Abstract
During operation of high voltage (HV) motors, different types of discharges, e.g. surface discharge, corona discharge and bar-to-bar discharge can occur at the same time, increasing the difficulty of partial discharge (PD) sources determination and PDs pattern identification. In this study, the end-winding of a 10 kV motor coil was artificially aged and the related PD was measured. The initiation and variation of different PDs under multi-factor stresses were studied. The localised fingerprints coexisting with multiple PDs were identified and analysed. The results confirm that the end-winding discharge process was significantly influenced by the experiment relative humidity (RH) and temperature. The bar-to-bar discharge was easily recognised at a lower voltage since the identification of bar-to-bar discharge pattern would be affected by the corona discharge pattern at a higher voltage. It is shown that it is more difficult for the corona discharge to be detected when RH exceeded 80%, while the surface discharge dominated at the higher RH. In addition, the PDs were more easily identified with the rise of the temperature. This study can provide a reference in PD identification test and be useful for the PD online monitoring of HV motors.
Highlights
High voltage (HV) motors are considered as one of the most important electrical equipment, and their failures can lead to serious economic and environmental consequences
The internal discharge is always unavoidable in high voltage (HV) motors and there is no damage to the insulation under operating conditions
The PRPD pattern of bar-to-bar discharge is characterised by symmetry with almost constant amplitude in both voltage half cycles, it is a typical gap discharge with much larger air gap spacing than for internal discharge occurring in minute voids into the insulation [17]
Summary
High voltage (HV) motors are considered as one of the most important electrical equipment, and their failures can lead to serious economic and environmental consequences. There are three most common types of end-winding discharges: surface discharge, bar-to-bar discharge and corona discharge. These discharges can be electrical natural, even though the initial cause may be not. The end-winding vibration, which is a typical mechanical problem, can lead to rubbing against coils and inadequate end-winding spacing, causing bar-to-bar discharge if the full phase-to-phase voltage is across adjacent windings [3]. This mechanism is easy to be spotted in a visual inspection of the end-winding. The end-winding discharges have not received enough attention and could eventually result in the ground and/or phase-to-phase fault
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