Dielectric test methods for rotating machine stator insulation inspection

Dielectric testing is generally carried out during quality assurance or within an overall preventative maintenance program and aids the user to determine the actual condition of the rotating machine insulation or components thereof and to help prevent losses due to unforeseen/undetected faults in the insulation. In part these tests are used to verify the efficiency of corrective measures as cleaning and drying procedures as well as repair measures. A set of test methods and their underlying physical concepts are presented, while describing their specific areas of application, strengths and disadvantages. In part these methods rely on a 30 years experience in field testing. In part these methods are fairly new: Out of service testing (off-line) (i) dielectric step response of stator windings (isothermal polarization and depolarization currents) and evaluation procedure (ii) loss factor and capacitance testing at high voltages (non-linearity and field effects), a novel digital test system without a bridge is presented (iii) Partial discharge pattern recording, digital test system and defect specific patterns. The presence of partial discharges is one of the most prominent indicators of manufacturing defects and the ongoing degradation process of an electrical insulation system. (iv) HLQ: harmonic loss quantity, a parameter which is associated to the non-linear losses created by ion movement as a result of partial discharges and corrosive processes. In service testing (on-line) (v) partial discharge testing (different procedures)