# ELECTRICAL100 IMPORTANT EXPECTED MCQ PDF WITH SOLUTION FOR VIZAG MT EXAM 2017

Here we are  providing 100 percentage expected questions with solution,these 100 questions have asked in various exam many times,that means this type questions will be surely ask in upcoming exam.
Q.1
The two windings of a transformer  is

(C)

# Ans : B

Q.2     A
salient pole synchronous motor is running at no load. Its field current is switched off.
The motor will
(A)
come to stop.
(B)       continue
to run at synchronous  speed.
(C)
continue to run at a speed slightly more
than the synchronous   speed.
(D)
continue to run at a speed slightly less
than the synchronous   speed.

# Q.3   The d.c. series motor should always be started with load   because

(A)    at
no load, it will rotate at dangerously high  speed.
(B)    it
will fail to start.
(C)    it
will not develop high starting  torque.
(D)    all
are true.

# Ans: A

Q.4  The
frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at
(A)   50 Hz.                                              (B)  20 Hz.
(C)   2 Hz.                                                (D)  Zero.

# Ans: C

Q.5
In a stepper motor the angular  displacement
(A)      can
be precisely controlled.
(B)       it
cannot be readily interfaced with micro computer based   controller.
(C)      the
angular displacement cannot be precisely  controlled.
(D)      it
cannot be used for positioning of work tables and tools in NC   machines.

# Ans: A

Q.6     The
power factor of a squirrel cage induction motor  is
(A)
(B)       low
(C)
low at light and heavy load  both.
(D)

# Ans: A

Q.7     The
generation voltage is  usually
(A)    between
11 KV and 33 KV.            (B)  between
132 KV and 400  KV.
(C)  between
400 KV and 700 KV.         (D)  None
of the above.

# Ans: A

Q.8     When
a synchronous motor is running at synchronous speed, the damper winding  produces
(A)
damping torque.
(B)
eddy current torque.
(C)
torque aiding the developed  torque.
(D)    no torque.

# Ans: D

Q.9     If
a transformer primary is energised from a square wave voltage source, its
output voltage will be
(A)       A square wave.                            (B)  A
sine wave.
(C)
A triangular wave.                           (D)  A
pulse wave.

# Ans: A

Q.14       In
a transformer the voltage regulation will be zero when it operates   at
(A)    unity p.f.                                         (B)  leading p.f.
(C)  lagging p.f.                                      (D)  zero

# Ans: B

Q.15 The
maximum power in cylindrical and salient pole machines is obtained

(A)  90○ ,90○ .                                         (B)  < 90○ ,90○ .
(C)  90○ ,
>
90○ .                                    (D)  90○ , < 90○ .

# Ans: D

Q.16  The
primary winding of a 220/6 V, 50 Hz transformer is energised from 110 V, 60 Hz
supply.   The secondary output voltage
will be
(A)  3.6 V.                                             (B)  2.5 V.
(C) 3.0 V.                                              (D)  6.0 V.

# Ans: C

Q.17       The
emf induced in the primary of a  transformer
(A)    is
in phase with the flux.                (B)  lags
behind the flux by 90  degree.
the flux by 90 degree.           (D)  is
in phase opposition to that of  flux.

# Ans: C

Q.18 The
relative speed between the magnetic fields of stator and rotor under steady
state operation is zero for a
(A)    dc machine.                                    (B)  3
phase induction  machine.
(C)  synchronous machine.                   (D)  single
phase induction  machine.
Ans: all options are correct
Q.19  The
current from the stator of an alternator is taken out to the external load
circuit through
(A)    slip rings.                                      (B)
commutator segments.
(C) solid connections.                           (D)  carbon
brushes.

# Ans: C

Q.20  A
motor which can conveniently be operated at lagging as well as leading power
factors is the
(A)    squirrel
cage induction motor.        (B)  wound
rotor induction  motor.
(C)   synchronous motor.                      (D)  DC
shunt motor.

