Faults identification of biodegradable oil-filled transformers based on polarization and depolarization current measurement (PDC) method

Polarization and depolarization current (PDC) measurements of insulation oil alone can be used for faults identification. From measurement of healthy oil conditions at different moisture levels and after faults, fault identification can be achieved by comparing the PDC pattern of an oil sample against the PDC fingerprints. Furthermore, a graph plot establishes a relationship between oil sample conductivity and moisture level as well as between oil sample´s measured capacitance and moisture level. These curves can be used to evaluate the oil moisture conditions and the fault type. This paper seeks to find the PDC pattern of the biodegradable oil (Envirotemp ® FR3™) at different moisture levels and after being subjected to different types of fault: partial discharge, arcing, and overheating. The experiment was carried out in the laboratory to obtain the PDC patterns generated by the oil. Changes in the PDC pattern of biodegradable oil from its fingerprint due to the increased moisture level in the oil or because of faults that occurred to the oil sample were identified. These can help in predicting the biodegradable oil-filled transformer´s condition and can give some indication of the maintenance work that should be taken on the transformer.