Recent important changes in IEEE motor and generator winding insulation diagnostic testing standards

IEEE standards and test procedures are widely used by motor and generator vendors and users to commission windings in new machines, as well as evaluate the condition of the winding insulation in operating machines. Until recent revisions, the basic procedures and standards in use were written over 25 years ago. Since the 1970s, motor windings have encountered many changes in their design and manufacture. The result was that the interpretation of results in many of the standards was no longer valid for the more modern motors. Over the past five years, the IEEE Power Engineering Society has conducted a major review and updating of most of these standards. Many important changes in test procedures and interpretation guidelines have resulted. This paper reviews the main insulation standards used for stator and rotor winding diagnostic testing, and discusses the changes that have been made. Standards discussed include: IEEE 43, 56, 95, 286, 522, and 1434. For example, IEEE 43-2000 now requires a minimum insulation resistance of 100 MΩ for new stator windings rated 2300 V or more, rather than the "kV+1" that was required in the past. Furthermore, the interpretation for polarization index has changed such that a motor with a polarization index of 1 is no longer automatically classed as bad.