Improvements in or relating to Safety Cut Outs for Electric Generators, Transformers, and Motor Generators Coupled in Parallel.
Year: 1892

page_text: Date of Application, 28th Oct., 1892
Complete Specification Left, 28th July, 1893-Accepted, 2nd Sept.. 1893
PROVISIONAL SPECIFICATION.
Improvements in or relating to Safety Cut Outs for Electric
Generators, Transformers, and Motor Generators Coupled in
Parallel.
I, JOHN SMITH RAWORTH, of 112 Belvedere Road, Lambeth in the County of
Surrey, Electrical Engineer, do hereby declare the nature of this invention to be
as follows:-
When a number of electric generators are arranged in parallel to supply current
through a common system of mains it is usual to place a safety cut out consisting
either of a fusible wire or of an electro magnetic device, between each generator
and the main conductors for the purpose of cutting out of circuit any generator
which while at work may from any cause have developed a short circuit or have
become incapable of maintaining its customary electro motive force.
In the event of such an accident occurring the current flows back through
the disabled generator from the main conductor, melting the fuse or actuating the
electric magnetic device thereby disconnecting the disabled dynamo from the
circuit.
It not unfrequently happens however that the cut outs of the other generators
in circuit at the time, are caused to act by the momentary excess of current to
which they are subjected. It is obvious that if at the time of the accident there
are in circuit only two generators of which one becomes disabled, then the other
generator will have to supply all the current necessary for the outer circuit plus
the current required to.actuate the cut out of the disabled generator, therefore,
caeteris paribus the cut out of the working generator would act as well as or instead
of that of the disabled generator causing a cessation of current. The object of
my invention is to ensure that the cut out of the disabled generator alone
shall act.
For this purpose I place in parallel with the cut out a transformer or (supple-
mentary) independently driven generator which will give to the current at that
point a slightly increased electric motive force sufficient to cause the main current
to pass through the said transformer or supplementary generator rather than
through the cut out, but in the event of the generator becoming disabled, the
effect of the transformer or supplementary generator will be to oppose the return
of the current through itself and to divert it through the cut out. The acting of
the cut cut alone would not in this instance break the circuit, as the transformer
or supplementary generator would still keep the circuit closed, but I provide for
this by a switch placed in series with the said transformer, or supplementary
generator and arranged in such a manner in conjunction with the cut out, that on
the latter coming into action a trigger or equivalent device permits the switch to
be opened by a spring or its equivalent.
My invention will be more readily understood by considering that the effect of
it is to cause the current from a generator to the main conductor to avoid the cut
out, and vice versa to compel it to pass through the cut out when returning from
the main conductor to the generator.
My invention is applicable both to alternating and continuous current generators;
it is applicable to transformers and motor generators whenever two or more are
used in parallel.
Dated his oth 1
1
2000
W. LLOYD WISE,
Per F. J. Brougham,.
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.

