Improvements in Controlling Alternating Electric Current Motors.
Year: 1899

page_text: Date of Application, 28th Nov., 1899-Accepted, 27th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Controlling Alternating Electric Current Motors.
We, THE BRITISHI THOMSON-HOUSTON COMPANY, LIMITED, of 83, Cannon Street,
in the City of London, Electrical Engineers, do hereby declare the nature of this
invention (which has been communicated to us from abroad by Charles P. Stein-
metz, of Schenectady, 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 controlling alternating current motors considerable difficulty is encountered
in the endeavour to extinguish effectually the arcs which result from opening
the motor circuits. Because of the nature of the alternating arc, the magnetic
blow-out is not always applicable, while the employment of other means such
for example as breaking the circuit under oil or other insulating fluid, is attended
with many disadvantages. For these reasons we have devised a method of and
Jeans for controlling alternating current motors which does away with the
necessity for any special means for extinguishing arcs which may be formed.
Our invention is more especially valuable where such motors, for any reason, have
a large magnetizing current.
Our invention in its concrete form as herein illustrated consists of a switching
mechanism with suitable electrical connections for connecting a non-inductive
resistance in circuit, first with one member of an induction motor, and then in
circuit with the other member, the operation being such that on stopping the
motor the resistance is first withdrawn from the windings of the secondary
member and then placed in circuit with the primary member. With resistance
thus placed in circuit with a primary member, the magnetizing current is
reduced to a value so small that no difficulty is experienced from arcing when
the circuit is opened. It will thus be seen that in accordance with this invention
the resistance which is ordinarily used for controlling the speed and torque of
an induction motor, possesses in this instance an additional function.
The details of this invention will be better understood by reference to the
following description taken in connection with the accompanying drawings,
while its scope will be pointed out in the claims appended hereto.
In the drawings. Fig. 1 is a plan view of a switching mechanism made in
accordance with this invention.
Fig. 2 is a view of the same, partly in section.
Fig. 3 is a diagram of circuits, while,
Figs. 4 to 8 inclusive represent changes in circuit connections effected by the
switching mechanism illustrated in Fig. 3.
Our invention in its detail will be more clearly apprehended by first describing
briefly its general features and this can best be done by referring to Figs. 4 to 8
inclusive which serve to illustrate the same in a general way.
Fig. 4 indicates connections corresponding to the off position of the switch,
both primary and secondary windings A and B respectively being open circuited
as indicated. As the controller handle is turned, the first connection made
causes a large resistance R to be inserted in series with the windings of the
inducting member A as shown in Fig. 5, while a further movement of the con-
troller handle causes the resistance to be gradually cut out until as shown in
Fig. 6, the free ends of the primary winding are connected together directly
at which time only the magnetizing current is flowing through the motor and no
torque is exerted by the secondary member.
After having been withdrawn from the primary member, the whole resistance R

page_text: is inserted in series with the secondary B of the induction motor. The motor is
thus started in the ordinary manner, and as it gathers speed the resistance is
gradually cut out by a further rotation of the controller handle until the normal
running condition is reached in which the resistance is entirely cut out as shown
in Fig. 8. The function of the starting resistance for induction motors is so
well understood that no explanation of the same is necessary, other than to refer
to the manner in which the starting resistance is employed in this particular
instance.
In starting the moter no useful purpose is served by first inserting the resistance
in the primary member and then cutting the same out. It is only when the
connections thus described are performed by the controller in the reverse order,
that the manipulation of the resistance with respect to the primary winding
becomes useful.
When running normally the connections of the motor are as indicated in
Fig. 8 and the first step in putting the motor out of circuit consists in inserting
resistance in the secondary member as shown in Fig. and then breaking the
circuit of said member as in Fig. 6. The same resistance is then gradually cut
into the primary winding as shown in Fig. 5, until the magnetizing current of
the motor has been reduced to a minimum when the primary circuit is opened,
thus leaving both members open circuited as indicated. in Fig. 4.
The arrangement of circuits whereby these changes are effected is indicated
diagrammatically in Fig. 3 in which a', a², denote the three primary windings
of the motor and 61 62 63 the secondary windings. One end of each of the
primary windings a¹ a² a³ is connected respectively with one of the terminals
1, 2, 3, of the reversing switch S by means of which the primary winding as a
whole is connected to the multiphase supply mains a, b, c. When the reversing
switch is thrown in one direction the terminals 1, 2, 3, are connected respectively
to the mains a, b, c, and by virtue of this connection the motor is given a
definite direction of rotation while when the switch is thrown in the opposite
direction the terminal 3 is as before, connected to the main e, while the con-
nections of the terminals 1, 2, on the other hand, are reversed, the terminal 2
being connected to the main a, and the terminal to the main b, thus causing
an opposite direction of rotation of the motor.
The opposite ends of the coils a¹, a², a³, are connected respectively with three
angularly displaced fixed contacts a1, a22 and 3, forming part of the switching
mechanism.
The secondary windings of the motor are indicated at 61, 62, 63 and are shown
with one end of each winding connected together in any suitable manner and
with the free ends connected to fixed contacts 61, 62, 63, forming part of the
switching mechanism and located adjacent to the fixed contacts all, a22, and 33
to which the free ends of the primary windings are connected.
A non-inductive resistance in three sections R, R, R³ is located adjacent to
the fixed contacts before mentioned, and each section of the resistance is con-
nected at intervals in its length to suitable contact blocks or contacts arranged.
concentrically with respect to the fixed contacts. One end of each section of
the resistance is connected to a common point, these connections being indicated
in the drawing at 1, 23, leaving the opposite ends of the resistances normally
disconnected. Suitably insulated contacts,, of conductive material are
located adjacent to the contacts connected to the respective sections of resistance
and with their surfaces flush with the surfaces of the resistance contacts so as to
allow the switch arms which co-operate therewith to move from one contact to
another.
The connections between the various contacts thus referred are effected by
means of two sets of bridging contacts, the two sets being individually movable
with respect to each other, and each set formed of three bridging contacts each of
which operates in conjunction with resistance contacts and with one of the fixed
contacts connected to the motor windings.

