Improvements in Devices for Protecting Electric Circuits and Apparatus or Instruments from Injury by Excessive Electrical Potential.
Year: 1896

page_text: Date of Application, 19th Sept., 1896
Complete Specification Left, 21st June, 1897-Accepted, 28th Aug., 1897
PROVISIONAL SPECIFICATION.
PROVISIONAL SPECIFICATION.
Improvements in Devices for Protecting Electric Circuits and
Apparatus or Instruments from Injury by Excessive Electrical
Potential.
I VALERE ALPRED FYNN of 13 Bexley Road Erith in the County of Kent
Electrician do hereby declare the nature of this invention to be as follows:-
My Invention relates to devices for protecting electric circuits and apparatus or
instruments from injury by excessive electrical potential in which devices metal
pieces are placed at short distances apart and so arranged and connected with the line
to be protected and the earth or with the two ends of the circuit to be protected that
when excessive rise of potential occurs by reason of lighting or other cause such for
example as the circuit of the dynamo or other electrical apparatus of high electrical
self induction being suddenly broken the high electromotive force set up expends
itself at the air space or spaces between the metal pieces or will pass to earth. An
apparatus on this principle is described in the Specification of my application for
Letters Patent No. 24471 of 1895 and my present Invention consists firstly of an
improvement in a device such as is therein described. According to my present
Invention I place around the metal pieces with the gaps between them a glass
cylinder of slightly larger diameter than the metal pieces (which I will refer to as
discs) but in close proximity thereto and the outside of this cylinder is coated with a
thin inetal coating such as one of tin foil. This metal coating is in metallic
connection with either the first or the last of the discs but preferably with the first.
Its object is to increase the sparking distance of a current of given potential across
the spaces between the discs the metal coating and glass cylinder forming a condenser
and rarifying the air on the inside of the glass cylinder. This arrangement allows a
greater number of air spaces to be put in series whilst still allowing a current of given
potential to spark across. The advantage in the greater number of air spaces is the
diminution of the danger of a continuous are being set up. Generally according to
this Invention I either rarify the air between the discs by means of condenser effects
obtained in some such manner as that described or I place all the discs in
a hermetically closed receptacle from which the air is exhausted and provided or not
with a relief valve.
This rarefication of air or condenser effect may also be applied to a protective
device consisting for instance of series of points or projections, sharp, or rounded,
opposing each other; one series being connected to the apparatus or line to be
protected and the other series to earth.
When the aforesaid metal dises or like surfaces separated by an air space or by air
spaces are used for preventing damage to dynamos or other electrical apparatus or
instruments with high self induction when on the current being suddenly discontinued
for instance high back electromotive force may be set up, the said discs may be
arranged in pairs or other suitable number but I will presume that they are used in
pairs. In a case for instance where two pairs are used one of the discs of each pair
may be connected to a metal case in contact with the base of the machine or otherwise
led to earth, the other discs being connected to the two ends of the circuit or part of

page_text: the circuit to be protected. Instead, of using an earth connection the discs of a pair
may be respectively connected with the two ends of the circuit to be protected there
being the requisite air space between the discs. The discs may be enclosed in a
The discs are preferably set vertically and their edges are curved away
from each other so that if an arc should be set up and maintained for a short time its
heat will cause an upward air current and the arc will follow this current and as it
reaches the edges of the discs it will be broken owing to the increased distance
between the opposed surfaces of the discs towards the edges.
Should the circuit of the apparatus or instrument be again completed whilst the
are so set up lasts the re-established current owing to its electromotive force being
opposed to that of the arc will destroy the said arc.
It is however possible that on account of the smallness of the gap, or gaps, this or
these air spaces may be bridged over by some conductive matter, in that case upon
"making" the circuit again a short circuiting may occur, to prevent this possibility
a suitably proportioned fuse may be provided and may conveniently be combined
with the case enclosing the apparatus.
1
1000
JOHNSONS & WILCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.
