Lightning Arresters.
Year: 1893

page_text: Date of Application, 18th Apr., 1893-Accepted, 20th May, 1893
COMPLETE SPECIFICATION.
Lightning Arresters.
I, ELIHU THOMSON, residing at Swampscott, County of Essex, State of
Massachusetts, United States of America, Electrician, do hereby declare 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 :-
My invention relates to the mauner of applying or connecting lightning arresters
used with electric lines or mains employed for the transmission of power for electric
lighting or for other purposes.
The object of my invention is to secure a more effectual protection of the
apparatus on such lines from lightning by so organizing or connecting the lines, the
apparatus and the lightning arrester, as to afford by the lightning arrester a more
ready path for the lightning stroke than is the case in present arrangements.
When lightning arresters are applied to lines or circuits in which the apparatus
connected to such circuit is in a ground wire or connection from the same it is the
practice to run a separate ground wire or connection from the ground plate of the
lightning arrester, and it very frequently happens that the self induction of
the latter ground wire or circuit is larger than that of the ground wire or con-
nection containing the apparatus to be protected, or is so large as compared with
the same that the apparatus is not thoroughly protected, the lightning stroke being
shunted off through such apparatus instead of passing through the lightning
arrester and over the ground circuit for the latter.
The object of the first part of my invention is to make this condition of affairs
impossible and to produce an organization wherein the self induction or resistance
from the ground plate of the lightning arrester can never be greater than that of
the ground connection or circuit leading from the apparatus to be protected.
My invention is especially applicable to dynamo electric machines supplying
electric lines or circuits with electricity for light, power or other purposes.
The invention consists essentially in forming the ground connection for the
dynamo or other apparatus by way of the ground wire for the lightning arrester
so that the self induction or resistance from the ground plate of the lightning
arrester can never be greater than the circuit for the line through the apparatus to
be protected and to ground. Or, in other words, I locate the lightning arrester in
a shunt around the dynamo or other apparatus from the line or main to the
connection leading from the dynamo or other apparatus to ground.
My invention further consists in certain improvements in the manner of
organizing and connecting the parts of a lightning arrester which is provided with
an arc rupturing magnet.
My invention consists essentially in locating the arc rupturing magnet in position
where its self induction will not oppose the passage of the lightning stroke by way
of the lightning arrester to ground, and further consists in locating it in the ground
wire or connection leading through the apparatus to be protected at a point beyond
the point of application of the lightning arrester to the line wire and the ground so
that by its self induction it shall positively oppose the passage of the lightning
stroke to the dynamo or other apparatus and shall act to force the lightning stroke
to pass by way of the arrester to the ground.
My invention consists also broadly, in locating the arc rupturing magnet on a
circuit of any description between the dynamo machine and the point of connection
of the ground lightning arrester.
In the accompanying drawings:
Fig. 1 is a diagram illustrating an arrangement of circuits and apparatus

