A quantative approach to estimate the life expectancy of motor insulation systems

Electric motors represent the largest single load in most power systems. With continuing increase in nonlinear loads, the effects of harmonic contents of power systems on various components is becoming more important. This paper is concerned with the effects of power system harmonics and voltage unbalance on the useful life of electric motors. A simple equivalent circuit is used to calculate the additional heat losses caused by supply distortions. A lumped-parameter thermal network is proposed to calculate the resulting heat distribution within the machine. An Arrhenius chart is then used to estimate motor insulation remaining life. The proposed approach is used to determine the effect of supply harmonics and voltage unbalance on the useful life of a three phase induction motor and the results are verified experimentally.