page_text: COMPLETE SPECIFICATION.
Improvements in or relating to Safety Cut Outs for Electric
Generators, Transformers, and Motor Generators Coupled in
Parallel.
I, JOHN SMITH RAWORTH, of 112 Belvedere Road, Lambeth in the County of
Surrey, Electrical 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 :—
When a number of electric generators are arranged in parallel to supply current
through a common system of mains it is usual to place a safety cut out consisting
either of a fusible wire or of an electro magnetic device, between each generator
and the main conductors for the purpose of cutting out of circuit any generator
which while at work may from any cause have developed a short circuit or have
become incapable of maintaining its customary electro motive force.
In the event of such an accident occurring the current flows back through the
disabled generator from the main conductor, melting the fuse or actuating the
electric magnetic device thereby disconnecting the disabled dynamo from
the circuit.
It not unfrequently happens however that the cut-outs of the other generators in
circuit at the time, are caused to act by the momentary excess of current to which
they are subjected. It is obvious that if at the time of the accident there are in
circuit only two generators of which one becomes disabled, then the other generator
will have to supply all the current necessary for the outer circuit plus the current
required to actuate the cut-out of the disabled generator, therefore, cæteris paribus,
the cut-out of the working generator would act as well as or instead of that of the
disabled generator causing a cessation of current. The object of my invention is to
ensure that the cut-out of the disabled generator alone shall act.
For this purpose I place in parallel with the cut out a transformer or (supple-
mentary) independently driven generator which will give to the current at that
point a slightly increased electric motive force sufficient to cause the main current
to pass through the said transformer or supplementary generator rather than
through the cut-out, but in the event of the generator becoming disabled, the effect
of the transformer or supplementary generator will be to oppose the return of the
current through itself and to divert it through the cut-out. The acting of the cut-
out alone would not in this instance break the circuit, as the transformer or
supplementary generator would still keep the circuit closed, but I provide for this
by a switch placed in series with the said transformer, or supplementary generator
and arranged in such a manner in conjunction with the cut-out, that on the latter
coming into action a trigger or equivalent device permits the switch to be opened by
a spring or its equivalent.
My invention will be more readily understood by considering that the effect of
it is to cause the current from a generator to the main conductor to avoid the cut-
out, and vice versa to compel it to pass through the cut-out when returning from the
main conductor to the generator.
My invention is applicable both to alternating and continuous current generators;
it is applicable to transformers and motor generators whenever two or more are
used in parallel.
The accompanying drawing illustrates diagrammatically an arrangement of
circuit with cut-outs according to this invention for an electric generator arranged
in parallel with one or more others not shewn to supply current into mains.
The current enters at the joint a' of the switch a³ and has the choice of two
paths one through the fuse or cut-out 61, the conductor 6' to the junction 6*; the
other through the switch a', the conductor a³, the thick winding of the trans-
former a to the junction, aº. The thin winding of the transformer forms a shunt
to the mains.

page_text: The transformer a' is so arranged that it imparts a slight additional electro-
motive force to the current sufficient to induce it to select the route through a³, a³, a³,
to the junction 63 a in preference to the route through 1 b.
In the event of the dynamo failing to give its normal electro-motive force
there would be a transference of energy from the mains to the dynamo, and in that
event the current would select the route through the circuit 3, 6 and through the
fuse b', as the electro motive force of the transformer at would oppose its passage
through the route a', a³, a². Under these circumstances the fuse or cut-out 6'
would act and liberate the switch a and thus cut off the dynamo from the main
conductor C¹.
In the drawing the fuse is shewu holding up a weighted lever which as soon as
the fuse acts drops and strikes open the switch a². This arrangement may however
be varied considerably in detail. An electro magnetic cut-out may be substituted
for or used in combination with the fuse b¹.
The tendency of the transformer a is to cause a current to circulate in the
closed circuit 61, b³, b³ a³, a², a³, a, a', and the amount of such circulating current
may be limited by the construction of the transformer or by the introduction of
resistance in the said closed circuit.
It is obvious that instead of placing the source of electro-motive force in the
branch a, a, at this invention may be carried into effect by placing such source in
the circuit b 62, but in the latter case it must be arranged to exert its influence in
the opposite sense that is to say to oppose the flow of the current through b₁ b
when the generator is working normally.
This invention is applicable to alternating currents and to continuous currents,
but in the case of the latter a motor generator, independent generator or battery
must be substituted for the transformer a*.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. For use with electric generators, transformers, or motor generators coupled in
parallel, the arrangement of a fuse or electro magnetic cut-out, and a switch or
mechanical contact maker in separate branches, and a transformer or other source
of electro-motive force for determining the flow of current in regard to such fuse or
cut-out substantially as described.
2. In the arrangement specified in the preceeding claim the combination with
the fuse or cut-out of mechanism adapted to be released thereby and to open the
switch or mechanical contact maker substantially as described.
3. The arrangement of safety cut-outs for electric generators, transformers, and
motor generators coupled in parallel, substantially as herein before described with
reference to the accompanying drawing.
Dated this 28th day of Jul 1902
W. LLOYD WISE,
Per F. J. Brougham,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.