Study On Measurement And Control System For Flameproof And Intrinsically Safety Intelligent Electric Magnetic Starters

Electric magnetic starters is a kind of important electrical equipments in underground distribution networks, which reliability directly effect the production of mine and the safety of power supply system, thereby it is of important realism signification to develop a high-powered measurement and control system of electric magnetic starters for improving the reliability, safety and continuity of the power supply systems. A new measurement and control system (MCS) of flameproof and intrinsically safety intelligent electric magnetic starters is introduced in this thesis. Based on the research of the protective systems for underground asynchronous motors, the measurement and control system has been designed in order to satisfy the demands of modern mines. The single-chip microcomputer control technology has been applied in the system to carry out monitoring and protective functions for the asynchronous motors controlled. Combined with suitable peripheral interface, disposition and flexible software, the MCS can measure the current and voltage signals of the motors. Based on the measurements, the computation, judgment and decision are made to implement the phase sensitive short circuit, overload, supply over-voltage, supply under-voltage, over-thermal, leakage lock-out and loss of phase protective function. In addition, the MCS provides intrinsically safe input and output interface, which can be connected with the monitoring system for the underground power networks.First of all, the starting process and failure characteristics of asynchronous motors under unbalanced operation condition are analyzed in the paper, which provides theoretical foundation for the design of the system. On the basis of these mentioned above, it has been proposed that the principle of phase-sensitive protection and negative sequence protection can be used in the system, which can not only improve the sensitivity of the protective system but also extend the protection range in underground distribution networks. According to the rule of Mine Safety Regulations, an intrinsically safe pilot circuit with perfect performance for underground motor intelligent protective systems is put forward, which can effectively avoid the phenomenon of self-starting that is caused by the earthing of control lines before starting motors, at the same time, can reliably cut off the switches to ensure the safety of underground production under operation condition no matter what the faults ofshort circuit, open circuit and earthing in the control circuits happened. It has been found that the performance and technical parameters of the system has come up to advanced world standards by literature search.According to the practical instance of underground distribution networks, the basic characteristics of interference signals produced by interference sources existing in the networks are also analyzed in the paper. The anti-interference measures have been taken in accordance with the interference signals, which has effectively improved the reliability and continuity of the measurement and control system.The measurement and control system designed in this thesis has been tested in laboratory. It has been verified by simulation tests that the symmetric short-circuit protection can not only avoid the starting current but also achieve higher sensibility; unbalance protection can distinguish unbalance short-circuit and loss of phase. The operation parameters of other protective functions has all reached the design requirements. It has been concluded that the measurement and control system is stable, reliable and is of great applied value in underground distribution networks.