THE OPEN UNIVERSITY OF SRI LANKA
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
EEX 5348 – ELECTRICAL MACHINES AND DRIVES
BACHELOR OF TECHNOLOGY – ACADEMIC YEAR 2020/2021
Academic Coordinator
: Eng. K.M.G.Y. Sewwandi
Course Coordinator
: Eng. K.M.G.Y. Sewwandi
E-mail
: kmsew@ou.ac.lk
ASSIGNMENT - 1
Due Date – 2021-04-22
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This assignment should be submitted as a hard
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Write answers in your own words and do not copy the course material, reference books or other
internet resources.
You will get ZERO marks for the copied assignments.
Write the answers in point form (where it is applicable)


copy on or before due date
Question 1
a) Compare the main three types of stepper motors based on their construction principle.
b) What is the difference between full switching sequence and half switching sequence of
stepper motors?
c)
Sketch the pole arrangement of 4/6 pole 2 phase permanent magnet stepper motor including
the value of basic step angle. Write down the phase switching sequence for the given motor
with respect to the clockwise and counter clockwise rotation.
d) Cross section of a three phase multi stack stepper motor is given by the Figure Q1 (A).
I.
Identify the type of given stepper motor
II.
Calculate the basic step angle
III.
Hence calculate the number of steps per revolution.
Figure Q1(A): Cross section of a multi stack stepper motor
e) Sketch the torque speed characteristics of stepper motor including all the necessary terms.
Define the terms given below.
I.
Detent torque
II.
Holding Torque
f) The torque speed characteristics of a 3-phase variable reluctance (VR) motor with 6 stator poles
and 16 rotor teeth stepper motor is given in figure Q1 (B). Calculate the power developed by the
motor when it is slewing
i. At 500 steps per second
ii. At 200 steps per second
Figure Q1(B)
Question 2
a) Brushless Direct Current Motor (BLDCM) is the latest addition to the family of DC motors.
What is the major difference of BLDCM when compared with the conventional DC motor?
What are the inherent advantages of BLDCM with regard to that difference?
b) Sketch the internal structure of the BLDCM and briefly explain how the motor operation
takes place with help of that diagram.
c) Briefly describe available rotor position sensing techniques used in BLDCM.
d) A BLDCM has following data.
Rotor radius = 8cm
Rotor axial length = 25cm
Airgap flux density due to rotor magnets = 0.7T
Number of turns per phase = 36 turns
Stator resistance per phase = 0.4 Ω
Stator Inductance per phase = 1 mH
The DC supply voltage at input terminals is 320V. Determine the motor speed and efficiency
when delivering a load of load-torque 65Nm. State any assumptions you made.
Question 3
a) Explain why single phase induction motor is self-starting and single phase induction motor is not?
b) Briefly explain the starting methods of single phase induction motor with relevant diagrams.
c) What are the applications of single phase induction motors? Why single phase induction motors
have poor performance than three phase induction motors.
d) Briefly explain the principle of operation of single phase induction motors with relevant diagrams.
e) What are the various converter topologies used in single phase induction motor drives? Briefly
explain two of them including relevant diagrams.
f) The following data pertains to a 230 V, 50 Hz capacitor-start singe phase induction motor at stand
still.
Main winding excited alone = 100 V, 2 A, 40 W
Auxiliary winding excited alone = 80 V, 1 A, 50 W
Determine the value of capacitance for determining the maximum starting torque.