1.
Introduction to transformers

2.
Outline
1. Introduction to Transformers
2. Transformer construction
3. Model of Transformer on no load
Performance
Management
Orientation

3.
Transformer
• A transformer is a static device comprising coils coupled through a magnetic
medium connecting two ports at different voltage levels in an electric system
allowing the interchange of electrical energy between the ports
• It is used in changing voltage and current levels in electric power systems
• Other important tasks include matching source and load impedance for
maximum power transfer, and electrical isolation
• A transformer, consists essentially of two insulated windings interlinked by a
mutual magnetic field established in a core of magnetic material

4.
Transformer
• When one of the windings, termed the primary, is connected to an
alternating-voltage source, an alternating flux is produced in the core
• This mutual flux links the other winding, called the secondary.
• A voltage is induced in this secondary of the same frequency as the
primary voltage but its magnitude depends on the number of
secondary turns
• The subscript “1”or “p” will be associated with the primary and “2” or “s”
with the secondary

5.
Transformer
• If the secondary voltage is greater than the primary value, the
transformer is called a step-up transformer;
• if the secondary voltage is less, it is known as a step-down transformer;
• if primary and secondary voltages are equal, the transformer is said to
have a one-to-one ratio. (these are mostly used for isolation purposes)

6.
TRANSFORMER CONSTRUCTION
• Construction of transformers will be dependent on a number of factors
such as:
• Winding voltage
• Current rating and operating frequency
• Heat removal from the core and windings

7.
TRANSFORMER CONSTRUCTION
• The primary and secondary coils are wound on the core and are
electrically insulated from each other and from the core
Two types of cores are commonly used—core-type and shell-type
• In core-type construction, the windings are wound around the two legs
of a rectangular magnetic core
• In shell-type construction, the windings are wound on the central leg
of a three-legged core
In either case, the core is constructed of thin laminations electrically
isolated from each other in order to minimize eddy currents

8.
TRANSFORMER CONSTRUCTION
• The primary and secondary windings
in a core type transformer are
wrapped one on top of the other
with the low-voltage winding
innermost
• Half of the low-voltage winding and
half of the high-voltage winding is
wound on each limb of the core

9.
TRANSFORMER CONSTRUCTION
• Such an arrangement serves two
purposes:
 It simplifies the problem of
insulating the high-voltage winding
from the core.
It results in much less flux leakage
than would be the case if the two
windings were separated by a
distance on the core.

10.
TRANSFORMER CONSTRUCTION
• In shell-type construction leakage is reduced by subdividing each
winding into subsections and interleaving LV and HV windings

11.
TRANSFORMER CONSTRUCTION
• The shell-type construction has better mechanical support and good
provision for bracing the windings. However, it requires more
specialized fabrication facilities than core-type,
• The core type offers the additional advantage of permitting visual
inspection of coils in the case of a fault and ease of repair.
• In addition, the core type windings can easily be insulated from each
other and from the core
• For this reason, the core type transformers are commonly used in large
high-voltage installations.

12.
TRANSFORMER CONSTRUCTION
• Transformer windings are made of solid or stranded copper or
aluminium strip conductors.
• The windings of huge power transformers use conductors with heavier
insulation (cloth and paper.)
• The winding layers are insulated with pressed boards and varnished
cloth