Transformer
is a device that uses mutual induction between two coils to convert alternating
voltage to larger or smaller alternating voltage across the other coil.
Symbols of Transformers
There are two types of transformers
- Step-up transformers
- Step-down transformers
STEP-UP
TRANSFORMERS
Step-up
transformers are transformers for increasing
alternating voltage.
The number of turns in primary winding is smaller than
in the secondary winding
STEP-DOWN TRANSFORMERS
Step-down transformers are transformers for decreasing
alternating voltage.
The number of turns in primary winding is larger
than in the secondary winding
TRANSFORMER EQUATION
The transformer equation describes the relationship
between the number of turns in the coil, voltage and current in primary and
secondary winding
For an ideal transformer,
Hence
the general transformer equation is given by;
Ideal
transformer is the transformer that has the
efficiency of 100%. The ideal transformer has negligible power loss
TRANSFORMER EFFICIENCY
The efficiency
of a transformer is the ratio of power in secondary coils to the power in
primary coils expressed as a percentage.
OR
The efficiency
of a transformer is the ratio of power output to the power input expressed
as a percentage.
Example
1
A transformer is used to step-down 240 V
main supply to 12 V for laboratory use. If the primary coil has 600 turns, determine
the number of turns in the secondary coil.
Solution
Example
2
A current of 0.6 A is passed through a
step-up transformer with a primary coil of 200 turns. A current of 0.1 A is obtained
in the secondary coil. Determine
a) The number of turns in the secondary coil
b) The voltage across the secondary coil, if
the primary coil is connected to a 240 V mains.
Solution
Example 3
A step-up transformer ha 10000 turns in
the secondary coil and 100 turns through the primary coil. An alternating
current of 5.0 A flows in the primary circuit when connected to a 12.0 V a.c
supply.
a) Calculate the voltage across the secondary
coil.
b) If the transformer has an efficiency of
90%, what is the current in the secondary coil?
Solution
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