Year: 1887

page_text: Date of Application, 19th Apr., 1887.
Specification Accepted, 20th May, 1887.
1, WILLIAM PHILLIPS THOMPSON F.C.S. M.I.M.E. of the Agency for Foreign Patent
Solicitors 6 Lord Street Liverpool, 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 devices employed for preventing the armature-
coils of electric generators from being injured by overheating.
The invention consists in connecting each junction between the bobbins with its
commutator-plate through a fusible conductor, which, while normally conveying the
currents produced by the generator without developing heat, will be fused by an
excess of current or by reason of currents being transmitted through the same
continuously.
It has been proposed to interpose fusible plugs in the circuit of dynamo and
magneto machines in such manner that they will entirely interrupt the circuit when
fused, but this construction causes the current to entirely cease when the plugs are
brought into action, so that the machine must be stopped at once for repairs.
By placing the fusible connections between each joint and the corresponding
cominutator-plate, the machine may continue to operate, even after one or more of the
connections have been severed.
In the accompanying drawing there is illustrated a portion of an armature, of the
Gramme type, together with the commutator or collector-plates and circuit connections.
Referring to the figures A¹, A2, A3, represent bobbins of the armature, and the
joints of the wire are connected respectively with binding-screws 61, 62, 63 etc. The
contact-plates c, c², c³ etc., are mounted in the usual manner and they are connected
respectively with the points 61, 62, 63, by means of fusible strips' d', d², d³. These

page_text: strips may be of lead or any suitable composition metal, such as is ordinarily employed
for fusible conductors. They preferably extend between the binding-screws or
points 1, 2, 3, to which the joints of the armature-coils are attached, and the
plates c¹, c², c³, and may be readily replaced.
The conductivity of the strips d', d², d³, is such that they will convey the currents
normally produced by the generator without injury or without becoming overheated.
As these strips are located where they are exposed to the air it is evident that they
may be of somewhat less conductivity than if they were more or less surrounded as
are the conductors of the bobbins; but the conductivity will be determined in each
case by the character of the machine, and the currents to be produced, it being
only necessary that it be such that they will convey the currents without undue
resistance.
During the normal operation of the machine a current is transmitted through each
commutator-plate twice during each revolution of the armature. In
case, however,
that two adjacent contact-plates become accidentally connected with each other, as
for instance by means of a metallic chip, currents will be transmitted through the
corresponding fusible strips continuously. This would result in injury to the bobbin
causing it to be burned out, were not means provided to prevent it, namely, the
fusible strips. These become heated more quickly than the bobbin and become
softened. The centrifugal force then throws them outward so that they sever the
connections between the plates and the bobbins before injury is done.
After any one of the connections has been thus severed the machine may continue
to operate, two plates being connected together, and in this manner currents will
continue to be produced by the machine which will serve to supply the system to
which it may be applied in a more or less perfect manner, until opportunity is offered
for stopping and repairing the machine.
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 correspondent I declare what I claim is
1. The combination with the armature of a dynamo-electric generator, of a fusible
connection between the junctures of the armature-coils and the commutator-plates,
substantially as described.
2. The combination with the armature-coils of an electric generator, of contact-
plates and fusible metallic conductors connecting the junctures of said bobbins with
said plates.
3. The combination in an electric generator with a series of commutator-plates and
a series of bobbins, of a fusible metallic strip between each juncture of each bobbin
and each contact-plate, and means for replacing any of said fusible strips, substantially
as described.