Transformer Capacity
& Power Factor

Say our substation is loaded to the maximum transformer capacity and we know it is delivering power at a poor power factor. Our options are:

1. unload the transformer by disconnecting loads from it,
2. buy a larger transformer,
3. provide additional cooling to it (this raises the transformer capacity) or
4. correct the power factor.

Lets look at an example of correcting the power factor (so I'll have something to do):

If the transformer is rated at 2,000 kVA and operates fully loaded at a .70 power factor, how much capacity can we free-up if we correct the power factor to .90? (Notice that the transformer is not rated in kW, but rather, by the amperage that it can carry at a specific voltage, kVA)

Since power factor is the percentage of the apparent power (kVA) that is used to supply real power (kW), then in this example only 70% of the kVA is used to deliver real power.
So the transformer delivers 2,000 kVA x 0.7 = 1,400 kW

It follows then, that this transformer delivers 1,400 kW of true power and if we correct the Power Factor to .90 we can deliver 1,800 kW. That's over a 28% improvement. This application can be one of the larger cost benefits associated with Power Factor Improvement.

Remember, capacitors must be installed on the secondary side of the transformer to correct what is delivered through the transformer.