Improvements in Devices for Protecting Electric Circuits and
Apparatus or Instruments from Injury by Excessive Electrical
Potential.
I, VALERE ALFRED FYNN, of 13 Bexley Road, Erith, in the County of Kent,
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 devices for protecting electric circuits and apparatus or
instruments from injury by excessive electrical potential, in which devices metal
pieces are placed at short distances apart and so arranged and connected with earth a
and with the line to be protected and the earth, or with the two ends of the circuit
to be protected, that when excessive rise of potential occurs by reason of lightning
or other cause, such for example, as the circuit of a dynamo or other electrical
apparatus of high electrical self induction, being suddenly broken, the high electro-
motive force set up expends itself at the air space or spaces between the metal pieces,
or will pass to earth. An apparatus on this principal is described in the Specification
of Letters Patent No. 24471 of 1895, and my present invention consists of
improvements in a device such as is therein described. I place all the discs in a
hermetically closed receptacle provided or not with a relief valve and from which the
air is partly exhausted. This arrangement allows a greater number of air spaces to
be put in series whilst still allowing a given potential to cause a discharge across that
increased number of discs.
The advantage of a greater number of air spaces is the diminution of the danger of
a continuous are being set up.
When the aforesaid metal discs or like surfaces, separated by an air space or by air
spaces, are used for preventing damage to dynamos or other electrical apparatus or
instruments with high self induction, in which on the current being suddenly
discontinued a high back electro-motive force may be set up, the said dises may be

page_text: arranged in pairs or other suitable number but I will presume that they are used in
pairs. In a case for instance where two pairs are used one of the discs of each pair
may be connected to a metal case in contact with the base of the machine, or
otherwise led to earth, the other dises being connected by a shunt to the two ends of
the main circuit or part of the circuit to be protected. Instead of using an earth
connection the discs of a pair may be respectively connected by a shunt with the two
ends of the circuit to be protected there being the requisite air space between the
discs. The discs may be enclosed in a suitable case. The discs are preferably set
vertically and their edges are curved away from each other so that if an arc should be
set up and maintained for a short time, its heat will cause an upward air current and
the are will follow this current, and as it reaches the edges of the discs it will be
broken owing to the increased distance between the opposed surfaces of the discs
towards the edges.
In order that my invention may be clearly understood I will further describe the
same with reference to the accompanying drawings of which Figure 1 represents in
vertical section a potential arrester constructed according to my invention, and
Figure 2 shews the arrester attached to a telegraph post or like support and
electrically connected to an overhead line, Figure 3 represents in transverse vertical
section and Figure 4 in front elevation and part vertical section, a potential arrester
constructed according to my invention for preventing damage to dynamos or other
electrical apparatus or instruments; Figure 5 is a plan corresponding to Figure 4.
Referring to Figures 1 and 2, A is a glass cylinder closed at top by a metallic
cover B and at bottom by a metal plate C, india-rubber or other suitable insulating
packing a being interposed between the glass cylinder A and cover B and bottom
plate C. The cover B is provided with binding screw b for making electrical
connection with the line wire, and the bottom plate C is provided with a terminal c
for making electrical connection with earth. The cylinder A with the cover B and
bottom plate C, constitute a closed chamber to contain a number of metal dises D
the said dises being superposed one above another and retained at a short distance
apart by insulating incombustible distance pieces d. The uppermost diše D is in
metallic contact with a projection B' depending from the cover B into the chamber,
whilst between the lowermost disc D and the bottom plate C is interposed a spring E,
or springs, which tends or tend to press the discs upwards. The chamber is
hermetically closed and the air exhausted therefrom, for which purpose the bottom
plate C is provided with a nozzle F communicating with the interior of the chamber,
to which nozzle an air exhausting device can be attached, and the nozzle is provided
with a cock F1 through which when opened the air can be exhausted after which the
cock can be closed and the air exhausting device be detached.
