Coherent Electro-Thermal Qualification of the Insulation System for Electrical Machines

Qualification of inverter-fed electrical machines through the procedure suggested in the IEC std. 60034-18-41 entails the application of thermal, mechanical, and ambient stresses, followed by measuring partial discharges (PD-proof test). For practical reasons, stress factors are applied sequentially, and measurements are conducted on the machine at room temperature. This procedure is simple but has two major limitations. The first is that testing will not activate synergies between stresses. The other one is that partial discharge inception voltage measurements under impulsive voltages sometimes provide overly optimistic results. This paper suggests an alternative procedure to conduct the qualification of inverter-fed machine insulation. The proposed procedure combines electrical and thermal stress, thus accounting for their synergies. As the applied electrical stress is like that experienced in service, partial discharges can be initiated during aging. This might lead to failure without the need for testing partial discharge.