Melting Brass in a Rocking Electric Furnace Page: 59
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EXPERIMENTS WITH LARGE ROCKING FURNACE.
to 600 kilowatts. Also, 105 volts was tried, without reactance, in
heats 3, 4, and 5, but did not give a high enough power input, so the
voltage was changed to 131 volts on open circuit during heats 6 to
218, inclusive. Three 100- kilovolt - ampere transformers were
used to step the current down from 4,600 to 110 volts; the voltage
was then boosted to 131 volts with a 50-kilovolt-ampere trans-
former. From heats 221 to 249, inclusive, 127 volts was used, and
from heats 250 to 301, 117 volts. The furnace was found to work
satisfactorily at any voltage between 115 and 140 volts.
The transformers could not be placed close to the desired position
of the furnace, and the secondary leads ran about 75 feet from trans-
formers to switchboard. On each side of the circuit four 500,000-
c. m. cables were used, or in all about 600 feet of cable. No reactance
other than that inherent in the furnace leads and transformers was
used in heats 1 to 77. In these tests, made before an external
reactance was added, the power factor would start at about 65 with
a cold furnace, rise promptly to 85, and then increase to more
than 90 as the furnace became hot. Most of the time the power
factor was 90 to 95 on the basis of instantaneous readings, or 90 to 99
by a power-factor meter.
In order to stabilize the are, make it require less attention from the
operator, and reduce surging, an external reactance was used after
heat 78. This reactance was made of four turns of a pair of 750,000-
c. m. cables, the turns being 14 inches in diameter, with.about 250
pounds of laminated iron strips, 2by 19 inches in size, held in a bag tied
within the turns. This crude reactance reduced the current on dead
short circuit from about 13,000 amperes without it to 4,000 amperes
with it. The voltage across the are and the reactance under full load
averaged about 115, the current varying from about 1,500 to 2,000
amperes. The power factor of the furnace, plus reactance, taken on
the secondary side averaged about 85 (instantaneous readings), while
that on the primary side (power-factor meter) averaged about 77.
The power factor was high enough to avoid a power-factor penalty
and to be satisfactory to the central station. The taking of an
average load of 200 kilovolt-amperes off one phase of the three-phase
circuit was not objectionable to the power company. The sub-
station operator could tell whether the furnace had current on or not,
but it did not disturb the voltage control of the circuit enough to
inconvenience other customers on the same line.
SWITCHBOARD AND METERS.
The switchboard was placed about 6 feet back of the furnace, where
the meters were readily visible to the operator. It carried an inte-
grating watt-hour meter readable to 1 kilowatt-hour, for the furnace59
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Gillett, H. W. & Rhoads, A. E. Melting Brass in a Rocking Electric Furnace, report, 1918; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc12367/m1/65/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.