Study on the methodology of detection for transformer winding insulation defects based on applied voltage test

Power transformer applied voltage test is one of the most effective and direct way to identify power transformer insulation strength and it is also an important part of preventive test. The methodology of diagnosing the transformer winding insulation defect using the transient voltage and current in voltage regulation process is put forward in this paper. In this methodology, the transient voltage and current during voltage increasing process in the applied voltage test are regarded as information sources. Whether insulation defect including serious degree of test equipment exists and whether insulation damage of equipment passing the applied voltage test exists can be diagnosed based on the minimum of discriminant functions related to the voltage and current. The detecting methodology proposed in this paper can take advantage of the information provided by the existing test, and contribute to the expansion and innovation of the existing detecting and diagnosing methodology based on applied voltage test.