Working towards a recommended practice for PD Measurements on individual stator coils and bars

IEEE 1434 Guide for the Measurement of Partial Discharges in AC Electric Machinery outlines available detection methods for on-line testing and off-line testing of windings as well as quality control testing of individual stator coils and bars. Following the 2014 revision of the document interest was expressed in developing a recommended practice for PD measurements on individual coils and bars which might eventually evolve into a standard. A working group on this subject began to meet in 2015. Several organizations have reported measurements. Some users wish to be able to calibrate in terms of apparent charge which implies measurement at ≤1 MHz. Others prefer measurement at higher frequency in an attempt to obtain optimal response to internal voids that is not overshadowed by discharges associated with the external coatings. It has been observed that time-frequency map clusters may provide an opportunity to separate internal void PD from surface discharges.