Design Of Fast Vacuum Switch Controller

With the expansion of the grid scale and a higher level of grid interconnection, short-circuit current level continues to increase while the short-circuit current determines the severity of the damage to the power system. The problem of limiting short-circuit current quickly is the current power system needed to solve. Fast vacuum switch based on electromagnetic repulsion actuator has advantages of simple structure, high opening speed, which provides an opportunity for rapid short-circuit current limit. Power system requires fast vacuum switch to achieve short-circuit current breaking in a few milliseconds of time. Fast vacuum switch controller based on synchronous control technology was designed, which included measurement, fast opening control and communication functions.Firstly, the principles of fast vacuum switch based on electromagnetic repulsion actuator and actuator’s kinematic characteristics were analyzed. Basic principles of synchronous control were introduced and the key technology of synchronous opening process was pointed. The key technology is prediction of fault current zero-crossing. Single-phase short circuit fault model of power system was established and short circuit current data were acquired by MATLAB simulation. Short-circuit current zero-crossing in synchronous opening control was predicted using recursive least square algorithm. Based on the fault current data from the MATLAB model, the proposed recursive least square algorithm was simulated using MATALB. The results showed that recursive least square algorithm can get sufficiently parameters in3ms and the prediction accuracy zero-crossing was in±0.1ms.The hardware part and software part of12kV/4000A fast vacuum switch controller were designed. The modular hardware design was based on functions of controller which used ARM7microprocessor, including power module, grid voltage and current signal acquisition module, opening coil and closing coil current acquisition module, control voltage measurement and setting module, electronic driving module of synchronous control and communication interface module. The design of software part was based on hardware part, included fast vacuum switch closing control, synchronous opening control, AD sampling and state checking. Then, the forgetting factor recursive least square algorithm was embedded in the program in order to fit fault current waveform and predict current parameters and zero-crossing. Lastly, the hardware and software debugging of fast vacuum switch controller was achieved and the test of this controller was conducted. The test results showed that the function of closing operation and synchronous fast opening operation can be achieved. When signal generator generated a fault current signal, the controller can accurately predict fault current zero-crossing in3ms and timing errors of the whole synchronous opening operation within the range of±0.5ms.