# Ans: C

 Q.21 A hysteresis motor (A)  is not a self-starting  motor. (B)  is a constant speed  motor. (C)  needs dc excitation. (D)  can not be run in reverse  speed. Ans: B
Q.22       The
most suitable servomotor for low power applications   is
(A)         a
dc series motor.
(B)
a dc shunt
motor.
(C)
an ac two-phase induction  motor.
(D)
an ac series motor.

# Ans: B

Q.23       The
size of a conductor used in power cables depends on   the
(A)    operating voltage.                           (B)  power factor.
(C)  current
to be carried.                      (D)  type
of insulation used

# Ans: C

Q.24       Out
of the following methods of heating the one which is independent of supply
frequency is
(A)    electric arc heating                          (B)  induction heating
(C)  electric resistance heating               (D)  dielectric heating

# Ans: C

Q.25   A
two-winding single phase transformer has a voltage regulation of 4.5% at
load the voltage regulation will be

(A)  4.5%.                                                (B)  less than 4.5%.
(C)  more than 4.5%.                               (D)  4.5%
or more than  4.5%.

# Ans: C

% R = Vr  cos F
+ Vx  sin
F
= Vr
p.f = cos F =1  F =00

kVA = kW & kVAR =0

No reactive power  component
Percentage regulation (%R) = Vr  cos F
± Vx  sin
F
When   cos F = 0.8 lagging
%R = Vr  cos F
+ Vx  sin
F
= Vr  (0.8) + Vx (0.6)
%R = (0.8)Vr +(0.6) Vx at
p.f 0.8 lagging and  %R = Vr   at   unity p.f
Q.26  In a dc shunt motor the terminal voltage is
halved while the torque is kept constant.

The resulting approximate variation in speed  ‘ w’  and armature current  ‘ Ia ‘  will be
(A)    Both  w  and  Ia are doubled.         (B)   w  is constant and  Ia is doubled.
(C)
w is doubled while Ia is halved.    (D)   w
is constant but   Ia  is
halved.

# Ans: B

N a V – IaR     or N a Eb T a Ia F ,  F  a Ia
T a Ia2
Q.27    A balanced three-phase, 50 Hz voltage is
applied to a 3 phase,  4 pole,
induction  motor. When the motor is
delivering rated output, the slip is found to be 0.05. The speed of the rotor
m.m.f. relative to the rotor structure  is
(A)   1500 r.p.m.                                  (B)  1425 r.p.m.
(C)  25
r.p.m.                                       (D)  75 r.p.m.

# Ans: D

NS = 120f /P = 120 x 50 /4 =1500rpm N = NS  ( 1-s) =
1500 (1-0.05) = 1425
relative
speed  = 1500 – 1425 = 75  rpm

Q.28  An
alternator is delivering rated current at rated voltage and 0.8 power-factor
lagging case. If it is required to deliver rated current at rated voltage and
0.8 power-factor leading, the required excitation will

be

(A)    less.                                               (B)  more.
(C)  more or less.                                  (D)  the same.

# Ans: B

power factor and under excitation gives lagging p.f   .

Q.29       A
ceiling fan uses
(A)    split-phase motor.
(B)      capacitor
start and capacitor run  motor.
(C)      universal motor.
(D)      capacitor
start motor.

# Ans: D

To give starting torque and to
maintain  speed.
Q.30     A stepper motor is
(A)    a dc motor.                                    (B)  a
single-phase ac motor.
(C)  a multi-phase motor.                     (D)  a
two phase motor.

# Ans: D

Stepper motor works on
1-phase-ON or 2-phase –ON modes of
operation
Q.31
The ‘sheath’ is used in cable  to
(A)    provide
strength to the cable.
(B)    provide
proper insulation.
(C)    prevent
the moisture from entering the  cable.
(D)    avoid
chances of rust on  strands.

