Page 537 - Basic Electrical Engineering

The windings of the transformer are made up of insulated copper wires.
The cross-sectional area of the winding wires will depend upon the
requirement of current-carrying capacity, and the number of turns are

calculated according to the voltage ratio of primary and secondary windings.
The core and the winding assembly are placed inside a tank filled with

transformer oil for the purpose of providing insulation to the windings and
also for cooling purpose. Transformer oil used is mineral oil having high

dielectric strength. The tank is provided with radiating tubes so that heated oil
gets circulated through the tubes and heat produced in the transformer is

radiated to the atmosphere through the oil circulating from the tank through
the radiating tubes.
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Heat is produced in the transformer due to I R loss in the windings and
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hysteresis and eddy current loss in the core. The I R loss in the windings will
depend upon the magnitude of current flow through the windings when the
transformer is supplying some electrical load. The core loss which is the sum
of hysteresis loss and eddy current loss remains constant at any load. Even

when the transformer output circuit, i.e., the secondary winding, is not
connected to any load, there will be core loss once an alternating voltage is

applied to its primary winding. As long as the primary voltage is kept
constant, the core loss will remain constant. That is why the core loss is
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called constant loss. The I R loss which is also called copper loss is a
variable loss, as it varies with the magnitude of load current.

These losses will overheat the transformer unless the heat generated is
radiated out to the atmosphere. If a transformer gets too overheated, its
insulation strength will reduce and ultimately there may be short circuit

inside the transformer damaging it completely.
Transformers are manufactured as single-phase transformers and as three-

phase transformers. In three-phase transformers three separate windings are
made for both primary and secondary sides. The windings are connected
either in star or in delta. Terminal connections are brought out through low

voltage (L.V.) terminals and high voltage (H.V.) terminals. A conservator
tank fitted with a breather is placed above the tank. The conservator is

connected to the transformer tank with a pipe and carries transformer oil. The