Improvements in Lightning Arrestors.
Year: 1894

page_text: Date of Application, 18th Dec., 1894-Accepted, 10 h Aug.. 1895
COMPLETE SPECIFICATION.
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Improvements in Lightning Arrestors.
We, SIDNEY PRATT BLACKMORE, of Johannesburg, South African Republic,
Electrical Engineer, and WILLIAM HENRY CARLIN, of Johannesburg, South
African Republic, Mechanical Engineer, do hereby declare that the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
The nature of our invention consists of improvements in lightning arrestors, for
arresting or diverting the course of lightning from electric light and electric
transmission of power conductors, and is described as follows:-
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A. is an "impedance
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or choking coil, composed of a ring of finely divided
charcoal iron wire, a, upon which are windings of insulated conductor, a', forming a
portion of the main conductors, b, conveying the useful electrical current connected
to the main conductor, b, is a branch conductor, 6', in metallic connection with the
upper one of a pair of metallic spring holders, g, g', which are mounted upon a base
of insulating material, h, and holding a glass tube, d, to which is fixed a pair of
metal caps,,, passing through which is a piece of safety fuse wire connected to
the caps, i, i, by means of small screws,j, j. In metallic connection with the
bolder, is the upper one of a pair of metallic spring clips, ff, the lower
clip, being in metallic connection with the earth by means of the conductor, k,
and the earth plate, P, hetween the clips, f, f, are a pair of carbon plates, c, c',
separated by means of a piece of good paper or thin mica, e.
B. is an automatic cut-out for breaking short circuit sparks, 1, 11, are a pair of
metal tongs, the contact points of which are provided with carbon points, n;
mounted upon a base of insulating material, o, the upper tong, l, is mounted between
a metal fork, m, made to swing upon its fulcrum, m³, and is balanced so as to bring
the pair of carbon points, n, together when at rest; ', is a laminated core of
finely divided iron wire, which is suspended from the end of the tong, , by means
of a small metal rod and pivot, o; surrounding the core, n', is a solenoid of
insulated conductor, p, with winding, g, the one end of the winding, y, is made in
metallic contact with the fork, m, by means of the wire, 7', and the screw, r, the
other end being in connection with the earthing wire, G, of the apparatus, D.
The tong, being actuated by the downward pull of the solenoid, p, on the
core, n, in virtue of its electrification by the passage of a current of electricity
through the winding, 7. The automatic cut-out E, as well as the apparatus C, D,
are shown in plan for convenience in illustration, being precisely similar in
construction to the apparatus H, M, B, which are shown in section. The apparatus
is shown in duplicate as constructed for two lines, for the sake of more graphic
description-the action of which is as follows:-
N, N', are the connections to the apparatus desired to be protected, the over head
or exposed conductors leading outward from O, O', in the event of the lightning
striking the exposed conductors it is compelled to pass the "impedance" or choking
coils A, F, before it can reach the terminals N, N', assuming the arrestors to be
working upon a dynamo circuit, the main useful working current would be passing
from N', through the conductor, a', of the impedance coil F, along, to exposed
conductor 010, and returning to dynamo from O, through the conductor a', of
impedance coil A to N.
Assuming that lightning bas struck the exposed wire and is travelling along
section of main conductor between O, and b, the working current will be augmented,

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on account of the auxiliary force of the lightning, thereby changing the electrical
conditions of the impedance coil A, such change causing an
"
"induction current to
be set up in a direction opposing the immediate flow of current, and travelling in
the direction of the arrows which will, in consequence, divert the course of the
lightning by its opposing action, through the conductor 1, to the apparatus M, and
thence by means of the holder g', cap, and screw through the wire in the
tube d, to the lower cap i, and screw j, holder g, to the clip f, and carbon plate c¹,
perforating the dielectric e, and passing to earth by means of the carbon plate c,
clip, and conductor k, to the earth-plate P. In the event of a decrement of the
main working current the "induction current would be established in a direction
opposing the direction of the arrows the lightning would therefore travel half way
through the impedance coil A, from b, to J, but would in consequence set up an
induction current in the other half of the coil from J, to N, opposing itself at J,
and would in consequence discharge itself at J, through the apparatus H., In the
event of both lines being struck at once the tendency is to set up an electric " arc
or short circuit across the carbon plate e, c', of any of the apparatus M, C, H, D,
by a passage of current along the wires K, or G, and passing through apparatus B
or E.
In the event of such an occurrence the apparatus B or E are actuated by
the consequent flow of electricity through the winding q, of the solenoid p,
thereby actuating the tong, by the downward pull of the solenoid p, on the iron
core, n, separating the carbon points, n, and establishing the insulation of the
main conductors by breaking the short circuit which destroys the electric "arc at
the carbon plates c, c', of either of the apparatus M, C, H, D, and passing the
lightning to earth by means of the conductor K, and the earth-plate P.
"
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Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is
In an arrestor for arresting or diverting the course of lightning from electric
light, and electric transmission of power conductors :-
:-
1. The use of carbon, metal or other suitable material separated by means of a
thin dielectric in the manner described and shown.
2. The use of a closed magnetic circuit "impedance" or choking coil in the
manner described and shown.
3. The use of a closed circuit automatic short circuit cut-out with carbon or
metal sparking points, in the manner described and shown.
4. The general combination of parts and connections as described and shown.
Dated this Sixteenth day of November 1894.
SIDNEY PRATT BLACKMORE.
WILLIAM HENRY CARLIN.