Improvements in Switches for Alternating Electric Currents.
Year: 1899

page_text: Date of Application, 24th May, 1899
Complete Specification Left, 26th Mar., 1900-Accepted, 19th May, 1900
PROVISIONAL SPECIFICATION.
Improvements in Switches for Alternating Electric Currents.
1, BERTRAM HOPKINSON, of 26, Victoria Street, London, S.W., Civil Engineer,
do hereby declare the nature of this invention to be as follows:-
Considerable difficulty is experienced in the interruption of large electrical
currents, when such currents are also associated with high potentials. Sometimes
the interruption is effected comparatively slowly in which case a large space
and a very long break are necessary in order to deal with the arc which is
drawn out, often to a length of several feet. In other cases an attempt is made,
by interrupting quickly in a closed space or under oil to suppress the are and
to limit the space occupied by the switch. If the interruption happens to occur
at an instant when the current is large the latter method involves great danger
to insulation, besides producing an almost explosive manifestation of energy at
the point of interruption.
When the current is alternating there are two instants in every cycle at which
its value is zero; and if the circuit be interrupted sufficiently rapidly at such
an instant there will be no strain on the insulation of any part of it, and there
will be no arc or other manifestation of energy at the point of interruption.
The purpose of my invention is to automatically effect the interruption of an
alternating current at or about the instant in the cycle at which its value is zero.
For this purpose I make use of a switch having very light and rigid moving
parts. A strong spring tends to pull the switch open and it is held closed by
a catch and also by the attraction of an electromagnet with divide iron excited
by the current which traverses the switch. On pulling away the catch so as to
release the switch, it is held closed by the attraction of the magnet only. When
the latter fails owing to the current falling (in the course of its cycle) to a
definite small value the switch is pulled open by the spring with very great
rapidity, so that by the time the potential has risen in the course of the next
cycle to any considerable value, the opening is sufficient to prevent the passage
of a spark.
The switch may be of the single or double pole type. The electromagnet
may attract an armature fixed to the moving parts of the switch or it may itself
form one pole of the switch, the current passing through it to the armature. I
may also use two electromagnets attracting two armatures carried on a light con-
necting bar. The current then passes through the core of one magnet, through
the armature, along the bar, and out through the core of the other magnet. The
circuit then opens when the bar and armatures are pulled away from the magnets.
Several of the switches may also be used in series.
I prefer to use the switch as a shunt to a hand switch or automatic circuit
breaker of the ordinary type. The hand switch or circuit breaker is then con-
nected mechanically to the shunt switch so that when it is fully opened it pulls
away the catch of the shunt switch. The shunt switch then opens automati-
rally at or about the instant rext following when the current is zero.

page_text: Improvements in Switches for Alternating Electric Currents.
I, BERTRAM HOPKINSON, of 26, Victoria Street, London, S.W., 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:---
Considerable difficulty is experienced in the interruption of large electrical
currents, when such currents are also associated with high potentials. Sometimes
the interruption is effected comparatively slowly, in which case a large space,
and a very long break, are necessary in order to deal with the arc which is
drawn out, often to a length of several feet. In other cases an attempt is made,
by interrupting the current quickly in a closed space, or under oil, to suppress
the arc, and to limit the space occupied by the switch. If the interruption
happens to occur at an instant when the current is large the latter method
involves great danger to insulation besides producing an almost explosive mani-
festation of energy at the point of interruption.
When the current is alternating there are two instants in every cycle at which
its value is zero; and if the circuit be interrupted sufficiently rapidly at such
an instant, there will be no strain on the insulation of any part of it and there
will be no arc, or other manifestation of energy at the point of interruption.
According to my invention I provide means whereby the interruption of an
alternating electric current is effected automatically at, or about, an instant at
which its value is zero. This can be effected for example by providing a switch
having very light moving parts rigidly attached to the armature of an electro-
magnet the electromagnet being of divided ion and its winding being traversed
by the current which traverses the switch. A spring tends to pull the armature
away from the magnet but is normally prevented from acting either by a catch,
or by a spring of greater strength pressing on the armature and holding it in con-
tact with the magnet. On pulling away the catch or suddenly removing the pres-
sure on the armature so as to release the first named spring the switch is held closed
by the attraction of the electro magnet during that portion of the cycle in
which the attraction is strong enough to overcome the power of the spring but
when the current falls in the course of its cycle, to a sufficiently small value the
said spring acts and pulls open the switch with very great rapidity, so that by
the time the potential has risen in the course of the next eyele, to any con-
siderable value the opening is sufficient to prevent the passage of a spark.
I prefer that the armature shall itself form the moving part of the switch
the current being taken through the core of the magnet and through the arma-
ture. If the moving part of the switch be separate from the armature the con-
nection between the two should be very rigid so that the switch commences to
open as soon as the armature begins to move. The switch is used as a shunt to
a hand switch or circuit breaker which may be of the ordinary type and the
moving part of which is so connected to the shunt switch that when just open
it pulls away the catch of the shunt switch or by its momentum suddenly removes
the pressure on the armature. The shunt switch is then opened by the spring
at or about, the instant next following when the current is zero.
In order that my invention may be well understood I will describe with
reference to the accompanying drawing how it may be carried into practical
effect.
Figures 1 and 2 are views at right angles to each other of a switch arranged
in accordance with my invention in which a catch is used to retain the circuit
closed normally. Figure 3 is a diagram of the electric connections and Figures 4

