Partial discharge analysis on rotating machines
Partial discharge (PD) occurs in the stator insulation system of rotating machines, where local electric field stress exceeds the local electrical strength. Compared with other dielectric tests, the differentiating character of partial discharge measurements allows localized weak points of the insulation to be identified.
PD measurements based on IEC 60034-27 standards can be performed on motors and generators either on-line during regular load service operation or off-line by energizing each winding successively during standstill of the machine.
Generally, several different partial discharge sources are present and active within the stator winding insulation at the same time. The key to successful PD measuring in stator windings is the separation of parallel active PD sources and the distinction between harmful PD, normal PD occurrences and outer noise, inevitably present in industrial surroundings.
This is best achieved by synchronous, multi-channel partial discharge measurement. This separates internal PD sources from each other and from noise signals. PD sources are evaluated individually within the stator winding.