On-line estimating the level of hydrophobicity of composite insulators using the digital images

The hydrophobicity of composite insulators is a very important property for composite insulators used on transmission lines. An off-line test to indicate the hydrophobicity of a composite insulator has been developed by STRI, but it can not be used under on-line conditions. The objective of this paper is focused on an on-line estimation of the hydrophobicity of composite insulators using the digital images taken in the field. In order to identify the hydrophobic class of an insulator based on the digital images taken in the field, four algorithms were studied for imaging analysis, which include the improved ANE (the average of normalized entropies) method, the SPS (the seed point statistic) method, the FMA (the frequent magnitude analysis) method and the improved SF (the shape factor) method. The results from our study indicate that the improved SF method shows the best results for estimating the hydrophobicity of composite insulators in service. The way to measure on-line the hydrophobicity of composite insulators has been developed. It consists of a set of portable devices and the relative measuring rules. The devices include a sprayer with an insulated operating arm, a digital camera, and software. For every composite insulator in service, the upper surfaces of three sheds closest to the tower are chosen for the measurement. The way to spray distilled water on to the surface of the insulator has been investigated and an operating method suitable for on-line testing has been developed. The photo analysis for an indication of hydrophobicity is also carried out in our laboratory. The results from our study show that it is possible to determine the hydrophobicity of the composite insulators from the photos taken in the field based on our hydrophobicity analysis software with the aid of the operator. On site testing for determining the hydrophobicity of composite insulators has carried out on certain 220 kV transmission line in central China on three occasions. The re- - sults from on-line measurement show that the method we developed is suitable for on-line measurement and several composite insulators on this line exhibited poor hydrophobicity (HC7). The reasons for the degradation of the hydrophobicity of the insulators are being investigated