IEEE Power & Energy Magazine - January/February 2022 - 98

✔ integral cooling fan-for increased
hp rating
✔ improved high-temperature
insulation.
Not only the motor itself but also the
means of controlling it has also improved.
Power semiconductors have played a
large part in this, especially in the area
of variable frequency control. No longer
is the motor's speed tied to multiples of
the line frequency. The induction motor
has finally become a replacement for the
dc shunt motor. Ironically, this has come
at a time when many electrical engineers
have never seen a dc motor.
figure 15. Tesla's motor on permanent display at the Nikola Tesla Museum.
(Courtesy of Ivona Zoric, senior curator, Nikola Tesla Museum, Vracar, Belgrade;
used with permission.)
For Further Reading
W. E. North, " Application of electricity
in cement mills, " Trans. Amer. Inst. Elect.
Eng., vol. XLVI, pp. 462-468, Jan./Dec.
1927, doi: 10.1109/T-AIEE.1927.5061376.
L. Duncan, " Alternating current electric
motors, " Trans. Amer. Inst. Elect.
Eng., vol. V, no. 7, pp. 211-235, Apr. 1888,
doi: 10.1109/T-AIEE.1888.5570384.
F. J. Patten, " Alternating current
motors: The evolution of a new type, "
Trans. Amer. Inst. Elect. Eng., vol. VI,
no. 5, pp. 388-410, May 1889, doi:
10.1109/T-AIEE.1889.5570234.
T. C. Martin and J. Weltzer, The Electric
Motor and Its Applications, 3rd ed. New
York, NY, USA: W.J. Johnson, 1892.
N. Tesla, " A new system of alterfigure
16. A World War II-era induction motor. (Source: E. Hawks, Popular Science
Mechanical Encyclopedia, p. 99, 1941.)
into use to replace wound rotor conductors
(Figure 14), the use of shaped rotor
bars was introduced. The shape of these
bars allowed the impedance of the rotor
to be automatically changed as the motor
came up to speed. There was no longer a
need for reduced voltage starting for industrial
duty induction motors.
The Modern
Induction Motor
The induction motor has undergone several
significant changes since the time of
Tesla's patents. Figure 15 shows Tesla's
98
ieee power & energy magazine
motor and Figure 16 illustrates a modern
induction motor. Several changes are
evident. The typical modern, generalpurpose
squirrel-cage induction motor
has the following features:
✔ distributed windings not salient
poles-for better flux distribution
✔ cylindrical not pancake shape-
for better heat dissipation
✔ secondary bars or squirrel cage-
for economy of construction and
across-the-line starting
✔ enclosed stator-for protection
in various environments
nate current motors and transformers, "
Trans. Amer. Inst. Elect. Eng., vol. V,
no. 10, pp. 308-327, Jul. 1888, doi:
10.1109/T-AIEE.1888.5570379.
H. D. Passer, The Electrical Manufacturers,
1875-1900: A Study in Competition,
Entrepreneurship, Technical Change, and
Economic Growth, Cambridge, MA, USA:
Harvard Univ. Press, 1953.
B. G. Lamme, An Autobiography, New
York, NY, USA: G. P. Putnam's Sons, 1926.
C. F. Scott, " Long distance transmission
for lighting and power, " Trans.
Amer. Inst. Elect. Eng., vol. IX, no. 1,
pp. 425-444, Jan. 1892, doi: 10.1109/
T-AIEE.1892.5570456.
P. N. Nunn, " Pioneer work in hightension
electric power transmission, "
Cassier's Mag., vol. 27, no. 3, pp. 171-
200, Jan. 1905.
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