IEC Standards for Variable Speed Drives and Motor Winding Insulation

Published Feb 28th, 2014 PCIC Middle East - G. Stone, B.Lloyd

Abstract – Modern inverter-fed motors often see short risetime, high magnitude voltage surges that may lead to partial discharge. Fast risetime transients from the drive, as well as possible voltage doubling caused by transmission line impedance mismatches, can result in partial discharges (PD) in the motor stator winding even in low voltage motors. Testing for such conditions is described in IEC TS 60034-18-41 [1] which indicates that the manufacturer must prove the motor will not have PD for the expected life of the motor and sets PD inception voltage limits, based on severity of the surge environment. Medium- and high-voltage motors may also suffer from this type of inverter – specifically the stress relief coatings may age prematurely. IEC 60034-18-42 [2] provides tests that motor manufacturers can perform to ensure that such premature failure will not occur. This paper describes these two standards and comments on their effectiveness.


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