Transformers
Transformers
Transformers
Principle of operation
Specific objectives:
At the end of the lesson students should be able to:
Define correctly the term ’transformer’
Define correctly the term ’Induced e.m.f.’
inductance’
Draw diagram of mutual inductance
transformer
Appreciate the importance of transformers
What is a Transformer?
A Transformer is a device used for changing
voltage/current values in a circuit.
Transformer
An A.C. device used to change high voltage low
current A.C. into low voltage high current A.C. and
vice-versa without changing the frequency
In brief,
1. Transfers electric power from one circuit to another
2. It does so without a change of frequency
3. It accomplishes this by electromagnetic induction
4. Where the two electric circuits are in mutual
inductive influence of each other.
Before considering the principle of a
transformer it is necessary to understand
the meaning of the following terms.
1. Induced emf (electromotive force)
It is based on
principle of MUTUAL
INDUCTION.
According to which
an e.m.f. is induced
in a coil when
current in the
neighboring coil
changes.
Working of a transformer
1.When current in the primary coil
changes being alternating in
nature, a changing magnetic field
is produced
2. This changing magnetic field gets
associated with the secondary
through the soft iron core
3. Hence magnetic flux linked with
the secondary coil changes.
4. Which induces e.m.f. in the
secondary.
How Transformer
Works
`
Transformer Construction (single-phase)
Where:
VP - is the Primary Voltage
VS - is the Secondary Voltage
NP - is the Number of Primary Windings
NS - is the Number of Secondary Windings
Φ (phi) - is the Flux Linkage
When a transformer is used to “increase” the voltage
on its secondary winding with respect to the
primary, it is called a Step-up transformer. When
it is used to “decrease” the voltage on the
secondary winding with respect to the primary it is
called a Step-down transformer.
Turns Ratio
It is necessary to know the ratio of the number of
turns of wire on the primary winding compared to
the secondary winding. The turns ratio, which has
no units, compares the two windings in order and is
written with a colon, such as 3:1 (3-to-1). This
means in this example, that if there are 3 volts on
the primary winding there will be 1 volt on the
secondary winding, 3 volts-to-1 volt.
A Transformers Turns Ratio