Study On The Integrated Automation Device For Low-voltage Electric Network Which Has Reactive Power Compensation And Other Functions

In electric power system, the hazard brought by reactive power deficiency must be paid attention to. Now reactive power compensation in low-voltage network mostly employed parallel capacitors. There were many switching device of capacitors and the degree of stability and operating life of which were different, so the selection of switching device was very important. On the basis of analyzing merits and faults of various switches of low-voltage reactive compensation device, electromechanical combination switch which had the merits of AC contactor and the solid state relay (SSR) was employed, and an integrated automation device was studied, which had reactive power compensation and other functions, such as voltage protection and current protection. The actuator of capacitors was combination switch which was constituted of AC contactor and SSR, the different characters of capacitor switching and running was divided two courses, transient state and steady state. In the course of transient state of switching SSR was employed and in the course of steady state after putting into capacitors or before withdrawing capacitors AC contactor was employed. So the switch had the merits of SSR, such as zero switching, little inrush current and no over-voltage. It also had the merits of contactor, such as high conducting capacity of main contacts and no power consumption. Using the switch could overcome the faults of thyristor electronic switch when long-time bearing capacitor current, such as high power consumption and high fever.Through analyzing various control modes,single control mode all existed corresponding faults, so the research adopted voltage and reactive power compound control mode, that was controlling according to reactive power and correcting by voltage. In the normal fluctuation range of voltage it could realize reactive power balance basically. The principle was that reactive power transmission from line was minimal under the precondition that the voltage was not over the bound, it was also said that upper limit value and lower limit value of network voltage were regarded as constraint condition that controlling the switching of capacitors. The control mode reduced the loss of network and gave attention to the quality of voltage at the same time.AT89C52 was a sort of cheap Single Chip Microcomputer and was applied to control system as the main part of reactive power compensation device. This device could rapidly and accurately compensate reactive power and was low-cost. So it had a good practicability and wide application...