Localization of partial discharge in a winding of dry-type transformers

Cast-resin windings of dry-type transformers in which partial discharge (PD) is detected cannot be repaired due to their solid insulation structure. To minimize production costs, the root cause of PD should be identified when the problem is detected. Therefore, it is important to understand exactly where PD occurs in the windings. Eleven different materials used in dry-type transformer windings were produced in samples like a real coil structure, and the PD behavior of these materials was analyzed and classified in the first section of the thesis. PD is investigated theoretically, and measurement methods are explained in the second section of the thesis. The electrical measurement method defined in IEC 60270 was analyzed, and a commercial PD measurement system is examined and modeled with each piece of equipment to use in simulation studies. To adapt a dry-type transformer model constructed using a ladder network structure for the PD analysis, the effect of newly proposed capacitive parameters on the model is verified by experimental studies in the third section of the thesis. Thus, a new model is developed for high-frequency PD studies. In the last section of the thesis, a simple approach has been proposed for the determination of PD location, with the studies carried out on a specially produced 2500 kVA dry-type transformer having different structures of high voltage windings. This approach is verified by simulation and experimental studies with a mathematically modeled winding and by experimental studies with a specially designed winding.