50MVA transformer

[rickypegasus]

For a 50MVA (138/69/13.8 KV) Transformer, what would be the maximum demand in order not to exceed 80% of its operating capacity.

 

[jim dungar]

The simple answer is 50 x .80 = 40.

Though, I assume there is a lot more behind your question.
What do you mean by 'demand'?
How does that relate to your limit of 80%

 

[BJ Conner]

For a 50MVA (138/69/13.8 KV) Transformer, what would be the maximum demand in order not to exceed 80% of its operating capacity.

ANSI Stansard C57.92 tells you everything you want to know about loading Oil immersed transformers.
IT's about 600 pages and some people have made careers out of using it and other standards. There is no one page "cheat sheet" to loading transformers.

You'll get a few pointers and general answers here but they'll be worth what you pay for them.
The book is $120, learning to read the book is priceless. :roll:

 

[rickypegasus]

The simple answer is 50 x .80 = 40.

Though, I assume there is a lot more behind your question.
What do you mean by 'demand'?
How does that relate to your limit of 80%

I mean Demand in MW or the equivalent MW to load the transformer @80% of its capacity.

 

[kingpb]

50 MVA and 50MW are not the same thing.

A transformer can be loaded to it's full nameplate rating.

A transformer with these voltages sounds like a 3-winding substation transformer (138/69/13.8 KV).

Why are you concerned with only loading it 80%?

 

[BJ Conner]

Transformer loads

Transformer loads

Transformer loading is usually done by considering a 12 or 24 hr time period.
They can be overloaded for short periods with no damage. Higher loading shortens the life, all that is covered in ANSI standards.
The name plate rating on a transfromer that size is probably AA/FA/( and maby FO). Cold weather allows most transformer to be loaded more than nameplate.

 

[skeshesh]

Why are you concerned with only loading it 80%?

My question exactly. I would think it is for future growth perhaps. I also agree with the guess that it's likely a substation plant. More detail would be helpful; so would reading through C57.92 as BJ Conner suggested.

 

[jghrist]

I mean Demand in MW or the equivalent MW to load the transformer @80% of its capacity.

OK, then the simple answer is 50 x 0.8 x power factor

 

[rickypegasus]

50 MVA and 50MW are not the same thing.

A transformer can be loaded to it's full nameplate rating.

A transformer with these voltages sounds like a 3-winding substation transformer (138/69/13.8 KV).

Why are you concerned with only loading it 80%?

Yap this is a 3 winding OA/FA/FA substation transformer that serves 36 years from manufactured date, that is why I'm concern in loading it to 80% only . Actually these are two identical transformer operated in parallel serving 3 feeders and 1 unit is due for replacement to a 100MVA unit. A 47MW plays during peak hours will be absorbed by the remaining transformer and to play safe, 1 feeder is being transferred to an adjacent substation via a 69KV Tie line to ease the burden of overloading the remaining transformer considering its operational age. With only one transformer operating, and thru its MW and Mvar reading and using the power triangle formula, actual MVA can now be computed. Assuming no transfer of feeder, actual MVA computed exceeded 80% of its operating capacity of the remaining transformer.

 

[kingpb]

I would have the transformer tested by a legit testing company, if it checks out OK, I wouldn't be concerned with loading to it's full rating.

There are many factors that affect the overall life of a transformer. As long as it checks out OK, and it hasn't had any historical issues, I don't see why you couldn't load it up to it's rating.