# Ans: A

The sheath in underground cable
is provided to give mechanical
strength.
Q.32       The
drive motor used in a mixer-grinder is  a
(A)    dc motor.                                       (B)  induction motor.
(C)  synchronous motor.                      (D)  universal motor.

# Ans: D

The universal motor is suitable
for AC & DC both supply   systems.

Q.33  A 1:5 step-up transformer has 120V across
the primary and 600 ohms resistance across the secondary.   Assuming 100% efficiency, the primary
current  equals
(A)    0.2 Amp.                                       (B)  5 Amps.
(C)  10
Amps.                                       (D)  20 Amps.

# Ans: A

I1=
V1  /R1  =
120/600 = 0.2  (h = 100%, losses are zero V1  = VR  = I1R1)
Q.34   A dc shunt generator has a speed of 800 rpm
when delivering 20 A to the load at the terminal voltage of  220V.
If the same machine is  run as  a motor it takes a line  current of 20A from 220V supply.  The speed of the machine as a motor will   be
(A)    800 rpm.                                        (B)  more
than 800 rpm.
(C)  less
than 800 rpm.                        (D)  both
higher or lower than 800  rpm.

# Ans: C

Ng= Eg  (60A
/ Fpz)                        Eg  = V + Ia  Ra ;
in generator
Nm= Eb  (60A / Fpz)                       Eb
= V – Ia  Ra ; in motor Eg
> E b  for same terminal voltage
Therefore,  Ng  > N m
Q.35
A 50 Hz, 3-phase induction motor has a full
load speed of 1440 r.p.m. The number of poles of the motor are
(A)  4.                                                   (B)  6.
(C)  12.                                                 (D)  8.

# Ans: A

N= Ns (1-S) = NS –NS x S 1440 = Ns
(1-S)
Ns     =  1440 / (1-S)
Ns = (120 f/ p) = 120 x 50/p = 6000 p Ns
will be closer to N i.e 1440
When P=2 ; Ns = 3000 rpm , not close to N
When P=4 ; Ns = 1500 rpm ,
it is closer to N Therefore P =4 for N=1440

Q.
36   In a 3-phase synchronous  motor
(A)        the
speed of stator MMF is always more than that of rotor  MMF.
(B)       the
speed of stator MMF is always less than that of rotor  MMF.
(C)       the
speed of stator MMF is synchronous speed while that of rotor MMF is zero.
(D)       rotor
and stator MMF are stationary with respect to each   other.

# Ans: D

Because, Motor is magnetically locked into position with stator, the
rotor poles are engaged with stator poles and both run synchronously in same
direction Therefore,  rotor & stator
mmf are stationary w.r.t each  other.
Q.37       In
a capacitor start single-phase induction motor, the capacitor is   connected
(A)  in
series with main winding.
(B)  in
series with auxiliary  winding.
(C)  in
series with both the  windings.
(D)  in
parallel with auxiliary  winding.

# Ans: B

To make single
phase motor self start. We split the phases at 90 degree. Hence, motor behaves
like a two phase  motor.
Q.38       A
synchro has
(A)       a
3-phase winding on rotor and a single-phase winding on   stator.
(B)       a
3-phase winding on stator and a commutator winding on   rotor.
(C)       a
3-phase winding on stator and a single-phase winding on   rotor.
(D)    a
single-phase winding on stator and a commutator winding on   rotor.

# Ans: C

Synchros : The
basic synchro unit called a synchro transmitter.  It’s
construction  similar to that of a
Three phase  alternator.
Q.39       As
the voltage of transmission increases, the volume of   conductor
(A)    increases.                                        (B)  does
not change.
(C)  decreases.                                       (D)   increases proportionately.

# Ans: C

Decreases due
to skin effect.

Q.40       The
size of the feeder is determined primarily  by
(A)    the
current it is required to  carry.
(B)    the
percent variation of voltage in the  feeder.
(C)    the
voltage across the feeder.
(D)    the
distance of transmission.

