IEEE Power & Energy Magazine - March/April 2016 - 14

then commented on the 133-, 125-, 60-,
50-, and 25-Hz frequencies on the way
to the historic 60/25-Hz dual standard.
Now, thanks to Thomas Blalock's third
publication on the subject matter, it is
manifested that, in the North American
"battle of the frequencies," 40 Hz was
also one of the party and had enjoyed
some initial, but short-lived success.
Congratulations, Mr. Blalock for the
excellent article!
For Further Reading

G. Neidhöfer, "Early three-phase power," IEEE Power Energy Mag., vol. 9,
pp. 88−100, Sept./Oct. 2007.
G. Neidhöfer, "50-Hz frequency,"
IEEE Power Energy Mag., vol. 9, pp.
66−81, July/Aug. 2011.
-Gerhard Neidhöfer

Author's Reply
I greatly appreciate the kind remarks
regarding my recent "History" column
article, both from Dave Hepburn and Gerhard Neidhöfer (T.J. Blalock, "An Unusual
Frequency," IEEE Power & Energy Magazine, vol. 13, no. 5, pp. 72-88, 2015).
The early 20th century "power plant"
that supplied various types of electric
power for the test of large transformers
in the Pittsfield, Massachusetts, works
of the General Electric Company contained a number of motor-generator
sets consisting of test power alternators
driven by dc motors.
A clever arrangement allowed each
of these drive motors to be switched to
one of five different voltages, thus controlling the base speed of the motor. The
ratios among these five voltages roughly approximated the ratios of the five

significant power system frequencies
of that era: 25, 30, 40, 50, and 60 Hz.
Therefore, any one of these frequencies
could be delivered by a test alternator for
the testing of a transformer built for that
frequency. In particular, this allowed for
the transformer "core loss" to be measured at the right frequency.
Physical remnants (switchboards
and rotating machines) of this unique
power system, as well as written documentation of it, survived until the
closing of the plant in 1987. It was the
discovery of this early installation that
"generated" my subsequent interest in
the use of multiple power system frequencies during the early 20th century.
-Thomas J. Blalock
p&e

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