On-Line Monitoring of Partial Discharge of Less-Oil Immersed Electric Equipment Based on Pressure and UHF

Abstract

For partial discharge (PD) detection of less-oil immersed electric equipment (CT, PT, bushing), frequent sampling of oil chromatographic is likely to cause negative pressure inside the equipment, and by modifying the terminal tap to access the detection impedance, it will endanger the reliability of the long-term grounding of the terminal tap. Based on this, in this paper, a combined on-line monitoring method for PD of less-oil immersed electric equipment based on pressure and UHF is proposed. UHF method is used to detect the real-time features of PD defect, and the pressure is used to detect the accumulative degree of insulation deterioration. An oil-immersed vertical CT PD detection scheme based on pressure and UHF is designed. The feasibility of the scheme is verified by experiments. And in the case of bubble insulation defects, the PRPS spectrum of leaked electromagnetic wave from non-metallic insulating gap is obtained in the UHF method, and the relationship between the accumulated severity of the defect and the pressure was also studied. The experimental results show that the pressure has a certain fluctuation during the initial period of PD. Under the condition of a certain discharge quantity, the oil pressure changes linearly with the increase of time, and the pressure growth rate varies with different discharge quantity. When the internal pressure reaches the pressure value required for expansion of the expander, the internal pressure of the device shows a non-linear growth trend. The method proposed in this paper provides a new idea for the PD insulation detection of oil-less equipment.