Electrical modeling of high voltage windings of power transformers for online partial discharge localization

Abstract

Partial Discharge (PD) is one of the most important factors in the gradual destruction of transformer insulation, more importantly if the problem is not resolved can cause complete insulation failure. Physical localization of the fault inside the transformers in terms of saving repair time and cost is important. In this paper, by modeling a high voltage winding of a power transformer as a single-layer disk winding with air core the localization of PD is investigated. In this configuration, winding consists of six disks. Here, by applying impulse voltage as PD signal to the beginning of each disk, the voltages are measured and saved online at the bushing and neutral ends of the winding. By using the curve fitting method, the equations of PD signals at these two ends are extracted, then by computing transfer function in Laplace domain the magnitude of this transfer function are saved as a reference diagram. We have done this for all 6 disks. When PD occurred at winding by measuring voltages at bushing and neutral ends and drawing transfer function and comparison with reference diagrams, each diagram that has minimum difference with drawn diagram is the place of PD. Finally, the proposed method is validated with a laboratory winding with six disks.