Check cooling water flow
I agree with Junglejetjock, With a higher voltage present you will be drawing more amps. Should be pretty easy to check with a volt meter. Most multi-meters also have a 10 amp ammeter so you could check it that way. It could be that the breaker is just operating at it's limit and the extra little bit of voltage is pushing it over. Not really an AC problem. Some breakers actually trip at a lower than advertised current. Try swaping out with another breaker of the same rating.