Research on the Wetting Mechanism of Oil-Paper Insulated Bushings and the Application of FDS Method

Bushing fault is one of the prime reasons causing transformer faults, among which the failure rates caused by humidified insulation is in the first place. Based on the experimental results of damp bushing models, Frequency Domain Spectroscopy (FDS) test and disassemble test were implemented on three 500kV bushings from two substations that failed to dissolved gas analysis (DGA) test. Multidimensional analysis of these fault bushings was carried out based on the results of FDS test, dielectric loss test and partial discharge test under high voltage, moisture content of the insulation paper, and a comparison with the FDS test of a new 500kV bushing. Results show that the technology of FDS has obvious advantage in diagnosing of the moistened bushing, and it shows high sensitivity at low frequency. It can be regarded as the criterion for moistened bushing whether the tangent value of the medium loss angle of 1mHz~10mHz frequency band of the FDS test exceeds 10%.