| In recent years,with the steady progress of China made 2025 strategy,the level of industrial quality has gradually improved,and the demand for power quality is increasing day by day.The most prominent power quality problem is voltage sag.Voltage sag is a phenomenon that the effective value of a connection point voltage in the power supply system drops to 0.1-0.9(i.e.0.1-0.9p.u.)times the rated voltage,and then returns to the rated value in a short time.Voltage sag will cause great loss to sensitive users,so the rapid disposal of voltage sag has become a hot topic.The paper first describes the basic working principle of the voltage sag rapid disposal device,and analyzes the feasibility of the scheme from the circuit principle.The principle of manual zero crossing circuit is briefly described.After short circuit fault,the quick vacuum switch is quickly disconnected by the cooperation of LC branch and zinc oxide arrester,and the bus voltage is maintained at a higher level and the power quality of other branch load can be guaranteed.In order to detect the occurrence of voltage sag and estimate the voltage parameters in a very short time,a fast detection algorithm for voltage sag is proposed,and its effect is verified by simulation.The fast detection algorithm of voltage sag mainly includes the detection algorithm of the starting time of voltage mutation and the identification algorithm of the characteristic value of voltage sag,namely,the identification algorithm of voltage,short circuit current amplitude,zero crossing and other parameters after voltage sag.The simulation results show that the proposed fast detection algorithm can quickly identify the voltage sag and give the correct action signal within 3 ms;The RTDS experimental model is built to test the controller equipped with fast detection algorithm.The results show that the proposed fast detection algorithm can quickly detect the occurrence of voltage sag after voltage sag,identify the relevant parameters and give the correct action instructions.Based on the principle of fast switch and manual zero crossing technology,the fast isolation circuit of voltage sag is designed,which is the device performance test circuit.The opening time of the developed fast vacuum switch is 1 ms,and the opening time is less than 2 ms,which meets the requirements of voltage sag disposal device.Then,the basic working principle of the test circuit and the parameter configuration of the circuit are analyzed,including the parameter design of the main circuit,the parameter design of the manual zero crossing circuit and the configuration of the nonlinear zinc oxide.The simulation results of PSCAD fault current in real system(10 k V)and test circuit(capacitor discharge)are compared and analyzed.The results show that the instantaneous value of the current flowing through the fast switch is basically the same at 2.5 ms,and the current zero crossing time is also basically the same.The voltage change rate is 67.1 V/μs in real system and 74.7 V/μs in test circuit.It shows that the transient process of the two artificial zero crossing is basically the same,and the test circuit can cover the real system breaking condition.According to the test circuit of the fast voltage drop disposal device,the open and off test scheme of the switch is designed,and the field connection is carried out in the laboratory.The waveform of manual zero crossing and the data of switch breaking result are obtained.The actual effect of the device is tested by comparing different test methods and simulation results.The test results show that the scheme can reliably disconnect the fault current under various working conditions within 10 ms,raise the bus voltage and complete the whole voltage sag treatment.It has the advantages of fast detection and recognition and good voltage compensation effect. |
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