IEEE Power & Energy Magazine - July/August 2021 - 87

breaker contacts and the subsequent
overvoltage that could result.
The overvoltage problem had been
noted in the late 1880s. Prof. George
Forbes, who had produced the first
Niagara alternator design, said in The
Electrician in 1893, " ... it is a piece
of culpable ignorance, ruinous to the
machinery, if anyone should ever, on
a large power circuit with alternating
current, suddenly break the circuit
while current is passing. " In 1893, Sylvanus
P. Thompson, a well-respected
electrical authority of the time, suggested
in " The Distribution of Power
From Niagara, " that " Difficulties in
stations from sudden rushes of current
are seldom experienced now; all engineers
slowed their machines before
breaking circuits and main switches
were practically not used. "
A modern engineer can only see
these two statements as gross oversimplifications,
but they were made by two
of the most respected engineers of the
19th century. It was for these reasons
that the first large alternators were installed
without circuit breakers, fuses,
or short circuit protection of any kind.
Although they were provided with disconnect
switches, the switches were
not intended to be opened under load. It
was expected that the alternator's fields
would be de-energized to clear the
fault. That was the solution that worked
in 1895, when the few large alternators
in existence typically supplied a single
load. Five years later, a different story
was about to unfold.
Circuit Analysis
To understand why these engineers and
others like them held these now-outdated
beliefs at that time, we need to look at
the state of understanding in the 1890s.
In those early days, the ac load was
mostly lighting, and the current was
only on the order of tens of amperes.
DC also was used for both lighting and
motor loads, but these circuits carried
fewer than a few hundred amperes. In
some cases, higher dcs were supplied
to railroad traction motors, but, even
as the traction business expanded, it
posed no problems.
DC was easy to understand. It followed
Ohm's law, Kirchoff's law, and
various other network theorems. DC
and voltage were easily computed at
any point in a network. Fuses and
circuit breakers were widely used to
protect circuits and equipment, and,
for the most part, that worked well.
Even the most vicious dc arcs could
be extinguished, usually by drawing
them out sufficiently. This could
be assisted by the use of a magnetic
blowout. The voltages were generally
not higher than 600 V dc. Fault currents
were not large because the " one
machine, one ci rcuit " philosophy
was common.
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IEEE Power & Energy Magazine - July/August 2021

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