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)

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.

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.

Thanks for the information so far.

Help me Please ANSI/IEEE C57.92

please send me

ANSI/IEEE C57.92

I needed this file

lebedlemo@yahoo.com


thank you

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