Characteristics of space charge behavior and conduction current in xlpe and annealed polyethylene under high DC stress

Space charge behavior and conduction current in XLPE and annealed LDPE under DC high electric field were investigated. One of the reasons for the different breakdown property in XLPE from that in LDPE may be based on the existence of cross-linking by-products in XLPE. Furthermore, a thermal history in cross-linking process for XLPE under high temperature may also cause of the difference. It is generally accepted that the existence of the cross-linking by-products increase the conduction current in XLPE under DC stress. It is also said that an anneal treatment in air atmosphere may affect to the properties of the space charge behavior and the conduction current in polyethylene under DC high electric field. Therefore, we investigated the effect of the cross-linking by-products and the anneal treatment on the space charge behavior and the conduction current in LDPE under DC high electric field. In our research, it is thought that the increasing dissipation power in the bulk of XLPE is the cause of the breakdown in it under DC high electric field. If the property of the behavior of dissipation power in XLPE is mainly based on the cross-linking by-products, a similar property to LDPE must be observed in degased XLPE, in which the cross-linking by-products were removed by the degassing procedure. On the other hand, if the property of it is affected by the thermal history, a similar property to XLPE must be observed in annealed LDPE. Therefore, to calculate the dissipation power in the bulk of degassed XLPE and annealed LDPE, we measured the space charge distribution and the external circuit current simultaneously in them. Based on the results, we discussed the reason of the difference of the space charge properties in XLPE and LDPE focusing on the residue of cross-linking by-products and the oxidation of the test samples.