2001 Summer Power Meeting Pictorial Review

Transformers supplying nonsinusoidal load currents are subject to increased losses. Of particular concern is the increase in the winding eddy current loss as it varies with a power q of the harmonic number n and increases winding and hot spot temperature rises. Clearly the value of q is of paramount importance. For transformers wound with copper strip, the value of q is generally taken to be close to 2. Analysis of a copper sheet winding presented in this paper shows that the power, q, for such a winding is about 0.8. Although sheet windings have high concentrations of loss intensity at the ends of the inner turn of the inner winding and the outer turn of the outer winding, they are not increased by harmonics as much as for the strip wound transformer due to the lower value of q.