Cast-resin transformers: development of health assessment technique based on electromagnetic partial discharge detection

Partial discharges (PD) are the most obvious signal to investigate the deterioration level of cast-resin transformers. As a cast-resin transformer is one of the main components of a power system, early PD detection is extremely important to ensure power system operation reliability. This experiment detected PD through a new electromagnetic sensor PD measurement module. Three cast-resin transformers of varying ratings, 50 kVA, 75 kVA, and 100 kVA, were employed to investigate transformer deterioration from high-voltage impulses. Each transformer received impulses with a range of 80–275 kV to accelerate insulation degradation. From the measurement results, it was found that two major factors are significantly related to the degradation level of cast-resin transformers. With these results, the study proposes a risk assessment algorithm for judging the residual life of cast-resin transformers based on two major factors; each a summation of the total PD magnitude during four cycles and discharge intervals. As the developed algorithm directly provides users with the current degradation state of the cast-resin and convenient PD measurement, it is expected to become a powerful diagnosis and inspection tool for the insulation health of cast-resin transformers.