access icon openaccess Identification of slot discharges in rotating machine insulation system using variable frequency PD measurement

This is an open access article published by the IET and CEPRI under the Creative Commons Attribution-NonCommercial-NoDerivs License (http://creativecommons.org/licenses/by-nc-nd/3.0/)
Received 29/11/2017, Accepted 13/05/2018, Revised 26/04/2018, Published 21/05/2018

Slot discharge studies are very important from the insulation diagnosis perspective. Further in practice, testing of rotating machines with power frequency requires sources which are quite bulky and costly. Instead if the diagnosis is carried out at lower frequencies (<50 Hz), the size and cost of the test source can be reduced significantly. Therefore, it is important to know whether the study at low frequencies can be considered equivalent to study at power frequency. Hence, in this study, a slot discharge phenomenon occurring in a rotating machine insulation system was investigated experimentally at different frequencies (50, 10, 1 and 0.1 Hz). Slot discharges are known to have a distinct phase resolved partial discharge pattern for power frequency (50/60 Hz) excitation. These distinct patterns are useful in identifying the presence of slot discharge activity in rotating machines. Slot discharges were created on a 6.6 kV mica-epoxy stator coil and the slot discharge characteristics measured at different frequencies are compared. Slot discharge measurements were repeated by varying the air gap between the insulation surface and grounded steel plate. The changes in slot discharge characteristics due to the increase in air gap were found similar at all frequencies. The comparison suggests that the identification of slot discharge is also possible from the partial discharge (PD) measurement at low frequencies.

Inspec keywords: electric machines; frequency measurement; high-frequency discharges; epoxy insulation; coils; partial discharge measurement; air gaps; stators

Other keywords: insulation surface; slot discharge phenomenon; insulation diagnosis perspective; air gap; power frequency; rotating machine insulation system; phase resolved partial discharge pattern; variable frequency PD measurement; slot discharge characteristics; mica-epoxy stator coil; slot discharge measurements; grounded steel plate; rotating machine testing; slot discharge activity identification

Subjects: d.c. machines; a.c. machines; Charge measurement; Frequency measurement; Inductors and transformers; Dielectric breakdown and discharges; Organic insulation

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