Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 6th Semester (Sixth Semester) 2014-2015 Special Electrical Machines Question Paper
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(Following Paper ID and Roll No. to be ?lled in you Answer Book)
PAPER ID : 121656
Roll No.
B. Tech.
(SEM. VI). THEORY EXAMINATION, 2014-15
SPECIAL ELECTRICAL MACHINES
Time : 3 Hours] [Total Marks : 100
l Attempt any four parts of the following : 5X4=20
(a) Explain the e.m.f. injection in rotor circuit of slip ring
(b)
(C)
(d)
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induction motor by means of suitable phasor diagram.
A three phase 400 V double-cage induction motor has
per-phase standstill leakage impedance of 2+j2.5 Q
and 0.5+le Q for its two cages. Find the relative values
of torques given by each cage.
(1) Atstarting
, (ii) At 5% slip
Explain the Leblanc constant power drive system with
suitable diagram.
Explain the principle of operation of double?cage
induction motor and also draw the equivalent circuit.
1 [ Contd...
(e)
(f)
(a)
(b)
03
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Attempt any two parts of the following :
A 20 kW, three-phase 400V, 4-pole, 50 Hz squirrel
cage induction motorwhen working at rated voltage and
frequency develops a ?ll] load torque at'1470 rpm. If
the motor is fed from 40 Hz source with its voltage
adjusted to give the same air ?ux as at-50 Hz, then
calculate the magnitude of the 40 Hz voltage source.
A three-phase 500 kW, 50 Hz, induction motor has
a full load slip of 2 1%. The rotor circuit has standstill
~ impedance of 0 3 + jl 8 9 per phase. If an external
V resistance of 1.5 9 per phase 15 inserted 111 each of
rotor circuit, determine the slip and power output when V
the stator current has us full load value. Neglect stator
impedance and rotational losSes
loxz?zo
Explain the working principle of capacitor start capacitor
run induction motor with suitable phasor diagram. The
1 following data is obtained from a 230 V, 50, Hz,
capacitor start single phase inductiOn motor at standstill.
Main winding : 100V, 2A ' 40W
Auxiliary winding: 80V 1.0 A 50W
Determine the value of capacitor for attair?ng the value
of maximum torque.
Explain the principle of operation, of two phase servo
motor with the help of neat illustrations. Also mention
its advantages.
A 230 V, 4-pole 50 Hz, sihgle-phase induction motor
has the following data :
r1= 2.3 9, r2 = 4.2 Q,x1= 3.2 9, x2 = 3.2 Q,
X,11 = 74 Q , core loss = 98 watts, ??iction and windage
loss = 30 watts. If the motor is iunning with a slip 0.05
at rated voltage and frequency, compute the following :
2 [ Contd...
3
G?
(b)
(o)
4
(a)
(b)
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Attempt any two parts of the following :
Attempt any two parts of the following :
(1) Stator current
(11') Power factor
(Iii) Power output.
(1v) . Torque
(v) Ef?ciency with its anxiliary winding open;
10X2=20
Explain the principle of operation of 6/4 pole variable
reluctance stepper motor. What is the motor torque
required to accelerate'the initial load of '10?4/gm2 from
(91 = 200 and co 2 = 300 rad/sec. Frictional load torque
is 0.06 N-m .
Explain the principle of operation and operating modes
of switched reluctance motor
Write the short notes on the following :
(1) Split power supply converter. 7
(n) Clamic converter
10 X2=20
Explain the principle of operation and torque production
of three-phase three-pulse bmshless DC motor. Also
mention the advantages of brushless DC motor over the
couvent'mnal DC motor.
A three-phase four pole bmshless DC motor has 36
stator slots, each phase winding is made up of three
coils per pole with 20 turns per coil. The coil span is
7 slots. If the ?mdamental component of magnetic ?ux
is 1.8 m Wb. Calculate the open circuit phase e.m.f.
(Es) of 3000 rpm.
3 '[ Contd...
(c) Write the short notes on any two of the following :
(1) Static and Dynamic chatacteristic of stepper
motor.
(ii) Hysteresis motOr
(1ii) Single phase reluctance motor. '
S Attempt any two parts of the following : 10X2=20
(a) Explain the oneration of DC sen'es motor when
connected to an AC source and also draw the
phasor diagram of a single-phase series motor.
A series motor has a total resistance of 25 Q
and a total inductance of 0.2 H. The'motor runs
at 1000 rpm when it draws 1A from 220 V DC
source. Calculate the speed and power factor
when it draws the same current from 220V,
50 Hz source.
(b) Four pole lap connected armature has 450 turns
and rotates at 1200 rpm in a sine distributed
pulsating ?ux of frequency of 50 Hz and of
amplitude 0.018 Wb per pole. Calculate the
voltage and frequeney of the e.m.f. at the brushes
if the brush axes are
(1) 90? away from the ?eld axes.
(u) aligned along the ?eld axis and
(ii) 30? away from the ?eld axes.
(c) Write the short notes on the following :
(1) Linear induction motor
(1i) .Improving commutation method.
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This post was last modified on 29 January 2020