多层油纸绝缘介质不同局放阶段的陷阱参数演变规律

陷阱是影响绝缘介质中电荷输运特性的重要因素,研究不同局放阶段绝缘介质陷阱参数演变规律对深入研究放电机理具有重要意义。为此,考虑车载变压器的匝间绝缘结构特点,设计了3层油纸绝缘缺陷模型,进行局部放电试验,选取起始到击穿不同放电阶段的试样,采用等温表面电位衰减方法研究不同放电阶段3层绝缘纸试样的表面电荷衰减特性,据此计算相应阶段试样表面电荷的陷阱分布规律,探究陷阱分布对局部放电的影响。研究结果表明:Nomex纸以深陷阱为主,随着放电的发展,第1层绝缘纸陷阱能级增加,第2、3层绝缘纸陷阱能级下降;陷阱能级和陷阱密度降低导致绝缘纸中自由电荷变化率增加,自由电荷数量增多,放电的剧烈程度增加;电荷的传输特性是局部放电过程中不同层绝缘纸陷阱参数演变规律不同的重要原因。

Evolution of Trapping Parameters of Multi-layer Oil-paper Insulating Medium at Different Partial Discharge Stages

Trap plays an important role in the transportation of charge and the investigation of trap parameters is significant to the further research of discharge mechanism. According to the turn-to-turn structure of on-board transformer, a three-layer oil-paper insulation defect model was designed for partial discharge experiments. The oil-impregnated paper from the beginning to the breakdown of partial discharge was selected to measure the surface potential attenuation curves of different layers of insulating paper in three layers of oil paper insulation medium by isothermal surface potential decay. The trap distribution of insulation paper in different stages of partial discharge(PD) was calculated and its influence on discharge characteristics was studied. The results show that the deep trap is the majority of Nomex paper, and the trap energy of the first layer increases with the development of partial discharge but the energy of the second and the third layers shows an opposite trend. The change rate of free charge increases with the decrease of trap density and trap energy, and the acute discharge increases with the increase of free charges. The transmission characteristic of charge contributes to the different evolution of the trapping parameters of different layers.