How much power do I need 1

[mikhe]

How much power do I need to start a 600 kW motor DOL. Is there a calcuation I can use to quickly determine this. Our electrical engineers will do actual calcs for the final design, but what I would like to do is a quick calc to understand, plus or minus 10%, what a generator would see as the starting load.

 

[jbartos]

Suggestion: The calculation should include the voltage drop to the motor terminal such that it does not drop below, e.g. 80% of the motor terminal voltage. Check the motor requirement for the minimum transient motor starting terminal voltage. If that voltage is below that limit, it will probably not start.
The calculation parameters used are:
1. Motor Locked-Rotor Amperes (LRA), e.g. 6xFLA (full load current)
2. Motor Starting Power Factor, e.g. 0.2
3. Motor Efficiency

Motor nameplate data or motor specification sheet data are supposed to be used.
NEC recommends to size the motor feeder for 1.25 x FLA which is good to verify for its validity to a specific application.

 

[rbulsara]

I have posted a FAQ on this subject. Hopefully you will find it useful.

To all repected members:

Please feel free to comment, correct and improve on the FAQ when becomes available.

Thanks

 

[mikhe]

Thanks for the FAQ, very helpful and pitched at the correct level for me. One of the problems I am having is that I am being confused by comments from electrical engineers. One comment is that the real power will in fact lag the kWA at the moment of starting and in so doing will see a slightly different pf to the order of approx say 0.4. This has implications for me as I am starting this motor in island mode with the gensets at 50% load. The gensets have a load step acceptance of 25% so I am going to be on the edge of our capability. Gensets = 6MW rated. alternators are 4 x 2MW rated.