page_text: Fig. 2 is a diagram illustrating the arrangement employed previous to my
invention.
I have shown in the drawings the application of the invention to an electric line
and dynamo forming a part of an electric railway, but the manner of applying the
invention to circuits and apparatus used for other purposes will be obvious from
the description given of the special application shown.
In Fig. 1 G is a generator of electricity which generator may have any form or
character such as an arc light dynamo, an incandescent or alternating current
dynamo, or may be a motor used upon any of these circuits or other electrical
apparatus.
Cis the work which is represented in the drawing as an electric car whose motor
is connected by a trolley T, into a circuit between the main wire L, and the track
and ground after the manner commonly employed.
P, P are the plates or electrodes of a lightning arrester of any desired
character in the ground circuit or connection from the line L, after the usual
manner.
A indicates the are rupturing magnet employed for dispersing or rupturing any
arc which may follow or tend to be maintained across the space between the
electrodes after the passage of the lightning stroke or other abnormal flow of high
tension current.
The
The dynamo G in this system has one pole connected to ground and the other to
line. The ground wire or circuit for said dynamo is by a wire or connection taken
to the arrester electrode P¹, or to a point near the same, so that the dynamo circuit
is by way of the ground wire or connection of the lightning arrester.
magnet A is placed in the connection from the line to ground by way of the
dynamo and at a point between the point of application of the arrester and
the dynamo or other apparatus to be protected and will therefore obviously oppose,
by its self induction, the passage of the lightning through the ground circuit in
which it is placed and by so doing will force or tend to shunt the lightning stroke
to ground by way of the arrester.
It will also be observed that the ground circuit from the dynamo to earth is
necessarily of greater length and self induction than the ground circuit from the
lightning arrester so that in this respect also the lightning arrester invites or
tends to take the lightning discharge in preference to the path which passes thereby
through the dynamo or other apparatus.
The operation of the apparatus is as follows:
Should a lightning discharge induce a powerful current in the line L, or find a
path for itself on the line L, it would have several outlets to earth. It could go
by the trolley arm T, to the car and thence to the track R, and also leap the space
separating the plates P, P₁, to earth E. There is also a path through the magnet A,
and the generator G, back to the plate P¹, and thence to earth E, but the static
charge will not follow this path on account of the self induction of A, added to
that of G, and the freer path of smaller or no self induction existing across the
slight space between the electrodes P, P¹, and to earth E. The spark however
establishes a path for the current of the generator G, between the plates P, P¹,
and short circuits the machine, but the arc being under the influence of the magnet
field of the magnet A, is instantly blown out and destroyed, leaving the line in
its normal working condition and the protective devices set for any other discharges
which may occur. It will thus be seen that the generator G, is electrically
isolated from the path of the lightning discharge, which is of a different character
from the current which it generates, and is thus preserved from harm. Should
motors be employed upon the line L, which might also be damaged by the
lightning discharge short circuiting them or jumping through their insulation I
provide similar protective arrangements the lightning in all cases finding a path
of lower resistance to its flow by leaping across plates P, P¹, placed in a circuit
to earth the space between which is subjected to the action of a magnetic field or
other arc rupturing devices. It is of course to be understood that the generator G,

page_text: well insulated from the earth except through the line leading to the plate P.
Because of the high self induction of the circuit through A and G, very little if
any of the lightning discharge upon the line L, can pass therethrough, the
resistance of this path for the discharge being very great as compared with that
from the line L, across the space between the plates P, P, to E.
In the arrangement illustrated in Fig. 2, however, it will be noticed that the
ground circuit or connection from the line L, through the dynamo G, and to R,
is independent of that through the lightning arrester contacts or electrodes and to
earth, and that moreover the arc rupturing magnet is in the latter path or
branch so that its self induction is added to the natural self induction of that
circuit.
It will be noticed further that the ground connection from the dynamo G,
itself being independent of that by way of the ground electrode P¹, is not as in
the previous instance necessarily of lower self induction than the arrester ground
circuit. Therefore, in this instance, the lightning discharge will find an easier
path through the generator than in the previous case because the conditious are
not so good for the provoking of the shunt or independent ground path or circuit
for the lightning.
While I have shown the magnet A, in Fig. 1, as included in the main line
circuit or in a ground connection therefore independent of the lightning arrester
so that it is constantly energized, I do not limit myself to such an arrangement
since the gist of my invention consists in removing the arrester magnet from the
position which it occupies in Fig. 2, in the circuit around the dynamo and placing
it in some independent circuit. I prefer however to place it in the main line
circuit since it may then be energized by the current flowing over such circuit and
is constantly energized while in the position shown in Fig. 2, it would only be
energized simultaneously with the flow of current across the space between the
lightning arrester electrodes and to earth.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is:
1. The herein described means of grounding a lightning arrester in shunt to a
dynamo electric machine or other protected apparatus, consisting essentially of
grounding the arrester and machine through a common earth connection.
2. The combination, with an electric line, and dynamo machiue connected with
such line and to ground, of a lightning arrester consisting of two electrodes
normally insulated from one another by a narrow insulating space, and placed in a
shunt around the dynamo from the line to the wire or connection leading from the
dynamo to ground.
3. The combination, with a line wire and apparatus such as electric motors fed
from such line to and through a ground return circuit, of a lightning arrester one
of whose separated plates or electrodes is attached to the line and the other of
whose plates or electrodes is attached to a ground connection or ground wire, to
which ground wire is also attached the terminal of the dynamo which is normally
to be kept grounded while the other terminal is connected to the line, and arc
rupturing devices for preventing the formation and continuance of an arc between
the separated plates of the lightning arrester.
Dated this 67th
1002
ELIHU THOMSON.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicant.