I hope to install an induction motor as a generator driven by a water turbine. The available torque will vary greatly (10 to 50KW) due to seasonal river levels.
I am therefore considering installing a 55KW motor to ensure that it is never driven past its nominal working torque/current to avoid overheating.
The graph in the excellent "Lessons in Electric Circuits" shows the current and torque to be more or less linear up to 100%, does this mean that running at half power or less will be more efficient with the added bonus of a lower pf?

If this is the case should I consider a larger motor/ generator?

 

Running at less than half power, will NOT increase efficiency nor will it improve power factor. No generator runs 'better' at a lower than designed output, except perhaps for the self heating of the generator itself would be smaller.

The variations in load will send the output voltage all over the place. Extremely large swings in load will put the generator out of regulation at the high and low ends of demand.

You need to research a little more on this idea; induction motor electricity generation may not be the best method for this large variation of load conditions.(Remember an induction generator CANNOT start an induction motor, unless it is VERY SMALL)

 

Kermit2

Thanks for your reply, I should have mentioned that the generator will be grid connected/excited, therefore will voltage variation be a problem?

It was my understanding that the power factor deteriorated due to the slip, a larger motor/generator would have less slip under the same load?