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Insulation Condition Assessment for Converter Transformer based on Frequency Domain Spectrum

During the operation of converter transformer, due to the long-term effect of temperature, electric field, mechanical and other stresses, the insulation state of converter transformer is degraded, which leads to faults and accidents. Therefore, the insulation condition assessment for the converter transformer is of great significance for the safety and stability of power system. However, the existing methods to assess the insulation condition of converter transformer are limited to some shortcomings, such as difficult sampling, vulnerable to interference and so on. To overcome these obstacles, an evaluation method based on frequency domain spectrum is proposed to assess the insulation condition of converter transformer. We apply this method on converter transformers to detect their dielectric loss frequency under three conditions of different moisture content, different temperature and different aging time. Then, we analyzed the dielectric loss frequency curve in the frequency band of 0. 001~1000Hz. The analysing results show that when the moisture content, temperature, aging time conditions change, the low-frequency part of the dielectric loss frequency curve detected by our method can sensitively reflect the different moisture content of the insulating paperboard of converter transformer, which can be used to assess the insulation condition of converter transformer. We test this evaluation method on 20 converter transformers in two substations to verify its effectiveness. The results show that compared with the traditional method based on power frequency dielectric loss, the domain frequency spectrum method can reflect the insulation condition of bushing more sensitively and comprehensively, and is of great value in engineering applications.