Question

What is the formula for the diameter of the circumscribing circle of the transformer?

(a) diameter of the circumscribing circle = 2*square root of ratio of cross sectional area of the core to the space factor

(b) diameter of the circumscribing circle = 3*square root of ratio of cross sectional area of the core to the space factor

(c) diameter of the circumscribing circle = square root of ratio of cross sectional area of the core to the space factor

(d) diameter of the circumscribing circle = 4*square root of ratio of cross sectional area of the core to the space factor

I got this question in an online quiz.

The doubt is from Overall Dimensions in chapter Design of Transformers of Design of Electrical Machines

Answer 1

Right choice is (c) diameter of the circumscribing circle = square root of ratio of cross sectional area of the core to the space factor

To elaborate: First the cross sectional area of the core is obtained by the formula cross sectional area = voltage per turn / 4.44 * frequency * magnetic field. Next the space factor is obtained. Substituting in the formula provides the diameter of the circumscribing circle.