Condition Monitoring Test Techniques for Medium Voltage OIP Bushings

A bushing is one of the most important parts of a transformer. Failure of the bushing may cause the transformer destruction, which can lead to the failure of the electrical power system. Therefore the insulation monitoring of the bushings is essential.This paper investigates the approximate 30 years in serviced medium voltage bushings. The 5 units of aged and deteriorated bushings were removed from the electrical power system, and the electrical testing was performed. The electrical testing included the insulation power factor (IPF) testing and the polarization and depolarization current measurement (PDC).The test results showed that the IPF of the main insulation was increased approximately 1-10 times from the nameplate values and the initial currents of PDC measurement were high for all bushings compared with initial currents of PDC measurement of the good bushing insulation condition from the database. From the test results, the combined test techniques between the power factor testing and the PDC measurement provided useful data for the insulation condition diagnosis of the service bushings.