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This paper deals with the analysis of leakage current and phase angle characteristics of porcelain and silicone rubber insulator in order to develop a better diagnostic tool to identify the pollution severity of outdoor insulators. In this work, laboratory based pollution performance tests are carried out on porcelain and silicone rubber insulator under ac voltage at different pollution levels and relative humidity conditions with sodium chloride as a contaminant. Multi Resolution Signal Decomposition (MRSD) using Discrete Wavelet Transform (DWT) is employed to understand the time-frequency characteristics of the leakage current signal. Fast Fourier Transform (FFT) spectral analysis is adopted to calculate the phase angle values of the applied voltage and leakage current signals. Reported results on porcelain and silicone rubber insulators show that the pollution severity of outdoor insulators could be identified from the DWT STD-MRA (Standard Deviation Multi Resolution Analysis) Distortion Ratio pattern analysis of leakage current signals. Index Terms--Porcelain insulators, silicone rubber, flashover, wavelet transforms, leakage currents.

An investigation on partial discharge (PD) propagation in power cables is carried out in this paper with the aim of inferring limits for PD detection as a function of the distance between PD source and detector. Although this problem has not an exact solution unless noise levels are not specified, useful information concerning detectability and error in estimates are provided in this paper for both medium and high voltage polymeric cables. The issue of calibrator characteristics with respect to sensitivity detection is also tackled. Index Terms--Partial discharges, power cables, condition based maintenance, risk assessment.

This paper presents a technique for outdoor ceramic insulator pollution assessment based on partial discharge detection and analysis. Laboratory tests and data coming from a monitoring activity carried out on some insulators of transmission lines are reported. They support the effectiveness of partial discharge detection and analysis as a tool to carry out condition-based maintenance of insulators of overhead lines. In particular, it can be seen that partial discharge analysis highlights the mechanisms bringing insulators to flashover (dry band arc activity) and is, therefore, well suited to predict increasing pollution and imminent flashover. As a consequence, algorithms are proposed to provide a quantitative evaluation of pollution severity. Index Terms--Outdoor insulators, partial discharge, diagnosis, maintenance, power transmission and distribution.