Step up transfomer oil temperature control issue 1

[npower0073]

Dear all, on site we have a 460MVA step up transformer. It is equipped with 6 collers (air to oil, with fans and oil pump). The transformer is ODAF(oil draught, air forced). during thermography survey we found out that the part of the main oil tank that is on the part of the coolers out of service have 30 degrees temperature higher than the part of the tank where the coolers work. I think that it is not so good to have this situation. I think to make a change over on the coolers automation in order to have them grouped one by one and not three on the left and three on the right. Let me know your opinion.

 

[slavag]

Hi.
I think for begining, better for you, ask to xfr. factory recommendation.
Regards.
Slava

 

[unclebob]

The way I see it, it is better to get an equal cooling for the left and right radiators. A 3 stages scheme (1 left - 1 right, 2 left- 2 right, 3left - 3 right) is more efficient.

The cooling of the oil is a 'top-to-bottom' motion. It is less likely the hot oil will be cooled by going 'sideways'. The cooling is less effective.

 

[ScottyUK]

Are there two pumps, one for each cooler bank? ODAF is actually 'Oil Directed' meaning that the pump forces oil through specific paths in order to provide cooling to hot spots in the transformer. Running only one pump will affect the cooling to one side of the transformer.


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If we learn from our mistakes I'm getting a great education!

 

[electricpete]

One thing to remember: if all the cooling is not on, then you are likely not near any thermal limits. If loading goes up, then all stages of cooling come on and your uneven distribution disappears. So I would check to verify that the the thermal wells don't appear to be in the portion of the transformer that is cool. As long as they are not, then I would not be concerned. I agree the manufacturer gives the final answer.

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[rcw retired EE]

Check with the manufacturer. We had an ODAF cooled transformer that needed to operate all oil pumps continuously when the transformer was energized. The cooling fans were cycled based on temperature, but the pumps had to run to maintain oil flow through the coil and core.

We also determined that the KW consumed by the fans was less than the reduction in I2R losses in the windings due to lower winding operating temperature. So we ran all fans regardless of temperature. (This was on old rectifier transformers with a low voltage high current windings.)