To guard against damage in case of an are being formed the device may be provided
with a relief valve or fuse as shown by dotted lines at e connected at one end to the
earth terminal e the other end passing through an opening el in the glass cylinder A
and being connected to the lowermost disc D. The portion of the fuse which is in
the opening el is preferably of reduced section so as to more readily fuse at this part,
the opening el being closed with suitable material to render it air-tight. When the
safety fuse e is used the bottom plate C of the chamber should be insulated from the
discs D which may be effected in any convenient way for instance by interposing
insulating material between the spring E and the said bottom C. Should an arc
form in the chamber by reason of the dynamo current following the discharge this
current will melt the fuse and thereby break the circuit.
The arrester may be supported in any convenient manner for instance as shewn in
Figure 2 the arrester is mounted in a holder G secured to a telegraph pole or other
support the glass cylinder A being provided with a shoulder g to rest on the said
holder. When a high electro-motive force is set up in the circuit from any cause it
will pass to earth through the discs D spring E or fuse e (in case such is employed)
5 by the terminal c.
For preventing damage to dynamos or other electrical machines or instruments
the apparatus illustrated by Figures 3, 4 and 5 may be employed, in which figures,

page_text: A represents a drum or chamber made in two parts, 1, 2, connected together by
screwing one part onto the other part as shewu at 3. The chamber A may be
secured by screws 4, or otherwise to the instrument to be protected. Each part, 1, 2,
carries a gun metal disc DD' so arranged that when the said parts are screwed
together the two discs D D¹ will face each other with the requisite air space between
them. The disc D carried by the part 1 of the chamber A is insulated therefrom by
washers 5 and 6 of insulating material but is in inetallic contact with the block 7 to
which one end of the electric circuit to be protected is attached, whilst the part 2
carrying the other disc D¹ is in metallic contact with the apparatus to be protected or
otherwise connected with earth. The peripheries of the discs D, D¹ are rounded or
curved away from each other as shewn at 8 in Figure 3 so that should an arc be set
up and maintained for a short time, owing to an increase of potential, the heat
generated thereby will cause an upward current of air which the arc will follow, and
will be broken when it reaches the edges of the discs owing to the increased distance
between the opposed surfaces of the discs towards the edges. 9 are sight holes
covered by glass through which can be seen whether or not the discs DD¹ are
adjusted to the requisite distance apart.
Should the circuit of the apparatus or instrument be again completed whilst the
are so set up lasts the re-established current, owing to its electro-motive force being
opposed to that of the arc, will destroy the said arc.
It is however possible that on account of the sinallness of the gap, or gaps, this or
these air spaces may be bridged over by some conductive matter, in that case upon
"making "the circuit again a short circuiting may occur, to prevent this possibility
a suitably proportioned fuse may be provided, and may conveniently be combined
with the case enclosing the discs.
Figures 6, 7 and 8 represent diagrammatically some of the possible arrangements
of the improved potential arresters, from which all other arrangements may be
readily understood. In these diagrams A represents the arresters arranged in a
shunt A, and B the circuit or instrument to be protected, and e the fuses.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. For protecting electric circuits from injury by abnormal rise of potential, a
hermetically closed receiver from which air is exhausted, the said receiver containing
metal plates or discs arranged at such distances apart as to prevent discharge of
current at normal potential but allow discharge at abnormal potential, substantially
as hereinbefore described.
2. For preventing damage to dynamos or other electrical apparatus or instruments
with high self induction, metal discs arranged in one or inore pairs the discs of each
pair facing each other and having their peripheries curved or rounded so as to
increase the distance between the discs at their edges, these discs being connected
with the circuit to be protected and with earth substantially as hereinbefore described
and illustrated.
3. The combinations and arrangements of parts constituting apparatus for
protecting from injury by excessive electrical potential, electric circuits and apparatus
or instruments substantially as hereinbefore described and illustrated in the
accompanying drawings.
JOHNSONS & WILCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.