Core Construction

This magnetic circuit, know more commonly as the “transformer core” is designed to

provide a path for the magnetic field to flow around, which is necessary for induction of the

voltage between the two windings.

In all types of transformer construction, the iron core is constructed from of a highly

permeable material made from thin silicon steel laminations (e.g. Hot rolled silicon steel,

cold rolled silicon steel i.e. CRGO). These thin laminations are assembled together to provide

the required magnetic path with the minimum of magnetic losses. Due to presence of silicon

the resistivity of the steel sheet itself is high, thus reducing any eddy current loss by making

the laminations very thin. These steel transformer laminations vary in thickness’s from

between 0.25mm to 0.5mm and as steel is a conductor, the laminations and any fixing

studs, rivets or bolts are electrically insulated from each other by a very thin coating of

insulating varnish or by the use of an oxide layer on the surface.

Core made of CRGO:

CRGO FULL FORM:cold rolled silicon steel

 By the cold rolling of the laminated sheets the grains are made to orient to some

extent in the direction of rolling

 has small hysteresis loop resulting low hysteresis loss.

 It has high value of saturation flux density, means magnetising current taken by the

primary winging is less.

 High resistivity means minimum eddy current loss.

The strips are cut at an angle of 450 at the two ends of the core so that the grains in the four

corners are perfectly oriented in the direction of the flux path. For providing mechanical

support between the laminations and also to distribute the air-gap in the corner region the

lamination sheets are cut at an angle of, say 470 and 430 and placed in staggered fashion so

the firm air gap has not been developed sharply.