Improvements relating to Cut-outs and Switches for Electric Motors and other Electrical Apparatus.
Year: 1898

page_text: Date of Application, 6th May, 1898-Accepted, 3rd Sept., 1898
COMPLETE SPECIFICATION.
(Communicated from abroad by HENRY H. CUTLER, of Chicago, Illinois, United
States of America.)
Improvements relating to Cut-outs and Switches for Electric Motors
and other Electrical Apparatus.
I, GEORGE AUGUSTUS MOWER, of 75, Queen Victoria Street, in the City of
London, 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:―
My invention relates to cut-outs and switches for electric motors and other
electrical apparatus, and has for its main object to provide an automatic cut-out
having combined therewith a device for introducing a time element into the opera-
tion of the same, so that the circuit will be opened or interrupted only after the
flow of an abnormal current for a predetermined period of time.
An electric cut-out is intended to open the circuit upon the flow of an abnormal
current, and thereby protect the electrical apparatus against damage caused by
the flow of a current exceeding that which the apparatus is designed to safely carry.
The damage is mainly due to the heating effect of the current and as it takes time
for any substance to be heated thereby, an abnormal current flowing for a very
short time may produce no bad effect, while the same current continued for a con-
siderablo time may destroy the apparatus. Cut-outs have usually heretofore been
constructed so that the flow of an abnormal current instantly opens the circuit.
It often happens, however, that the abnormal flow continues for a very short period
of time and then returns to the normal, the short flow of abnormal current being
not prejudicial to the machine, although such current would produce deleterious
effects if continued long enough to permit the conductors to heat up.
By the present invention I provide a cut-out which, upon the flow of an abnormal
current, will not open the circuit unless the abnormal flow be continued for a pre-
determined period.
According to another part of the present invention, I arrange the cut-out to
instantly open or interrupt the circuit upon the flow of an excessively large current,
say, for instance, a current exceeding a predetermined maximum below which the
time limit device will operate.
A magnetic coil is usually provided which serves to actuate the device for open-
ing or interrupting the circuit, and this coil I will hereinafter term the active
coil" of the cut-out. I combine, with this coil, a device the resistance of which
varies with temperature, and consequently with the strength of the current flowing,
so that a momentary abnormal current will not actuate the cut-out, while an
abnormal current flowing for a considerable period of time will alter the resistance of
the temperature-device, thus permitting an operating current to flow through the
active coil to actuate the cut-out. In practice one or more metal rods or wires
have been employed, such, for example, as iron, copper, or other metal the resis-
tance of which increases with rise of temperature, the said rods or wires being
TD 027

page_text: placed in shunt with the active coil, and when several rods or wires are employed,
they are preferably arranged in multiple, with one another. The current is thus
divided between the active coil and the temperature-wires, and upon the momentary
flow of an abnormal current, the wires do not heat up perceptibly, and consequently
the active coil, which is wound to respond only to a current of a predetermined
value, is not actuated. If, however, the abnormal current be continued for some
time, the resistance of the temperature-wires is increased, thus shunting more and
more current through the active coil until the abnormal current has flowed for so
long that, if continued, it would heat up and damage the apparatus; the current
through the active coil then becomes sufficient to operate the cut-out and open the
circuit. The active coil is so arranged that even the momentary flow of an abnormal
current exceeding a certain value, will instantly operate the cut-out, so that exces-
sively large currents which would damage the apparatus by flowing for a very
short time, may be immediately checked.
To intensify the range of the operation of the cut-out, I sometimes employ, in
addition to the temperature-device in shunt with the active coil, a series tempera-
ture-device. Carbon possesses the peculiar property of decreasing in resistance as
the temperature rises, and if a carbon resistance be placed in series with the active
coil, the resistance of the branch through the active coil will be decreased at the
same time that the resistance through the other branch is increased. The carbon
resistance in series with the active coil may be employed alone, although I prefer
in practice to employ the shunt temperature-wires, or where large range is desired,
a combination of the shunt and series temperature-devices.