page_text: and 5 are views at right angles to each other of a modification in which a
stronger spring is used to retain the circuit closed normally. Figure 6 is a
diagram shewing switches arranged in series as herein before described.
In the arrangement Figures 1 and 2 the electro-magnet A is made up of soft
iron plates arranged in a plane at right angles to the winding and rivetted
between end plates or otherwise secured together. The poles are tapered to con-
centrate the induction and increase the tractive force. The magnet is wound
full of insulated winding of about No. 25, S. W. G., and is supported by a spring
against three set-screws whereby its position can be adjusted. The armature B
is similarly luminated and slides inside guides C, C of ebonite. The opposing
faces of the armature and magnet poles are worked to a good fit.
The armature is attached by a flexible wire E to the cylinder F which slides
in the tube G. The cylinder F is attached through a slot in the tube to the
spring H which tends to draw it, and with it the armature, away from the magnet.
The plunger I sliding in the tube G is connected to the moving part K of
the main switch through the link L. On closing the main switch the plunger
pushes the cylinder F down until it gets low enough for the catch to engage it.
The catch slides in a hole in the block N and is forced inwards by a spring in
the tube 0. The end of the cylinder F is coned so that it pushes the catch
aside in its descent.
The main switch being closed the set screws determining the position of the
magnet A are adjusted until the flexible connection between the armature, and
the cylinder F is just slack the armature resting on the magnet poles by its own
weight.
The spring Hand (through it) the armature are electrically connected to one
terminal P of the main switch. The winding of the electro magnet is electri-
cally connected at one end to the other terminal Q of the main switch, and at
the other end to the body of the electro-magnet. The armature, the electro-
magnet, and the winding thus form a shunt to the main switch in the manner
shewn diagrammatically in Figure 3
The inside of the tube G is of insulated material so as to insulate the moving
part K.
On opening the switch, either automatically or by hand the catch M is with-
drawn by means of the lever R and the strings S. T. The length of the string T
is so adjusted that the catch is withdrawn when the main switch is just clear
The whole current is
of its contacts as shewn by the dotted lines in Figure 2.
then traversing the coil of the electro-magnet and the armature is held down
only by magnetic attraction. On the latter falling sufficiently low the armature
is pulled away by the spring and the circuit finally broken.
In the arrangement according to my invention shewn in Figures 4 and 5 the
spring H for pulling the armature away from the magnet is contained within a
tube G which is screw threaded on its outer side and is attached by the
flexible wire E to the armature at one end and to the cross bar U at the
other end, the said cross bar projecting through holes in the tube and engaging
with the milled nut U outside the tube whereby the tension of the spring H
can be adjusted. Outside the tube G is another spring H' which bears at one
end against the nut V and at the other end against the T piece W the arms of
which project through holes in the side of the tube G. The leg of the T piece W
bears against the armature B and is hollow to admit of the passage of the flexible
wire E. The pressure exerted by the spring H¹ is adjusted by the motion of
the nut so as to be slightly greater than the tension of the spring H so that
by means of the T piece W the armature is ordinarily kept pressed against the
electro-magnet with a small amount of force.
I prefer the main switch K in this case to be of the circuit breaker type that
is one in which the moving part is forced away from the contacts by a spring,
upon the withdrawal of a catch either by hand. or by the strength of the current
exceeding a certain value.

