Transformer Efficiency and Impedance

[dnobs]

I'm working on a calculator for a work project and recently had this discussion with a coworker.

In essence, is it correct to assume that the efficiency of a transformer is directly related to the resistive losses?
Or is the X/R Ratio required to correctly calculate X & R values?

ie is it true that:
P_losses = I_rated² x R

Or is there more to the story?

 

[jim dungar]

I'm working on a calculator for a work project and recently had this discussion with a coworker.

In essence, is it correct to assume that the efficiency of a transformer is directly related to the resistive losses?
Or is the X/R Ratio required to correctly calculate X & R values?

ie is it true that:
P_losses = I_rated² x R

Or is there more to the story?

Efficiency is much more complicated than just the resistance.
In fact efficiency and impedance are not always negatively correlated.

Don't forget there are two types of losses, core and conductor. It is only the conductor losses that are directly related to resistance.

 

[David Castor]

As Jim says, it's more complicated than just thinking about winding resistance. The transformer impedance on the nameplate is mostly reactance. X/R ratios are quite high.

Excitation losses including iron losses are nearly constant regardless of load. The winding losses vary with the square of the load. If you have the winding losses from the test reports and the impedance, you can calculate the X/R ratio.

 

[junkhound]

OP occupation says EE.

If true, I despair of the curriculum of his alma mater to have not heard of eddy current, core losses, proximity effects, reason ac transformers have laminations, etc, etc...