Partial Discharge Testing Basics for Rotating Machines
To understand partial discharge testing, it’s best to first understand partial discharge. Partial discharge can be described as small electrical sparks that occur in stator windings whenever there are small air gaps or voids in or around the insulation. Once sparking occurs, the stator windings start to deteriorate. The larger the void in insulation, the larger the possible discharge resulting in possible machine failure.
Why does Partial Discharge Testing Matter?
Partial discharge testing is a leading indicator of machine failure. If left undetected, it can eventually lead to complete deterioration of the electrical insulation which is one of the principal causes for forced outages of generators and motors.
Using online monitoring to identify partial discharge can help avoid service failures, extend the time between rewinds and outages and plan maintenance based on machine condition.
How to Test for Partial Discharge?
There are two different methods for partial discharge testing. Off-line measurements occur where the machine is disconnected and the testing occurs from an external source. Online testing occurs when the rotating machine is kept running or energized. Continuous or online measurements are made under real operating conditions; however, noise can be a factor. To circumvent this problem, one would need to ensure that there is adequate distance, and higher filter frequencies are used.
Depending on the size of the asset, partial discharge can be detected using different sensors and monitors. Epoxy-Mica Capacitor (EMC) sensors are typically used on small to medium-sized assets and for larger assets Stator Slot Couplers (SSCs) are used for testing. Diagnostic software is usually added in conjunction with sensors and monitors to truly understand the condition of the insulation.
Qualitrol provides a variety of partial discharge testing equipment and software. For more information contact us.