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The current paper presents an alternative and innovative technique to predict the severity of pollution of high voltage insulator using a higher harmonics component with up to the 7 th component of leakage current. The leakage current was measured using a current transformer and a shunt resistor. Next, laboratory tests were conducted on glass and porcelain insulators with artificial pollution under salt-fog pollution state which is further represented by three levels, namely light, medium, and high contamination. In this case, the formulation of a new severity of harmonic index refers to a ratio of the sum of 5 th and 7 th to the 3 rd harmonic component. More importantly, the new index managed to provide more accurate results when used as a diagnostic tool for the levels of pollution, compared to the ratio of the total harmonic distortion (THD) to the number of odd harmonics components (n) as the boundaries. In this case, the insulators were found to be in a clean and normal condition when the K (5+7)/3 value was greater than 3%. Contrastingly, the insulators were in an extreme condition when the K (5+7)/3 was lower than 3%. Nevertheless, there is a high probability of a flashover in glass and porcelain insulators if the K (5+7)/3 value is less than 2%. The present study shows the possibility of utilizing the value of strange harmonics up to the 7 th component of leakage current as the parameter for the monitoring of leakage current in overhead insulators in the presence of contamination. Overall, it can be concluded that the 3 rd , 5 th , and 7 th harmonics details extracted from the leakage current act as a good indicator for the level of contamination. INDEX TERMS Polluted insulators, leakage current, harmonic components, total harmonic distortion, fast fourier transform, salt fog.

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In this paper, an innovative approach to assess the risk of uniform/non-uniform pollution and wet high voltage glass insulator is proposed. The assessment is based on a new index, named as R hi , which is derived from the 3 rd , 5 th and 7 th harmonics of the leakage current. Two 33 kV strings of cap and pin glass insulators having three units with different profiles are employed to evaluate the risk level, based on measured critical voltage gradient (Ec). Critical voltage stress tests are executed on the contaminated insulators under different ratios of lower to upper surface (J) and wetting rates. Furthermore, the effects of ratio of soluble deposit density (ESDD) to non-soluble deposit density (NSDD) on the flashover occurrence are analyzed. It was found that the insulator profile has significant influences on the likelihood of flashover which is estimated as 38% and 24% for type A and B insulators, respectively. From the results, it can be concluded that the proposed R hi index is able to predict the risk level of the insulator and the probability of flashover occurrence more accurately than the 5th/3rd index, which is widely published in literature. INDEX TERMS Polluted insulators, Risk assessment, leakage current harmonics, Fast Fourier Transform, glass insulator.

<span>Frequency response measurements are used for power transformer winding failures detection. The variation between frequency responses indicate mechanical changes in the transformer winding. One method to investigate winding failures in transformer is to develop a reliable circuit model which can simulate the frequency response of an actual winding. The main reason to use the model is because it is expensive to create damages on an actual winding. This paper proposes n-stages circuit ladder network to simulate the response of a winding which has unique design. It presents a new technique to calculate the resistance, inductance and capacitance of the winding. Then, the relationship between the RLC parameters and the frequency response is studied. The winding chosen in this investigation is a single phase 33kV transformer winding. The simulated frequency response was compared with the measured response to verify the proposed model. The model can give a comprehensive understanding about the effect of RLC parameters on the frequency response.</span>