Fault Monitoring Method With Impedance Variation For Capacitive Reactive Power Compensation Device

Capacitive reactive power compensation device is widely used in power systems,its main role is to increase the power factor of the power grid,reduce power transmission losses,improve the quality of power supply.In order to maintain the stability of the power system when the load changes,capacitive reactive power compensation device requires frequent switching,over-voltage and inrush current in the switching process so that capacitor banks and series reactors often fail.Existing capacitive reactive power compensation device fault monitoring methods can only monitor the capacitor bank,the series reactor protection is in the dead zone.In response to this problem,this paper presents a new capacitive reactive power compensation device fault monitoring method,while reflecting the capacitor bank and the series reactor failure,it is of great significance.In this paper,the method of solving the impedance variation of capacitive reactive power compensation device before and after the failure of series reactor and capacitor bank is given,and a set of experimental model of capacitive reactive power compensation device with nominal voltage of 0.5k V and nominal capacity of 90 k VA is established.This model as an example calculates the parameter variation before and after the fault,based on the analysis of calculation results,a monitoring method based on the variation of the resistance and the failure of the series reactor is proposed.The signal is processed by the weighted algorithm of guasi-synchronization algorithm and the variation of resistance and reactance is solved by harmonic analysis.The experimental model is taken as an example to conduct the experimental study.The relative change of the impedance of the reactor after inter-turn short circuit and the relative change of the impedance of the capacitive reactive compensation device are related to the inter-turn short circuit and have the same pattern of thechange.The relative variation of the capacitive reactive compensation device is much smaller than the relative change of the reactor.The relative change in impedance of a capacitor bank after a single breakdown is smaller than the relative change in impedance of the capacitive reactive compensation device.The measured impedance change of the reactor by the power analyzer is similar to the theoretical calculation value.The resistance variation increases with the short circuit position moving from the top to the center.Short-circuit ring current measurements and theoretical calculations are similar,the current value decreases with the increase of short-circuit turns.Thus it is proved that the method of monitoring capacitive reactive power compensation device fault based on the variation of impedance is accurate and reliable.Acquisition card and power analyzer impedance changes in the measured values are similar,proved the measurement accuracy of method of monitoring based on harmonic analysis and quasi-synchronous sampling is high.The relative change of the resistance of the capacitive reactive power compensation device measured by the acquisition card is close to the theoretical value,The variation of the short-circuit turns is greater than 2% when the number of turns is twenty five turns,which proves that the existing monitoring system with a resolution of 0.2% can reflect the failure of a single breakdown of the capacitor bank and the short circuit of twenty five turns of the series reactor based on the variation of the impedance.