jlh'— Good overview. All I can add is a copy of a motor horsepower derating curve from ANSI Standard C84.1 §D that reflects your numbers of reduction versus voltage imbalance. 1% imbalance requires no significant derating. 3% yields a derating of 11%. 5% imbalance needs a derating to 25%, or stator-insulation life will be significantly shortened.
D chart
