Study of PD behaviors on a crossed sample of magnet-wire with repetitive bipolar impulses for inverter-fed motor coil insulation

PD behavior with repetitive bipolar impulse has been investigated on "crossed sample" of magnet wires in comparison with a conventional twisted-pair sample. The crossed sample is suitable for optical PD observation, surface potential distribution measurement and SEM observation during or after PD test without loosening wires. Fluctuations of PDIV and PD charge were reconfirmed on it as reported on twisted-pair. The averaged values of PDIV and PD charge in each condition are consistent considering the size effect, since the crossed sample has contact length of c.a. one hundreds of that of twisted-pair sample. Surface potential distribution near the crossing point showed the direct evidence of charge-assisted discharge model. SEM observation suggests that surface erosion was not found after the saturation of PDIV, which suggests the trend of fluctuation may be due to surface properties change.