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Electrical Applications 2 by David W. Tyler

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6 DC machines
Aims:
At the end of this chapter you should be able to:
Describe
the construction of
a
d.c. machine.
Describe
the
principle
and construction of
armature
windings.
Describe
the function of a commutator and the process of commu-
tation.
Derive the e.m.f equation of
a
d.c. machine.
Understand that a
reversal
of
armature
current is
necessary
for a
reversal
of energy flow so that E
=
V ±
I
a
R
a
.
Discuss the connection between magnetic flux, armature current
and torque.
Describe
the necessity for and the
operation
of a d.c. motor starter.
Describe
the
losses
which occur
in,
and
draw
a power flow
diagram
for, a d.c. machine.
PRINCIPLE OF ACTION
From Faraday's original work we know that e
=
d<b/dt volts for a