Force Air cooling of transformer

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Sajid khan

Sajid khan

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For the dry type transformer what are the conditions/situation when the force air cooling of the transformer starts automatically?? I know that the capacity of the transformer will increase by 33% in case of force air cooling.

Thanks in advance
 
If the load drawn go beyond 100% on specific temp mentioned on the nameplate.
 
I have seen fan kits that can be added to some smaller air cooled transformers that have a thermostat to run the fan so it only runs when the transformer gets warm.

Some seem to have more elaborate controls than others.
 
In our case the allowable Avg temp of transformer as per manufacturer is 30C and it can go up to 40C Max Ambient temperature. The Transformer room is equipped with Air conditions with temperature set at 30C so the transformer cannot go above 40C temp rise unless there is a failure of the AC unit. Other thing that can rise the temperature is the overload but don't know if it can go beyond 40C or not??
 
Forced air cooling

Forced air cooling

The forced air cooling sometimes during the design stage considered to be forced air cooling and loaded more than 100% to 133% from it is rated load, on other cases the air cooling is rated to temp and in case of overloading.
 
Sajid khan said:
In our case the allowable Avg temp of transformer as per manufacturer is 30C and it can go up to 40C Max Ambient temperature. The Transformer room is equipped with Air conditions with temperature set at 30C so the transformer cannot go above 40C temp rise unless there is a failure of the AC unit. Other thing that can rise the temperature is the overload but don't know if it can go beyond 40C or not??
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Ambient temperature is reference temperature. It is 30C or 40C per your manufacturer. The transformer winding temperature is different. It depends on the load. On full load it may be 150C or more depending on the design. Check with the manufacturer.
 
Sahib said:
Ambient temperature is reference temperature. It is 30C or 40C per your manufacturer. The transformer winding temperature is different. It depends on the load. On full load it may be 150C or more depending on the design. Check with the manufacturer.
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Thanks the winding temperature in our case is 115C.
 
Caution, the transformer nameplate rating must be rated for that. Yes, a 115deg rise transformer does have the overload capability because the insulation rating imost likely is 220degC. The normal 150degC rise transformer is based upon a 40degC ambient+a 30degC winding hot spot allowance + 150degC rise= 220degC. With a 115degC rise design you have a 35degC margin which is basically intended to extend transformer life because of the lower temp rise.
Also note that the internal conductor and terminations are based upon the transformer's nameplate rating and unless the transformer is designed for the extra load such as an FFA (future fan to air) rating on the nameplate it isn't rated for fans nor should a 115degC rise transformer by applied as though it were 150degC rise.
What is included in the nameplate on the transformer is the key.
But for temporary overloads a 115degC and 80degC transformer have a 15% and 30% overload capacity respecively without exceeding the insulation class of 220degC.
It must be noted that ambient temperatures is also an important consideration.
 
I am by no means a transformer expert when it comes to their design.

But I believe if you have a 100 kVA transformer it will mean it can handle 100 kVA if the actual operating temp doesn't exceed it's design temp rating.

So if you can find a way to move more cooling air through it you can get more kVA capacity out of it. There may still be limitations though that are not quite so straight forward.

What I think I am trying to say is adding a cooling fan doesn't automatically make the 100 kVA into a 115 kVA unit but does give the possibility of running over nameplate kVA as long as temp rating is not exceeded. Something tells me there is still other limitations - you likely do not get 200 kVA out of it without developing other problems even if you can keep it well cooled.
 
The people to consult are the manufacturers, only they can give the correct information.

Our transformers were specified for 130% or 150% cyclic loading, this was dependant on ambient air temperature.
If you?re relying on an air con unit then I can see a disaster on the horizon.
 
Tony S said:
The people to consult are the manufacturers, only they can give the correct information.

Our transformers were specified for 130% or 150% cyclic loading, this was dependant on ambient air temperature.
If you?re relying on an air con unit then I can see a disaster on the horizon.
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Or high operating costs. Many times I've walked through a local parking garage here in the winter with below freezing temperatures outdoors and can hear the AC units cooling the electrical room. Crazy.
 
As a former application and sales engineer I can attest to the fact that no matter what I say that a transformer is good for only the nameplate on the transformer is accepted as valid. If there is no FFA rating shown fans are not a valid modificatio in order to obtain additional capacity. If a transformer were to have the capability but the NP doesn't show it I would have to have the drawing changed to indicate it as such and the issue a new NP for it. An then I just can not freely authorize the installation of that new NP in the field as it would violate the UL listing.
 
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