Frequency Domain Spectroscopy for Non-Uniformly Distributed Moisture Detection in Transformer Bushings

Frequency domain spectroscopy (FDS) has been widely used to evaluate the moisture fault of oil-impregnated paper (OIP) bushings. However, there is no reliable method for the location detection of moisture faults in bushings, which frequently initiate its insulation failure. In this study, we developed a distributed FDS measurement method for OIP bushings with two taps. Three times FDS will be measured to acquire the FDS parameters from 0.001 Hz to 10 kHz between the rod (a) and end foil (c), rod and second end foil (b), and second end foil and end foil at room temperature over time. The results show that the $C_{1mHz} /C_{10kHz}$ ratio of $C_{ab}$ is more sensitive for detection of the inner damp layer. The rate of $C_{1mHz} /C_{10kHz}$ of $C_{bc}$ is more sensitive to the outer layer damp bushings. The layer ratios of complex capacitance ( $V_{12}/V_{1}$ and $V_{2}/V_{1}$ ) are key features for the detection of non-uniformly distributed moisture for a capacitance bushing.