EE321.
ABET Exam
Spring 2004
Name:
Student ID:
Instructions:
Work ALL Problems.
When you have completed exam, turn in to Professor Sudhoff,
Brandon Cassimere, or Brant Cassimere, any of whom will check it on the spot, and let
you know which ones are wrong if you need to revise any problems.
The last possible
moment to turn in the exam is immediately prior to the final exam (at which point you
will not have the opportunity to revise your work).
All problems must be worked
correctly in order to be eligible for a passing grade in the course.
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Problem 1 – Magnetic Equivalent Circuits and Design of Electromechanical Devices
Consider the electromagnet shown in Figure 1 (back page).
Suppose that
b
d
is very thick, so that the
reluctance associated with the top (and bottom) may be ignored.
Further suppose
c
r
is 1 cm, and
s
w
is 2 cm,
and
s
d
is 2 cm, and
g
is 0.1 mm.
In this problem, neglect fringing flux.
The relative permeability of the steel is
1000.
Determine the following:
(a)
What should
e
t
be in order to keep the flux density the same in the center post as in the edge area ?
(b)
With the value of
e
t
from part (a), if the flux density in the center post is to be limited to 1.1 Tesla, what is
the maximum product of turns and current (
Ni
)
(c)
Derive an expression for the resistance of the winding in terms of
s
d
,
s
w
,
c
r
,
N
, the packing factor
pf
, and
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 Spring '08
 Staff
 Electromagnet, Magnetic Field, DC MACHINES, Electric motor, flux linkage equations, DC Source Voltage

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