IEEE Power & Energy Magazine - November/December 2020 - 105
The material surrounding the core
was a mixture of 20 parts, by weight,
of coal, coke, or other form of carbon
reduced to small particles; 29 parts
of sand; five parts of common salt;
and two parts of sawdust. After a few
hours of operation, the heat from the
core caused the surrounding mixture to ignite, as depicted in Figure 7.
This both increased its temperature
and produced savings in the amount of
electric energy expended. The process
lasted approximately 24 h, after which
the power was turned off, and the pig
was left to cool.
The furnace was a simple rectangular structure, as shown in Figure 8.
The walls and ends were made of brick
with no mortar between the bricks. The
walls were 7 ft long and the ends 6 ft
figure 8. The U.S. patent issued for the electrical furnace. (Source: The U.S. Pat-
ent Office, U.S. Patent 560,291, 19 May 1896.)
november/december 2020
An induction
regulator is like
an induction
motor that
does not rotate.
wide. The height was 6 ft. At each
end of the furnace there was a large
bronze plate to which the power cables
were connected. These cables were
connected to bus bars located beneath
the operating floor. Projecting into the
furnace from the bronze plates were
60 carbon rods, each with a length
of 30 in and a diameter of 3 in. The
charge, consisting of powdered coke
mixed with sand, sawdust, and salt,
was loaded into the furnace. The carbon rods allowed for intimate contact
to facilitate the flow of current, which
produced a temperature in the 1,700-
2,500 °C range. The cycle took roughly
24 h. The SiC developed as a solid cylindrical ingot around the core, with
radial layers ranging from graphite in
the inside to various SiC grades toward
the outside. After completion, the furnace walls were pulled down, which
allowed for the carborundum that had
formed around the core to be removed
for further processing for various applications, most commonly, abrasive
wheels and papers.
The control of the furnace was
manual, with the operator using an
induction regulator to change the
voltage applied. During operation,
the chemical changes in the mix
caused its resistance to gradually
reduce. To keep the reaction drawing
power at a more-or-less constant value (750 kW), the voltage was reduced
as the process progressed. A typical
set of values for this early furnace
was 240 V, 3,000 A and 100 V, 7,500
A at its start and completion, respectively. An induction regulator is like
an induction motor that does not rotate. The "rotor" is turned to change
the ratio of the primary (stator) to the
secondary (rotor), and this changes
ieee power & energy magazine
105
IEEE Power & Energy Magazine - November/December 2020
Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - November/December 2020
Contents
IEEE Power & Energy Magazine - November/December 2020 - Cover1
IEEE Power & Energy Magazine - November/December 2020 - Cover2
IEEE Power & Energy Magazine - November/December 2020 - Contents
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IEEE Power & Energy Magazine - November/December 2020 - Cover3
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