600 / 2017-05-15 14:38:55

Measurement of Charge Distributions inside of Cylindrical Alumina Insulator with Shield Rings after Repeating AC Voltage Application

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会场 > Fundamental Physics and Electrical Insulation in Switchgears

Vacuum circuit breakers (VCBs) are expected to have higher voltage classes from the viewpoint of environmental loads and life cycle costs. When developing the higher voltage class of VCB, we meet the difficulty in which the surface flashover occurs via charging of the vacuum side surface of the vacuum interrupter (VI). As a method of suppressing the flashover event, the shield rings that relax the electric field at the triple junction are applied to the VI. In order to optimally design the shield ring, it is important to grasp the charging characteristics on the inner surface of the VI.
In this study, we have measured the charge distribution characteristics inside a cylindrical type insulator employed as the model insulator of VI after the AC voltage application. This insulator has shield rings at both ends of the insulator. We investigate the charging characteristics for three types of samples having different diameter of the shield rings. This difference gives the different clearance between the shield and insulator.
As a result, each sample showed a tendency to increase the charging as the applied voltage increased. When AC voltages were repeatedly applied to the same sample, the values of surface charge were reduced comparing with that of the first one. This phenomenon is called as “conditioning effect”. The sample with the narrower clearance (Sample A) has a larger reduction rate of charging than that with the wider clearance (Sample C). Further, in the case of Sample C, the charging appeared in a wider range than sample A. Specifically, the charging was formed only in the vicinity of the tip of the shield rings in sample A, whereas in the case of Sample C, the charging was also formed on the surface facing the shield ring. Such difference of charging distribution could be caused by the strength of electric field at the end of shield and cathode triple junction.
From above results, we have obtained data of the charge characteristics and found that it is effective to repeat AC voltage application to suppress charging and to design the proper width between a shield and insulator.