Effects of Environmental Factors on Partial Discharge Activity and Estimation of Insulation Lifetime in Electrical Machines

Partial discharges (PD) are produced in the stator insulation of electrical machines while energized. The sources of PD are internal voids, crack, and manufacturing defects, which keep on extending with its normal operation, leading to the complete failure of insulation. The intensity of PD is considerably influenced by the environmental factors, including surrounding temperature, pressure, humidity, and contamination. This paper investigates the influence of these factors on the PD activity in electrical machines and estimates the lifetime of insulation. The PD measurements were conducted by placing the motors in a climate-controlled chamber. The PD trend under varying environmental stresses was investigated over time. Accordingly, PD inception voltage and various discharge characteristic parameters such as accumulated apparent charge, cumulative energy function, average discharge current, discharge power, and quadratic rate have been determined. The combined effect of various environmental stresses on the PD activity was also investigated. The mathematical relationships were developed to estimate the discharge characteristics as the functions of pressure and temperature using the Gaussian model and the Exponential model. Finally, the endurance of insulation was estimated under different environmental conditions based on the average discharge current to differentiate between correct and incorrect PD measurements and to develop a right maintenance schedule for motors in service.