Experience with DC polarization-depolarization measurements on stator winding insulation

DC insulation resistance (IR) and polarization index (PI) testing is very widely used to assess the condition of the rotor and stator windings in motors and generators. The IR/PI tests are good at identifying contaminated windings; however, such issues as thermal deterioration or abrasion of the insulation due to coil vibration, are not detected by the IR/PI test in modern insulation. The polarization/depolarization current (PDC) test, where the charging current is measured for several minutes and then the test object is grounded and the discharging current is measured for several minutes, may provide more diagnostic information. This paper presents PDC data from a stator as well as individual stator coils and bars and compares it to results from other off-line tests including the low- and high-frequency PD, dissipation factor tip-up, and DC ramp tests. It seems that partial discharge tests are more sensitive to some insulation problems than PDC, however, more results are needed.

[1]  G.C. Stone,et al.  Objective methods to interpret partial-discharge data on rotating-machine stator windings , 2006, IEEE Transactions on Industry Applications.

[2]  H. Borsi,et al.  Dielectric response studies on insulating system of high voltage rotating machines , 2006, IEEE Transactions on Dielectrics and Electrical Insulation.

[3]  J. Stein,et al.  High voltage DC ramp testing as a diagnostic of stator insulation condition , 2004, Conference Record of the 2004 IEEE International Symposium on Electrical Insulation.

[4]  G. C. Stone,et al.  Relevance of phase resolved PD analysis to insulation diagnosis in industrial equipment , 2010, 2010 10th IEEE International Conference on Solid Dielectrics.

[5]  S. A. Bhumiwat.  Field experience in insulation diagnosis of industrial high voltage motors using dielectric response technique , 2009, 2009 IEEE Electrical Insulation Conference.

[6]  G. C. Stone,et al.  Stator winding hipot (high potential) testing , 2009, 2009 IEEE Electrical Insulation Conference.

[7]  E. David,et al.  Condition assessment of rotating machine winding insulation by analysis of charging and discharging currents , 2006, Conference Record of the 2006 IEEE International Symposium on Electrical Insulation.

[8]  G. Stone,et al.  Electrical Insulation for Rotating Machines , 2003 .