Department of Electrical and Computer Engineering

The Islamic University of Gaza

Faculty of Engineering

Department of Electrical and Computer Engineering

Final Exam

Electrical Machines (EELE 3351)

Time: 2 Hours

Student’s Name
Student’s Number
Grade

Problem #

Grade

Problem 1

20

Problem 2

20

Problem 3

20

Problem 4

Student Grade

20

Good Luck
Dr. Assad Abu-Jasser
Tuesday May 27, 2008

All kinds of calculators are allowed

1.

The coil on the magnetic core shown has 500 turns. The core has a depth of 5 cm with an airgap length of 0.07 cm. The remaining dimensions are shown in the figure Fringing and leakage flux are to be neglected. The core is composed of steel having a relative permeability of μr=1000.
a)
b)
c)
d)
e)

Calculate the reluctance of the air-gap [3 pts]
Calculate the reluctance of the core [5 Pts]
Sketch the analogous equivalent circuit of this magnetic arrangement [4 Pts]
What current is required to produce a flux density of 0.5 T in the air-gap? [4 pts]
What flux density is produced in the right leg if the air-gap is removed? [4 Pts]

0.07102
g 

 222817 A.t/Wb
o Ag 4 107 55104 l r .leg
(40  0.07)102
r .leg 

127101 A.t/Wb
r o Ar .leg 1000 4 107 55104 ltot 115102
l ,u ,d .leg 

 61009 A.t/Wb
r o A 1000 4 107 105104
core 127101 61009 188110 A.t/Wb
total core g 188110  222817
total  410927 A.t/Wb
g  Bg  Ag  0.50.050.05  0.00125 Wb
g 1.25 mWb
Ni
500i
g 

1.25103
total 410927
4109271.25103
i
1.027 A
500
l r .leg
40102
127324 A.t/Wb
r .leg 

r o Ar .leg 1000 4 107 55104
core 127324  61009 188324 A.t/Wb
total core 188324 A.t/Wb
Ni 5001.027
core 

 0.00273 Wb
total
188324
core  2.73 mWb

0.00273
Br .leg  core 
1.09 T
Ar .legg 25104 lg 2.

A 100-kVA, 1000/100-V, 60-Hz single-phase transformer gave the following test result:
Test
Open-circuit test (HV side