Improvements in Electric Switches.
Year: 1898

page_text: Improvements in Electric Switches.
I, ARCHIBALD WILSON, of the Leith Electric Works, Prince Regent Street,
Leith, in the County of Midlothian, Scotland, Electrical Engineer, do hereby
declare the nature of my invention to be as follows:-
My invention relates to improvements in electric switches whereby certain
advantages are obtained and for the purposes of this specification I shall describe
one form of my invention which I have illustrated with a sheet of drawings.
In the drawings Figure 1, is a plan of a motor starting switch and
Figure 2, is a general plan of said switch with its connections.
In Figure 1. A¹ is a regulating arm fixed to a central spindle S. On this
spindle S is also mounted the main circuit arm B which rides loose on S but is
constantly drawn to the off" position by means of a spiral spring surrounding
"
the socket in which S works. The arm A makes contact on the metal contact
pieces K, to K, which are connected by a series of resistance coils and to the
armature in the usual well known way."
The arm B makes contact with the brass piece E which is coupled directly to
one of the supply mains of the system from which the motor is worked. 1 is
provided with teeth which engage with a magnetic catch F which forms the
armature of the electro-magnet G and whose action is regulated by the spring H,
G being magnetised by means of a winding in series with shunt winding of the
motor, shown in Figure 2.
C is a metal arm fixed to A¹ and arranged to engage with the spring M¹ screwed
to B so that when S (and therefore C) is rotated, B also is pulled round until
it makes contact with E when a circuit is formed between the mains through
the winding of G and the shunt coils R of the motor. G is consequently
magnetised and pulls on the catch F which then prevents B from breaking
contact with E.
On further rotating S, the spring M strikes a wedge shaped piece L which
presses M down until C¹ is clear when S, A¹ and C¹ can be further rotated till A'
makes contact with K and the armature of the motor is connected with the main
circuit and is started gradually. In the drawing the letters A, B, C, M, indicate
the parts of the switch in the "off" position while the letters A¹, B', C', M¹
indicate the parts in the "on" position.
N is a spring mounted on an upright and connected to the winding of G
between G and the field magnet coils. P is a pillar screwed on A¹. One side
of P is covered with insulating material so that on A being actuated and
switching on the armature no metallic contact is made between N and P; but
on A being rotated in the reverse direction, N makes contact with P, the winding
of G is short circuited, and G demagnetised. F is therefore released and
releases B which flies. off and thus, by automatically breaking in quick manner
the circuit before A¹ leaves K it prevents a slow break at K, and the consequent
arcing between A¹ and K.
-
Should by any accident the main or shunt circuit become broken, the magnet G
in the same fashion releases B¹ and the circuit is broken, and it is impossible

page_text: that the circuit can be again made without switching off the armature arm so
that Cengages again with M' when the shunt circuit must again be completed
before the arniature can be put into circuit.
When the blade B is in position and the shunt circuit is closed, the speed
of the armature may be regulated as desired between the contacts K₂ to K, without
in any way affecting the position of B.
Should it be desired to safe guard the armature of the motor from the effects
of excessive current due to overload or 'otherwise, the magnet G may be differenti-
ally wound by carrying round it, in a reverse direction to that of the shunt
current, the current from the armature. In the event of the current through
the armature becoming too great, the magnetism of G would be correspondingly
reduced until F would be released and the circuit broken as before.
I, ARCHIBALD WILSON, of the Leith Electric Works, Prince Regent Street,
Leith, in the County of Midlothian, Scotland, Electrical Engineer, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
This invention relates to improvements in electric switches whereby certain
advantages are obtained.
It is well known that a switch intended for use in starting and regulating an
electric motor is liable to be a source of danger. For instance, if the field circuit
should be interrupted while the switch is closed, the current in the armature may
increase to such an extent as to cause serious damage. Also, if the switch should
be accidentally turned on, the field circuit not being complete, damage would
result. Further, it is well known that it is advisable to have a resistance in the
armature circuit when a motor is started. If the switch and the handle con-
trolling the resistance are independent of one another there is a danger lest
the switch should be closed when the resistance is all out of the circuit.
My invention affords protection to an electric motor under such circumstances
since by its use is is impossible to complete the armature circuit unless the magnet
circuit is previously made, and should the magnet circuit become interrupted
while the motor is running the switch is automatically turned off. Further, with
my invention it is impossible to start the motor with the starting resistance out
of the circuit
I will now describe how I carry out my invention, referring to the accom-
panying drawings. I wish however that it be understood that I do not limit
myself to the particular design of the mechanical details shown in these drawings
as it is obvious that modifications might be made without departing from the
scope of my invention.
Referring now to Figure 1, I provide a spindle lettered S in the drawings which
is rotated in a fixed socket by means of a handle which is not shown in the
figure. This spindle carries a regulating arm A rigidly connected therewith
and capable of moving through a considerable angle. As shown in Figure 1
the motion of A is from its "off" position shown in dotted lines round until it
covers K, the last of a series of contact pieces. These contact pieces are con-

