The design of ultrasonic - electromagnetic detecting circuit and application on partial discharge

Abstract

Electromagnetic waves and ultrasonic waves are all generated when partial discharge occurs inside the electrical equipment. We used this feature to design a set of ultrasonic detection and detection of electromagnetic waves in one part of the PD detection circuit. The acoustic signal received by the ultrasonic probe was converted into a same frequency electric signal through electro-acoustic conversion. The signal displayed on the oscilloscope was an envelope similar to the amplitude modulated signal. Because of its low energy and wide frequency band, we chose the AD8129 and AD8139 with low noise and adjustable gain as preamplifier to reduce noise and amplify the signal. We referred to a symmetrical symmetric antenna with a bandwidth of 150MHz-400MHz as the partial discharge electromagnetic wave receiving antenna. But the electromagnetic waves did not need to go through the pre-amplifier circuit. We took the two signals through the logarithmic amplifier AD8310 non-linear compression to the extent that can be processed to remove the envelope signal. According to the transmission speed difference between acoustic signal and electromagnetic signal, in the partial discharge experiment, we took the time of the electromagnetic signal as the time origin, the two signal time interval as the ultrasonic signal transmission time, calculated the distance between the PD source and the detection circuit. The PD location of this method was compared with the actual measurement, and the error was within the allowable range.