A Numerical Method for Prediction of Standard Partial Discharge Test Performance of an Open-Ventilated Dry-Type Transformer at Design Stage

Partial discharge in an (open ventilated dry type) OVDT sub-transmission transformer with 30 MVA 63kV/20kV rating has been studied in this work. Nomex has been used in this transformer in the form of insulation paper. The goal of this paper is to present a method to predict the result of the standard partial discharge test on a dry-type transformer based on its design parameters. The importance of such a method is in the prevention of manufacturing a power transformer that might be rejected due to its lack of endurance in the partial discharge test which can lead to cost savings. In this method, important areas in transformer winding insulation design are identified and in turn, effective factors on electric field magnitude in these areas are determined. Then, using a Monte Carlo-based method, a numeric algorithm for calculating the electric field magnitude in these areas is developed. Finally, based on the electric field magnitude distribution in these important areas it will be determined whether the transformer insulation would pass the requirements of the IEC standard partial discharge test or not. A comparison of the results obtained using the algorithm against the finite element simulation results showed an error of less than 1%.