Cooling Fans on MV Substation Transformers
Cooling Fans on MV Substation Transformers
(OP)
Is there any advantage gained by running the cooling fans on a distribution substation transformer that is normally loaded on peak to approximately 70% of the base rating? This particular unit has two stages of fan forced air cooling with ratings of 18/24/36 MVA respectively. To my knowledge 17 MVA was the most ever put on this unit, and that was during a contingency.






RE: Cooling Fans on MV Substation Transformers
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If we learn from our mistakes I'm getting a great education!
RE: Cooling Fans on MV Substation Transformers
RE: Cooling Fans on MV Substation Transformers
RE: Cooling Fans on MV Substation Transformers
One problem was the 64G protection was driven by a CT that connected the transformer case to ground. The CT could not tell the difference between 13.8kV fault current and a 208V fan motor failure. A 1/2 HP fan motor ground fault would trip the 50MW rectifer station.
As the other experts recommend - just run in auto.
RE: Cooling Fans on MV Substation Transformers
But running the fan throughout ie during ON cooling is not a very good idea.Rcwilson has brought in a new angle.The drop in copper loss due to temp drop may off set the cooler power consumption.Actual checking on some trfs does not justify such a line.One thing-though I2R loss goes down with temperature,stray losses goes up with lower temperature.At ON rating of say 70%load, the copper loss will be only half at full load.For a temp drop of 10 C due to fans,the reduction in loss will be only half of 3% of full load loss.In many cases cooler loss will be more than that saving.
A new trend is coming up-to use variable frequency drive for coolers ( some type of intelligent coolers)so that same oil temperature is amintained by changing the cooler speed to save energy.
Regarding 64 G Tank current protection.I have seen this only in France and other French influeced regions.But in such cases, it is a must that coolers,marshalling boxes and OLTC drive box shall be kept insulated from main tank and separately earthed to avoid mal operation of relay from auxiliary power break down to earth.So it has to be assumed that the rectifier trnsformer cooler mounting was not designed correctly.
RE: Cooling Fans on MV Substation Transformers
It would be very unusual to find a modern transformer where the I2R losses would be as high.
The 64G's main function was to detect winding faults on the low voltage(800V) side that would be back fed from the other 7 rectifer units via the DC negative bus. A sister facility did have a LV winding failure and the 64G unit did clear the line quickly.