Improvements in and relating to Lightning Arresters.
Year: 1897

page_text: Date of Application, 10th Aug., 1897-Accepted, 25th Sept., 1897
Improvements in and relating to Lightning Arresters.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Edward M.
Hewlett, of Schenectady, County of Schenectady, 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:-
The present invention relates to lightning arresters which are employed for
protecting electric apparatus from, lightning discharges, and has for its object to
provide a cheap, compact and reliable arrester, so arranged that the electrodes over
which the lightning discharges pass may be readily inspected and removed.
In the accompanying drawing, Fig. 1 is a plan of the arrester with the cover
removed; Fig. 2 is a longitudinal section taken on the line 2-2 of Fig 1;
Fig. 3 is a transverse section taken on the line 3-3 of Fig. 1, and Fig. 4 is a
diagram of the circuit connections.
The enclosing box A is made of porcelain or other insulating material, and is
preferably formed in one piece. Extending parallel with and adjacent to one side
of the box are two graphite rods B mounted in a metallic support C at one end,
and in a metal support E at the other end. The support C is electrically con-
nected to the ground terminal D. The graphite rods form a non-inductive
resistance on the ground side of the arrester, and prevent the dynamo current
following the lightning discharge.
Secured to the bottom of the box by screws is a blow-out magnet F having
rectangular pole pieces F1, F2, which are located on opposite sides of the cover
extension Ki and the arcing electrodes G, G¹. Located on the graphite rods
between the supports C and E is a clamp H, and to the support E and the clamp H
are connected the terminals of the energizing coil I of the blow-out magnet. The
coil I is provided with a suitable core, and is insulated from the core and the
pole-pieces by mica or other insulating material. The coil is energized when
the dynamo current follows a lightning discharge to ground, and the current therein
depends upon the relative resistances of the coil and that portion of the graphite
rods between the support E and the clamp H.
Extending diagonally along the base of the box is a metal strip J connected at
one end to support E, and provided at the other end with a contact J¹ extending
at right angles thereto and engaging with a spring contact d carried on the
cover K. Mounted in line with the contact J¹ is a similar contact L in electrical
connection with the line terminal L¹; the contact L also engages with a contact
on the cover K.
The cover K is preferably made of porcelain, and formed integral therewith on
its under side is an extension K¹. Binding posts M are secured in sockets in the
ends of the extension by screws N; each binding post consists of a pair of arms c
adapted to clamp the copper electrodes G in position, and a pair of spring contact
arms d adapted to engage with the stationary contacts on the base of the box
D
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page_text: The electrodes G, G¹ are separated by a slight air space over which the lightning
passes to ground. Extending below the electrodes and on both sides are
projections which protect the pole pieces F, F2 from arcing. A slightly tapered
chute l' carries off the vapour formed between the arcing electrodes, and at the
same time restraining the arc to a direction transverse to the magnetic lines of
force.
By reference to Fig. 3 it will be seen that the electrodes are in close proximity
to the chute and that the ends of the chute protect the binding posts M from
arcing.
On the cover is a spring clip Q secured thereto by a screw and adapted to engage
with the pin Q1 on the pole-piece F, to hold the cover in place. Beads a, a are
provided on the underside of the cover to prevent it from slipping endwise on the
box.
The arcing electrodes and binding posts which are most readily injured, are so
arranged that they may he readily inspected or replaced, and if the insulation
between the electrodes and the pole-pieces is destroyed, a new cover can be
substituted at small expense.
In Fig. 4 we have shown a diagram of the circuit connections, in which
I represents the circuit to be protected, and connected thereto is the terminal L'.
Terminal D is in circuit with the graphite rods B and also with ground, and the
coil of the blow-out magnet is connected to support E and clamp H. When a
lightning discharge takes place, it passes over the electrodes G, G₁ through the
rods B to ground; at the same time a certain amount of current from the line
passes through the coil I, the resistance being less than that of the rods between
the clamp and support. The dynamo current is prevented, except momentarily,
from following the lightning discharge by the non-inductive resistance of the
rods B, and any are formed between the electrodes is immediately disrupted by
the blow-out magnet.
We have shown the non-inductive resistance connected to the ground side, but
it is within the scope of our invention to reverse the connections and put it on the
line side of the arrester.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is:―
1. In a lightning arrester, the combination of arcing electrodes, a non-inductive
resistance in circuit with one of the electrodes, and a blow out magnet having the
ends of its coil or coils connected to the non-inductive resistance at points between
which there is a difference in potential due to the dynamo current following a
lightning discharge.
2. In a lightning arrester, the combination of an enclosing box, a cover formed
with an extension on its under side, binding posts secured to the extension, arcing
electrodes mounted in the binding posts, and an opening or chute through which
the vapour formed at the time a lightning discharge takes place can pass to the
outside of the box.
3. In a lightning arrester, the combination of an enclosing box, an extension
formed on the under side of the cover, binding posts secured to the extension,
arcing electrodes mounted in the binding posts, a chute formed in the cover and
its extension communicating with the external air, and a blow-out magnet arranged
to blow the arc formed at the electrodes outward through the chute.
4. In a lightning arrester, the combination of an enclosing box of insulating
material, a cover therefor, provided with an extension, on its under surface, bind-
ing posts secured to the extension, arcing electrodes separated by an air space
mounted in the binding posts, spring contact arms forming a part of the binding
posts, ground and line terminals making electrical connection with the spring
contact arms, and means for securing the cover to the box.
5. In a lightning arrester, the combination of an enclosing box, a cover therefor

page_text: provided with an extension on its under side, binding posts secured to the
extension, contacts on the binding posts engaging with fixed contacts on the box,
arcing electrodes, a non-inductive resistance, an opening in the box communicat-
ing with the outside, and a spring clip engaging with a fixed part of the box to
hold the cover in place.
6. As an article of manufacture, a cover for a lightning arrester, provided with
an extension on its under side in which is formed a chute, projections on the
extension, and sockets in which the binding posts are mounted.
For the Applicants,
J. C. CHAPMAN,
70 Chancery Lane, London, W.C., Chartered Patent Agent.