Effects of ultraviolet radiation and artificial pollution on the leakage current of Silicon Rubber insulators

Environmental and electric stresses have great ageing impacts on the polymer insulators. Ultraviolet (UV) radiation is one of the most important environmental factors that affects the degradation of Silicon Rubber (SiR) insulators. This paper presents the accelerated ageing records of a 20 kV SiR insulator in a chamber containing nine UVC lamps with intensity of 50 W/m2 for 65 days. Ageing process has been performed in order to analyze the effects of UV on the hydrophobicity and the surface leakage current level (LC) of SiR insulators. The results indicate that the variations of LC in clean insulator surface comparing with the insulators exposed to UV are negligible; however, UV has direct impact on the hydrophobicity of insulator surface. Solid layer pollution method is applied according to IEC60507 standard and quantitative comparisons are performed between the hydrophobicity of aged and clean insulator surfaces. Fast Fourier transform (FFT) method used to find the harmonic spectrum of the LC for three distinct cases: 1) without arc (nominal voltage), 2) in presence of dry band arcing and corona discharge and 3) continuous arc. In two latter cases, the level of 3rd harmonic component of leakage current waveform is closely related to the amount of pollution on the insulator surface.