My time limit cut-out is particularly applicable to electric motors used on
clectric elevator systems, and for other purposes where it is necessary to start under
load, thus requiring a large current for a short time in starting and a much less
current during normal travel. The improved cut-out permits the flow of the large
current for a time sufficient to start the motor from rest, while responding to a
much smaller current if long continued, thus protecting the motor against damage
from overheating.
In the accompanying drawings I have illustrated the time limit cut-out in con-
nection with an electric elevator controller or resistance-switch, which also forms a
feature of the invention herein described.
Figure 1 is a view of that side of the controller or resistance-switch carrying
the rheostat terminals, the parts being shown in the position which they occupy
when the rheostat-resistances are out of circuit.
Figure 2 is an edge view of the said controller, some of the parts being removed.
Figure 3 is a view of that side of the said controller carrying the starting or
reversing contact-arm, the parts being shown in the position which they occupy
when the rheostat-resistances are in circuit.
Figure 4 is a diagram illustrating the circuit arrangement the parts being
shown in the position which they occupy immediately after the switch-arm has been
brought into one of its "on" positions and before the contact-bar of the rheostat-
switch has descended so as to disconnect the contact plates 64, 65.
Figure 5 is a view showing another modification of the invention.
Figure 6 is a front elevation, and
Figure 7 a side elevation showing the time limit cut-out applied to an ordinary
electric switch.
Like letters indicate corresponding parts throughout the drawings.
Upon the front of the controller-box a is a contact-arm a'. A shaft a² extends
through the box, and carries the wheel a³ over which passes the operating hand-
rope R of the elevator. Upon the contact-arm or lever a¹ are provided two teeth
or lugs, between which extends a pin a mounted on an arm or crank on the
shaft a², so that, as the said shaft is turned in one or the other direction, the contact-
arm is rocked or turned about its pivot. Mounted upon the shaft a² and at the rear
of the box, is a cam b, which, when rotated in either direction, raises the contact-
bar which carries contacts engaging with two series of rheostat contacts or

page_text: terminals 2, 3, arranged equidistant in a straight line and situated in a vertical
plane. When the cam is moved away from the contact-bar b', the said bar descends
by its own weight, its motion being controlled by a dash-pot b7.
One wire of the supply circuit is connected with the binding post c (Figure 4)
which is connected with the contact plates c, c². With the contact arm a¹ in the
position illustrated, the circuit extends thence to contacts c³, c, to the contacts d, d'
conductor 1, magnet e, conductor 2, contacts 64, 65 which are connected by the
brush or switch 66 on the contact-bar 6 when the said contact-bar is elevated to
include all the resistance of the rheostat in circuit. From the contact 6 the circuit
extends by the conductor 3 through the contacts e¹, e³ connected by a spring
contact arm e controlled by the magnet e, thence by the conductor 4 to the opposite
wire of the supply circuit. Between the conductors 2 and 4 extends a resistance et.
The circuit being closed as above described through the magnet e, the latter is
energized, and moves the contact arm. e³ onto the contacts e, e, thus connecting
the same electrically, after separating or disconnecting the contacts e¹, e. The
circuit now extends from the magnet e to the conductor 4 through the resistance e',
whereby so much resistance is interposed in the circuit of the magnet e, that while
the said magnet will hold its armature, it cannot attract and move the same when
once released, until the local circuit through the conductors 2 and 3 is again
completed.
The motor-circuit now extends from the binding post through contact c¹,
contact arm a¹, contact, conductor 5, armature f, conductor 6, resistance 62, con-
tact bar 61, resistance ³, conductor 7, releasing-magnet g, conductor 8, contact co
through the contact arm a¹ to contact plate e, conductor 9, series winding f¹ of
the motor, contact e, arm e³, contact to the conductor 4. Contact 8 is con-
nected with contact 6, and contact with contact . The shunt field circuit
of the motor extends from the contact arm a¹ to contact c10, conductor 10, shunt
field to contact e6.
In starting the motor, the hand-rope R is pulled to move the conduct arm at
into the position illustrated in Figure 4, thus closing the circuit through the
retaining electromagnet e in the manner above described so as to energize the same,
and move the arm to close the armature and field circuits of the motor. The cam b
is at the same time moved from beneath the contact-bar b¹ and the latter descends
so as to gradually cut the resistance from the armature-circuit as shown in
Figures 1 and 2. The movement of the arm also separates or disconnects the
contacts e, e and puts the resistance et into circuit with the magnet e as above
described so that the magnet will not have power to retract the armature-
lever if onco released. The descent of the contact-bar of the rheostat
separates the contacts 6+, by moving the brush 66 out of engagement therewith.
