MENTS IN ELECTRICAL APPARATUS."
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by William Scott at the Office of the
Commissioners of Patents on the 18th October 1878.
WILLIAM SCOTT, of 23, Rood Lane, in the City of London, Engineer.
MENTS IN ELECTRICAL APPARATUS."
"IMPROVE-
My improvement consists in an apparatus for distributing electric currents
produced by any kind of galvanic batteries, magneto electric or dynamo electric
machines, thermo electric piles, or any other electricity producing agent, and which
for the sake of brevity I call an automatic or self-acting shunt.
By preference I construct this apparatus of a compound bar composed of metals
expanding in different degrees under the influence of heat, which bar may be
straight or bent, but by preference bent in the form of a helix fixed at one end and
attached at the other end to an arm.
Through this apparatus the whole or a portion of the current generated may pass
according to circumstances, so as to heat the compound bar and thereby cause it to
alter its form and give motion to the arm to which one end is attached.
This arm is provided with sliding pieces so arranged as to vary the resistance in
two or more rheostats or resistance coils or pieces, and vary the current passing
through each rheostat.
One of the rheostats is connected with a branch current which passes through the
compound bar and the other is connected with the main current from the generator;
and their arrangement is such that as the branch current passing through the
compound bar and thus expanding it by change of temperature, increases the
resistance it meets with by the movement of the arm, and is thus retarded; so at
the same time the current on the main wire from the generator by the same
movement may pass in increased quantity by the reduction of the other resistance
or rheostat.
Thus the current is automatically controlled and the overheating of either of the
rheostats or resistances is prevented, and the branch current kept uniform.
I affix to this apparatus a screw or other regulating arrangement to determine
the maximum current passing through the branch wire before the automatic shunt
comes into action to keep it at that limit.

page_text: By this arrangement a series of currents may be taken from one main line, and
either one or more of them may be thrown off without interfering with the
remaining ones.
In cases where the current through the branch wires varies but little, instead of
the compound bar, I may use a simple piece of metal which controls the motion of
the arm by its expansion and contraction. Or I may use a small column of mercury
through which the current is passed, and which acts upon a piston. The said
mercury expands or contracts from the increase and decrease of temperature owing
to the passing current, and thus gives motion to the said piston which controls the
movement of the aforesaid arm.
I also may use a similar arrangement of compound automatic shunt by which
when the whole of the branches are thrown off, the main wire may be short cir-
cuited or thrown off to prevent it overheating.
In order to indicate the amount of electricity passing from a large generator, I
use a compound bar similar to that used in my automatic shunt, which gives motion
to an index on a graduated dial marked to represent auy unit or arbitrary value of
the current.