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Electrical Engineering
Transformers
Quiz 1
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Q.1
The starting torque of a squirrel-cage induction motor is
low
negligible
same as full-load torque
slightly more than full-load torque
Q.2
Which of the following is not the standard voltage for power supply in India?
llkV
33kV
66 kV
122 kV
Q.3
When the equivalent circuit diagram of doouble squirrelcage induction motor is constructed the two cages can be considered
in series
in parallel
in series-parallel
in parallel with stator
Q.4
The use of higher flux density in the transformer design
reduces weight per kVA
reduces iron losses
reduces copper losses
increases part load efficiency
Q.5
A transformer has a 1:6 turns ratio and a secondary coil load resistance of 470 Ω. The load resistance as seen by the source is
1.3 Ω
7.8 Ω
78 Ω
13 Ω
Q.6
While conducting short-circuit test on a transformer the following side is short circuited
High voltage side
Low voltage side
Primary side
Secondary side
Q.7
Spacers are provided between adjacent coils
to provide free passage to the cooling oil
to insulate the coils from each other
both (A) and (B)
none of the above
Q.8
A shell-type transformer has
high eddy current losses
reduced magnetic leakage
negligibly hysteresis losses
none of the above
Q.9
The magnetising current of a transformer is usually small because it has
small air gap
large leakage flux
laminated silicon steel core
fewer rotating parts
Q.10
Which of the following insulating materials can withstand the highest temperature safely?
Cellulose
Asbestos
Mica
Glass fibre
Q.11
An ideal transformer has infinite values of primary and secondary inductances. The statement is
true
false
Q.12
During open circuit test of a transformer
primary is supplied rated voltage
primary is supplied full-load current
primary is supplied current at reduced voltage
primary is supplied rated kVA
Q.13
Which of the following is not a routine test on transformers?
Core insulation voltage test
Impedance test
Radio interference test
Polarity test
Q.14
In a transformer the tappings are generally provided on
primary side
secondary side
low voltage side
high voltage side
Q.15
No-load current in a transformer
lags behind the voltage by about 75°
leads the voltage by about 75°
lags behind the voltage by about 15°
leads the voltage by about 15°
Q.16
During short circuit test iron losses are negligible because
the current on secondary side is negligible
the voltage on secondary side does not vary
the voltage applied on primary side is low
full-load current is not supplied to the transformer
Q.17
If a transformer is continuously operated the maximum temperature rise will occur in
core
windings
tank
any of the above
Q.18
In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be
Ns
s.N.
(l-s)Ns
(Ns-l)s
Q.19
Distribution transformers are generally designed for maximum efficiency around
90% load
Zero load
25% load
50% load
Q.20
In case of 3-phase induction motors, plugging means
pulling the motor directly on line without a starter
locking of rotor due to harmonics
starting the motor on load which is more than the rated load
interchanging two supply phases for quick stopping
Q.21
The main reason for generation of harmonics in a transformer could be
fluctuating load
poor insulation
mechanical vibrations
saturation of core
Q.22
The purpose of providing iron core in a step-up transformer is
To provide coupling between primary and secondary
To increase the magnitude of mutual flux
To decrease the magnitude of magnetizing current
To provide all above features
Q.23
If R₂ is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be
R₂/√K
R₂/K²
R₂²/K²
R₂²/K
Q.24
Two transformers operating in parallel will share the load depending upon their
leakage reactance
per unit impedance
efficiencies
ratings
Q.25
The primary coil of a transformer is connected to a 60 V ac source. The secondary coil is connected to a 330 Ω load. The turns ratio is 3:1. What is the secondary voltage?
2 V
20 V
180 V
18 V
Q.26
Greater the secondary leakage flux
less will be the secondary induced e.m.f.
less will be the primary induced e.m.f.
less will be the primary terminal voltage
none of the above
Q.27
A transformer core is laminated to
reduce hysteresis loss
reduce eddy current losses
reduce copper losses
reduce all above losses
Q.28
Hysteresis loss in a transformer varies as (Bmax = maximum flux density)
Bmax
Bmax1-6
Bmax1-83
B max
Q.29
The no load current in a transformer lags behind the applied voltage by an angle of about
180°
120°
90°
75°
Q.30
Power transformers are generally designed to have maximum efficiency around
no-load
half-load
near full-load
10% overload
0 h : 0 m : 1 s
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