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Old 12-16-2010, 06:46 AM   #1
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Default ATS Sizing Question

We are going to install a service entrance ATS with a utility disconnect switch MCCB, input power coming from utilities 13.8KV secondary trafo of 220Vac,3Ph and from 200KVA,3Ph, 525 Ampere generator

Downstream is a 2 x 30KVA AC UPS (parallel Redundant) to supply power to the plants SCADA Control Room.(max.load in the room)

The engineer incharge for this project (client side) ask for a 400A service entrance ATS(with a utility disconnect switch MCCB), however i find it too big for its total load requirement (assumming UPS full load of 60kVA/72KW [p.f=0.8])

generally i would size the ATS rating using [Total System Load] divided by [square root of 3]*[220V] = 72,000 / 381 = 189 Ampere, hence i would say 200 Ampere Service Entrance ATS is more suitable.

Am i correct with my sizing calculation? if im wrong, please advice me correct sizing calculations.
what will be the effects if we use the 400A SE ATS??? technical issues???

advice?anyone?

thanks......

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Old 12-16-2010, 07:20 AM   #2
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I am sorry but that was kind of hard to follow.

At what point are you installing the ATS??

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Old 12-16-2010, 08:16 AM   #3
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Let me preface this by saying I know very little about generators but IMO, a load of 189 amps may be too much for a 200 amp ATS. Is the 189 a,ps continuous load? Is the ATS rated for 100% of a continuous load?
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Old 12-16-2010, 08:36 AM   #4
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Is the price or the physical size the issue?
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Old 12-16-2010, 11:27 AM   #5
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تحتاج إلى حجمه في 125 ٪ من تحميل الخاص المستمر. لماذا أنت هنا يكمن في
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Old 12-18-2010, 03:01 AM   #6
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Default ATS Sizing question

if i rate the ATS at 125% of the total system load of 200A then it will give me a 250A rating.

If i will go ahead and use the 400A rating are there gonna be any technical issues to arise?
Do i have to consider the generators ampere rating as it gives 525A at continous load.

if so then i would be needing atleast 600A SE ATS rating, am i correct?
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Old 12-18-2010, 08:26 AM   #7
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Standard size for MOST ATS manufactures would be a 200, 230 or 260.
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Old 12-21-2010, 10:34 AM   #8
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didnt you say the generator is 525 amps?

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