Transformer Heat Loss
Transformer Heat Loss
(OP)
Is there a standard way/formula to calculate heat loss (in watts) of a transformer?
I'm assuming you'd have to take into accountthe power factor and the efficeny of the transformer?
Is it just the real power throughput of the transformer multiplied by the 1-effy?
Also...does anyone know of a table(s) of standard transformer efficiencys and power factors?
Thanks in advance!
I'm assuming you'd have to take into accountthe power factor and the efficeny of the transformer?
Is it just the real power throughput of the transformer multiplied by the 1-effy?
Also...does anyone know of a table(s) of standard transformer efficiencys and power factors?
Thanks in advance!






RE: Transformer Heat Loss
Depending on winding material, temperature rise, and construction type, the losses can vary by more than a factor of 2 for the same size transformer. When considering large transformers installed indoors it can be less expensive to buy the lowest loss transformer and save the cost of the air conditioning and the ongoing operational losses than to buy the lowest cost transformer and pay for the losses and the air conditioning necessary to remove the heat of the losses.
RE: Transformer Heat Loss
Another factor to consider is maximum fault current. You may have to spec a minimum impedance (%Z) to ensure a particular worst-case fault level. This in turn has a dramatic effect on the amount of steel core and copper windings used in the xmfr design, which affects the heat losses.
BTW, less heat generated is another way of saying 'less electrical energy lost to transformation', which means reduced electricity purchases on top of reduced ventilation/AC (if the revenue metering is on the source side of the xmfr). Don't forget to include this in your cost model.
RE: Transformer Heat Loss
RE: Transformer Heat Loss
RE: Transformer Heat Loss
Power factor isn't going to have any impact on the heat generated, except to cause more current to flow and increase the kVA load on the transformer.
For a 75 kVA, 150 deg rise dry-type, Cutler-Hammer gives an efficiency of 97.2% at 1/4 load and 96.7% at full load. So figure 3% loss at 75 kVA which would be 2250 watts.
If you're looking for greater precision, you need to know the amp load on the transformer and separate out the core losses (which are constant) and the winding losses (which vary as the square of the current).
RE: Transformer Heat Loss
If all you are looking for is how much cooling does the transformer need, dpc's 3% of rating is a good rule of thumb, but it may be rather over sized if the transformer is never fully loaded.
The energy star transformers are another matter; they are designed for maximum efficiency at 35% (or there 'bouts, I don't have the literature at hand) and you can find transformers that are more efficient at full load or at no load.