With the continuous growth of economic demand, the power industry has gradually developed into a large-capacity, ultra-high voltage level, and the requirements for safe and stable operation of the power system and power quality have also been continuously improved. In the huge power transmission and distribution system, the oil-immersed power transformer is an extremely important and expensive electrical equipment.

According to statistics, in large-scale power outages caused by power equipment failures, faults caused by the aging of the insulation of power transformers account for the main proportion. The oil-paper insulation structure is the main component of the internal insulation of a large oil-immersed transformer. Directly and effectively diagnosing the oil-paper insulation status of the transformer is of great significance to the safe and reliable operation of the power system.

At present, a large number of related researches have been conducted on the diagnosis technology of transformer oil-paper insulation state, which can be summarized as the traditional characteristic quantity diagnosis method and the medium response characteristic quantity diagnosis method.

The parameters used to diagnose the insulation status of oil-immersed transformers in traditional eigenvalue diagnosis methods mainly include: chemical parameters represented by dissolved gas in oil, furfural content and polymerization degree of cellulose insulating paper; electrical parameters represented by insulation resistance, polarization index , Dielectric loss factor, partial discharge characteristics, etc.

Diagnosis methods of characteristic value of dielectric response mainly include: return voltage method (RVM), polarization depolarization current method (PDC) and frequency domain spectroscopy (FDS). It is a non-destructive and easy-to-operate electrical diagnosis method for insulation systems. Compared with traditional diagnosis methods, it is more suitable for on-site testing, diagnosis and evaluation of the oil-paper insulation status of power transformers, and has a good engineering application prospect.

Generally speaking, the dielectric response characteristic value diagnosis method has the advantages of non-destructive, simple operation, anti-interference, etc., and is more suitable for on-site diagnosis of transformer insulation than traditional methods.