An On-line Insulation Diagnosis Method for Transformer Bushing Based on Frequency Domain Spectroscopy under Transient Voltage Excitation

Oil-paper insulation bushing is one of the key components of power transformers, which has been subjected to high voltage, high current and strong mechanical load as well as the external complex environment for a long time during operation. So the insulation reliability of transformer bushings faces severe challenges and timely, effective evaluation of the insulation status of transformer bushing is of great significance. Frequency domain dielectric spectroscopy (FDS) is widely used in non-destructive evaluation of bushing insulation, which has the advantages of strong anti-interference ability and abundant insulation information. But the transformers need to be cut off from power system in traditional FDS test. In this paper, the simulation model of a 330kV substation was established to simulate the transient voltage generated at the bushing when noload lines, no-load transformers, capacitors and reactors were put in. The frequency components and amplitude characteristics of the transient voltage can meet the requirements of dielectric response test. Standard operation pulse with an amplitude of 50kV was applied to transformer bushings with different moisture content based on the extended Debye model, and the calculated FDS of the two bushings under transient voltage excitation is compared. Results show that the FDS under transient voltage excitation is expected to achieve online diagnosis of transformer bushing insulation.