It is thus impossible to energize the magnet e again sufficiently to retract the
armature until the contact-bar 1 is moved upward to include all of the resistance
into the motor-circuit.
Upon the flow of an abnormally small current, the retaining magnet e releases
its armature and thus opens the motor-circuit. Upon the flow of an abnormally
large current, the overload or releasing magnet g, by the attraction of its armature,
separates or disconnects the contacts d, d and thus de-energizes the magnet e and
opens the motor-circuit.
In shunt or multiple with the magnet g are included a number of wires or
rods h,,of metal or other suitable material the resistance of which increases
with rise of temperature. In practice ordinary iron wires are employed. The
current thus divides between the active coil g and the said wires, and the current
flowing through the coil during the passage of the large starting current is not
sufficient to actuate the said coil to attract its armature. The flow of a much
smaller current. however, if long continued will heat up the wires h, h¹ etc., thus
raising the resistance thereof and diverting an increased proportion of the current
through the active coil g so as to energize the same. The time during which the

page_text: abnormal current will flow before operating the cut-out or circuit-opener may be
adjusted by varying the sizes of the wires h, h', &c. For a given current, if it be
desired to operate with a short time limit, the separate wires may each be of small
cross-section, the combined cross-section of all the wires being of the desired value
to carry the current. If a longer time limit be desired, the individual wires may
be made larger in cross-section and fewer of them be used, so that the combined
cross-section will remain practically the same. The smaller the cross-section of
the individual wires, the more rapidly the resistance will increase under the flow
of the abnormal current, and consequently the shorter will be the time limit.
In order to give a greater range to the time limit cut-out, a resistance of carbon
is sometimes included in series with the active coil as indicated at k in Figure 5.
The resistance of carbon decreases with rise of temperature, thus, as is well known,
the ohmic resistance of an ordinary 16-candle-power 110-volt lamp averages in
round numbers about 500 olims, cold, and 250 ohms hot. A filament of carbon
enclosed in a lamp-globe in which the air is exhausted, or a small stick of carbon
in the open air may be connected in series with the active or operating coil of the
cut-out, while in shunt with the coil is included a material the resistance of which
increases with the heat. Suppose, for example, the resistance of the active coil
of the cut-out to be one ohm, the cold resistance of the piece of carbon eight ohms,
and the 'cold resistance of the shunt around these two, one ohm. Now imagine
eighty amperes of current flowing through this combination. This current would
then for a moment divide so that 10 or 8 amperes would go through the active
coil of the cut-out, and 10 or 72 amperes would go through the shunt. Now if
the cut-out was set to open at 8 amperes, the instantaneous flow of 80 amperes
would not open the circuit, but the circuit would be opened instantly if the cut-out
were set at 8 amperes. After this current of 80 amperes has flowed for a very
short space of time, the resistance of the shunt-circuit will increase, and the
resistance of the cut-out will decrease, so that much more current will go through
the cut-out and cause it to act. Suppose that a current of only 28 amperes be
sent through a combined cut-out and time limit device; suppose further, for the
sake of clearness, that after this current of 28 amperes has passed for some time,
the resistance of the shunt-circuit will have increased through the heating effect of
the current to two ohms, and the resistance of the carbon will have decreased
through the heating effect of the current, to four ohms. Under these conditions
7 of 28 amperes, or 8 amperes would flow through the cut-out, and the remaining
/ or 20 amperes would How through the shunt. It is clear, therefore, that a
current even as small as 28 amperes, if allowed to flow a sufficient length of time to
heat up the time limit devices, as above pointed out, would cause the cut-out to
open, while a current of 30 amperes would instantaneously open the circuit.
Of
course this is an extreme case, and it would probably not be necessary to put as
wide a range of current on the time limit cut-out in practical operation. These
figures are given to show the wide variation which it is possible to obtain.
