Page 570 - Basic Electrical Engineering

V is the volume of the iron core in m 3
η is the steinmetz constant.

To keep the hysteresis loss low, the material with a lower value of

steinmetz constant, such as silicon steel, is chosen as the core material.

(b) Eddy current loss

When the core is subjected to an alternate magnetic field, EMF is induced in
the core material also. This EMF causes circulating current in the core, and
thereby producing loss-resulting generation of heat. If the core gets heated

up, it produces an undesirable effect on the insulation material used in the
windings. Eddy current loss is expressed as

where W is the eddy current loss in Watts
e
B is the maximum value of flux density
m
f is the supply frequency
t is the thickness of the core material.

Eddy current loss is minimized by using a thin laminated sheet steel as the
core material instead of a solid core. The laminated steel sheets are assembled
together and are insulated from each other using insulating varnish. This

creates an obstruction to the flow of eddy current, and hence reduces the eddy
current loss.

6.18 SOLVED NUMERICAL PROBLEMS

Example 6.1 A transformer has 1000 turns on its primary and 500 turns on

the secondary. When a voltage, V of frequency f is connected across the
−3
primary winding a maximum flux of 2 × 10 Wb is produced in the core
which links both the windings. Calculate the value of the EMF induced in the

two windings.