Gen set starting time

[Gyo]

I have a 1050kW 6600V 50Hz motor connected to a gen set for a centrifugal pump testing. The gen set supplier planned to use the frequency start to ramp up the motor to full speed, while varying the voltage accodingly to the speed of the generator. They suggested that the ramp up time would be within 30 secs.

Since the motor is designed for direct-on-line starting, and the allowable safe stall time is about 5 secs and the acceleration time is about 1 sec at 100%V, I am concern that the motor will overheat if allowed to ramp up from 0rpm to full speed.

The gen set consists of 2 generator, each with 1000kW, connected in parallel.
Motor power factor is 0.8
Motor efficiency is about 87%

What is your advice?

 

[Gyo]

Correction. The above should read "I am concern that the motor will overheat if allowed to ramp up from 0rpm to full speed in 30 secs"

 

[dpc]

Shouldn't be a problem if the V/Hz is kept within bounds. This is how motors on VFDs are started all the time. In fact the motor heating may be less starting this way than across the line.

If it isn't done this way, a much larger engine/generator may be needed.



David Castor

http://www.cvoes.com

 

[waross]

If you follow the Hz/V curve fairly closely, there should be less heating than a DOL start regardless of the starting time.
You may have better luck and an easier time coordinating if you start on one generator and sync in the second gen-set before full load is applied.
Depending on the test schedule you may even be able to use one generator. If the generators are prime rated you would only need the second set for full load tests lasting several hours and for testing at severe overload conditions.
In many applications a 1000 kW prime rated set will happily run a 1040 kW rated pump if speed and voltage ramp-up starting is applied.


Bill
--------------------
"Why not the best?"
Jimmy Carter