page_text: nected to the ends of resistance coils and to the motor armature in a way well
known in the art and illustrated in Figure 2.
in Figure 1 the regulating arm is shown in full black lines just touching
the first of these contact pieces.
Upon the spindle S is centred the main circuit arm B which turns upon the
spindle but is not rigidly connected therewith. A spiral spring is coiled round
the spindle, one end of which is fixed on to the main base plate of the switch
and the other on to the arm B in such a way that the arm B is continually urged
in a counter-clockwise direction towards a stop T, against which it is shown
resting, as indicated in dotted lines, in Figure 1. When turned away from the
stop this arm B comes into contact with a metallic piece E which is connected
directly to one of the main line terminals as shown in Figure 2 and is held there
by a catch F. This catch is actuated by an electro-magnet G whose winding
is in series with that of the field magnets of the motor as shown in Figure 2,
one end of this winding being connected to one end of the field winding and
the other end being connected to the spindle S.
It will be seen that in order to hold the arm B in contact with E the magnet
circuit of the motor must be excited. This will take place as soon as the arm B
touches E provided that the magnet circuit is complete for the current will pass
as shown in Figure 2 from the main terminal to the piece E, through the arm B
to the spindle S then through the winding of G, through the field winding of
the motor and so to the second main terminal.
When the magnet G is not excited the catch F is drawn back clear of B by
means of a spring H.
I provide a steel spring M segmental in shape fastened in a suitable manner
upon the arm B, as shown in Figure 1. At one end of the spring I fix a wedge-
shaped piece X of brass or other suitable material, firmly secured on to the said
spring and tapering towards the end of the spring as shown in Figure 3, which
shows the relative positions of the parts I am now describing.
The rear end of the said wedge-shaped piece X is made so that the end of the
arm C butts up against it as shown in Figure 3.
I also provide a stop L of brass or other suitable material fixed to a pillar Y
and projecting therefrom as shown in Figure 1. The said stop L has its under
side tapered as shown in Figure 3 and is so placed that the arm C can pass freely
over its upper surface.
In the position shown by the dotted lines in Figure 1, B is resting against
the stop T and the arm C is butting against X. When the spindle S is turned
in a clockwise direction the arm C pressing on X moves B. round until B come:
in contact with E. At this moment current will pass through the magnet G
and the field magnet of the motor and will actuate the catch F, so that when
the spindle S is still further turned round, B is held in position independently
of the arm C.
If now the spindle S is still further turned round, the wedge X comes in
contact with the stop L. It will now be seen that as S is turned round, X is
depressed, leaving C free to be still further rotated. Since the catch F is hold-
ing B the spring M is no longer needed and C can be turned as much as desired.
In Figure 1 the full lines show the position of A. B and C just at the moment
when C has come up to the stop L. The angular distance between A and C
is such that contact between B and E is effected before A touches the first of the
contact pieces K. The effect of this is that the magnets of the motor are excited
before the armature circuit is made. When B is held by the catch F the regu-
lating arm A can be turned round, making contact at successive points K,, K.
K, and so on and the motor can thus be gradually started. The arm A may
be left resting on any one of these contacts and is now quite independent of
the arm B.
In the event of any interruption in the field magnet circuit of the motor the
magnet G ceases to hold the catch which is therefore pulled down by the

page_text: spring H and ceases to hold the arm B. This arm is immediately thrown out
of contact with E by the spiral spring and the motor circuit is thereby broken
and the motor stopped.
During this process the arm A is unmoved but it will be seen that in order to
re-make the main circuit it is necessary to turn back the arm A until the arm C
picks up the spring M. This ensures the impossibility of making the main
circuit while the motor is at rest and the starting resistance out of the
circuit.
In some cases I add a series winding to the shunt winding on the electro-
magnet G by winding a few turns of stout wire round the magnet, such turns
being in series with the armature circuit as shown in Figure 2 but wound in
such a direction as to magnetize the magnet in the reverse direction to the shunt
winding. By this means am able to arrange that in the event of an overload
of given amount coming upon the motor G is de-magnetized, the switch is opened
and the main circuit broken. The motor is thus protected from injury caused
by_overloading.
In order to avoid the sparking that frequently takes place between a contact
such as K and an arm A when the circuit is broken I provide upon the arm A a
small metallic stud P so placed as to come in contact with a spring N mounted
on the main base plate of the switch. This spring is connected with one end of
the shunt winding of G in such a way that when N touches P G is short-circuited.
I arrange that P can touch and pass N when moving in either direction but I
cover one side of P with some insulating material so that when I touches N
moving clockwise no contact is made but that when P touches N moving counter
clockwise G is short-circuited. It is immaterial which of the two parts N or P
is attached to A so long as the other is so fixed that G is short-circuited when A
is moved in the "off" direction. In the case where the spring is mounted on A,
P may consist of a metal angle piece fixed to the base of the switch, one side
of which is covered with some insulating material.
The effect of this is that when A is turned off, at the moment when the circuit
is about to be broken between A and K₁, G is short-circuited and the main circuit
is quickly broken between B and E instead of being slowly broken between A
and K. This avoids destructive sparking between A and K₁.
In an alternative form of my invention the spring M, and the wedge-shapesi
piece L might be omitted and the motion of B obtained by means of a pin pro-
jecting in such a way as to come in contact with C. In this case A would first
be turned round one way carrying B with it until B was held by F and then A
would be turned round the other way to complete the armature circuit through
the resistance coils.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
.
1. In a switch of the type specified the employment of a main circuit arm
and a regulating arm each fulfilling functions substantially as set forth.
2. In a switch of the type specified the means for avoiding destructive sparking
between the regulating arm A and contact point K, substantially as set forth.
3. The specific form of switch illustrated in Figure 1.
Dated this 29th day of Tasamban
1000