Effects of Temperature and Pressure on Failure Risk of Electric Motors Based on Partial Discharge Measurements

Typically, partial discharge (PD) diagnostic tests are carried out in laboratories under standard atmospheric conditions. However, during the operation of electric motors (EMs), environmental stresses may increase due to variations in the atmospheric pressure and temperature. This is, for example, the case of electric aircraft and, in general, other aerospace applications. Experimental results show that these stresses may affect the level and phenomenology of PD, thereby compromising the reliability of insulation system. Therefore, neglecting the actual environmental stresses involved in PD testing or monitoring may result in an incorrect interpretation of the health condition of the EMs. This study presents a framework to properly assess the impact of environmental stresses on PD activity and estimate the failure risk of EM insulation. For this purpose, PD diagnostics were carried out by performing a number of experiments on seven EMs in a climate-controlled chamber. PD characteristic features at different levels of environmental stresses are extracted from measurements in order to investigate the PD severity and infer their effect on the resulting insulation degradation. Also, various probability distribution functions are used to estimate the probability of failure and risk assessment corresponding to the PD severity at different levels of environmental stresses. The proposed risk assessment technique can be helpful to plan regular maintenance activities and repair-replacement actions, keeping the reliability at the level requested for most industrial applications involving variable temperature and pressure operations.