page_text: The bridging contacts 11, 12 13 operate in conjunction respectively with the fixed
contacts, and are carried on the ends of three arms fixed with respect to
each other and simultaneously rotatable by means of the controller handle. One
end of each bridging contact makes connection with one of the fixed contacts
, and slides over the surface of one of the corresponding fixed contacts 1, 2,
633 as indicated.
In a similar manner the fixed contacts m', m² and. m³ bear upon one of the
contact blocks, and upon one of the corresponding fixed contacts a", "
and connected to the windings of the other member of the motor. The last
described set of bridging contacts, as in the case of the first set is carried by
projecting arms also rotated by nieans of the controller handle: These two sets
of arms are interrelated in a manner hereinafter to be described. The con-
nections made by the bridging contacts which are carried by these armis will
however be evident from Fig. 3.
In the position of the parts shown both of the windings of the motor are open
circuited. When the controller handle is first turned the set of bridging con-
tacts m, m2, m³ is rotated in the direction of the hands of a watch and moved off
of the insulated contacts 1, 2, 3, upon which they rest when the motor is out of
circuit, and then on to the set of contacts connected with the sections of resist-
ance R R R³. When the bridging connections are thus shifted a section of
resistance is placed in circuit with each of the primary windings a', a², a³. Thus
for example, the coil a¹ would be connected through the fixed contact a to the
free end of the resistance Re, and then through the resistance to the neutral
point o to which the corresponding ends of the other sections of resistances are
connected. As the controller handle is moved forward the bridging con-
tacts and are moved along over the fixed contacts connected to the
resistance sections, until finally all the resistance is cut out, this condition being
reached when the bridging contacts rest upon the contacts directly connected
with the connections 1, 2, 103. At this point the arms carrying these bridging
contacts are uncoupled from the controller handle and the other set of arms
carrying the other set of bridging contacts is caused to engage with the handle.
The bridging contacts 1, 2, thus set into motion by the further movement.
of the controller handle are each connected to one of the windings 61, 62, 63 of
the secondary member and operate to insert resistance in the secondary member.
Thus for example, when the bridging contact is moved forward it passes off
of the insulated contact and on to the first contact of tlie resistance R', thus
connecting the free end of the winding 63 of the secondary member of the motor
In a similar manner the other
through the resistance R' to the neutral point o.
coils, of the secondary member are connected through corresponding
resistances R and R to the same common or neutral point o.
The connections thus made correspond to the starting connections in which
the primary is connected directly across the mains while the secondary windings
are connected together through a large non-inductive resistance. After the
motor starts the controller handle is moved along still further thus cutting out
the sections of resistance and so increasing the speed of the motor, up to the
point where all the resistance is cut out and the terminals of the windings of the
secondary member are connected directly together through the medium of the
bridging contacts, and the connecting wires or circuits 1, 2, µ³¸
This corresponds to the running connection of the motor.
In disconnecting the motor from circuit the operations thus described are gone
through with in the reverse order.
After the resistance has been cut out of the secondary member the same
resistance is then gradually cut into circuit in the primary member and the
circuits of the latter member are then broken, the break taking place as the
bridging contacts 11, 12, pass off of the contacts connected with the resistance.
on to the insulated contacts ¹, upon which they rest in the off position of
the controller.
•

