Effects of Temperature Gradient Induced Aging and Moisture Distribution on Dielectric Response Measurement for Transformer Insulation

Internal temperature distribution of an oil-immersed transformer is not uniform, resulting in an axial moisture gradient. Thus, the internal insulating paper ages unevenly with the synergetic impact of temperature and moisture. To examine the aging characteristics and moisture dispersion mechanism of insulating paper in a nonuniform system. A discretized aging kinetic model is proposed to analyze the nonuniform aging impact of insulating paper. Then, dielectric response spectroscopy (DRS), including frequency-domain spectroscopy (FDS) and polarization and depolarization current (PDC), is measured to illustrate the effect of nonuniform effect on the DRS test. Findings indicate that: 1) temperature gradient is a more important factor in nonuniform aging of paper than moisture distribution; 2) both the amplitude of FDS and PDC decrease as the moisture distribution becomes more uniform; and 3) the conductance of insulating paper with diverse nonuniform moisture content and aging degrees can be interpreted by the proposed mathematical model, in which the identified parameters are positively correlated with the deterioration degree of internal insulation materials.