Transformer Losses and Efficiency:

All transformers must have copper and core losses.  A Copper loss is power lost in the primary and secondary windings of a transformer because of to the ohmic resistance of the windings.  Copper loss, in watts, could be found by using Equation (13-7).

Copper Loss I²_P   R_P +I²_S R_S (13-7)

where

I_P     =  primary current

I_S     =  secondary current

R_P   =  primary winding resistance

R_S   =   secondary winding resistance

Core losses are caused through two factors:  eddy and hysteresis current losses.  Hysteresis loss is that energy lost through reversing the magnetic field within the core as the magnetizing AC rises and falls and reverses direction.  An Eddy current loss is a output of induced currents circulating in the core.

The efficiency of a transformer could be calculated using Equations (13-8), (13-9), and (13-10).

Efficiency = Power Output/ Power Input = (P_S/P_P) x 100                                      (13-8)

Efficiency = Power Output/ Power Output + Copper Loss + Core Loss x 100 (13-9)

Efficiency = V_SI_S x PF / (V_SI_S x PF) + Copper Loss + Core Loss x 100             (13-10)

where

PF =    power factor of the load