page_text: By thus utilizing the motor starting resistance the spark which takes place
upon opening the primary circuit is very greatly reduced and so much so as to
cause but little if any trouble due to arcing.
The switch mechanism which we employ for the purpose of effecting the above
described dissimultaneous movement of the two sets of bridging contacts is
shown in Figs. 1 and 2. At 4 is shown a shaft secured to the top 5 of the
resistance box or other support for the starting resistance. A sleeve 6 sur-
rounds the shaft 4 and rests with its lower end against the top of the support 5.
This sleeve is loosely mounted so as to rotate about the shaft 4 and has secured
thereto a three armed carrier 7, to the arms of which one of the sets of bridging
contacts is secured. This carrier is secured to the sleeve 6 by means of a set
screw S or in any other suitable manner, and like the sleeve 7 rests with its lower
edge adjacent to or in contact with the support 5.
The other carrier 9 for the other set of bridging contacts is loosely mounted
upon a sleeve 6 and rests upon the top of the carrier 7 as shown. The con-
troller handle is indicated at H and is secured in any suitable manner to a
sleeve I loosely mounted upon the shaft 4. This sleeve carries a hooked arm E
secured thereto by means of the set screw 10. The hooked arm at its lower end
carries a spring actuated locking pawl F which operates in conjunction with a
cam G and with two notched plates J and N. The cam is secured to the shaft 6 by
means of a set-screw, and in Fig. 1 is shown as consisting of two semi-circular
portions of different radius merged into each other. The notched disk J is
secured to the sleeve 6 and is thus fixed with respect to the carrier 7 while the
notched disk N is an integral part of the carrier 9. The locking pawl F carries
an anti-friction roller X which moves over the working surface of the cam G and
is urged against the same by means of the spring Y connected at one end to a
downwardly projecting arm of the pawl F and at its other end to a finger formed
integral with the hooked arm E.
In the position of parts indicated in Fig. 1 the locking pawl F engages the
notch in the disk J while its anti friction roller bears upon that portion of the
working surface of the cam G nearest to the shaft 4. The forward motion of
the controller handle thus causes the carrier 7 to rotate by reason of the locking
connection between the hooked arm E and the disk J, this locking connection
as already described being formed by means of the pawl F engaging a notch in
the disk. After the carrier has moved across all of the resistance contacts and
the outer or last contact of the series, the antifriction roller X reaches that part
of the cam surface indicated at 11. The upper end of the pawl F is then thrown
out, thus causing its lower end to move inwardly and engage the notch in the
disk N attached to the carrier 9. As will readily be understood, a reverse move-
ment of the controller handle will cause these operations to be performed in the
reverse order, so that whereas, on its forward motion, the first operation of the
controller is to insert resistance in the primary member, and gradually cut it
out, on the return motion on the contrary, the last operation is to insert
resistance gradually and then break the circuit of the winding of said member.
Each arm of the carriers 7 and 9 carries a bridging contact which is of the
character indicated in plan in Fig. 1 and more in detail in Fig. 2 in section.
Each carrier arm has an extension 12 secured to the arm but insulated therefrom
by means of suitable insulating material 13. Carbon brushes projecting down
from the extension 12 are spring pressed against the co-operating contacts by
means of suitable springs 14 the tension of which may be varied by adjusting
nuts 15.
The apparatus which we have just shown for carrying out this invention is
well adapted to the purpose but it will readily be understood that many modifica-
tions of the same may be effected for securing the same end, and for this reason
we do not limit ourselves to the employment of the above described apparatus
but include within this invention all devices that may perform the same function
even though the same be radically different in operation.

page_text: And although we regard the use of a single resistance both for starting and
for limiting the primary current or stopping the motor, as a valuable feature of
this invention we do not wish to be limited thereto since it is evident that if
desired, separate resistances may be employed for the purposes mentioned. This
invention is therefore not to be understood as restricted to the use of a single
resistance.
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-The method of opening the circuit in an alternating current motor which
consists in gradually inserting resistance in the circuit and then breaking the
circuit.
2 The method of stopping an induction motor which consists in inserting a
resistance in circuit with the windings of the induced member, open-circuiting
said windings, inserting a resistance in circuit with the induction windings
and then open circuiting said inducing windings.
3-The method of stopping an induction motor which consists in opening the
circuit of the induced windings, decreasing the current then flowing in the
inducing windings and then opening the circuit of the inducing windings.
4 The combination with an induction motor, of a resistance, and means for
inserting the resistance in circuit with the inducing winding of the motor, and
then interrupting the supply of energy to said winding.
5 The combination with an induction motor, of means for dissimultaneously
varying the resistance in circuit with the inducing and induced windings
respectively.
6 The combination with an induction motor, of a resistance, and means for
inserting the resistance in circuit either with the inducing..or with the induced
winding of the motor.
7 The combination with an induction motor, of a resistance, and means for
inserting the resistance first in circuit with the windings of one member of
the motor, then in circuit with the windings of the other member of the motor.
8 The combination with an induction motor, of means for inserting a
resistance in the windings of either member of the motor.
9 The combination with an induction motor, of means for dissimultaneously
inserting resistance in circuit with the inducing and induced windings of the
motor.
10 The combination of two independently movable switch arms, a controlling
handle and means for causing a successive movement of the switch arms.
11 The combination of a plurality of switch arms, a controller handle and
means for causing a movement of the controlling handle to operate the switch
arm dissimultaneously.
12-The combination of contacts, a plurality of switch arms movable over
said contacts and means for successively moving said switch arms.
13 The combination of a switch arm, a controlling handle therefor, and
means for automatically disengaging the controlling handle from the switch
arm when the switch arm has been moved a determined distance.
Dated this 28th day of November 1899.
THE BRITISH THOMSON-HOUSTON CO. LTD.,
W. MARTINDALE,
T. R. THOMPSON,
Directors.
ALFRED CLEMENTS,
Assistant Secretary.