Partial discharge theory and technologies related to traditional testing methods of large rotating apparatus

Partial discharge monitoring is an effective online predictive maintenance test for motors and generators at 4160 volt and above, as well as other electrical distribution equipment. The benefits of online testing allow for equipment analysis and diagnostics during normal production. Corrective actions can be planned and implemented, resulting in reduced unscheduled downtime. An understanding of the theory related to partial discharge, and the relationship to early detection of insulation deterioration is required to properly evaluate this predictive maintenance tool. This paper presents a theory to promote the understanding of partial discharge technology, as well as various implementation and measurement techniques that have evolved in the industry. Data interpretation, corrective actions and application to electrical distribution equipment are also reviewed.