Improvements in Safety Devices for High-pressure Electrical Currents and Indicating Apparatus in connection with same.
Year: 1890

page_text: Date of Application, 15th Mar., 1890
Complete Specification Left, 15th Dec., 1890-Accepted, 24th Jan., 1891
PROVISIONAL SPECIFICATION
Improvements in Safety Devices for High-pressure Electrical
Currents and Indicating Apparatus in connection with same.
BERNARD MERVYN DRAKE and JOHN MARSHALL GORHAM Electrical Engineers
both of 2 Princes Mansions Victoria Street in the City of Westminster do hereby
declare the nature of this invention to be as follows:-
Our invention refers to a modification of the static safety device patented by
Philip Cardew No. 15484 1887, and consists substantially of a foil attached to a
metal plate at one end, the two being suspended vertically, & the other end of the foil
being left free. The combined foil and plate are connected either to earth or the
circuit which it is desired to protect and at a short distance a separate plate is fixed to
which the other connection is made.
This second plate must be insulated from the first.
The second plate may have a projection opposite to the free end of the foil.
The action will be as follows:
The suspended foil will be attracted by the adjacent plate, but repelled by the plato
with which it is in contact. When a high difference of potential is established the
foil will make contact between the two plates & the action will then be the same as
described in Patent No. 15484 1887. It is evident that the same arrangement can be
used simply as an indicator of high pressures, but in this case two flexible foils should
be connected at one end and suspended so that the two foils may fly apart after the
well known method of the electroscope, the foils being attracted by a cylinder of
metal or plates placed at a distance from the foils.
When used for this purpose alone it may be desirable that a metallic contact should
not be established between the two poles, or between the earth & lines when the
instrument is used as an indicator of the insulation of the main conductors. In such
cases a cylinder of glass or plates of glass, or other insulator may be interposed
between the foils and the surrounding conductor so as to prevent the foils when flying
apart from establishing an electrical circuit.
An aperture must be left so that the position of the foils may be easily seen and in
the case of central stations the attendant will be able to see at a glance whether or
not the insulation of the mains has been maintained to the required standard by the
divergence or otherwise of the combined foils which would then be attached the foils
to earth & the surrounding cylinder to the lines, or vice versa.
Dated this 15th day of March 1890
BERNARD MERVYN DRAKE.
JOHN MARSHALL GORHAM.
COMPLETE SPECIFICATION.
Improvements in Safety Devices for High-pressure Electrical
Currents and Indicating Apparatus in connection with same.
We, BERNARD MERVYN DRAKE and JOHN MARSHALL GORHAM, Electrical Engineers,
both of 2 Princes Mansions, Victoria Street, in the City of Westminster 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
Our invention relates to a modified construction and arrangement of electrical
safety device of the kind described in the Specification No. 15484 of 1887, and to a
farther modification thereof constituting indicating apparatus shewing the condition
of conductors as we shall describe referring to the accompanying drawings.

page_text: Fig. 1 is a vertical section of the modified safety device according to our invention
and
Fig. 2 is a vertical section of the indicating apparatus. Referring to Fig. 1, A is
a vertical metal plate to which is fixed the upper end of a strip B of gold leaf or
aluminium foil. C is a metallic contact disc which is fixed at a certain distance from
the plate A or which can be screwed as shown in a metal column D so that it can be
adjusted nearer to or further from the plate A. E is a base and F a cover both of
insulating material, and G is a glass cylinder enclosing the parts above described.
The plate A and the column D are connected by conductors HK, the one to the
main supplying a house. with electricity, the other to earth. The foil B being repelled
from A and attracted towards C, will, when there is a high difference of potential
between H and K such as involves danger, make contact with C thus connecting the
load H to earth.
In Fig. 2 M N are two strips of gold leaf or foil connected together at their upper
ends and to a metallic bolt O fixed in the cover of a glass jar P, which has its lower
part covered with tin foil Q and is seated in a metal base R. The bolt O and the
hase R being connected by conductors ST respectively to a main supplying electricity
and to earth, the strips M N will be repelled from each other and attracted towards
the foil Q causing them to spread apart to a greater or less extent according as there
is a greater or less difference of potential between the conductor under test and earth.
Thus an attendant can see at a glance if the insulation of the conductors from earth is
up to the required standard.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. The safety device for high pressure electrical currents consisting of a plate A
having suspended in front of it a metallic strip B, and of a contact disc C, the plate
and the disc being connected respectively to an electric main and to earth substantially
as described with reference to Fig. 1.
2. The indicating apparatus consisting of two metal strips or foils M N attached
together within a glass jar P having part of its surface covered with metal, the
junction of the strips M N and the metal covering of the jar being connected
respectively to an electric main and to earth, substantially as described with reference
to Figure 2.
Dated this 15th day of December 1890.
ABEL & IMRAY,
Agents for the Applicants.