Improvements in Electric Switches.
Year: 1899

page_text: Date of Application, 22nd Dec., 1899-Accepted, 31st Mar., 1900
Improvements in Electric Switches.
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 Eustace
Oxley, of Lynn, in the County of Essex, State of Massachusetts, Electrical
Engineer) and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
This invention relates to circuit breakers, the object being to provide a circuit
breaker with a double set of contacts, one of which ruptures later than the other,
the latter acting through a poorly conducting liquid, by which resistance is cut
into the circuit before final rupture. We prefer to employ as the liquid in which
the final rupture is made, a watery solution of chloride of zinc,, which we find by
experience is well adapted for the purpose, especially on account of its highly
deliquescent property, by reason of which the liquid is not liable to dry out during
long periods of disuse or thorough neglect.
Our invention comprises a circuit breaker having a plurality of points of circuit
rupture, the movable element of the circuit breaker being so disposed that the
final rupture occurs in a liquid which interposes a comparatively high and pre-
ferably gradually increasing effective resistance. More specifically the invention
comprises the use of a solution of chloride of zinc at the point of rupture of a
circuit breaker. The several features of novelty will be more particularly described
hereinafter and will be definitely indicated in the claims appended to this specifica-
tion.
In the drawings, which illustrate the invention, Fig. 1 shows a simple type
of knife circuit-breaker embodying our improvements; Fig. 2 shows a modifica-
tion in the arrangement of the cup to contain the fluid employed; Fig. 3 shows a
double pole switch embodying our improvement and Fig. 4, shows a structural
detail of the form shown in Fig. 3.
Referring first to Fig. 1, 2, 2 represent the terminals of an electric circuit, or the
contiguous points of rupture in a circuit and 4 represents a lever provided with
a handle for manual operation and carrying a metal blade adapted to be pushed
in between the elastic jaws of the terminals 2 so as to form an electric bridge and
establish electrical continuity between the terminals.
The switch is organized so that when the lever is pulled over as shown in the
figure, the metallic rods which constitute the contacts 13, 13, will rise through a
body of liquid formed of a solution of chloride of zinc and water, as shown at 9;
this liquid may be held in a reservoir formed by casting or boring a hole part
way through the supports 5 for the terminals 2, 2. A convenient way of lifting
the contacts 13 is shown in the drawing, where the operating lever is journalled
in the slotted bracket 3, and a crank 14 fastened to the lever gives vertical motion
to a stem or rod 12 of which the contacts 13 form a part. This rod may be
arranged to be guided in any suitable bearings to prevent displacement.
As thus organized, when the lever is withdrawn from the terminals 2, the
metallic bridge between the terminals is first removed, while the integrity of the
circuit is preserved through the liquid. The parts are so related that at the
moment of rupture at the metallic bridge piece the contacts 13 will be well

page_text: immersed in the fluid. The passage of the current sets free a considerable volume
of hydrogen, some of which clings to the movable electrode and some to the casing
thereby greatly increasing the resistance during the operation of rupture, both
by reason of the polarization due to the presence of the hydrogen, and by reason
of the mechanical tendency of the hydrogen bubbles to form a discontinuity of
the circuit. During the period of transit of the metallic terminals through the
liquid, the resistances rapidly increases from the causes just mentioned, and from
the increase in distance of the moving contact from the walls of the containing
coil.
With a switch of this construction only a very small are is made on final
rupture, even with currents of considerable potential and amperage. It is of
course quite immaterial that the switch should have the mechanical organization
just described, as the essential feature is that at the time of rupture of the metallic
contacts the liquid shall be in circuit and the movable contact or electrode have
a range of movement through such liquid. A highly deliquescent salt does not
dry out during a long period of service, and is therefore eminently adapted for
the use herein described. The invention is not limited to the use of a deliquescent
salt, as a solution of zinc sulphate or chloride of sodium, or any other electrolyte
may be used with good results, though not so good as with zinc chloride.
In Fig. 2 we have shown a bed of mercury 17, at the bottom of the metal
cup or coil in which the liquid is contained. This affords an admiral contact of
exceedingly low resistance when the movable element shown diagrammatically
at 19 is fully immersed.
The organization shown in Fig. 2 may be employed as a circuit breaker without
metallic contacts to shunt it when the circuit is closed, as the circuit is opened
under the electrolyte 17" when the movable terminals 19ª leaves the mercury,
and but little arcing occurs by reason of the evolution of hydrogen or other
electrolytic gases at the terminals, as before explained. In this type the vessel
containing the mercury may be lined or col with insulating material and the
upper part of the movable terminal similarly ed, as shown at 22, thereby
shunting off all circuit through the electrolyte when the circuit is closed. This
provision is not important, however, as but little current will follow the path owing
to the greatly superior conductivity of the mercury. In all types of this invention
the terminal should be of a cross section to permit a current of high density to
How through it, thereby liberating considerable volumes of gas and greatly
increasing the resistance. The apparatus may be arranged to throw the electrolyte
out of circuit after the latter has been closed through the metallic terminals and
cut it in again before the circuit is opened; this however is unessential, as the
resistance of the electrolyte is so high relatively to the metallic shunt that almost
no arcing occurs.
In Fig. 3 we have shown an example of the application of our invention to a
double pole switch, 2, 2, 2", 2ª representing the terminals, and 4, 4 the metallic
bridge pieces insulated from one another and pivoted in suitable standards secured
to a base of slate or other suitable material. A crank arm 14 gives vertical
movement to the frame 12 formed of two vertical pieces insulated from one another
and guided in suitable brackets and having depending rods 13 arranged to move
into and out of cups secured to and forming part of the terminal castings. In
the types of construction shown the liquid contacts are in parallel with the metal
contacts, but while this is the preferred form of construction, it is not absolutely
essential to the practice of our invention, since the pairs of contacts might be
in series relation without departing from its spirit.
Having now particularly described and ascertained the nature of our said
invention (as communicated to us from abroad) and in what manner the same is
to be performed, we declare that what we claim is :-
1-A circuit-breaker having a rupturing contact immersed in and movable
through a solution of chloride of zinc.

page_text: 2-A circuit breaker controlling two pairs of contacts, one made in a liquid
and the other metallic, the parts being so arranged that final rupture occurs at
the liquid contacts.
A circuit-breaker having a plurality of contacts, one pair of which is made
in a liquid, the parts being related so that an operation of the circuit breaker
produces final rupture at the liquid contact, the conducting terminal at the moment
of rupture of the metallic contacts being submerged in the liquid, so as to have
a range of movement therein.
4-A circuit breaker having a plurality of contacts, one of which is made
beneath an electrolyte, the parts being related so that an operation of the circuit
breaker ruptures the metallic contact first and then the liquid contact.
5 A circuit breaker provided with a plurality of contacts connected in parallel
relation, one pair of contacts being made beneath an electrolyte.
6 A circuit breaker provided with a plurality of contacts connected in parallel
relation, one pair of contacts being made beneath a solution of zinc chloride.
7-A circuit breaker having its movable terminal in co-operative relation to
a vessel containing mercury, and a supernatant electrolyte, both in the path of
the terminal.
8-A circuit breaker having its movable terminal in co-operative relation to
a vessel having a conductive cover connected in circuit, and an electrolyte engaging
the wall.
9 The combination of a switch contact, of a circuit in shunt therewith, and
automatic means for introducing a resistance in said shunt circuit.
Dated this 12th day of December 1899
THE BRITISH THOMSON-HOUSTON CO. LTD
ALFRED CLEMENTS,
Assistant Secretary,
J. J. MANHEIM,
T. R. THOMPSON,
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Directors.