Al-Majma'ah University
Electrical Machines
College of Engineering
6 rd level
Time: 1.5Hrs
First Exam, October 2013
Answer all the following questions
1- A circular ring of magnetic material has a mean length of 1.0 m and a crosssectional area of 0.001m2 . A saw cut of 5mm width is made in the ring.
Calculate the current required to produce a flux of 1 mWb in the air gap if the
ring is wound uniformly with a coil of 200 turns. Take the relative permeability
of the ring material µr= 500 and neglect leakage and fringing.
[ 6 points ]
Fig. 1
Al-Majma'ah University
Electrical Machines
College of Engineering
6 rd level
Time: 1.5Hrs
First Exam, October 2013
2- Reduce the circuit shown and find the total impedance referred to the
generator side.
[ 7 points ]
Fig. 2
Al-Majma'ah University
Electrical Machines
College of Engineering
6 rd level
Time: 1.5Hrs
First Exam, October 2013
3- Consider the magnetic core with an air gap as shown in Fig. 3. The core material
has a relative permeability of 6000 and a rectangular cross-section of 6 cm2. The coil
has 500 turns. Determine (a) the current required to establish a flux density of
Bgap=0.25T in the air gap considering fringing 5% at the air gap (b) the flux in the iron
and airgap.
[ 7 points ]
i
N=500
Best Wishes
Al-Majma'ah University
Electrical Machines
College of Engineering
6 rd level
Time: 1.5Hrs
First Exam, October 2013