Unusual PD pulse phase distributions in operating rotating machines

Abstract

The position of partial discharges (PD) with respect to power frequency phase position has long been known to provide useful information on the nature of deterioration of electrical insulation. In the past, virtually all such data has been from P D tests performed in the laboratory on static models or equipment. Improvements in the past 15 years in noise elimination technology have made it possible t o monitor the P D activity (number, magnitude and phase position) in the HV stator windings of operating motors and generators. Over a two year period, the PD activity was recorded on more than 100 motors, hydrogenerators and turbine generators, and the pulses analyzed with respect to the ac phase position, with a resolution of 3 . 6 ' . In the majority of stator windings, the P D pulses occurred in the expected portion of the ac phase, i.e. between 0 and 90' as well as between 180 and 270'. However a significant number of instances were recorded where the pulses appeared t o be shifted -30'. This is probably due t o the phase-

Partial discharge signal interpretation for generator diagnostics

“…Our experience is that bar-to-bar discharges between planes of top and bottom bars or in the same plane, give exactly the same signature of clusters at almost constant amplitudes. This confirms the results w x of Stone et al 28 . Sometimes, when more than one gap spacing exists, several clusters can be observed at different amplitude levels.…”

Standardization of on-line VHF PD measurements on turbo generators

“…The shape of the PD pattern clearly changes due to this particular kind of defect. Different kinds of defects have different kinds of PD pattern shapes [4].…”

Insulation diagnosis method for generator winding by measuring microwaves associated with dielectric breakdown

“…This phase angle of microwave emissions, too, is thought to be helpful to diagnosis [13,16]. In this study, however, the amplitude and occurrence frequency of microwave emissions are used because these values exhibit pronounced growth as the applied voltage is increased (that is, as breakdown is approached).…”