PD acceptance tests for GVPI insulation of rotating machines

Partial Discharge (PD) detection and analysis is playing an increasingly important role in the validation and quality control of insulation systems for ac stator windings, [1]. The availability of advanced PD instruments provided by separation and defect identification facilities, has opened interesting perspectives in insulation system characterization, [2, 3]. However, constrains based on existing standards do not allow to fully exploit the capabilities given by modern PD instruments. In fact, pass/fail criteria based on amplitude threshold levels are still attractive for the ease of interpretation but incorrect decisions may be taken because different defect typologies can be active as well as PD amplitude can change during time due to discharge conditioning or defect evolution, and lower level PD not necessarily indicate good quality insulation. Moreover, it is well known that PD measurement systems (instruments and couplers) provide non-comparable results, [4]. Thus, it is almost impossible to establish threshold levels of general validity on this basis.