Error Analysis of Measuring Capacitive Current by Traditional Gear-Shifting Method Considering Lower System Imbalance

In recent years, China's medium-voltage distribution network has continued to carry out cable transformation. The three-phase unbalance of the distribution network with a high proportion of cable access is small, which makes the traditional method of measuring the capacitance current by using the neutral unbalanced voltage produce a large error. In this paper, the influence of the reduction of system unbalance on the measurement accuracy of capacitance current by the traditional shift adjustment method is studied. It is found that the measurement error of the zero-sequence current is the main factor affecting the measurement accuracy, and the measurement accuracy can be guaranteed when the amplitude of the zero-sequence current and the change of the zero-sequence current before and after the shift adjustment are greater than 20 times the sampling accuracy of the controller ADC device. At the same time, this paper gives the calculation formula of the gear adjustment gear that meets the accuracy of capacitor current measurement, which is helpful for the rapid selection and design of the gear adjustment gear of the are suppression coil. In addition, when the three-phase imbalance of the system is low, even if the resonance point is crossed during the shifting process, a large voltage jump may not occur.