page_text: The operation of the switch is as follows:-
The link L connected to the moving part K of the main switch has in it a
slot in which slide the arms of the T piece W. The length of the hole is so adjusted
that the arms of the T piece W engage with its ends immediately after the
moving part of the main switch has left its contacts. By that time the moving
part of the main switch will have acquired sufficient momentum to jerk the
Tpiece W sharply into motion, thus removing the pressure of the spring H¹
from the armature B and leaving the latter under the influence only of the
spring H and the electro-magnet A. The circuit is then finally broken by the
withdrawal of the armature when the current falls to a sufficiently small value.
The spring actuating the main switch must be sufficiently strong to hold it open
against the balance of force exerted by the springs H and H and its moving
parts must be of such mass that they are not sensibly checked by the engage-
nent of the T piece with the bottom of the slots.
The armature B, as before, slides in an ebonite box C, into the mouth of which
the electro-magnet is driven by light springs. On closing the main switch the
spring H forces the armature through the T piece W against the electro-magnet,
correct seating being ensured by the springs X, X.
A switch such as that just described will ensure that the current shall not be
broken unless its value is less than 1 ampère. This current, though small, may
produce a spark between the surface of the armature and the magnet sufficient
with high potentials to start an arc and in such cases the spark must be killed
by placing a condenser, or a fluid resistance, as a shunt across the terminals of
the switch (Z in Figure 3). For very high potentials it may be necessary to use
two, or more, shunt switches placing them in series as a shunt across the ter-
minals of the main switch as shewn in Figure 6. In such a case the catches of
the several switches would each be connected to the moving part of the main
switch so that on opening the latter they would all be withdrawn at the same
time.
The mechanical connection between the main switch the catch (or the spring)
and the armature may be arranged in many different ways and are not of the
essence of my invention. The form of the magnet and the size of the winding
may also be varied but the following principles govern the design.
1. The wire of the winding should be of such size that the current density
when the maximum alternating current which the switch is to break is passing
shall be about 100,000 ampères to the square centimetre when the frequency is
25 per second. With higher frequencies proportionately higher densities may
be used.
2. The strength of the spring should be so adjusted that the armature pulls
off when the induction in the mass of the ion is about 10,000 lines per square
centimetre, that on the contracted faces being about 15000 lines. In a switch
of the size shown in the drawings, the tension of the spring should be about
40 lbs.
3. Subject to these considerations the armature must be as light as it can be
made without unduly throttling the induction.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what
I claim is:--
1. A switch for alternating electric currents operating automatically so as to
break the current at, or about, the instant in the cycle when its value is zero
substantially as hereinbefore described.
2. For use with alternating electric currents, the combination with a main
switch of means whereby, when the said switch is opened, the circuit is auto-
matically broken at, or about, the instant in the cycle when its value is zero
substantially as herein before described.
3. In a switch for alternating electric currents means for holding it closed by

page_text: magnetism induced by the current and a spring (or its equivalent) retained out
of action by a catch which when withdrawn allows the spring to break the
circuit at the instant in the cycle when the value of the current is at, or about,
zero; substantially as herein before described.
4. A switch for alternating electric currents consisting of an electro magnet
the coil of which is traversed by the current to be broken and a light armature
in such connection with a spring that when the current falls to a sufficiently
small value in the cycle the spring will open the switch substantially as herein-
before described.
5. In a switch for alternating electric currents, the combination of a lami-
nated electro-magnet one end of whose coil is electrically connected to one ter-
minal of the switch the other end being connected to the core of the magnet;
a laminated armature electrically connected to the other terminal of the switch;
and a spring which pulls the armature away as soon as the current falls to a
certain small value substantially as herein before described.
6. A switch for alternating currents substantially as described and illustrated
in the accompanying drawings.
nd thi. Ofth day of Novo 1900
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.