# Ans: A

Size of conductor depends upon
amount of current  flow.
Q.
41   The boundary of the protective zone is
determined by   the
(A)    Location of CT                              (B)  sensitivity
of relay used
(C)  Location of PT                               (D)  None
of these

# Ans: B

The boundary of
the protective zone is determined  by the
sensitivity of relay used. If  the relay
is more sensitive, the protective zone will be
increased.

Q.42 In
a three phase transformer, if the primary side is connected in star and
secondary side is connected in delta, what is the angle difference between
phase voltage in the two cases.

(A)   delta
side lags by -30°.                    (B)  star side lags by -30°.
(C) delta side leads by 30°.                    (D)  star

# Ans: C

This is vector group and has +30° displacement. Therefore, delta side
Q.43       To
achieve low PT error, the burden value  should
be                   .
(A)       low                                                (B)  high
(C)  medium                                          (D)  none of the above

# Ans: A

In a Potential
transformer, burden should be in permissible range to maintain errorless
measurement.
Q.44 Slip
of the induction machine is 0.02 and the stator supply frequency is 50 Hz. What
will be the frequency of the rotor induced  emf?
(A)   10 Hz.                                            (B)  50 Hz.
(C)  1
Hz.                                               (D)  2500 Hz.

# Ans: C

Given : s = 0.02 ; f = 50 Hz
Therefore, frequency of rotor
induced emf = s  f
=
0.02 x 50 = 1.0 Hz
Q.45  A
4 pole lap wound dc shunt motor rotates at the speed of 1500 rpm, has a flux of
0.4 mWb and the total number of conductors are 1000. What is the value of   emf?
(A)  100 Volts.                                        (B) 0.1 Volts.
(C)  1
Volts.                                           (D)  10 Volts.

# Ans: D

Given  N = 1500 rpm, F
= 0.4 mWb,   Z = 1000,  P = 4, &
A=   4
Therefore, Eb  = NFPZ
/ 60 A
= 1500 x 0.4 x 4 x 1000 x 10-3 / 60 x 4
= 60/6 = 10 volts
Q.46       The
synchronous reactance of the synchronous  machine is                      .
(A)       Ratio
between open circuit voltage and short circuit current at constant field
current
(B)       Ratio
between short circuit voltage and open circuit current at constant field
current
(C)       Ratio
between open circuit voltage and short circuit current at different field current
(D)       Ratio
between short circuit voltage and open circuit current at different field
current

# Ans.  A

The Synchronous
reactance of a synchronous machine is a total steady state reactance, presented
to applied voltage, when rotor is running synchronously without    excitation.
Therefore , XS  = Ef  / IS
= Emf of OC for same If  / short
circuit  current
Q.47       A
3
stack
stepper
motor
with
12
numbers
of
rotor
teeth
has
a
step
angle
of
.
(A)   12°                                                (B)
(C)  24°                                                  (D)  10°

# Ans. D

Given m = 3,  Nr  = 12
Step angle = 360 / m x Nr  = 360 /3 x 12 =  10°

Q.48       In
case of a universal motor, torque pulsation is minimized  by
_          .
(A)   load inertia                                      (B)  rotor inertia
(C) both rotor and load inertia               (D)  none of the above

# Ans: C

In a
universal motor, torque pulsation is minimized by rotor and load   inertia.
Q.49       Oil-filled
cable has a working stress of               _ kV/mm
(A) 10                                                    (B) 12
(C) 13                                                    (D) 15

# Ans: D

This is
defined by dielectric strength of mineral oil i.e. 15   kV/mm.
Q.50       Inverse
definite minimum time lag relay is also  called
(A)     pilot relay.                                      (B) differential relay.
(C) over current relay.                           (D) directional overcurrent  relay.

