How do you select core in Transformer Design?

Answer 1

The material used in the manufacture of transformer cores must have a hysteresis loop with a very small area, as it is the area of the hysteresis loop that determines the hysteresis losses of the core material. The core material should also be resistive, in order to reduce eddy current losses (which is further improved by laminating the core). Many transformer manufacturers use their own variations on what is basically a silicon-steel.

A hysteresis curve, or loop, is a graph of flux density plotted against magnetising force, and basically describes the ease (or difficulty) with which the core material can be magnetised and demagnetised as the magnetising current changes magnitude and direction.