On the Thermal Insulation Qualification of Low Voltage Electrical Machines

Electrical motors are required to perform reliably for a certain number of hours/cycles. Assuming the insulation breakdown as the predominant source of failure, then the lifetime of an electrical machine can generally be said to correspond to that of its weakest insulation sub-system. Among all the insulation stressing factors, thermal aging is a primary source of progressive deterioration, and, eventually, failure. In order to guarantee a satisfactory lifetime, motors are designed to have thermal operational points which are always lower than their insulation thermal class. However, this design choice does not allow to maximize the exploitation of the insulation lifetime capability. Technical standards report methods for the thermal qualification of electrical machines based on accelerated thermal aging tests. Such assessment, despite enabling the insulation lifetime estimation, might require several thousand hours of testing. This paper, therefore, proposes and validates a new methodology which considerably shortens the thermal qualification of electric motors.