The alternating current system of the Westinghouse Company has come
to the front in the United States with extraordinary rapidity, and,
although it is not three years since the first plant was erected, at
the present time over 190,000 incandescent lamps are operated from a
number of central-stations. The fundamental principles of the Goulard
system have been retained in the Westinghouse converter; but the manner
in which these principles are applied has been greatly modified, while
most of the details have undergone a radical change at the hands of the
engineers and electricians whose researches have been utilised by the
Westinghouse Company. The form of converter as now designed consists of
a number of thin sheet-iron plates, shaped like the letter =E=, they
are slipped alternately from opposite directions over the primary and
secondary coils, which are disposed side by side; the inductive core
is, therefore, composed of a mass of detached plates insulated from
each other by paper, and forming a discontinuous magnetic circuit.
In order to protect the converter from mechanical injury as well as
dampness, and also to avoid the possibility of contact with wires
carrying currents of high potential, it is enclosed in a cast-iron case
or box, made in two parts and adapted to be secured to any convenient
support. Fig. 12 is a transverse vertical section of such a converter
box, with the converter in position. The terminals of the primary
coil, P, of the converter are led into the compartment D¹, and the
terminals of the secondary coil into D². The terminals are secured
to bolts or couplings, _f f_, mounted upon insulating plates, _e_¹
and _e_². Fusible mica-foils, _g_, and switch plates, _h_ and _i_,
with plugs _k_, are provided for protecting and disconnecting the
circuits. The open front of the compartments D¹ and D² are closed by
glass plates, T, which permit inspection of the connections without
entering the box. The converter box occupies little space, and may
be placed in any convenient situation in or about the premises to be
lighted, much the same as a gas-meter. The practice where overhead
conductors are employed, is to mount the converter box on a pole in
the vicinity of the premises to be lighted, as shown by Fig. 13, and
thus it is only necessary to lead the secondary or low potential wires
into the building, the high potential wires remaining in an accessible
position upon the pole. Fig. 14 is a view of North Street, Pittsfield,
Massachusetts, engraved from a photograph, and shows a very neat form
of tubular pole with its converter box on top. This arrangement is used
throughout the city, and is a great improvement on the ordinary form
of telegraph poles which so greatly disfigure American cities, and are
really the most objectionable feature of the overhead wire system.
[Illustration: Fig. 12.]
[Illustration: FIG. 13.]
[Illustration: FIG. 14.
_To face page 37._]
The potential ordinarily employed in the main circuits of the
Westinghouse installations is about 1000 volts, and that in the lamp
circuits 50 volts, the ratio of conversion, therefore, being as 20
to 1; the dynamos are manufactured, as a rule, in three sizes, No. 1
for 650, 16 candle-power lamps; Nos. 2 and 3 for respectively 1300
and 2500 lamps. The converters are also made in three ordinary sizes
to supply 20, 30, and 40 lamps of 16 candle-power each. A 40-light
converter contains about 85 pounds of iron and 25 pounds of copper,
so that the total weight of metal is less than 3 pounds per lamp;
the electrical efficiency of the converter is said to exceed 95 per
cent. when the potential is reduced from 1000 volts in the primary to
50 in the secondary. “It is claimed that the trifling loss of energy
in conversion from high to low potential at the point of consumption
is made up for by gain at other points, especially in the increased
efficiency of the lamps, so that an alternating current plant may be
counted on to give 10-16 candle-power lamps per indicated horse-power,
as against 7 with the direct system;” the comparative gain is doubtful,
but by using 50 instead of 100 volts the life of the lamps is
increased, the former having a much stronger filament and consequently
a longer life.