Improvements in Interrupting Devices for Electric Circuits, Applicable for Protecting Electrical Apparatus connected in such Circuits.
Year: 1889

page_text: Date of Application, 29th Oct., 1889
Complete Specification Left, 6th Aug., 1890-Accepted, 13th Sept., 1890
PROVISIONAL SPECIFICATION.
Improvements in Interrupting Devices for Electric Circuits,
Applicable for Protecting Electrical Apparatus connected in
such Circuits.
A communication from abroad by THE WESTINGHOUSE ELECTRIC COMPANY, of
Pittsburg, in the County of Allegheny, in the State of Pennsylvania, United.
States of America.
I, WILLIAM PHILLIPS THOMPSON F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors 6 Lord Street Liverpool & 6 Bank Street Manchester both in the
County of Lancaster & 323 High Holborn in the County of Middlesex, Civil
Engineer, do hereby declare the nature of this invention to be as follows:-
The invention relates to the class of inventions employed for automatically
interrupting electrical circuit connections upon the passage of currents of abnormal
strength, for the purpose of protecting the electrical apparatus connected in such
circuits.
It has been customary heretofore to interpose strips of fusible material in the
circuits of dynamo electric generators liable to be traversed by currents of abnormal
strength, and these strips have been so constructed as to offer but little resistance
to the current of normal strength, but to become heated and fused under the
influence of currents of abnormal strength, thus interrupting the circuit connections.
It is found in practice that the fusible materials usually required for this purpose
are such that-thus fused-they form a vapour which acts as a conductor of electricity..
An arc is thus formed across the space intervening between the ends of the fused
strip, and the current developed by the dynamo then continues to flow across the
space. The object of the invention is to prevent the occurrence of such an are,
and to insure that a current of sufficient strength to fuse the strip will cause a
complete interruption of the circuit.
The invention consists in forming a shunt circuit around the fusible strip, so
constructed as to receive the entire current immediately upon the destruction of
the fusible strip and then itself become interrupted in such a manner as to form
an opening of the circuit.
In carrying the invention into practice, a second fusible strip may be connected in
the shunt circuit, and this is of such material and so proportioned as to be brought
into action immediately after the first strip has been destroyed, but to convey the
current for a sufficient period to prevent it from bridging the space between the fused
ends of the first strip. The second or shunt fuse may consist of one or more strips of
German silver or iron or other material, which does not readily establish an are when,
melted. In practice, German silver is found to serve the purpose exceedingly well;
iron also is found to operate very successfully on account of its tendency to separate.
into globules when heated to a high temperature, and thus avoid the formation of
an arc.
In one or both of the two lines leading from the poles of the generator to the.
work-circuit, there is inserted a safety fusible device. These devices consist of a strip
of some suitable well-known fusible compound or metal, such as lead for instance and
a shunt circuit through a fusible wire or strip. This latter may, with advantage, be
of German silver and of greater-resistance than the strip aforesaid so that normally it
conveys but a comparatively small proportion of the current. The strip may be held
in binding plates which also carry arms of greater conducting capacity supporting the
strip. A second strip may be placed upon the same supporting block, the design
being to use the second as a reserve, in case the first is destroyed. A switch plug
employed for connecting the two plates. By connecting the lines with one of the
:

page_text: binding plates of the strip and the other binding plate of the second strip the first
named strip will be connected in circuit. By placing the switch plug between the
other two plates the second strip aforesaid will be placed in circuit. This is a con-
venient form of device to employ, but it will be evident that the invention is equally
applicable to other forms of devices.
The fusible wire or strip may be constructed of one or more strands of German
silver wire or strips of iron or other suitable material. The relative conductivities of
the two fusible strips thus connected in shunt upon each other are such that each will
conduct its proportion of the normal current of the circuit without fusing or becoming
over heated. If, however, a current of excessive strength should traverse the main
line, then the increase of the current flowing through the safety strip would be
sufficient to cause it to fuse, whereupon the circuit would remain complete through
the fusible wire or strip alone. The presence of this circuit however, would prevent
the formation of an are between the terminals of the safety strip, but the increase of
current compelled to traverse the shunt circuit would immediately fuse the fusible
wire or strip. This strip, however, is of such construction or formation as to prevent
the establishment of an arc. It simply serves to entirely interrupt the circuit
connections by being suddenly fused or exploded under the influence of the entire
current.
Don
1000
Improvements in Interrupting Devices for Electric Circuits,
Applicable for Protecting Electrical Apparatus connected in
such Circuits.
A communication from abroad by THE WESTINGHOUSE ELECTRIC COMPANY, of
Pittsburg, in the County of Allegheny, in the State of Pennsylvania, United
States of America.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 6, Lord Street, Liverpool, and 6, Bank Street, Manchester, both in
the County of Lancaster and 323, High Holborn in the County of Middlesex, Civil
Engineer, 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 :-
The invention relates to the class of inventions employed for automatically
interrupting electrical circuit connections upon the passage of currents of abnormal
strength, for the purpose of protecting the electrical apparatus connected in such
circuits.
It has been customary heretofore to interpose strips of fusible material in the
circuits of dynamo electric generators liable to be traversed by currents of abnormal
strength, and these strips have been so constructed as to offer but little resistance to
the current of normal strength, but to become heated and fused under the influence of
currents of abnormal strength, thus interrupting the circuit connections. It is found
in practice that the fusible materials usually required for this purpose are such that,
thus fused, they form a vapour which acts as a conductor of electricity. An are is
thus formed across the space intervening between the ends of the fused strip, and the
current developed by the dynamo then continues to flow across the space. The object
of the invention is to prevent the occurrence of such an are and to insure that a current
of sufficient strength to fuse the strip will cause a complete interruption of the
circuit.
The invention consists in forming a shunt circuit around the fusible strip, so con-
structed as to receive the entire current immediately upon the destruction of the
fusible strip and then itself become interrupted in such a manner as to form an

