充油电缆纸绝缘老化中局部放电特性的研究

Study on the Characteristics of Partial Discharge During the Aging of Oil-paper Insulation in Oil-filled Cable

为开发高压充油设备局部放电在线监测系统及诊断油纸绝缘老化状态。根据充油电缆油纸绝缘结构特性,制定了电老化和热老化试验方案以了解局部放电时间分布参量、相位分布参量以及统计分布参量—Sk、Ku随老化时间的变化关系,从而确定油纸绝缘的老化状态。研究发现随着老化时间的增加,最大放电量和平均放电量均显著增加,起始放电脉冲的相位越来越接近0、180度,Sk和Ku均呈明显减少的趋势。

High voltage oil-filled cable is one of key equipments in the HV transmission and distribution system. High voltage oil-filled cable is exposed to a combination of electrical, thermal, and environmental stresses in service. For the long term, its oil-paper insulation gradually ages. Especially, with the development of partial discharge （PD）, age becomes more serious and even the breakdown is inevitable. Therefore, it is very important to study the characteristics of partial discharges during aging of oil-paper insulation for estimating condition and predicting residual life of the high voltage oil-filled cable for long time operation. According to the characteristics of the oil-paper insulation structure of oil-filled cable, this paper presents the electrical and thermal aging experiment methods. The experimental samples are designed with 12-alkyl-benzene composed cable oil and high voltage craft paper as basic materials. High voltage craft paper are dried firstly, then completely vacuum-dipped in cable oil to eliminate the gas in paper. Three pieces of paper are piled up as a sample. The electrical aging voltage takes 1.4 times of incept partial discharge voltage of paper. The thermal aging temperature takes 105 C, the highest permitted temperature in operating state. An aging cycle is 48 hours and 12 aging cycles are done. Parameters of PD is measured and analyzed after each aging cycle. Characteristics of time distribution parameters, phase distribution parameters and statistic distribution parameters-skewness and kurtosis along with aging time have been studied emphatically. It is found that, with the aging time increasing, qmax （t） and qmean （t） increase observably, phase distributions of initiative discharge pulse are close to 0° and 180° gradually, both Sk and Ku present the decreasing trend obviously. These parameters effectively characterize the aging condition of oil-paper insulation. The study provides the bases for researching and designing the PD on-line monitoring system for high voltage oil-filled equipments and diagnosing the aging condition of oil-paper insulation.