| Power capacitor is an important reactive (Var) compensation device in the power system which is usually installed in the low voltage side of the transformers. However, due to the restrictions of the design and manufacture level and the improper maintenance during operation period, the failure of capacitor has happened frequently which affect the safety of the electric power system seriously and even cause enormous economic losses to power supply companies. Thus, it is of great significance to configurate protection devices of capacitor bank reasonably and improve capacitor’s protection measures for the safe operation of electric power system by analyzing failures of capacitor correctly.The structure and function of the power capacitors are depicted in this thesis and present state and trends of the power capacitors’development are described as well. Operational status and common failure types of power capacitors would be introduced, and simulations of the failure process for power capacitors are analyzed based on MATLAB/Simulink. Algorithms, principles and positive definite calculating formulas of relay protection which are often used in power capacitor protection are also mentioned in this thesis. Especially, protection of differential phase voltage, unbalance current protection in dual-Y connection and protection on differential current bridge are analyzed compared to the advanced electric power capacitor. According to the capacity, voltage grade and function of the power capacitor, the configuration principles of relay protection about electric power capacitor are illustrated.In order to research and develop a microcomputer protection device about electric power capacitors, hardware system with a DSP core is designed. TMS320F28335 from Texas Instruments has been chosen as the advanced core processor. Besides, conditioning circuit, AD conversion circuit, output tripping circuit, signal circuit and power supply circuit have been carefully designed and analyzed. Circuits of hardware have been test elaborately, and it has proved that the whole hardware system with strong anti-interference ability operate reliably which has met the design requirements.With the help of CCStudio software, programs about relay protection have been accomplished. Otherwise, current instantaneous trip protection, overcurrent protection, overload protection, overvoltage protection, low voltage protection, open delta voltage protection, differential phase voltage protection, protection in dual-Y connection and protection on differential current bridge of power capacitors have been realized base on DSP.In order to test the performance of the developed microcomputer protection device of power capacitor, RT-LAB real-time simulation platform is used to analyze the prototype in the experiment of "hardware-in-the-loop". Electric power system and power capacitor are simulated in RT-LAB simulation platform by Simulink with the same simulation speed as actual dynamic process of power system. Faults are set in simulation model of power system, and RT-LAB outputs relative voltage and current to the prototype, while the prototype keeps sampling, A/D converting, digital computing and logical judging, then actuating signal would be sent to RT-LAB for purpose of circuit breaker tripping in the simulation model of power system. Experimental results have proved that the developed prototype with strong anti-interference ability can remove faults selectively, reliably and rapidly which can safeguard the operation of electric power system.The work done in this thesis benefits the popularization and promotion of advanced microcomputer protection of power capacitor. Furthermore, the operating condition of power capacitor is improved as well as the reliability of power supply. |
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