A partial discharge–based health index for rotating machine condition evaluation

It is well known that partial discharge (PD) is a threat to electrical insulation in all electrical apparatus, but we also know that PD harmfulness, and thus damage, depends on the type of defect generating the PD. As an example, having corona PD in switchgear boxes, rather than surface PD on bushings or internal PD on cable terminations, will trigger completely different actions from maintenance managers, even if the amplitude of the first (corona PD) is much larger than those of the last (internal PD). Indeed, corona PD may not need any medium- to short-term action, surface PD can just require some careful periodic checking, and internal PD in cable joints/terminations will have to be addressed promptly.