다중 뇌충격전류에 의한 ZnO 소자의 전기적 특성 변화에 관한 연구

Abstract

This thesis deals with the changes of the electrical characteristics of ZnO blocks by the application of a single and a multiple-lightning impulse current.

Lightning arresters are the best protective device on electrical power systems against transient overvoltages caused by lightning impulse current and switching operation. Until these days, lightning arresters are estimated only by a single-lightning impulse current in its performance test. However, a multiple-lightning impulse currents are a general feature of natural lightning-ground flashes. It is therefore necessary for lightning arresters to be estimated by applying not only a single-lightning impulse current but also a multiple -lightning impulse current.

In this study, ZnO blocks of 6[㎸], 5[㎄] used in power distribution system have been estimated repeatedly until 200 times by a single and a multiple-lightning impulse current of 8/20[us], 5[㎄].

The multiple-lightning impulse current generator which can produce quadruple 8/20[㎲], 5[㎄] with discrete time between 30∼120[㎳] is designed and fabricated. The total energy applied to the ZnO blocks at each pulse is about 1,200[J].

In experiment, various parameters such as leakage current components, reference voltage, and surface temperature of ZnO blocks are measured with the number of applied impulse current. Also, micro-structure changes of ZnO blocks after applying the single and the multiple-lightning impulse current of 200 times are compared.

From the experimental results, the peak value of the leakage current and the surface temperature of ZnO blocks are increased continuously with the number of applied impulse current, but no significant changes in the RMS value of the leakage current and in the reference voltage are observed.

Also, it is confirmed that the type of ZnO blocks are more vulnerable in deterioration or damage to the multiple-lightning impulse current.