Study On PD Detection In Transformer Ultrasonic-based Method Inside And Outside The Insulation Oil

Ultrasonic method is an important means for monitoring and evaluation of partial discharge of power transformers. As usual, the sensors are placed outside the transformer. In order to increase ultrasonic sensor sensibility, a new PD detection method that puts ultrasonic sensor into the insulation oil is put forward in this paper. To simulate discharges in transformers, 4 typical PD models: point to plane, surface discharge, internal discharge, and floating discharge are made. The ultrasonic detection system that can measure inside and outside the insulation oil simultaneously is constructed in the lab. By the experiments, it proves the feasibility of ultrasonic detection in the oil, compares the difference between inside and outside the oil from the waveforms, signal amplitudes and spectrums, and shows the advantages of detection inside the oil that the signal amplitudes are 1.5 to 3.8 times than that outside the oil. To simulate the electromagnetic interference on the site, it tests the influence of strong electrical field to the ultrasonic sensor, and tries to avoid it by shield. In this paper, the fundamental research about ultrasonic detection in the oil is done.