Pump power factor OK on mains, but low on generator
Ah, love it when the customer only gives you half the information.... Site visit yesterday, 2Hr drive to get there, problem fixed in 1/2Hr.


My motor protection unit was tripping on Low Power Factor... 
Because the power factor was 0.0... 
Because the Soft Starter wasn't starting... 
Because the voltage was too high (above 110%).


The Soft Starter trip was indicated on my Motor Protection unit (via digital input), but the customer had never mentioned that before.

Nominal voltage was 415V; the generator was running at 438V, my meter caught a peak of 493V when the pump was started. Interestingly, when the pumps started on mains power, the voltage dropped down to 405V during the startup; when starting on generator, the voltage went up. There is a mains transformer behind the building, I think it is feeding just this plant.

Fortunately, the customer had a colleague who knew the generator, and we were able to open it up and adjust a tiny pot on the alternator regulator board and bring the voltage down. Took two adjustments, but we have the station running fine on generator now.

Thanks for everyone's suggestions though!