The development of the way of measuring the leakage current to evaluate the deterioration of the insulation material in the snowy cold region

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This research was done for the purpose of evaluating the deterioration of the polymeric insulation material used under snowy cold condition by the measurement of leakage current. Leakage current magnitude in wet and contaminated condition is one of significant indicators to assess electrical performances of outdoor insulators during operation.. However, because conductive current and discharge current flow alternately and intermittently on the surface of the polymeric insulator, therefore these magnitudes change seriously. So it is difficult to evaluate the deterioration of the insulator only by that level. It seems that apart from the leakage current magnitudes, the shape of the waveform, namely high frequency components, also can provide useful information the state of the polymeric insulator surface. In this research we employ IEC587 test for measuring leakage current. Tests have been carried out under -20〜+25℃ in a laboratory chamber.Early stage of this test, polymer surfaces resist being wetted and allow extremely low leakage current. At this time minute glow discharges are scattered on the surface of the material. With the test duration, the polymer surfaces gradually transfer to wet and allow leakage current to develop. As for this discharge, polymeric insulation material does final tracking deterioration. Leakage current has high frequency components at this time. This harmonic component shows that failure of the polymeric insulation material will happen soon.When silicon rubber suffers the damage of the discharge, the type of the failure is not tracking breakdown, and becomes erosion. Not only erosion makes it lose the insulation function of the silicon rubber but also its structure is destroyed. When leakage current is interrupted once, erosion will appear on the silicon rubber.