Improvements in Lightning Arresters for High Potential Electric Circuits.
Year: 1895

page_text: Date of Application, 24th Dec., 1895-Accepted, 25th Jan. 1896
COMPLETE SPECIFICATION.
Improvements in Lightning Arresters for High Potential Electric
Circuits.
I, JAMES DEVONSHIRE, Secretary of The British Thomson Houston Limited
of 38 Parliament Street, Westminster, London do hereby declare the nature of this
invention (a communication from abroad by William B. Potter, Electrical
Engineer, of Schenectady, in the State of New York, United States of America).
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 lightning arresters, and has particular reference to
arresters for high-potential electric circuits, especially for those employing alter-
nating currents; it has for its object to provide an arrester in which the character
of the current will not affect the result, and which may be capable of adaptation
to any voltage by an extension of the principles involved in its construction for
moderate potentials.
As ordinarily constructed, lightning arresters have been efficacious only upon
continuous current circuits or upon alternating current circuits of very moderate
potentials. A lightning arrester capable of working with certainty upon potentials
of a thousand volts or upwards has been practically unknown. This is particularly
the case where an inductive load is thrown upon a circuit, in which case, where the
self-induction and capacity of the circuit balance each other, a resonant condition
may be brought about, and the potential may rise very greatly, even to such a
point as to are across the ordinary discharge spaces or spark-gaps without the
intervention of the static discharge. Increasing the size of the parts does not give a
corresponding protection and in practice it has been found impossible to insure
protection to lines, between which exist electro-motive forces of several thousand
volts.
33
My invention therefore consists in an arrester provided with a plurality of
spark-gaps arranged in series. Each of the spark-gaps is placed in an insulating
chute and is separated from the others in such a manner that it is impossible for
the discharge to arc across from one gap to another. In conjunction with the
spark-gaps as thus arranged, I provide a magnetic blow-out. The coil which
I prefer for this blow-out has no iron core. By preference I provide two of these
coils, one upon each side of the series of chutes, and so arrange them that the lines
of force are transverse to the path of the arc. By dispensing with the iron in the
core I avoid hysteresis effects, and also prevent the "backing up or impedance of
the discharge which would tend to force it from the ground path and compel it to
pass through the machine. The coil without iron is not only free from hysteresis
effects, but provides a substantially uniform magnetic field, so that a number of
arcs formed simultaneously at different gaps in the series will be acted upon with
practically equal power. In the arrangement of circuits which I prefer, the coil
is connected between two of the electrodes forming the series of spark-gaps so that
it is in a shunt to the path of the arc. This arrangement I have found efficacious,
the amount of current flowing in the coil being ample for the purposes for which it
is designed.
In installing a lightning arrester of my design, it is of course intended to place
one in each line, and between each arrester and the machine which it is intended
to protect I place an impedance coil, which is ordinarily composed of a number of

page_text: turns of the main or feeder in which the arrester may be placed, and by preferen
has no iron core.
The accompanying drawings show an embodiment of my invention in practical
form;
Fig. 1 being a side elevation with one side removed showing the interior 5
construction of the arrester;
Fig. 2 is a plan view, partly in section ;
Fig. 3 is a diagram of the circuits in the arrester itself; Fig. 4 is a diagram
showing the manner of installing it.
In Figs. 1 and 2, A is a base of suitable non-conducting material; B, B are 1
supports ordinarily made of metal, designed to support the side pieces C, C, which
are made of slate or other refractory insulating material; D, D are dividing walls
between the spark-gaps which are formed between the clectrodes E, E. By this
construction it will be seen that when the two parts or side walls C, C are in
position, the intervening septa D, D form with them enclosing chutes, so that the
are is confined in a small space, and the lines of force from the coils act energetically
upon it.
I, I are the coils, which are formed without an iron core, as already expressed
in my statement of invention; two of these are employed, one upon each side of
the arrester. Intervening blocks O, O enable the parts B to form a common
support for the coils and the side walls of the apparatus.
The circuits will be more readily understood from Fig. 3. N is the terminal
connected to line, from which the path of the current is through the coils I,
connected to the second of the electrodes E by the lead H. The lead H passes
from the terminal N directly to one of the electrodes. Thus the static discharge
will pass directly from the terminal N over the lead H, across the spark-gaps to
the terminal G', and from there to ground. The line current, however, will pass
partly over the lead H and partly through the coils I and the lead H', energizing
the coils and blowing out the arc at the first air-gap. If the resistance of the
series of air-gaps be not sufficient to prevent it, the line current will follow down
the series, but the coils I will remain energized, and will blow out the arcs as fast
as they form.
Fig. 4 shows the arrangement of the installation. K, K are the induction coils
to which I have referred; m, n the lines or mains. LA indicates the lightning
arrester connected between the mains and the ground at G. M is the machine to
be protected. The lightning discharge passes along one of the lines, but penetrates
with difficulty through the coil K, the self-induction of which tends to prevent the
passage of the high-potential alternating discharge; and the current, as it is
ordinarily expressed, is "backed down" through the lightning arrester to ground,
the arcing across being interrupted by the magnetic field, as already explained.
By the construction which I have described, I have been enabled to break arcs
upon a potential of ten thousand volts with certainty and without the damaging
effects so often noticed in discharges of this character. I have also been enabled
to adjust the lightning arrester to various potentials by employing various numbers
of spark-gaps in series, and so far as my experiments have gone, I believe that
potentials of any amount may be broken by having a sufficient number of
such gaps.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed as communicated to
me from abroad I declare that what I claim is :
1. A lightning arrester comprising a number of spark-gaps in series, each gap
enclosed in a chute of refractory insulating material, and a common arc-extinguishing
means for all of the spark-gaps.
2. A lightning arrester comprising a number of spark-gaps in series, cach
spark-gap enclosed in a chute, and a common magnetic blow-out for all o
the reno

page_text: 3. A lightning arrester comprising a number of spark-gaps in series, each
spark-gap enclosed in a chute, and a common magnetic blow-out for all the
spark-gaps composed of coreless coils.
4. A lightning arrester consisting of a number of spark-gaps in series, each
spark-gap enclosed in a chute, and a common arc-extinguishing means for the
spark-gaps, comprising coils connected between the line terminals and one of
the spark-gap electrodes, forming a shunt to the path of the main discharge.
5. A lightning arrester consisting of a number of spark-gaps in series, each
spark-gap enclosed in a chute, and a common arc-extinguishing means for the
spark-gaps, comprising coreless coils connected between the line terminal and one
of the spark-gap electrodes forming a shunt to the path of the main discharge.
Dated this 24th day of December 1895.
J. C. CHAPMAN,
70, Chancery Lane, London, W.C., Chartered Patent Agent.