EEL1206
INTRODUCTION TO MACHINES AND POWER SYSTEMS
7 JULY 2023
Question 1
(a) Identify TWO statements that are FALSE:
A. Generator is an electric machine that converts mechanical power to electrical
power through the action of magnetic field and rotation.
B. Transformer is a static device with two or more windings, which converts
electrical power from one voltage level to another voltage level at different
frequencies.
C. A motor is supplying 60 N-m of torque to its load, where the shaft of the motor
is turning at 1800 revolution/min. The corresponding mechanical power supplied
to the load is 18.16 hp.
D. Figure Q1(a) depicts a wire carrying a current in the presence of a magnetic field,
with a magnetic flux density of 0.5 T, directed into the page. The wire has a
length of 1.25 m, and carries a current of 0.8 A in the direction from the bottom
to the top of the page. The induced force is 0.5 N, directed to the left.
[2 marks]
XXX
XXX
+XXX
XXX
$l = 1.25 \text{ m}$ $i = 0.8 \text{ A}$
XXX
XXX
XXX
XXX
$B = 0.5 \text{ T}$
XXX
XXX
Figure Q1(a)
(b) Figure Q1(b) illustrates a ferromagnetic core structure with a relative permeability of
2500, where a current-carrying coil of wire with 850 turns is wrapped around the left
leg of the core. The depth of the core is 9 cm, and the other dimensions of the core
are indicated in the diagram. Due to the fringing effect, the effective area of the air
gap is 14% larger than the physical core area. Given that a flux of 8 mWb is
established in the air gap.
(Permeability of free space, $\mu_0 = 4\pi \times 10^{-7} \text{H/m}$)
(i) Determine the total reluctance of the core structure.
[5 marks]
(ii) Calculate the magnetic field intensity of the air gap.
[3 marks
(iii) Find the current $i$ that is required to establish the flux.
[3 marks
Continued
MFAFIEL
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