Start with IEC 60034-1 "Rating and Performance".
Then 60034-2 "Standard methods for determining losses and efficiency from tests".
Then on down the 60034 chain, using the applicable standards to obtain what you're really looking for (some are performance related, some are in-process and/or quality control type tests) and others are more application-oriented. The last standard in the series would be 60034-31.
Note that not all sections will apply to all motor (or generator) types. They may also point you to several other IEC standards along the way - which you'd have to review as well.
Converting energy to motion for more than half a century