The Transformer

The principle parts of a transformer and their functions are:

• The core, which makes a path for the magnetic flux.

• The primary coil, which receives energy from the ac source.
• The secondary coil, which receives energy from the primary winding
and delivers it to the load.
• The enclosure, which protects the transformer from dirt, moisture, and
mechanical damage.



Transformer Core

• The composition of a transformer core depends on voltage, current, and
frequency. Commonly used core materials are air, soft iron, and steel. Each of
these materials is suitable for certain applications. Generally, air-core
transformers are used when the voltage source has a high frequency (above 20
kHz). Iron-core transformers are usually used when the source frequency is low
(below 20 kHz).
• A soft-iron-core transformer is very useful where the transformer must be
physically small, yet efficient. The iron-core transformer provides better power
transfer than does the air-core transformer. A transformer whose core is
constructed of laminated sheets of steel dissipates heat readily; thus it provides
for the efficient transfer of power.
• The majority of transformers contain laminated-steel cores. These steel
laminations are insulated with a nonconducting material, such as varnish, and
then formed into a core. It takes about 40 laminations to make a core of 2 cm
thick. The purpose of the laminations is to reduce losses which will be discussed
later in this chapter.
• The most efficient transformer core is one that offers the best path for the most
lines of flux with the least loss in magnetic and electrical energy.

Ideal Transformer

Center-tapped Transformer

Impedance Reflection Across a Transformer

The Maximum Power Transfer Problem in AC Circuits

Maximum Power Transfer in an AC Circuit with a Transformer

Electric Power Transmission:

(a) Direct Power Transmission                         (b)Power Transmission with Transformers

Electric Power Transmission:

 (c) Equivalent Circuit Seen by Generator    (d) Equivalent Circuit Seen by Load

Structure of an AC Power Distribution Network:

More About the Transformer:

 The principle parts of a transformer and their functions are:
• The core, which makes a path for the magnetic flux.
• The primary coil, which receives energy from the ac source.
• The secondary coil, which receives energy from the primary winding
and delivers it to the load.
• The enclosure, which protects the transformer from dirt, moisture, and
mechanical damage.


Efficiency of Transformer: