Figure 1.9 shows spiral core-type transformer where the core is assembled either of a continuous strip of the transformer steel wound in the form of a circular or elliptical cylinder or of a group of short strips assembled to produce the same elliptical shape. In this construction, the core flux always follows along the grain of iron. Cold-rolled steel of high silicon content allows the designer to use higher operating flux densities with lower loss per kilogram. The main advantage of using the higher flux density is that weight/kVA is reduced.
Figure 1.9 Spiral Core-type Transformer