In Figures 6 and 7 I have shown the time limit cut-out applied to an ordinary
switch. This time limit cut-out comprises a strip or ribbon m of any suitable
material the resistance of which will increase with rise of temperature. This strip or
ribbon m is arranged in multiple with the coil of the active magnet g of the cut-
out in a manner that will be readily understood on reference to the drawing.
It is obvious that I can modify the construction and arrangement of my time-
limit cut-out according to the various applications thereof.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I declare that what I claim is:-
1. The combination, with the active coil of an electric cut-out, of one or more
sections of an electric circuit composed of a material whose resistance will vary
with rise of temperature due to the current, substantially as hereinbefore described
and for the purposes specified.

page_text: 2. The combination, with the active coil of an electric cut-out, of one or more
sections of an electric circuit in multiple with the said coil and composed of a
material whose resistance will increase with rise of temperature due to the current,
substantially as, and for the purpose, herein before described.
3 The combination, with the active coil of an electric cut-out, of one or more
sections of an electric circuit in series with the said coil and composed of a
material whose resistance will decrease with rise of temperature due to the current,
substantially as, and for the purpose, herein before described.
4. The combination, with the active coil of an electric cut-out, of one or more
sections of an electric circuit in multiple with the said coil and composed of a
material whose resistance will increase with rise of temperature, and one or more
sections of the electric circuit in series with the said coil and composed of a
material whose resistance will decrease with rise of temperature, for the purposes
above specified.
5. The combination of a retaining electro-magnet, a releasing electro-magnet,
and one or more sections of an electric circuit composed of a material whose
resistance will vary with rise of temperature due to the current, substantially as,
and for the purposes, herein before described.
6. The combination, with an electric motor or other electrical apparatus, of a
movable contact arm, a retaining electromagnet for holding the said arm in
position to close the circuit of the said motor or other apparatus, means for moving
the said arm when released so as to open the said circuit, and one or more sections
of an electric circuit composed of a material whose resistance will vary with rise
of temperature due to the current, substantially as, and for the purposes, herein-
before described.
7. A starting resistance-switch for an electric motor, comprising a retaining
electromagnet included in a shunt or local circuit, a releasing electromagnet
included in the armature-circuit, and one or more sections of an electric circuit
in multiple with the said releasing magnet and composed of a material whose
resistance will vary with rise of temperature due to the current, substantially as,
and for the purposes, above specified.
8. The combination of a series of rheostat terminals arranged equidistant in a
straight line and situated in a vertical plane, a contact arm or bar movable
vertically across the said terminals, and a cam adapted to raise the said contact-bar
through equal distances for approximately equal angles through which the said
cam is rotated, substantially as, and for the purposes, above specified.
9. The combination of a series of rheostat terminals arranged in a vertical plane
on one side of a rheostat-box, a contact-bar vertically movable across the said
series of terminals, and a shaft extending through the said box and having fixed
upon it at one. side of the box a cam for raising the said contact-bar, and at the
other side thereof a starting or reversing contact-arm, substantially as, and for
the purposes, above specified.
10. An apparatus for the purpose above specified, comprising a retaining electro-
magnet which is included at starting in a local circuit through contacts separable
by the said magnet, a switch arranged to be closed only when the rheostat
resistance is in circuit, means for closing the motor-circuit when the magnet is
energized and the said contacts are separated, and for including a resistance in the
circuit of the said magnet, and a releasing magnet for de-energizing the said
retaining magnet, substantially as, and for the purposes, herein before described.
11. The combination with an electric motor, of a rheostat in circuit with the
armature thereof, a movable contact-arm in the circuit of the said motor, a magnet
for controlling the said contact-arm placed in a circuit in shunt with the said
armature, and a switch in the circuit of the said magnet operated by the movable.
element of the rheostat and arranged to be closed only when the starting resistance
of the rheostat is in the armature-circuit, substantially as, and for the purposes,
herein before described.
12. The improved apparatus constructed substantially as described with reference

page_text: to Figures 1 to 4 of the accompanying drawings (with or without the variable
resistance illustrated in Figure 5) all operating as, and for the purposes, above
specified.
1 1
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D. YOUNG & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agents for the Applicant.