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WorksheetsTransformer 1
Total questions: 36
Worksheet time: 19mins
A laminated transformer core reduces the amount of energy that is wasted in the form of........
solidifying
flux
heat
Why transformers work with A.C. current but not D.C.
A.C current produces changing magnetic field.
D.C current produces changing magnetic field.
D.C current is weak
A.C current is powerful
Which of the following does not change in a transformer?
Voltage
Current
Power
Frequency
Ratio of voltages is equal to ratio of _______________________.
number of iron sheets in core
number of coil
number of turns in coil
number of electromagnetic
The magnetic material for the core needs to be made of soft iron where its permeability is high
to reduce eddy current loss
to reduce hysteresis loss
to avoid fringing in the core
to reduce copper loss in the winding
Transformer works on which of the following principle
Lenz’s Law
Ampere's Law
Faraday's Law of Electromagenetic Induction
Fleming's Law
What is the material used for construction of transformer core?
Aluminium
Copper
Iron
Wood
Mutual inductance is
interactions of one coils magnetic field on other coil as it induces a voltage in the adjacent coil
Interactions of one coils magnetic field on other coil as it induces a current in the adjacent coil.
Interactions of one coils magnetic field on other coil as it induces electrical energy in the adjacent coil
Induced voltage in primary and secondary winding depends on the following except for
Resistor, R
number of turns, N
magnetic flux
Frequency
In a transformer electrical power is transferred from primary to secondary
Through air
By magnetic flux
Through insulation medium
None of these
The efficiency of the power transformer is
50%
60%
80%
95%
The two windings of transformers are
Conductively linked
Inductively linked
Not linked at all
Electrically linked
Transformer action requires a
constant magnetic flux
increasing magnetic flux
alternating magnetic flux
alternating electric flux
The flux created by the current flowing through the primary winding induces emf in
primary winding only
secondary winding only
transformer core only
both primary and secondary windings
The iron core in a transformer provides a _______ path to a main flux
low reluctance
high reluctance
low resistance
high conductivity
If rated dc voltage applied instead of ac to the primary of a transformer
secondary of transformer will burn
primary transformer will burn
secondary voltage will be excessively high
there will be no secondary voltage
The core flux in transformer depends mainly on
supply voltage
supply voltage and frequency
supply voltage frequency and load
supply voltage and load but independent of frequency
The power factor of a power transformer on no load will be about
1
0.75
0.5
0.35
The power factor of a transformer on no load is poor due to
magnetizing reactance of the transformer
open-circuited secondary
low primary winding resistance
low no-load current
The flux in transformer core
increases with load
decreases with load
remains constant irrespective of load
none of the above
The primary ampere-turns are counter balanced by
secondary ampere-turns
primary flux
increase in mutual flux
increase in secondary current
In a transformer_________ decreases with the increase in leakage flux
primary induced emf
secondary induced emf
secondary terminal voltage
none of the above
The phasor diagram of a transformer on load can be drawn only if we know
equivalent circuit parameters of the transformer
load current
load p.f.
all of the above
In a transformer zero voltage regulation at full load is
not possible
possible at leading power factor load
possible at lagging power factor load
possible at unity power factor load
The main purpose of performing open circuit on a transformer is to measure its
Copper losses
Iron losses
Total losses
Insulation resistance
The transformer efficiency will be maximum at a power factor of
0.8 lead
Unity
0.8 lag
0.5 lag or lead
For a transformer copper losses are also known as
variable loss
iron loss
eddy current loss
losses in shunt parameter
For a transformer, core losses are not equivalent to
iron loss
sum of eddy current losses and hysteresis losses
losses in series parameters
losses in shunt parameters
In transformer which quantity do not remain same after transformer action at another winding end.
magnetizing flux
current
kVA
frequency
Which one is not the condition for ideal transformer.
Resistance of primary and secondary winding must be zero
Leakage flux must be zero.
Permeability must be zero.
Eddy current and Hysteresis losses must be zero.
For a 10 kVA single phase transformer, at what load efficiency would be maximum if iron loss and full rated copper losses are 200 W and 800 W respectively.
5 kVA
10 kVA
8 kVA
7.5 kVA
Which one is not correct for auto transformer
It has better voltage regulation in resistance and reactance of the single winding is less
It has lower efficiency than two winding transformer.
Used only for slight variation of the output voltage from input voltage
It is also used as a voltage regulator
Eddy current is the current which flows
at the surface of magnetic core
at the surface of primary and secondary copper winding
due to change in orientation of
magnetic dipoles
due to leakage of flux in air
If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be
Small
Zero
None of the these
Large
The main advantage of auto transformer over a two winding transformer is
Hysteresis losses are reduced
Saving in winding material
Copper losses are negligible
Eddy losses are totally eliminated
The efficiency of a transformer is maximum when
It runs at half full load
it runs at full load
its Cu loss equal iron loss
it runs over load
