reliably and operate conveniently. In addition the color display designed in the system provides the running and faults parameters for theoperators. It can be predicted that...
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