Combined in-oil PD sensor with AE and UHF methods for PD detection in transformer

Abstract

In the present study, a combined in-oil partial discharge (PD) sensor based on oil valve with acoustical emission and ultra high frequency (AE/UHF) methods for PD measurement in transformer is proposed. The combined PD sensor is designed by placing an AE sensor in front of a UHF antenna, and resorting to be fixed on an oil valve to invade inside the transformer to simultaneously couple the AE/UHF signals from PD source. Besides the AE/UHF signals coupling, construction design of the combined PD sensor with oil sealing are shown in particular. And considering the phenomenon of air entering the transformer box due to the improper installation to the oil valve, an installation method using air extraction for the combined PD sensor based on the oil valve is also shown with a discussion on safety and detection sensitivity caused by the sensor insertion depth. Discharge tests in air and insulation defects prove that the combined PD sensor with AE/UHF methods proposed and processed can simultaneously measure or detect the AE/UHF signals produced by PD source effectively with an obvious time difference value Δt, which presents a innovative mixed AE/UHF method of PD measurement for transformer.

Keywords

• Partial discharges (PD)
• Ultrasonic acoustic emission
• Ultra-high frequency (UHF)
• Combined sensor
• Transformer