Improvements in Circuit Breakers for Alternating Electric Currents.
Year: 1899

page_text: Date of Application, 30th Oct., 1899-Accepted, 2nd Dec., 1899
COMPLETE SPECIFICATION.
Improvements in Circuit Breakers for Alternating Electric Currents.
We, THE BRITISH THOMSON-HOUSTON COMPANY LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of our
said invention (which has been communicated to us from abroad by Thomas J.
Johnston, residing at Schenectady, in the County of Schenectady, State of New
York, United States of America, Electrical Engineer), and in what manner
the same is to be performed, to be particularly described and ascertained in
and by the following statement:—
In the application of circuit-breakers to alternating electric currents, it is
found that the inductive component of resistance in the series coil may amount
at times to considerable loss. The ohmic resistance of these coils is practically
negligible, because of their very large section; while they are designed to
carry large currents, the amount of metal is so great that the drop is very small.
However, the larger the current the greater the inductive component of the
coil's impedance, and increase of the metal section does not avoid the difficulty,
which is a function of the ampere turns. We have sought to obviate this trouble,
or at least in some degree to compensate for it by using instead of the ordinary
iron armature which operates the trip of the circuit-breaker a close circuited
coil through which the magnetic circuit of the series coil is closed, and which
acts to cut down the self-induction and to diminish the loss in the coil.
The accompanying drawing shows an arrangement within the invention. In
this, Fig. 1 shows in front elevation with parts in section, a circuit breaker of
an ordinary type, to which the invention is applied, while Fig. 2, is a modified
form.
In Fig. 1, A is the base of the instrument. B, B, are the circuit terminals
spanned by the bridge C. The latter is closed by the toggle T against the force
of the spring and the toggle is held in position by a latch F. M is a blow
out magnet, and N is a chute housing the shunting terminals, which are not
illustrated. All of these parts are of the ordinary type, now well known.
I is the series coil, and K is a closed circuited coil wound to act as a core to
the solenoid formed by the coil I. The coil K is mounted on a rod, and of
course is insulated from the coil I; the usual handle L to the rod may he
employed to open the circuit manually. G is a lever attached to the upper end
of the rod, which when moved opens the latch or trip F. permitting the circuit
breaker to open. The motion of the coil K is opposed by a spring H with
which the usual calibrating screw H₁ co-operates to determine the current flow
at which the circuit breaker will open.
In Fig. 2, we show a modified form of coil. In this figure the parts are as
before, except that the coil K¹. of flat or "pancake" form, as it is commonly
called, is disposed in place of the usual armature, the action being the same as
in the former case.
The operation of the illustrated parts is as follows: when the current in the
coil I rises to a determined maximum, regulated by the tension of the spring II.

page_text: it induces sufficient current in the coil K to overcome the spring. The repulsive
action of the two alternating currents, one flowing in the coil I and the other
in the closed circuited coil K and K', as the case may be, is sufficient to force
the movable coil away from the other, operating the lever G, opening the trip
and permitting the circuit breaker to open.
The size of wire and number of turns in the closed coil K will be selected
to give the repulsion desired; where only a small induction is needed, a fine wire
of considerable resistance may be used, for larger currents a wire of greater
gauge. These things are too well understood in the art to require further
elucidation.
Having now particularly described and ascertained the nature of our said
invention (which has been communicated to us from abroad), and in what
manner the same is to be performed, we declare that what we claim is:-
1-In a circuit-breaker, the combination of contacts to be opened or closed,
a trip, and a series coil, with a close-circuited coil or conductor connected to the
trip so that the repulsive effect between the series coil and the close-circuited
coil shall actuate the trip and open the circuit breaker:
2 The combination in a circuit-breaker, of the trip, the series coil and the
closed circuited coil acting by repulsion to open the trip, with a calibrating
spring for determining the current at which the trip shall be opened.
In a circuit-breaker, the combination of a trip, a series coil and a close
circuited conductor formed into a core for the series coil, with a spring for
determining the point at which the trip shall act.
4 The art set out of diminishing the impedance of the series coil in an alter-
nating current circuit-breaker which consists in closing the magnetic circuit of
the coil through a closed conductor disposed adjacent thereto.
Dated this 25th day of October 1899
ITISH THOMSON-HOUSTON CO. LTD.
W. MARTINDALE,
A. R. MoxкS,
}
ALFRED CLEMENTS,
Directors.
Assistant Secretary.
THE BRITISH THOMSON-HOUSTON CO. LTD.
W. MARTINDALE,}
A. R.
ALFRED CLEMENTS,
Directors.
Assistant Secretary.