1
Question
Write the principle and explain the construction and working of a transformer. Define its efficiency.
Open in App
Solution
Principle : The transformer is based on the principle of electromagnetic induction. The phenomenon of producing an induced emf due to the changes in the magnetic flux associated with a closed circuit is known as electromagnetic induction.
Construction and Working:
This principle can be demonstrated and explained through Faraday's experiments.
A transformer consists of primary and secondary coils insulated from each other, wound on a soft iron core (figure). To minimise eddy current a laminated iron core is used. The a.c. input is applied across the primary coil. The continuously varying current in the primary coil produces a varying magnetic flux in the primary coil, which in turn produces a varying magnetic flux in the secondary. Hence, an induced emf is produced across the secondary.
Let EP and ES be the induced emf in the primary and secondary coils and NP and NS be the number of turns in the primary and secondary coils respectively. Since same flux links with the primary and secondary, the emf induced per turn of the two coils must be the same
i.e., EPNP=ESNS
(or) EPEP=NSNP ....(1)
For an ideal transformer, input power = output power
EPIP=ESIS
where IP and IS are currents in the primary and secondary coils.
i.e., ESNP=IPIS ....(2)
From equations (1) and (2)
ESEP=NSNP=IPIS=k
Where k is called transformer ratio.
(for step up transformer k>1 and for step down transformer k<1)
In a step up transformer ES>EP implying that IS<IP. Thus a step up transformer increases the voltage by decreasing the current, which is in accordance with the law of conservation of energy. Similarly a step down transformer decreases the voltage by increasing the current.
Efficiency of transformer is defined as the ratio of output power to the input power.
η=OutputpowerInputpower=ESISEPIP
The energy losses of a transformer are (i) Copper less, (ii) Hysteresis loss, (iii) Eddy current loss, (iv) Flux loss.
Construction and Working:
This principle can be demonstrated and explained through Faraday's experiments.
A transformer consists of primary and secondary coils insulated from each other, wound on a soft iron core (figure). To minimise eddy current a laminated iron core is used. The a.c. input is applied across the primary coil. The continuously varying current in the primary coil produces a varying magnetic flux in the primary coil, which in turn produces a varying magnetic flux in the secondary. Hence, an induced emf is produced across the secondary.
Let EP and ES be the induced emf in the primary and secondary coils and NP and NS be the number of turns in the primary and secondary coils respectively. Since same flux links with the primary and secondary, the emf induced per turn of the two coils must be the same
i.e., EPNP=ESNS
(or) EPEP=NSNP ....(1)
For an ideal transformer, input power = output power
EPIP=ESIS
where IP and IS are currents in the primary and secondary coils.
i.e., ESNP=IPIS ....(2)
From equations (1) and (2)
ESEP=NSNP=IPIS=k
Where k is called transformer ratio.
(for step up transformer k>1 and for step down transformer k<1)
In a step up transformer ES>EP implying that IS<IP. Thus a step up transformer increases the voltage by decreasing the current, which is in accordance with the law of conservation of energy. Similarly a step down transformer decreases the voltage by increasing the current.
Efficiency of transformer is defined as the ratio of output power to the input power.
η=OutputpowerInputpower=ESISEPIP
The energy losses of a transformer are (i) Copper less, (ii) Hysteresis loss, (iii) Eddy current loss, (iv) Flux loss.
Suggest Corrections
0
Similar questions
View More
Join BYJU'S Learning Program
Explore more
Join BYJU'S Learning Program