# Ans: B

Inverse definite minimum time lag relay characteristic is inverse but
minimum time is fixed. The operating time is inversely proportional to the
magnitude of actuating quantity.
Q.51       Specific
heat of nickel –chrome is                     _
(A)  0.112                                              (B)  0.106.
(C)  0.108.                                             (D)  0.110.

# Ans: None of these

Specific heat
of Nickel-Chrome is 440 J/kg°C to
450   J/kg°C

Q.54       The
speed-torque characteristics of a DC series motor are approximately similar
to   those of the    _motor.
(A)    universal                                         (B)  synchronous
(C)  DC
shunt                                         (D)  two-phase

# Ans: A

Universal motor
has same characteristics as DC series motor and also known as an a.c series
motor.
Q. 55    The rotor  frequency for
a 3  phase  1000
RPM  6  pole induction  motor
with  a slip of
0.04 is             _Hz
(A)    8                                                    (B) 4
(C)    6                                                   (D)  2

# Ans: D

Given: N=1000 rpm ; P= 6; s=
0.04;
and
f  =  N×P/ 120
= 1000×6/120
= 50 Hz
Rotor frequency         fr=s×f   = 0.04×50
= 2.0 Hz

Q.56       The   torque-speed   characteristics   of
an   a.c.   operated
universal   motor   has
a
characteristic and it

(A)
inverse, can                             (B) nearly inverse, can
(C)       inverse, cannot                        (D) nearly inverse, cannot

# Ans:  C

If torque is
zero then speed may exceed up to infinite, that is dangerous for machine and
machine can be  damaged.
N
a 1/ T

Q.57  In
the heating process of the              type
a simple method of temperature   control is possible
by means of a special alloy which loses its magnetic properties at a particular
high temperature and regains them when cooled to a temperature below this   value.

(A)
Indirect induction over               (B)  core
type induction  furnace
(C)      coreless induction
furnace          (D)  high
frequency eddy  current

# Ans: D

Magnetic
property of alloy changes with change of the temperature and Heat is  produced due to eddy current = i2R  and i a
f2

Q.58       Q.58 In order to reduce the harmful effects of harmonics on the A.C. side of a high voltage
D.C.
transmission system _        are provided.
(A)  synchronous condensers                (B)  shunt capacitors
(C)      shunt filters                                 (D)
static compensators

# Ans: C

Xc=
1/ c
Q.59   An  a.c.
tachometer  is   just  a               with  one
phase  excited  from  the carrier frequency.
(A)     two-phase A.C. servomotor          (B)
two-phase induction  motor
(C)
A.C. operated universal motor      (D) hybrid stepper motor.

# Ans: D

This is a
special purpose machine whose stator coil can be energized by electronically
switched current.

Q.60       The
torque, in a                        is
proportional to the square of the armature  current
(A)      DC shunt motor                             (B) stepper motor
(C) 2-phase servomotor                         (D) DC series motor

# Ans: D

Ta a 0.Ia  and  0 a Ia  ;
therefore  Ta a Ia2

Q.61 The
synchronous speed for a 3 phase 6-pole induction motor is 1200  rpm.
If  the number of poles is now
reduced to 4 with the frequency remaining constant, the rotor speed with a slip
of 5% will be        .

(A) 1690 rpm                                        (B) 1750 rpm
(C) 1500 rpm                                        (D) 1710 rpm

# Ans: D

Given : Ns1 =1200 , P1= 6, P2  = 4, s = 0.05,
Frequency   f
= Ns×P/120
= 120×6/120   = 60 Hz
rotor frequency  f/  = s.f =
0.05 ×60  = 3.0
Hz
Now, Ns2 = 120 ×60 /4  = 1800  and   Ns – N = 120 f / P2
Therefore, N=Ns- 120 f / P2 = 1800-120×0.05×60/4 = 1800-90 =    1710
Q.62
The eddy current loss in an a-c electric
motor is 100 watts at 50 Hz. Its loss at 100 Hz will be
(A)  25 watts                                          (B) 59
watts
(C) 100 watts                                        (D) 400 watts

