Space charge distribution measurements in insulating materials of commercially available enameled wire

A generation of PD (partial discharge) in motor windings is a significant problem to develop a high voltage driving system, which is expected to improve the motor efficiency. A space charge accumulation in an insulating material of motor windings has been pointed out as one of reasons, for the PD generation because the space charge accumulation sometimes enhances the electric field in an insulating material. Therefore, measurement of the space charge in the insulating layer of motor windings is required. Space charge accumulation characteristics in film shape sample are usually measured using the PEA (pulsed electro-acoustic) method. However, since a manufacturing process of actual windings wire is different from that for film shape sample, the characteristics are assumed to be different from actual one. It means that it is difficult to evaluate the influences of the space charge on the insulating layer of the actual wire from the measurement result of the film shape sample. Therefore, in this research, we tried to measure the space charge distribution in the insulating material of actual enameled wires using an improved PEA measurement system. As a result, it is found that there are different types of space charge accumulation characteristics, even between nominally same insulating materials.