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gkkumar
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Join Date: Sep 2010
Posts: 46

Gen. Capacity

09/19/2010 8:46 AM

what is the capacity of a generator needed to run a 340 KW motor alone
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justinanto1987
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India - Member - Justin Anto Engineering Fields - Electrical Engineering - Marks never made me laugh, but good memories did

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#1

Re: gen.capacity

09/19/2010 9:01 AM

If the pf of the generator is 0.8, you need 340/0.8 = 425 KVA.

If it is 0.9, you need 340/0.9 = 378 KVA

If you can compensate the reactive power, you need just 340 KVA

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#3
In reply to #1

Re: gen.capacity

09/19/2010 1:13 PM

Eerrr. What size of crank handle does he need to get the drive started?
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TonyS
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#4
In reply to #1

Re: gen.capacity

09/20/2010 3:03 AM

Justin,

Engineering has to be based on practicality.

Based on you figures the generator would start, press the start button for the motor, the generator stops dead!

You've got to have the generating power available to supply the starting load of the motor.

Get out in to the real world!

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TonyS
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#5
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Re: gen.capacity

09/20/2010 4:14 AM

A real world experience.

I had to change a MCCB in a MMC panel. To do so the panel had to be isolated, unfortunately this panel supplied a drive that was process critical. Don't worry about it I was told, "there's a stand by generator just for that one drive". What I didn't know was it had never been tested on load! So, start generator set, start motor, generator set stop!

We did get it going eventually but as to how we did it would have most members of this board cringing!

What should have taken me 2 to 3 hours took 12

The generator was soon up rated.

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msamad
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#2

Re: gen.capacity

09/19/2010 9:33 AM

There is a good and helpful information in the previous thread: http://cr4.globalspec.com/thread/58246/Power-Generator-Sizing. Please see it first.

- MS

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Tornado
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#6

Re: Gen. Capacity

09/20/2010 12:19 PM

For DOL starting, the genset kva needs to be about 3x the the motor kva. For VFD starting, 1.5x might suffice. These are just round numbers, and it would be best to ask the genset manufacturer what the starting capability is.

Msamad's detailed information is also excellent.

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