Partial discharge testing on air-cooled generators in marine environments

Partial discharge activity has long been known to be an indicator of the presence of some deterioration mechanisms at work within, or on, the solid insulation of the stator windings of high voltage rotating machines. Partial discharges (sometimes also known as corona) are known to occur in deteriorated stator winding insulation systems, as well as new systems with manufacturing or installation flaws or shortcomings. Advances in on-line detection and measurement of partial discharges has resulted in monitoring equipment that provides a knowledgeable user with reliable and repeatable information regarding the behavior of an insulation system while a machine is in operation. Power plant generators on marine vessels present a unique challenge in monitoring due to the presence of system harmonics from the POD motors. Though off-line PD has often been used for marine vessels, it fails to detect problems related to mechanical, thermal, ambient and even normal electrical stresses. This paper will highlight some of the benefits of on-line PD testing using these results with case studies and signal analysis from marine vessel applications.