# Ans: D

Eddy current losses a f2 New loss a (2f)2
New loss a 4f2

4 times

Q.63 The
maximum power for a given excitation in a synchronous motor is developed when
the power angle is equal  to

(A)    0o                                                                  (B) 45o
(C) 60o                                                                  (D) 90o

# Ans: A

P = VI cosF Pmax  = VI
F = 00

Q.  64    A
commutator in a d.c.  machine
(A)
Reduces power loss in  armature.
(B)
Reduces power loss in field  circuit.
(C)
Converts the induced a.c armature voltage
into direct   voltage.
(D)
Is not necessary.

# Ans: C

As name suggests, it commutes ac
into  dc.
Q.65   The speed of a d.c. shunt motor at no-load  is
(A)     5 to 10%                                     (B) 15 to 20%
(C)    25 to 30%                                    (D)  35
to 40%
higher than its speed at

# Ans: A

Ta a F Ia ,, F = constant,
T a Ia
N a Eb / F  or  N a Eb  initially Eb less , so
speed  is less.
Q.66   The efficiency of a transformer is mainly
dependent  on
(A)   core losses.                                   (B) copper losses.
(C)   stray losses.                                  (D) dielectric losses.

# Ans: A

Core loss has prominent value
over other  losses
Q.67  When two transformers are operating in
parallel, they will share the load a under:
(A)  proportional to their  impedances.
(B)
inversely proportional to their  impedances.
(C)  50%
– 50%
(D)  25%-75%

# Ans: A

High rating transformer has higher impedance. kVA rating a Impedance of transformer

Q.69  A 3-phase, 400 votts, 50 Hz, 100 KW, 4 pole
squirrel cage induction motor with a
rated slip of 2% will have a rotor speed  of
(A)     1500 rpm                                    (B) 1470 rpm
(C)     1530 rpm                                    (D) 1570 rpm

# Ans: B

N = NS  (1-S) and NS  =120 f / p
=120 x 50 /4  = 1500 rpm
N=
1500 (1-0.02) =1470  rpm
Q.71
The voltage at the two ends  of a transmission line are 132 KV and its
reactance is      40 ohm. The Capacity of
the line  is
(A) 435.6 MW                                      (B) 217.8 MW
(C) 251.5 MW                                      (D) 500 MW

# Ans: A

Line capacity is
determined by power of line P = (V2/R)
or   (V2/Z) when cos F  =1
Q.72 A
220/440 V, 50 Hz, 5 KVA, single phase transformer operates  on
220V,  40Hz supply with secondary
winding open circuited.  Then
(A)    Both
eddy current and hysteresis losses  decreases.
(B)    Both
eddy current and hysteresis losses  increases.
(C)
Eddy current loss remains the same but
hysteresis loss   increases.
(D)    Eddy
current loss increases but hysteresis loss remains the   same.

# Ans: A

Wh  =
khfBm1.6  and  We  = kef2Bm2.k
Therefore,
hysteresis and eddy current losses will be decreased when frequency decreases.

Q.73   A synchronous motor is operating on no-load
at unity power factor. If the field current is increased, power factor will  become
(A)
(B)
Lagging & current will  increase.
(C)
Lagging & current will  decrease.
(D)

# Ans: A

Initially synchronous motor is operating at no load  and
unity power  factor.  When field current increases, the excitation
will increase. Therefore, p.f will be leading and current will be I CosF < I

Q.74 A
d.c. shunt motor runs at no load speed of 1140 r.p.m. At full load, armature
reaction weakens the main flux by 5% whereas the armature circuit voltage drops
by 10%. The motor full load speed in r.p.m.  is

(A) 1080                                                (B)  1203
(C) 1000                                               (D)  1200

# Ans: A

N2 / N1  =Eb2 /Eb1   x F1 / F2 ;      F2  = 0.95F1  ;   Eb2 = 0.9Eb1
N2 /1140 = 0.9 x 1/0.95 N2   = 1080
Q.75
The introduction of interpoles in between
the main pole improves the performance    of
d.c.
machines, because
(A)
The interpole produces additional flux to
augment the developed   torque.
(B)
The flux waveform is improved with reduction
in   harmonics.
(C)       The inequality of air flux on the top and
bottom halves of armature is removed.
(D)
A counter e.m.f. is induced in the coil
undergoing   commutation.

