X射线激励下的油间隙放电现象

PARTIAL DISCHARGE PHENOMENA WITH X-RAY IRRADIATION IN OIL-GAP

目前变压器局部放电定位广泛采用超声波定位方法。由于变压器局部放电信号微弱以及现场干扰强烈等原因 ,使这一方法的有效性受到限制。本文实验研究了X射线激励下油间隙局部放电现象。实验发现 ,在X射线照射下 ,油 /纸绝缘中的某些局部缺陷部位会因此发生局部放电 ,其效应与X射线光子对金属导体表面产生的光电效应以及油介质状态有关。在封闭型油间隙中 ,导体表面受激产生了大量的电子并注入油间隙中。由于油的流动性受到极大限制 ,其间聚积的带电粒子可能在油和固体绝缘界面形成空间电荷层 ,在外加电压作用下 ,油间隙局部电场明显加强 ,从而导致油间隙的放电起始电压降低、局部放电加强。利用这一特性有可能为变压器局部放电的检测和定位提供一种新方法。

With conventional (PD) measurement technique, the tiny defects are difficult to be discovered in oil/paper insulation system. The partial discharge phenomena induced by X-ray irradiation in transformer oil-gap were investigated experimentally in this paper. It is found that PD activities in the oil-gap wrapped by insulating materials are enhanced under X-ray irradiation, which could be associated with charge injection and space charge distribution in the oil gap. Some free electrons could come from the HV metal electrode by Photon effect at metal electrode surface with X-ray irradiation, that is, free electrons in conductor could get energy from X-ray photons to leave the metal surface. The oil gap formed between the electrode and the wrapped cloths in the transformer model was small so that the electrons escaped from the electrode surface were limited in the tiny oil gap. Therefore a charge accumulation occurred in the oil gap, causing partial electric field stress intensified greatly. When the partial field was strong enough to ionize the oil, PD occurred in the oil gap with X-ray beam irradiation. This process resulting in PD occurrence with a lower voltage and an increase of PD amplitude and frequency is compared to that without X-ray irradiation, which was indicated in our tested results. The location of partial discharge signal because of X-ray beam irradiation and detecting partial discharge can been fixed on by modulating orientation of X-ray beam irradiation. The test results will be a basis to develop a new PD location technique by using X-ray beam irradiation to power transformer.