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 Post subject: Power transformer
PostPosted: Sat Apr 09, 2011 12:43 pm 

Joined: Thu Apr 02, 2009 4:33 pm
Posts: 29
Location: OH
How does a power transformer get it's power ratings? For example, a power transformer has a rating of 15 MVA, 25 MVA, and 30 MVA all on the same transformer. Are these ratings based on transformer cooling?


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PostPosted: Sat Apr 09, 2011 6:52 pm 
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Joined: Wed Jun 04, 2008 9:17 am
Posts: 428
Location: Spartanburg, South Carolina
rayman37 wrote:
How does a power transformer get it's power ratings? For example, a power transformer has a rating of 15 MVA, 25 MVA, and 30 MVA all on the same transformer. Are these ratings based on transformer cooling?


Yes. Usually, the 15/25/30 ratings are based on ONAN/ONAF/ONAF; Oil Natural (as opposed to forced with pumps), Air Natural (no fans) / Oil Natural, Air Forced (fans) / Oil Natural, Air Forced (second stage fans)


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PostPosted: Mon Apr 11, 2011 10:18 am 

Joined: Mon Jan 26, 2009 5:00 pm
Posts: 46
Location: Midwest
I've also seen ratings by temperature rise.

Example:

AA/AA/FA
2500/3375/4500

The first 2 AA ratings indicate capacity for 80C and 150C rise respectively.


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PostPosted: Tue Apr 12, 2011 4:10 pm 

Joined: Wed Nov 12, 2008 10:26 am
Posts: 46
Location: CA
Self-Cooled kVA & %Z

It is important to use the 'self-cooled rating" of the transformer, usually the smallest kVA, when entering kVA and impedance data into your arc flash software. The transformer's impedance, shown on its nameplate, is based on its self-cooled kVA rating.


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PostPosted: Tue Apr 12, 2011 7:40 pm 

Joined: Thu Apr 02, 2009 4:33 pm
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Location: OH
Thanks for the information so far.


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PostPosted: Mon Aug 15, 2011 8:29 pm 

Joined: Tue Dec 07, 2010 1:44 am
Posts: 2
Help me Please ANSI/IEEE C57.92

please send me

ANSI/IEEE C57.92

I needed this file

[email protected]


thank you


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PostPosted: Tue Aug 16, 2011 2:47 am 
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Location: Scottsdale, Arizona
lebed wrote:
please send me

ANSI/IEEE C57.92

I needed this file

[email protected]


thank you


This standard can be obtained from [url="www.ANSI.org"]www.ANSI.org[/url]It is protected under United States Copyright. Providing copies is not permitted. Please obtain an original version from ANSI.

_________________
Jim Phillips, P.E.
Brainfiller.com


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