# Ans: D

Counter e.m.f  is produced, it neutralizes the reactive  emf.

Q.76 The
rotor power output of a 3-phase induction motor is 15 KW and corresponding
slip  is 4%. The rotor copper loss will  be

(A) 600 W.                                            (B)  625 W
(C)  650 W                                           (D)  700 W

# Ans: B

Rotor copper
losses = rotor input- rotor output and output = (1-s) input

Input = output/(1-s) = 15000 /1-0.04 =
15625

loss = 15625 -1500 = 625  watt

Q.77 The direction of rotation of hysteresis
motor is reversed  by
(A)
Shift shaded pole with respect to main  pole
(B)
(C)
Either A or
B
(D)
Neither A nor B

# Ans: A

This motor used
single phase, 50Hz supply and stator has two windings. These are connected
continuously from   starting to running.
Q.78  A 1.8°step, 4-phase stepper motor has a
total of 40 teeth on 8 pole of stator. The number of rotor teeth for their
rotor will  be
 (A)   40 (C)  100 (B)  50 (D)  80 Ans: B Step angle ‘þ’ = NS  – Nr  / NS Nr x 3600 1-8 = -40 + Nr/40 Nr  x 3600 Nr   = 50 Q.79 Low head plants generally  use (A)     Pelton Turbines (B) Francis Turbine (C)     Pelton or Francis Turbine (D) Kaplan Turbines

# Ans: A

In the hysterisis motor, the direction of rotation can be reversed by
shifting the shaded pole region with respect to main pole. But not by changing
supply lead because it has ac supply.

Q.80 The
charging reactance of 50 Km length of line is 1500fi. The charging reactance
for 100Km length of line will  be

(A) 1500 fi                                       (B) 3000 fi
(C) 750 fi                                        (D) 600 fi

# Ans: B

Characteristic reactance per km
= 1500/50 = 30  ohms

Characteristic reactance per 100km =  30
x 100 = 3000   ohms

Q.81  Electric ovens using heating  elements of                           can produce
temperature upto 3000°C.
(A)    Nickel                                            (B)  Graphite
(C)  Chromium                                     (D)  Iron

# Ans: C

Chromium has high melting  point.
Q.82   In DC generators, armature reaction is
produced actually   by
(A)    Its field current.                             (B)
Armature conductors.
(C)  Field pole winding.                        (D)  Load current in  armature.

# Ans: D

current in armature gives rise to armature mmf which react with main field mmf.
Q.83  Two transformers operating in parallel will
share the load depending upon   their
(A)    Rating.                                           (B)
Leakage reactance.
(C) Efficiency.                                     (D)
Per-unit impedance.

# Ans: A

Transformers having higher kVA

Q.84  As
compared to shunt and compound DC motors, the series DC motor will have the
highest torque because of its comparatively                                                          at the start.

(A)   Lower armature
resistance.           (B)  Stronger
series field.
(C)  Fewer series turns.                         (D)   Larger armature
current.

# Ans: D

T a F Ia
(before saturation)
F a Ia
T a Ia 2

Q.85 A
400kW, 3-phase, 440V, 50Hz induction motor has a speed  of 950 r.p.m. on full-  load. The machine has 6 poles. The slip of
the machine  will be

.

