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Guru Tegh Bahadur Institute of Technology
Department of Electrical and Electronics Engineering
Semester - 7
Electric Drives - ETEE – 401
ASSIGNMENTS
Assignment – 1 (A1)
1. State some applications of electric drives.
2. What are main components of an electric drive system? Show a block diagram.
3. State in brief advantages of electric drives over other drives.
4. What are functions of a power modulator in an ED system?
5. State five criteria for selecting an electric drive.
6. What motor will you select to drive a light load with speed above 10,000rpm?
7. Mention four quadrants of operation of an electric drive. Illustrate with example.
8. What are different types of load requirements (torques)?
9. Which of the following are stable operating points?
Speed
A
TL1
B
Te
C
Tl2
D
Torque
10. What are types of closed loop control? Draw block diagram for a typical closed loop
speed control of an electric drive?
Faculty: Harshpreet Kaur
Assignment – 2(A2)
1. A single phase full converter is used to control the speed of a 5hp, 110V, 1200rpm,
separately excited DC motor. The converter is connected to a single phase 120V, 60Hz
supply. The armature resistance is 0.4Ω and armature circuit inductance is 5mH. The
motor voltage constant KØ=0.09V/rpm.
a. Rectifier operation: The DC motor runs at 1000rpm, and carries an armature
current of 30A. Assuming ripple free current, determine 1.Firing angle α, 2.Power
to the motor, 3.Supply power factor.
b. Inverter Operation: The polarity of motor back emf E is reversed, by reversing the
field excitation. Determine 1. Firing angle α to keep motor current at 30A at
1000rpm, and 2. The power fed back to the supply at 1000rpm.
2. A 3-ϕ full converter is used to control the speed of a 100hp, 600V, 1800rpm, separately
excited DC motor. The converter is operated from 3-ϕ, 480V, 60Hz supply. The motor
parameters are Ra=0.1 Ω, and La=0.5mH, KØ=0.3V/rpm. Rated armature current is 130A.
a. Rectifier Operation: The motor is running at rated conditions at 1500rpm.
Assuming ripple free current, Determine, 1.Firing angle α, and 2.Supply power
factor.
b. Inverter Operation: The DC machine is operated in regenerative braking mode at
1000rpm and rated motor current. Determine: 1. Firing angle α, 2. The power fed
back to the supply, and 3. Supply power factor.
3. A separately excited DC motor is supplied from 230V, 50Hz source, through a single
phase half controlled bridge converter. Its field is fed through single phase semi-converter
with no firing angle delay. Ra=0.7 Ω, and motor constant = 0.5V-sec/rad. For rated load
torque of 15Nm at 1000rpm, and for continuous ripple free current, determine
a. Firing angle for the armature converter
b. Rms value of thyristor and freewheeling diode current
c. Input Power factor of the armature converter
4. A separately excited DC motor, operating from a single phase half controlled bridge at a
speed of 1400rpm, has an input voltage of 330sin314t and a back EMF E of 80V. The
firing angle is 30o in every half cycle and armature resistance is 0.4 Ω. Calculate average
Ia and motor torque T.
Faculty: Harshpreet Kaur
5. The speed of a 15hp, 220V, 100rpm dc series motor is controlled using a single phase half
controlled bridge converter. The combined armature and field resistance is 0.2 Ω.
Assuming a continuous and ripple free motor current and speed of 1000rpm and K
=0.03Nm/A2, determine
a. Motor current
b. Motor torque for firing angle = 300. AC voltage is 250V.
6. A separately excited DC motor drives a load torque of 85Nm at 1200rpm. Ra=0.2 Ω, and
Rf=200 Ω. The field winding is connected to a 1-phase, 400V source through a single
phase full converter with firing angle = 00. The armature converter is also connected to
the same supply through a single phase full converter. The motor constant is 0.5V-sec/Arad. For ripple free armature and field currents, determine:
i. Rated armature current
ii. Firing angle of armature converter at full load
iii. Speed regulation at full load
iv. Input power factor of the armature converter and the drive at rated load
7. In the above problem, the polarity E is reversed by reversing the field excitation to its
maximum value. Calculate
a. Firing angle of the field converter
b. Firing angle of the armature converter at 1200rpm and constant armature current
of 50A
c. Power fed back to the supply during regenerative braking of the motor
Faculty: Harshpreet Kaur
Assignment – 3(A3)
1. What are different methods of power factor improvement in electric drives?
2. Compare voltage source inverter and current source inverter for Induction Motor Drives.
3. Show that a variable frequency Induction motor drive develops at all frequencies, the
same torque for a given slip-speed when operating at a constant flux.
4. How can you obtain Ward Leonard type characteristics from a three phase induction
motor?
5. A three phase squirrel cage induction motor drives a blower type load. No load rotational
losses are negligible. Show that rotor current is maximum, when motor runs at a slip
s=1/3.
Faculty: Harshpreet Kaur