Temperature Rise on an Oil Filled Transformer 2

[bdn2004]

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?

 

[davidbeach]

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.

 

[bdn2004]

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?

 

[itsmoked]

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

 

[davidbeach]

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.