(A)  0.06                                               (B)  0.10
(C)  0.04                                               (D)  0.05

# Ans: D

N = Ns  (1-S)
950 = 120 x 50 (1-S)/6
S = 0.05
Q.86 Reduction in the capacitance of a
capacitor-start motor, results in   reduced
(A)
Noise.                                         (B)  Speed.
(C)     Starting torque.                            (D)
Armature reaction.

# Ans: C

Reduction in
the capacitance reduces starting voltage, which results in reduced starting
torque.
Q.87  Regenerative braking
(A)
Can be used for stopping a  motor.
(B)
Cannot be easily applied to DC series  motors.
(C)
Can be easily applied to DC shunt  motors
(D)
Cannot be used when motor load has
overhauling   characteristics.

# Ans: B

Because reversal of Ia  would
also mean reversal of field and hence of
Eb
Q.88 At present level of technology, which of the
following method of generating electric power from sea is most  advantageous?
(A)       Tidal power.                               (B)  Ocean
thermal energy  conversion
(C)     Ocean currents.                           (D)  Wave power.

# Ans: A

At present
level of technology, tidal power for generating electric power from sea  is most advantageous because of constant
availability of tidal   power.

Q.89  If
the field circuits of an unloaded salient pole synchronous motor gets suddenly
open circuited, then

(A)    The
motor stops.
(B)    It continues to run at the same  speed.
(C)    Its
runs at the slower speed.
(D)    It
runs at a very high speed.

# Ans: B

The motor
continues to run at the same speed because synchronous motor speed does not

Q.90   Electric resistance seam welding
uses                  electrodes.
(A)    Pointed                                         (B) Disc.
(C)  Flat                                                (D) Domed

# Ans: B

Disc type electrodes are used
for electric resistance seam   welding.
Q.91  For LV applications (below 1 kV),

cables are used.
(A)    Paper insulated.                             (B)

Plastic.
(C)  Single
core cables.                         (D) Oil filled.

# Ans: C

For low voltage applications
single core cables are   suitable.
Q.92   No load current in a  transformer:
(A)    lags
the applied voltage by  90°
(B)    lags
the applied voltage by somewhat less than  90°
the applied voltage by  90°
the applied voltage by somewhat less than  90°

# Ans: B

The primary input current under no load
conditions has to supply  (i) iron
losses in   the core i.e hysteresis loss
and eddy current loss (ii) a very small amount of Cu loss in the primary (there being no Cu loss in
secondary as it is   open)
Q.95   The armature of a dc machine is laminated to reduce:
(A)    Eddy current
loss                          (B)  Hysteresis loss
(C)  copper losses                                (D)  friction
and windage  losses

# Ans: A

Thinner the laminations, greater is the resistance offered to the  induced
e.m.f.,  smaller the current and
hence lesser the I2R loss in the   core.
Q.97
A single phase Hysteresis  motor
(A)    can
run at synchronous speed  only
(B)    can
run at sub synchronous speed  only
(C)    can
run at synchronous and super  synchronous
speed
(D)    can
run at synchronous and sub  synchronous  speed

# Ans: A

The rotor
revolves synchronously because the rotor poles magnetically lock up with  the revolving stator poles of opposite  polarity
Q.  98    The
temperature of resistance furnaces can be controlled by changing   the:
(A)    applied voltage                             (B)
number of heating elements
(C)  circuit configuration                     (D)  All
of the above

# Ans: D

Temperature of
resistance furnaces can be controlled by changing either applied voltage or by
number of heating elements or by circuit
configuration.
Q.99     The line trap unit employed in carrier
current  relaying:
(A)
offers high impedance to 50 Hz power
frequency  signal
(B)    offers
high impedance to carrier frequency  signal
(C)
offers low impedance to carrier frequency  signal
(D)    Both
(A) & (C)

# Ans: B

The line trap
unit employed in carrier current relaying
offers  high  impedance
to  carrier frequency signal.
Because carrier
frequency range is 35 km – 500 kHz XL =
2M f
Where f increases XL  will also increases