page_text: opening of the circuit. In carrying the invention into practice, a second fusible strip
may be connected in the shunt circuit and this is of such material and so proportioned
as to be brought into action immediately after the first strip has been destroyed but
to convey the current for a sufficient period to prevent it from bridging the space:
between the fused ends of the first strip. The second or sliunt fuse may consist of one
or more strips of German silver or iron or other material, which does not readily.
establish an arc when melted. In practice, German silver is found to serve the
purpose exceedingly well; iron also is found to operate very successfully on account
of its tendency to separate into globules when heated to a high temperature and thus
avoid the formation of an arc.
In the accompanying drawings,
Figure 1 is a side elevation of a fusible cut-out embodying the invention.
Figure 2 is a plan of the same, and
Figure 3 is a diagram of a system of circuits supplied with the safety devices.
Referring to the Figures,
A represents a dynamo electric generator or other suitable source of electric
currents, and W represents a work-circuit supplied with currents from the lines I, 1
L2
leading from the poles of the generator to the work-circuit. In one or both of
the two lines L, 12, there is inserted a safety fusible device. These devices are con-
structed as more particularly shown in Figures 1 and 2. They consist of a
strip B¹
of some suitable well-known fusible compound or metal, such as lead for instance and
a shunt circuit through a fusible wire or strip b. This latter may, with advantage, be
of German silver and of greater resistance than the strip B₁ so that normally it
conveys but a comparatively small proportion of the current. The strip B is shown
as held in binding plates 61 and 62 which also carry arms d', ² of greater conducting
capacity, supporting the strip b. In the drawing, a second strip B² is shown as
placed upon the same supporting block D, the design being to use the second as a
reserve, in case the first is destroyed. A switch plug e is employed for connecting
the two plates b62. By connecting the lines with the plate 61 of the strip B1 and the
plate 62 of the strip B2, the strip B₁ will be connected in circuit. By placing the
switch plug e between the other two plates b¹, the strip B² will be placed in
circuit. This is a convenient form of device to employ, but it will be evident
that the invention is equally applicable to other forms of devices.
The strip b may be constructed of one or more strands of German silver wire or
strips of iron or other suitable material. The relative conductivities of the two
fusible strips thus connected in shunt upon each other are such that each will conduct
its proportion of the normal current of the circuit without fusing or becoming over
heated. If, however, a current of excessive strength should traverse the main
line, then the increase of the current flowing through the strip B¹, would be
sufficient to cause it to fuse, whereupon the circuit would remain complete through
the strip balone. The presence of this circuit, however, would prevent the formation
of an are between the terminals of the safety strip B₁, but the increase of current
compelled to traverse the shunt circuit would immediately fuse the strip b. This
strip, however, is preferably of greater resistance than the strip B₁ and is of such
construction or formation as to prevent the establishment of an arc. It simply serves
to entirely interrupt the circuit connections by being suddenly fused or exploded
under the influence of the entire current.
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 by my foreign correspondents, I declare that what I claim is :-
1. An interrupting device for electric circuits consisting of the combination, with
a fusible strip, of a normally closed shunt-circuit around the same, and a second
fusible strip of conducting material through which the connections of said normally
closed shunt-circuit are completed, said second strip having a greater resistance than
the first-named strip and serving to permanently interrupt the shunt-circuit
connections when the first named fuse has been destroyed.

page_text: 2. An interrupting device for electric circuits consisting of the combination, with a
fusible strip, of a normally closed shunt-circuit around the same and a second fusible
strip of conducting material through which the connections of said normally closed
shunt-circuit are completed, said second strip being of a different material from the
first named strip and serving to permanently interrupt the shunt-circuit connections
when the first-nained fuse has been destroyed.
3. An interrupting device for electric circuits consisting of the combination, with
an electric circuit, of a fusible strip, a normally closed shunt-circuit, and a second
fusible strip of conducting material through which the connections of the said
normally closed shunt-circuit are completed, said strips being so proportioned to cach
other and to the circuit that an abnormal increase of current in the circuit will
destroy the first named strip while the second will be destroyed by the resultant
current traversing its circuit, thereby permanently interrupting both circuits.
Dated this 29th day of July 1890.
WM. P. THOMPSON & Co.,
Agents for the Applicant.