Ozone concentration impact on the lifespan of enameled wires (conventional and corona-resistant) for low voltage rotating machines fed by inverters

Since the introduction of the power electronic power supplies, the electrical insulation of low voltage motors faces new hazards. Especially the primary insulation of the magnet wire is endangered due to the use of frequency inverters. As an effect, partial discharges may appear causing degradation of the electrical insulation to lead finally to a premature breakdown of the machine. This study shows the impact of ozone, generated during partial discharge activity, on the lifespan of samples used to model the winding of the machine. Different types of magnet wires, composed of different enamel polymer, both conventional and corona-resistant, were tested in this paper. The results state that the mean time to failure is up to 25% shorter if the ozone is not evacuated from the test chamber and samples are exposed to its degrading properties. This is the case for close machines, in which the air embedded between the stator and the rotor and within the slot is not ventilated, thus allowing ozone to accumulate to significant concentrations.