IEEE Technology and Society Magazine - June 2017 - 20

motor and three phase power were
"in the air" in the last two decades
of the 19th century. Tesla's priority
of invention for both the motor and
his system of distribution was challenged in the American courts, where
he did eventually prevail, but reading
Cooper one comes away with the
feeling that an Italian, Galileo Ferraris, has a pretty good claim to both
inventions. Tesla's collaboration with
Westinghouse did lead to the implementation of large scale systems
of power and motors, and generally
it is such commercial success that
leads to glory for an inventor. This is
why you've surely of Alexander Graham Bell and perhaps not Elisha Gray.
Cooper is indebted to the prior
work of Bernard Carlson and his
book is heavy with footnotes giving reference to not only Carlson
but to one other author, whom I will
name presently. But the pleasure of
reading Cooper is that it's a slender
engaging book that cuts right to
the issues of priority. After reading
him you will never let anyone tell
you that Tesla invented AC power.
Single phase AC power (which is
ordinary house current) was already
an important source of distribution
well before Tesla formed his famous
alliance with Westinghouse.
Cooper has a law degree but
apparently no background in electrical engineering. If I wrote a book
where law is paramount I'd have a
lawyer read it. By having a technically trained person read his book the
author would not have asserted, for
example, that for an electromagnetic
wave the higher the frequency the
more energy it carries. A plane radio
wave with a field strength of 1 volt
per meter carries the same energy if
its frequency is 1 megahertz or 100
times higher. He has confused the
energy of the associated photons with
the energy of the wave.
I have mentioned one other author
to whom Cooper is indebted. This

Three Phase Current for 60 Hz. ac

1.5

Current

1
0.5
0
-0.5
-1
-1.5
-2
0

0.005 0.01 0.015 0.02 0.025 0.03 0.035
Time (s)

FIGURE 1. Current in three wires over an interval of time.

the rotating device. These spinning
conductors connected with the wires
on the armature.
This commutator, as it was called,
was undesirable for several reasons:
it added to the frictional force countering rotation, it resulted in sparking and a loss of energy, and it wore
out. Tesla's contribution, as generally
understood, was to eliminate the
commutator and all electrical con-

Tesla's work, most especially
with Westinghouse, brought
a new level of efficiency to
AC power.
duction to the armature by having a
rotating magnetic field present in the
motor which was created by a set of
wire turns surrounding the armature;
this was a specially wound field coil,
as it was known. To create the rotating field the simplest way is to connect
the motor to a set of three conducting

wires each carrying a current that is
out of phase with the others. An example of three phase current is shown in
Figure 1. The plot shows the current
in three wires over an interval of time.
One advantage of supplying such
a current, which requires that three
insulated wires comprise the power
transmission line feeding the motor, is
that the power moving down the line
does not pulsate in time but remains
constant. With the ordinary
single phase AC electric current supplied by 2 wires to
your toaster, for example, the
power flow reaches a peak
120 times per second and is
zero just as often.
Tesla's work, most
especially with Westinghouse, in the late 19th
century, led not only to the
popular adoption of the
induction motor - a breakthrough in quality - but also to the
widespread use of three phase
power which remains the dominant
standard for industrial power transmission today. It brought a new
level of efficiency to AC power.
Cooper does convince us, however, that Tesla's ideas for both the
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june 2017

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