典型缺陷油浸纸套管绝缘劣化特性研究

Study on Insulation Degradation Characteristics of Oil Impregnated Paper Bushing with Typical Defects

油浸纸电容式套管是目前电力系统中应用最为广泛的套管,发生的故障也相对较多。为研究油浸纸套管缺陷发展过程及绝缘劣化规律,采用多只72.5 kV油浸纸套管分别模拟进水受潮、极板边缘尖端、极板偏差及油中气泡等典型缺陷,在60℃油温下同时对缺陷套管施加42 kV电压和630 A电流进行长时电热联合试验,测量并分析套管绝缘电阻,tanδ、电容量、局部放电特征、频域介电谱曲线等参数的变化规律。测试结果表明,tanδ及电容量对套管绝缘受潮缺陷较为敏感,通过tanδ-f曲线及C-f曲线可分析套管内部水分热扩散过程;通过局部放电测试能有效发现套管油中气泡、极板偏差和极板边缘尖端缺陷,3种缺陷的主要区别在于局部放电t-f图谱中的脉冲放电等效频率范围不同;长时电热联合作用下,油中气泡缺陷套管最早出现绝缘劣化,总体劣化速率相对平缓。极板尖端缺陷套管前期劣化速度慢,但累积效应明显,tanδ及电容量在稳定一段时间后呈阶跃式增长。极板偏差缺陷套管出现绝缘劣化的时间最晚,出现劣化后的趋势与极板边缘尖端缺陷套管类似。研究结果可为套管故障分析及绝缘诊断提供参考。

Oil Impregnated Paper(OIP)condenser bushing is the most widely used bushing in present power system and the fault is also relatively more. In order to study the defect development process and the rule of insulation degradation of OIP bushing,multiple pieces of 72.5 kV oil impregnated paper bushings are used to simulate such typical defects as water dampness,tip on the edge of the plate,plate deviation and air bubble in oil. At transformer oil temperature of 60 ℃,the voltage at 42 kV and current at 630 A are applied simultaneously on the defect bushing for long term combined electro-thermal test. The variation of such parameters as dielectric loss factor(tanδ),capacitance,partial discharge characteristics and frequency-domain dielectric spectroscopy(FDS)curve of bushings are measured and analyzed. Test results show that tanδ and capacitance are sensitive to the damp defects of the bushing.The process of moisture thermal diffusion inside the bushing can be analyzed by tanδ-f curve and C-f curve. The defects of bubbles in oil,deviation of the electrode plate and tip on the edge of plate in the bushing can be effectively found by partial discharge test.The main difference among the three defects is the equivalent frequency range of pulse discharge in the t-f diagram is different. Under the long-term combined electrothermal action,insulation degradation occurs on the bushing with bubbles firstly and the overall degradation rate is relatively smooth.The degradation rate of electrode tip defect bushing is slower in the early stage,but the cumulative effect is obvious.The tanδand capacitance increase step by step after a period of stability. As for the plate deviation defect bushing,the occurrence time of insulation degradation is the latest,and the degradation trend is similar to that of the electrode tip de-fect once degradation occurs. The research results can provide reference for fault analysis and insulation diagnosisof the bushing.