There has been much said in recent times about the distribution of
electricity by means of induction coils, and the use of this process has
given rise to several systems that differ but little from one another in
principle.
The following are a few details in regard to a system due to a Dutch
engineer:
In the month of December, 1881, a patent relating to the distribution of
electricity was taken out in Germany and other countries by Mr. B.
Haitzema Enuma, whose system is based upon a series of successive
inductions. The primary current developed by a dynamo-electric machine
gives rise to secondary, tertiary, etc., currents. The principal line runs
through the streets parallel with their axes, and, when the arrangement of
the places is adapted thereto, it is closed upon the generator itself. In
those frequent cases where it is necessary to cause the line to return
over a path that it has already traversed, it is more advantageous to
effect the return through the earth or to utilize the street water mains
or gas pipes as conductors. This return arrangement may likewise be
applied to the lines of secondary, tertiary, etc., order, as may easily be
seen.
The induction is effected by the aid of bobbins whose interior consists of
a bundle of soft iron. The wire of the inducting current is wound directly
around this core. The wire of the induced current is superposed upon the
first and presents a large number of spirals. It is useless to say that
these wires must be perfectly insulated from each other, as well as from
the soft iron core. We shall call primary bobbins those which are
interposed in the principal line, and secondary bobbins those in which the
inducting current is a secondary one, and so on.
It will be at once seen that this arrangement permits of continuing the
distribution of electricity to the interior of buildings by the simple
adjunction of one or several bobbins. Each electric apparatus, whether it
be a lamp or other mechanism, is furnished with a special current. If the
number of these apparatus be increased, it is only necessary to increase
the number of bobbins in the same ratio, on condition, be it understood,
that the intensity of the currents remain sufficient to secure a proper
working of the apparatus in question. When such intensity diminishes to
too great a degree, the bobbin must be replaced by a stronger one.
[Illustration: DISTRIBUTION OF ELECTRICITY BY INDUCTION.]
It results from what precedes that each apparatus must be put in in such a
way as to permit, of the opening and closing of the corresponding circuit.
This arrangement, moreover, has no need of being dependent upon the
apparatus, and may just as well be transferred to any part of this same
circuit. As regards lighting, it is preferable to employ alternating
current dynamo machines; yet there is nothing to prevent the use of
continuous current ones, provided that there is an arrangement that
permits of constantly opening and closing this same circuit. That portion
of the line which is placed under ground is insulated in the ordinary way
at the places where it is necessary. As for the underground circuit and
the induction coils connected therewith, these are protected against all
external influence, and are at the same time insulated very economically
by covering them with a coat of very fine silicious sand mixed with
asphalt.
It is only necessary to inspect the annexed figure to get an accurate idea
of this system of distribution. C represents the building in which the
generator of electricity, D, is placed; B, the public street, and Q the
house of a subscriber. The principal line, E, starts from the terminals,
_a, b_, of the machine, passes through the primary bobbins, G, and is
closed through the earth at F. It will be seen that the primary current
communicates through _d_ and _c_ with the internal winding of the bobbins,
G, while the secondary currents, H, are connected through _e_ and _f_ with
the external winding. The same arrangement is repeated for the tertiary
currents, M, and the quaternary ones, _o, p_. In the annexed example all
the lines that run parallel with the axis of the streets are closed
through the earth, while those that have a direction perpendicular thereto
enter the houses of subscribers and form a closed circuit. In the interior
of these houses the wires, as well as the induction coils, are insulated
and applied to the walls. At Q is represented the arrangement that would
have to be adopted in the case of a structure consisting of a vestibule,
_r_, and two rooms, _s_, lighted by two electric lamps, R. In the portion
of the figure situated to the left it is easy to see the process employed
for insulating the line. A commencement is made by digging a ditch in the
street and paving the bottom of it with bricks. Upon these latter there is
laid a mixture of sand and asphalt, and then the wires and bobbins are put
in, and the whole is finally covered with a new insulating layer.
It is a simple statement that we make here, and it is therefore not for us
to discuss the advantages and disadvantages of the system. If we are to
believe Mr. Enuma, the advantages are very numerous, to wit: (1) The
cables have no need of being of large size; (2) the intensity is the same
through the entire extent of the primary circuit, secondary one, etc.; (3)
the resistance is invariable in all portions of the line; (4) the
apparatus are independent of each other, and consequently there may be a
disturbance in one or several of them without the others suffering
therefrom; (5) either a strong or weak luminous intensity may be produced,
since, that depends only upon the size of the coil employed; (6) there is
no style of lamp that may not be used, since each lamp is mounted upon a
special circuit; (7) any number of lamps may be lighted or extinguished
without the others being influenced thereby; (8) when a fire or other
accident happens in a house, it in no wise interferes with the service in
the rest of the line; (9) the system could, were it required, be connected
with any other kind of existing line; and (10) the cost of installation is
infinitely less than that of a system of gas pipes embracing the same
extent of ground.--_La Lumiere Electrique._
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