Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 7th Semester (Seventh Semester) 2015-2016 EEE 035EEE 702 Electric Drives Question Paper
(Following Paper ID and Roll No. to be ?lled in your
Answer Book)
Paper ID :120754/
121702 RollNo.
B.Tech.
(SEM. VII) THEORY EXAMINATION, 20l5-16
ELECTRIC DRIVES
[Time:3 hours] [Total Marks: 100]
SECTION?A
l. I Attempt all parts.A11parts carry equal marks.(2>< 10:20)
(a) Differentiate between ?group drive? and individual
drive?.
(b) Why a motor smaller rating can be selected for a
short time duty?
(c) A motor is couples to a load having the following
characteristics:
Motor : Tm=15-0.5 (Um
Load: T a) 2m
I=ll.5
(d) Enumerate different types of braking of do motor.
Which one is usually employed and why?
8300 (1) EEE-O35/EEE-702
(e)
(1')
(g)
(h)
(i)
G)
Attempt any five question from this section.
What is the function of Power modular in an
electric drive?
Why DC series motor is more suited to deal with
torque overloads than other DC motor.
Why the V/f is kept constant while controlling the
speed of a 3-phase induction motor?
What are the disadvantages of dc drives due to
which the three-phase induction motor drive is
replacing it?
Why half-wave converter is not used for supply to
the ?eld circiiit of dc motor?
What do you mean by Load Equalization?
SECTION?B
(10x5=50)
2. A drive has following parameters: J=10kg.m2,
T=15+0.05N, N-m and Tl=5+-().06N, N-m, where N is
the speed in rpm. Initially drive is working in steady State.
Now the drive is braked by the electric braking. Torque
ofthe motor in braking is given by T=10-0.04N, N?m.
Calculate time taken by the drive to stop.
8300
(2) EEE?O35/EEF?702
8300
(a)
(b)
What is heating time constant? Explain how the
rating of motor is affected by the temperature rise
ofElectric Motor.
A motor has a heating time constant 0f60 min and
a cooling time constant of 90 min. When run
continuously on full load of 20 kW. ?nal
temperature rise is 40?C. What load can be
delivered by the motor for 10 min if the initial
temperature rise is zero?
Describe selfcontrolled and load commutated inverter
controlled synchronous motor drive and compare them.
(a)
(b)
A 220 V, 970 rpm separately excited motor having
an armature resistance of 0.05 Q draws 100 A
from the source. The motor is to be braked by
plugging from an initial speed of 1000 rpm.
Calculate : (i) the resistance to be connected in
series with armature to limit the initial braking
current to twiceIthe rated current (ii) initial braking
torque (iii) the braking torque when the speed has
reduced to zero.
Explain dynamic braking of three phase induction
motor.
(3) P.T.O.
8300 (4)
A three phase fully controlled bridge converter is feeding
a separately excited dc motor. Assuming continuous load
current, derive the equation relating speed and torque of
the motor as a function of triggering delay ? a ?.
Explain stator voltage control of three phase induction
motor. Why this control is suitable for fan and pump
drives?
Discuss the problem arising in the operatibn of impact
load. Explain, With the help of diagram, how these
problems are minimized using ?y wheel.
Based on the rms torque, estimate the kW rating of 750
rpm motor used for driving equipment having the
following load torque curve:
(i) For ?rst 10 seconds, the torque is constant at 40
kg-m;
(ii) For next 30 seconds, the torque varies linearly with
time from 35 kg ?m to 15 kg-m;
(iii) For the last 50 seconds, the torque is constant and
equal to 10 kg-m.
EEE-03 5/EEE-702
Attempt any two questions from this section.
10.
11.
8300
(a)
(b)
(a)
(b)
? SECTION?C
(15 ><2=30)
Perform the transient analysis of separately
excited DC motor started usin g armature control
scheme.
A motor drives two loads one has rotational motion.
It is coupled to the motor through a reduction gear
of teeth ratio a=0.1 and ef?ciency as 90%. The
load has a moment of inertia of 10 kg-m2 and a
torque of 50 N-m. Other load has a translational
motion and consists of 600 kg weight to be lifted
at a uniform speed of 2.0 m/s. coupling between
this load and the motor has an ef?ciency of 88%.
Motor has inertia of 0.4 kg-m2 and runs at a
continuous speed of 1500 rpm. Determine the
equivalent inertia referred to the motor shaft and
the power developed by the motor.
Compare CSI and VSI fed shcemes applied for
speed control of induction motors.
Speed of DC series motor coupled to a fan load is
controlled by a variation of armature voltage. When
the armature voltage is 400 V, motor takes 10 A
and the fan speed is 250 rpm. the combined
resistance of the armature and ?eld is 1 Q.
Calculate
(5) P.T.O.
12.
8300
(i) Motor armature voltage for the fan speed of 350
rpm.
(ii) Motor speed for the armature voltage of 250 V.
Explain static Scherbius scheme for speed control of a
slip ring induction motor. Draw a neat circuit diagram
of the complete shceme. Mention its advantages
compared to rotor resistance control method.
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(6) EEE-O35/EEE-702
This post was last modified on 29 January 2020