Motor Starting

[bob14]

Hi,

 

I will continue a thread which I started relative to the starting of a fan. The genset , capacity 635 kVA is having trouble to meet the starting demand of the fan, capacity 90 kW. From a theoretical point of view, the Genset should have been able to start a fan of this size but for some reasons is unable to do so.

I am thinking of the possibilty to reduce the voltage on the Genset so that the Genset acts as a reduced primary starter. I know that by doing so, the motor will be underfluxed but this will reduce the locked rotor current and the Genset might be able to pick up the load. The actual primary starter is of very little use.

Any comment.

 

Bob

[marke]

Hello Bob

 

The primary resistance starter is not a good starter to use when starting on a genset due to the very high KW losses in the primary resistors.

Reducing the voltage will reduce the locked rotor current, but so will reducing the speed.

Dropping the speed down very low and then DOL, or even connecting the motor and then starting the genset could make a difference.

It all depends on what other things are connected to the genset.

 

Another thing to consider, is to look at the potential of adding a permanent magnet generator excitation system. This will provide a much higher overload current capacity for a short period of time.

The combination of PMG excitation and a three phase averaging AVR system will alow a much larger motor to be connected and started by a given genset.

 

Best regards,

Mark

[bob14]

Thanks Mark for your very fruitful advice.

 

Bob

 

 

[jraef]

Just to reiterate something from the older thread, is this a paddle fan or a cage fan? If it's a cage type, you do have the dampers closed at start correct?