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Temperature Rise on an Oil Filled Transformer
2

Temperature Rise on an Oil Filled Transformer

Temperature Rise on an Oil Filled Transformer

(OP)

The rated temperature rise is 55 deg C and 65 deg C.

First I don't really understand why the two ratings. I mean if heat is the enemy and this is a fan rating, it's still heating up 10 degrees higher - why is a higher rating allowed?

Second how can you tell if the transformer is running within its ratings...

Say it's zero deg C outside. And I read the gauge and it says its 55 deg C...then it's at rated temp right?

RE: Temperature Rise on an Oil Filled Transformer

The temperatures are rise over a specified ambient, generally 40°C, so you can get to 95°C or 105°C.  55°C was the traditional rating, 65°C is a newer rating.  55/65°C is a transformer with a 65°C rated insulation but sized as though it had a 55°C rated insulation system.  That gives some "overload" capability above the 55°C rating without exceeding the °C rating.

RE: Temperature Rise on an Oil Filled Transformer

(OP)
So what you are saying is that the outside ambient doesn't really matter...because the max is 105 deg C.

If that's the case...why don't they just rate it 105 deg C and be done with it?

RE: Temperature Rise on an Oil Filled Transformer

Because the number is rise.

If they just gave the number 105 you would never know what the ambient is limited to.

If the aforementioned transformer is located somewhere with a high ambient then you can not even run the transformer up to its specified load.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Temperature Rise on an Oil Filled Transformer

On the other hand, if it is really 0°C outside, you have another 40°C of rise without risking damage.  The real rating is a hot spot temperature rating, but that is difficult to measure.

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