Do these pumps sag the voltage on start, or also during run ? Around here, we have to inform the POCO if we connect anything larger than a 100 HP motor and it can not be started across the line. You said you are using drives, so I assume you are ramping up the start ?
Most POCO's that I have dealt with say 5 to 10 % is an acceptable voltage tolerance.
Master Electrician -Electrical Contractor
"The Code doesn't say what you think it says" - Charles E. Beck, P.E.