Page 538 - Basic Electrical Engineering

empty space above the level of oil in the conservator is provided to allow the
expansion of oil in the tank due to heating and for the removal of gas formed.

6.4 CORE-TYPE AND SHELL-TYPE TRANSFORMERS

There are two types of core constructions, viz core type and shell type. In
core-type construction, the primary and secondary windings are placed

around the limbs of the transformer core. The windings are made in
cylindrical form and are placed around the core limbs. First, the low-voltage

winding is placed around the limbs. Over the low-voltage windings are
placed the high-voltage windings. The high-voltage winding is placed
somewhat away from the core so as to reduce the insulation problem. The

windings are insulated from the core through insulating cylindrical disc made
of insulating material. The windings are made up of insulated copper wires in

two sections or parts and are connected after they are placed in positions to
form primary and secondary windings, respectively.

In a shell-type construction, the windings are placed in the central limb.
The windings are wound in the form of a number of circular discs, and are

placed one above the other. The extreme two discs on the central limb are
low-voltage winding sections. These, l.υ sections and h.υ. sections are then
connected to form low-voltage- and high-voltage windings. The width of the

central limb is twice the width of the outer limbs so that the flux density is
the same in all the limbs.