Key points are not available for this paper at this time.
This paper proposes a 0.1% limit for subharmonic voltages. It is shown that the additional temperature rise in the stator winding of a typical induction motors, caused by a 0.1% subharmonic, is about the same as the temperature rise caused by 1.0% voltage imbalance.
Abreu et al. (Thu,) studied this question.