# Transformer heat losses

The (I^2R) heat losses in a transformer are caused by the primary and secondary winding resistances, as the page below lists the transformer losses:

But what about the eddy currents don't they generate resistive losses?

I found the following:

Eddy current loss is conductive I2R loss produced by circulating currents induced in response to AC flux linkage, flowing against the internal resistance of the core. So, based on the above is eddy current loss a heat loss?

SOURCES:

1. The Principles and Practice of Engineering (PE) Electrical and Computer: Power exam Reference Handbook Version 1.1.1 Pub. NCEES

2. science direct Eddy Current Loss

... is Eddy current loss a heat loss?

Yes, it is.

Since the eddy currents flow "through" the core itself, the eddy current loss is still a kind of I2R loss (where I is the eddy current and R is the resistance of the eddy currents' return path). Thus, the eddy current loss produces heat and increases the temperature of the transformer.

For the iron core transformers, the core is made up of thin iron sheets (i.e. laminations) insulated among themselves, instead of a solid iron block. This method decreases the eddy currents, and thus the eddy current losses.

• But in the question eddy current losses formula doesn't even contain iron core resistance (Rc)?? instead it's given in reference to Bm = (1/Xm). Why?
– OMAR
May 29, 2021 at 10:55
• Well, look at the formula in your question again. It contains K, B and f. Now, remember what dB / dt is (f comes from 1/dt). And, remember that K contains the core's physical properties like sheet thickness, core volume, and core material resistivity (rho). So, still, it's a kind of I²R or V²/R. May 29, 2021 at 11:45

In the transformer we have copper and iron losses. The copper loss is due to the electrical current I^2*R, while the iron loss is due to eddy currents and hysteresis of Weiss domains. They both produce heat, but the copper loss is relative to the electric current, while the iron loss is relative to the frequency.

But what about the eddy currents don't they generate resistive losses?

Yes they do, but in iron and they are the same and regardless of the load current. They do increase with the frequency.

• But in the question eddy current losses formula doesn't even contain iron core resistance (Rc)?? instead it's given in reference to Bm = (1/Xm). Why?
– OMAR
May 29, 2021 at 10:55