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(a) Explain speed torque characteristics of single phase
semi-converter fed series motor withappropriate circuit and
waveforms.
(b) A dc series motor is coupled to a load whose torque varies
as square of speed. The motor
is fed through a semi-converter from a transformer whose
secondary voltage is 675V. When
the firing angle is 90.5 , the motor speed and armature current
are 350rpm and 30A. It is
desired to raise the speed to 50Orpm. Find armature current and
firing angle of semi-
converter. Assume that magnetic circuit is unsaturated. Armature
and field resistances are0.22 ohm each.
(a) Explain the chopper control of de separately excited motor•
for forward motoring andbraking control.
(b)A 200V, 94Orpm separately excited dc motor has armature
resistance of 0.02ohrn. The
motor is fed from single quadrant step down chopper. The input
to chopper is 200V.
Assume continuous conduction and find duty cycle of chopper for
motoring at rated torqueat 500rprri. The rated armature current is
100A.
Q2.
Q3.
Q4.
Q 5
Q6 a) Explain each component of block diagram of PLC and the
different ways of itsprogramming.
(b) Draw and explain the block diagram of separately excited de
drive for fou• quadrantoperation.
(a)Calculate the starting and plugging time analytically for
induction motor under no load
condition in terms of mechanical time constant and the slip at
which maximum torqueoccurs.
(b)A 400V, 50Hz, 8-pole, three phase star connected induction
motor has following
parameters: R = R =0.1 Q, X r = X = 0.4 Q .The inertia of motor
is 10 kg-m . Find the starting time.(a)
Compare the slip power recovery methods of speed control for
slip ring induction motorwith appropriate circuit diagrams.
(b) A 400V, 50Hz, 4-pole, 1350rpm star-connected induction motor
is driving a load whose
torque varies as square of speed. The motor speed is controlled
by stator voltage control.
Find torque and applied voltage at a speed of 900rpm. The
parameters of the given motorare : 1.5 0, R = 4 Q, X2 = 4 Q.
(a) Explain the 3- induction motor V-f method of speed control
and different modes of
operation and variations of synchronous speed, stator current,
torque and power output withper unit frequency.
(b) Explain the CSI induction motor drives and enumerate its
features.
Name of the student:oll No.:
THAPAR UNIVERSITY, PATIALADEPARTMENT OF ELECTRICAL
ENGINEERING
B.E. EE (VII - Semester) ESE EE-80I : Electric DrivesDecember
16, 2014 Tuesday, 9.00 — 12.00 Hrs
Time: 03 Hours; Maximum Marks (M. M.): 40ame of Faculty: Dr.
Amrita Sinha
Note:
• Answer all the questions.
• nswer all parts of the question at same place only, otherwise
it may attract negative marks.• Complete answer of any question
should be written at one place only, otherwise it may attract
negative marks.
• Draw the neat diagrams, wherever required.
