EM Measurements Between MV Switching Sources and Colocated Sensitive Circuit

Abstract

With the development and increasing use of intelligent vacuum circuit breaker (VCB), the electromagnetic compatibility problem between VCBs and their low-voltage electronic equipment is becoming increasingly prominent. Switching operations of circuit breakers are known to be serious sources of electromagnetic interference (EMI) to their secondary equipment, which can lead to the control and protection devices display error and malfunction. Hence, it is very important to study the EMI problem of the secondary equipment (such as current transformer (CT), PT, and controller) caused by the operations of circuit breakers. This paper carried out the tests of a 10 kV medium-voltage outdoor pole-mounted switch by a synthetic test circuit with large current and high impulse voltage sources, and collected the current signals of the secondary circuit at the same time, then obtained the frequency and energy distributions of the disturbance signals, caused by the breaking operation of pole-mounted switch, by time and frequency characteristic analysis with the wavelet analysis. Results show that the secondary side of the CT and the feeder terminal unit (FTU) controller are bearing EMI when pole-mounted switch is in operation and the distribution of the frequency spectrum is wide. The most serious disturbance appears at the time of arc current passing zero and the frequency distribution is mainly in 7.81–15.63 MHz. The EMI caused by transient recovery voltage is mainly distribution in 31.25–125.0 MHz. The maximum amplitude of disturbance pulses is about 4.5 times as large as that of the normal case. The results can provide a reference to the measures against the EMI for the pole-mounted switch's FTU controller.