Application Of Compound Switch In Reactive Power Compensation

Because transmission of reactive power in electric network can lead to network loss and step-down voltage, and a lot of transmission of reactive power in electric network must make the electricity utilization greatly reduced and seriously affect the quality of power supply. It becomes necessary means to meet the demand of the grid reactive power that reactive power compensation devices are installed in proper position of electric network. In recent years, the importance of reactive power compensation in power system is widely recognized by people. The low-voltage reactive power compensation device is mainly comprised of capacitance, throwing cut switch component and controller. Among them, the performance of the throwing cut switch plays a vital role to the reliability of the low-voltage reactive power compensation device.In the low-voltage reactive power compensation device, the problems are large inrush current, contacts easy to be damaged and slow reaction by using AC contactor alone, besides, the problems are big power, low capability of the anti-interference and harmonic easy to be produced by using power electronic device alone. In order to overcome the shortages of the above two kinds of throwing cut switches, a kind of low-power compound switch with AT89S51 as the core has been designed in this paper. The device uses the parallel connection of thyristor and magnetic latching relay in the main loop. The throwing cut process is the cooperation action between the thyristor and the magnetic latching relay. The thyristor works when the voltage is zero. During the device is switch-on, the electric current is taken on by the magnetic latching relay alone. The compound switch has the advantages of low power consumption, small inrush current, strong capability of the anti-interference to harmonic and high speed responsibility.This paper firstly expounds systematically the relevant principles of the reactive power compensation, the working principle, the compensation mode and the realization method of the compound switch, which lay theoretical basis for the compound switch.Secondly the hardware system of the compound switch which puts AT89S51 as the core is designed. The hardware system mainly includes zero detection circuit, thyristor trigger circuit, power supply circuit, reset circuit and show circuit. And a protection circuit of the compound switch has been designed, which can effectively solve the problem caused by the thyristor that can not been cut off due to the strong interference of the single-chip microcomputer, otherwise it will cause short-circuit.Then the software programs have been designed to realize the basic function of the compound switch. In addition, according to various interferences on the influence of the compound switch, the anti-interference measures have been studied to improve the reliability and the stability.One of the important characteristics of the compound switch is zero input, which can avoid overvoltage and inrush current, and the necessity of zero input has been proved by the simulation waveform. In the existing test conditions, the feasibility of the compound switch has been proved by working properly one month.Finally, on the basis of the low-voltage compound switch, this paper makes a preliminary outlook in high-voltage aspects of the compound switch, and constructs the basic structure. And through the simulation about the input capacitors and short-circuit fault aspects, a broad prospect of application of the compound switch has been foreseen.