Ministry of Higher Education
& Scientific Research
Erbil Polytechnic University
Erbil Technical Engineering College
Mechanical and Energy Eng. Dept.
Note:
2018 – 2019
Final Exam
Class : Third Class
Subject : Electrical & Electronic Eng.
Time : 3 hr.
Date : 20.05.2019
Code : ME 308
1st Attempt
Q1 (20 Marks):
A 6 pole dc machine armature has 36 slots each slot containing 16 conductors and is wave wound.
The flux per pole is 0.0188 wb. Find the gross torque and mechanical power output when the
machine is operating as a motor at 1200 rpm with an armature input current of 10A.
HINT: Assume Mechanical Power = Electrical Power, that’s means neglected the armature losses.
Q2 (20 Marks):
For the circuit of Fig. 1, determine the circuit current and the voltages (VR, VL & VC).
Take v(t) = 12 sin (3t + 30).
Fig. 1
Q3 (20 Marks):
The following results were obtained on a 50 KVA, 2400/120 V single phase transformer.
(i)
OC test: 2400 V, 120 V, 396 W.
(ii)
SC test: 92 V, 20.8 A, 810 W
Find efficiency and the voltage regulation at 0.85 lagging power factor.
Q4 (20 Marks):
An 8 pole three phase induction motor operates at 50 Hz supply. Calculate,
1. The speed at which the magnetic field of the stator is rotating (Ns).
2. The speed of the rotor when the slip is 0.06.
3. The frequency of the rotor when the slip is 5%.
4. The frequency of the rotor at standstill.
Q5 (20 Marks):
A. Explain power losses in the three phase induction motors. Also draw the power flow
diagram?
(5 Marks)
B. What is the condition for developing the maximum power in the DC motors?
(5 Marks)
C. State and classify the power diodes. Also explain the forward biase and revers baise?
(10 Marks)
GOOD LUCK!
Zana OZAIRAGHALI
Examiner