Effect of Inverter Drives on
Rotating Machine Electrical Insulation


Tuesday, June 15, 2021 – 1:00PM – 5:00PM (1300-1700) Eastern Time


Greg Stone

Dr. Greg Stone
Iris Power-Qualitrol

Dr. Greg Stone is employed at Iris Power-Qualitrol in Toronto Canada, a rotating machine condition monitoring company he helped to form. From 1975 to 1990 he was a Dielectrics Engineer with Ontario Hydro’s Research Division.  His current research interest is the effect of inverter voltage surges on electrical insulation.  He is a past-President of the IEEE Dielectrics and Electrical Insulation Society, and continues to be active on many IEEE and IEC standards working groups.  He has published three books and many papers concerned with rotating machine insulation.  Greg Stone has a PhD in Electrical Engineering from the University of Waterloo (Canada), is a Fellow of the IEEE, a Fellow of the Engineering Institute of Canada and a registered Professional Engineer in Ontario, Canada.


Thousands of short risetime voltage pulses per second are created by invertors of the pulse width modulated (PWM) voltage source type.  These voltage pulses may adversely affect the stator winding insulation in variable speed motors and the rotor insulation in DFIG wind turbines and hydrogenerators.  In random wound machines rated less than 690 V, partial discharge (PD) can occur that lead to insulation failure.  In form wound machines, the inverter voltage pulses cause dielectric heating, higher PD and more rapid aging of the stress control coatings.  This seminar reviews the characteristics of the voltage pulses from drives and the insulation failure processes.  Avoiding insulation failure using the test methods described in IEC 60034-18-41 and 42 are also discussed.


  • Reasons to use inverters
  • Types of drives
  • How inverters cause PD in random wound windings
  • Avoiding failure due to inverters in random wound windings
  • Qualifying random wound insulation systems (IEC 60034-18-41)
  • Failure mechanisms in form wound windings accelerated by inverters
  • Qualifying form wound insulation systems (IEC 60034-18-42)
  • PD measurement during short risetime voltage impulses from inverters


Registration now open!