Power factor measurements on high voltage stator bars and stator windings

Power Factor (PF) measurements have been made for years on high voltage stator coils as a means to determine how well the coil consolidation is and to obtain a measure of the quality of the insulation system on newly manufactured stator coils. power factor measurements are also made on stators that have been in service and on coils after being subject to voltage endurance and thermal cycling tests. The subject is revisited in this paper, providing a tutorial on the basic theory associated with this important test method. In addition, a presentation of the most commonly used measuring techniques and typical equipment setup used to make power factor measurements are given. IEEE 286-2000, "IEEE Recommended Practice for Measurement of Power Factor Tip-Up of Electric Machine Stator Coil Insulation"; has been revised and it serves as the reference document for this paper. The coil manufacturing industry has a lot of experience performing this test and had a major part in updating the current standard. Although measured values are a function of the coil insulation system, some typical values are mentioned.