Lifetime monitoring and estimation strategy for large power transformer

Large power transformers play a vital role in power system. With the operation time going, there are more and more old transformers in China, which are still in service. However, based on the present time-based preventive test code for electric power equipment, it is difficult to conduct the decision-making. It is imperative to develop and carry out the condition monitoring and diagnosis (CMD) technologies. There are several parameters to characterize the aging condition, i.e., tensile strength (TS), degree of polymerization (DP), CO/CO₂ contents, furfural concentration, water content, etc. Based on the dielectric response theory, some promising methods are analyzed, such as the recovery voltage method (RVM), polarization and depolarization current (PDC), and frequency domain spectroscopy (FDS) of oil-immersed insulation. It seems possible to achieve the water content in solid insulation by dielectric response measurement. However, the aging of transformer insulation is a complicated kinetics process of chemical reaction, and it is definitely urgent to combine all the effective methods together and synthetically analyze the data and parameters for achieving a comprehensive conclusion.