固体绝缘材料热老化电气特性的研究

Research on Thermal Aging Electrical Properties of Polymer Materials

油浸式变压器所用固体绝缘材料的介电常数大小和耐高温性能是影响变压器容量和尺寸大小的重要因素。本文选择了聚酯薄膜、聚碳酸酯、聚苯硫醚三种耐高温聚合物材料为试验对象,在130℃条件下进行了最长1 200 h的热老化试验,测试了各试样老化前及老化各阶段的介电谱(相对介电常数、介质损耗因数随温度变化特性)和击穿强度。测试结果表明,三种聚合物材料老化前后的相对介电常数值均比油浸变压器目前常用的绝缘纸板的小(更加接近变压器油),相应的介质损耗因数也远远低于绝缘纸板;聚苯硫醚和聚酯薄膜的相对介电常数和介质损耗在90℃附近明显增大,但聚碳酸酯的相对介电常数和介质损耗基本不变;在油中热老化后,三种聚合物材料的介电常数和介质损耗随温度变化的趋势与未老化的相似;在老化各阶段,聚酯薄膜、聚碳酸酯和聚苯硫醚材料的工频击穿强度基本与热老化时间无关。综合聚酯薄膜、聚苯硫醚和聚碳酸酯三种聚合物材料热老化前后的介电特性变化情况,对比常用的绝缘纸板的特性,考虑到相对较低的介电常数与介质损耗因数和较高的击穿场强,聚碳酸酯是一种相对理想的有可能用来替换常用绝缘纸板的替换材料。

The dielectric constants and the high temperature resistant performance of solid insulation used in oil-immersed transformer would limit the capacity and size of an oil-immersed transformer.In this paper,3 polymers(polyester film,polycarbonate and phenylene sulfide) are aged under 130℃ up to 1 200 hours.The dielectric spectroscopy(here refers to the change tendency of relative permittivity and tan along with the change of temperature) and the AC electric breakdown strength of 3 polymers are investigated at different aging stages.According to the test results,the dielectric constants of three polymers is always less than the dielectric constant of insulating paper/board and more close to that of transformer oil,and their tan are also less than that of insulating paper/board.Before aging test,the dielectric constants and tan of polyester film and phenylene sulfide would be increased obviously at about 90℃,but not the polycarbonate.There shows the same change tendency of the dielectric constants and tan for 3 polymers at different aging stages as without aging test.It is also found that the AC breakdown voltage of 3 polymers at different aging stages have almost kept the same as the value of non-aged state.Considering the dielectric properties of these 3 polymers,comparing the properties of insulating paper/board,in terms of the lower dielectric constant and the higher ac breakdown voltage,polycarbonate may be used as one of suitable replacement materials for insulating paper/board used in oil-immersed transformer.