Partial discharge pattern characterization of different defects using 3D phase resolved technique

This paper describes the procedures to characterize defects in the insulation of an 11 kV Voltage Transformer (VT) by evaluation of the 3D phase-resolved partial discharge patterns. The 3D Phase-Resolved Technique provide a method to identify defects where partial discharges occur by means of the unique character of the phase relationship - the magnitude of the partial discharge activity and the discharge rate of the defects. Partial discharges occurring in solid insulation can be characterized by means of the shape of the defect, viz spherical, ellipse, cracks in the insulation and delamination on interfaces with electrodes. The location of the defects in relation with the distance from the high voltage electrode or earth electrode also connoted in the pattern displayed. The last variable that determines the final pattern is the number of discharges occurring over a specific time, or which can be given as the rate of discharge in the specific defect. The methodology consists of measurement of the partial discharges in solid samples insulation; having known the defects of different shapes and at the specific locations in the insulation. The defects were manufactured into the samples at predetermined locations and having different shapes and sizes. The specific defect patterns obtained from the samples were used to identify the type of defects and locations in the insulation of the voltage transformer. The paper further describe the different results obtained based on the method of excitation of the voltage transformer.