improvements in Lightning Arresters.
Year: 1897

page_text: Date of Application, 8th June, 1897-Accepted, 31st July, 1897.
improvements in 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 Axel Ekstrom,
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 :-
Our invention relates to lightning arresters; and has for its object to provide
an apparatus of this description, which shall be efficient and reliable in operation,
able to take care of a number of static discharges in succession, and yet which
shall maintain a substantially constant resistance so that lightning discharges may
not be diverted from the ground path provided for them into the line circuit
through the machines to be protected, or the line current follow the static
discharge by lessening the resistance of the ground connection.
To this end we arrange the lighting arrester with a number of spark gaps in series,
and to those of the electrodes nearest to the ground in the series, we connect fuses in
multiple to the ground terminal. By this arrangement the lightning or static
discharge passes across the series of spark gaps until it reaches one of the electrodes
connected by a fuse with the ground terminal, when it passes over this conductor to
earth. The line current, if it have sufficient potential to bridge the spark gaps, also
passes by the fuse. This latter however is made of small capacity, and is readily
ruptured by excess of current. There may of course be as many fuses as may be
desirable.
With the rupture of each fuse an additional gap would be introduced in the series
of spark gaps in the arrester. The passage of the line current is also liable to melt
the electrodes slightly so that the resistance of the several gaps may be decreased.
For this reason we prefer as the basis of our improved arrester to employ one of the
so-called "ball" type, in which a series of brass or composition balls are arranged upon
a base of insulating material, the balls being rotatable about the studs affixing them
to the base.
The accompanying drawing shows an embodiement of our invention, Figs. 1 and 2
being a front and side elevation respectively of a lightning arrester constructed
according to its principles.
A is the base of the apparatus, B, B, are the balls or electrodes, C, C are the
conductors leading from the lower ones of these electrodes to the fuses indicated at D.
The path of the discharge would be from the line L through the series of spark gaps and
over one of the conductors C to one of the fuses D which are connected in multiple,
and to the ground terminal G. The fuse and its connector forming a circuit of low
resistance, the discharge would ordinarily take this path.
A non-inductive resistance might be included in the ground circuit with the
lightning arrester, and an inductive coil in the line between the arrester and the
dynamo. We have not illustrated these devices however, as they are well understood
in the art and are not claimed by us.

page_text: The operation of the device as thus described is briefly as follows: After each
discharge it will be found that one of the gaps, sometimes more, will be partly bridged
by the fusion of the electrodes, and the resistance of the arrester will be thus decreased.
Its efficiency is also decreased, the line current following the discharge more
readily; but as each discharge takes place, a new gap is introduced into the line
by the melting of one of the fuses, so that the substantial equality of resistance
to which we have referred is maintained.
The essential feature, therefore, of our invention is maintaining the substantial
equality of resistance across the terminals of the lightning arrester; and this is
obtained by employing a number of spark gaps in series, and means for increasing
the number when the resistance of one of the gaps is diminished.
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. A lightning arrester comprising a number of spark gaps in series, of a kind
to have their resistance decreased by use, combined with means controlled by
such decrease in resistance for increasing the number of spark gaps in series.
2. A lightning arrester comprising a number of spark gaps in series, a part of
those in series being short-circuited, and means for opening the short-circuit as the
resistance of the gaps already operating decreases.
3. A lightning arrester comprising a number of spark gaps in series, the electrodes
of the spark gaps nearest the ground terminal being connected to that terminal by a
number of fuses arranged in multiple.
4. A lightning arrester comprising a number of spark gaps in series, the electrodes
being substantially of ball shape, and those nearest the ground terminal being
connected thereto by fuses.