1. Distinguish between core and shell type
type, the windings surround the core considerably and in shell type the core
surround the winding.
an ideal transformer and how does it differ from a practical transformer.
Ø An ideal
transformer is one which does not involve any power loss and does not have any
change in frequency. It decreases or increases the input voltage.
transformer is one which involves power loss and does not have any change in
frequency. It decreases or increases the input voltage.
3. Define voltage regulation in a transformer.
transformer is loaded with a constant primary voltage, the secondary voltage
decreases for lagging Power factor load, and increases for leading power factor
load because of its internal resistance and leakage reactance. The change in
secondary terminal voltage from no load to full load expressed as a percentage
of no loads or full load voltage is termed as regulation.
4. Write down the emf equation of a transformer.
induced in primary coil E1 = 4.44 fΦ mN1 volt Emf induced in secondary coil E2
= 4.44fΦ mN2 volt
is the frequency of AC input Φ m is the maximum value of flux in the core N1,
N2 are the number of primary and secon dary turns.
5. Define a transformer.
transformer is a static piece of apparatus by means of which electrical power
is transformed from one alternating current circuit to another with desired
change in voltage and current without any change in the frequency. It works on
the principle of mutual induction.
6. Why transformers are rated in kVA?
loss of a transformer depends on current and iron loss on voltage. Hence total
losses depend on Volt- Ampere and not on the power factor. That is why the
rating of transformers is in kVA and not in kW.
7. Why the core of a transformer is is laminated?
purpose of laminating the co re in a transformer is to reduce eddy current
8. Draw the equivalent circuit of a transformer.
9. An 1100/400 V, 50 Hz single phase transformer
has 100 turns on the secondary winding. Calculate the number of turns on its
V1 / V2 = k = N2 / N1
400/1100 = 100/N1
100/400 x 1100 = 275 turns.
the advantages of a transformer?
Ø Less I2R
loss in the transmission line
voltage drop in the line
of the transmission line is increased
Ø Volume of
the conductor required is less.
voltage transformation ratio of transformer.
of secondary induced emf to primary induced emf is called as voltage regulation
ratio devoted by K.
12. Draw the no load phasor diagram of a
13. Define all day efficiency.
efficiency is the ratio energy (in kwh) delivered in a 24 hours period to the
energy (in kwh) input for the same length of time.
efficiency = Output in kwh/Input in kwh (for 24 hrs)
factors that determine the thickness of the lamination or stampings.
the properties of ideal transformer?
It has no
winding has zero resistance.
Leakage flux is zero i.e 100% flux produced by
primary links with the secondary
of core is so high that negligible current is required to establish the flues
the losses occurring in a transformer?
meant by core or iron losses?
iron losses are caused as the core gets subjected to an alternating flux.
18. What is meant by copper loss?
copper losses are due to the power wasted in the form of I2R due to the
resistances of the primary and secondary windings.
19. What is meant by eddy current loss?
induced emf in the core tries to set up eddy currents in the core and hence
responsible for the eddy current losses.
20. What is meant by hysteresis losses?
alternating flux set up in the magnetic core of the transformer, it undergoes a
cycle of magnetization and demagnetization.
hysteresis effect there is loss of energy in this process which is called
21. What do you mean by step down transformer?
secondary voltage is greater than primary value, the transformer is called step
22. What are the functions of no-load current in a
current produces flux and supplies iron loss and copper loss on no-load.
the typical uses of auto transformer?
Ø To give
small boost to a distribution cable to correct for the voltage drop
induction motor starters
control equipment for single phase and 3 phase elective locomotives