High Field Dielectric Relaxation Process of Nonpolar Polymer Insulating Materials

TOKORO Tetsuro

Nonpolar polymers such as polyethylene or polypropylene are being widely used for insulating materials and are being studied from many points of view. They are greatly expected for the insulation of superconducting power cables. Dielectric loss tangent (tanδ) is a very important factor in designing the insulation of these cables. Therefore, high field dielectric properties of polymer insulating materials in the wide range of temperature are now under investigation. The purpose of this paper is to study the detailed behavior of tanδ in polyethylene films under high electric field. It is found that tanδ varies according as the time of high ac field application passes. At the level above the room temperature, tanδ decreases in correspondence with the time of ac high field application, and it is accelerated by the increase of electric field or temperature. In a certain electric field existing at the room temperature, tanδ increases at first and then decrases. By using a personal computer, these phenomena are simulated through a multi relaxation (deaccomodation) process. Then the experimental results are compared with the calculated values in order to discuss the behavior of tanδ. The variation of time dependence of tanδ in each electric field agrees very well with the experimental and the calculated values. On the contrary, however, the variation of tanδ in accordance with the difference of temperatures does not.

High Field Dielectric Relaxation Process of Nonpolar Polymer Insulating Materials

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