Improvements in Methods of and Means for Synchronizing Electrio Motors.
Year: 1899

page_text: Date of Application, 30th Oct., 1899-Accepted, 9th Dec.,
1899
COMPLETE SPECIFICATION.
Improvements in Methods of and Means for Synchronizing Electrio
Motors.
We. THE BRITISH 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 Frank E. Case,
residing at Schenectady, in the 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:
The present invention has for its object to provide a method and means for
equalizing the action of electric motors when connected in series. It is well known
that when two electric motors are connected in series, they should, for best results.
be geared to the same load, as if one runs faster than its normal rate it tends to
stop the other. For example when two motors connected in series are geared to
different axles of a railroad car, if one of them slips, and then speeds up, its
counter-electro-motive force rises to such a degree that the torque of the other
motor is materially reduced, as the slipping motor exerts practically no useful
effect, the car tends to stop entirely. It is then necessary to cut in resistance
until the speed of the slipping motor is reduced to that corresponding to the speed
of the car, when it will "catch," an operation causing some considerable relay and
annoyance. This action is particularly troublesome in wet weather when it some-
times renders the maintenance of schedule time impossible.
This trouble is obviated by connecting in a shunt around each motor a device
which when the motor slips and its counter electromotive force runs up, opens a
circuit to the other motor so that current may flow in its circuit in a measure
independently of the current flow in the circuit of the slipping or racing motor.
The improvement therefore in the art of regulating electric motors which is
now devised consists in one aspect of thus establishing a current path around the
slipping motor whenever its counter electro-motive force runs up, which tends to
weaken the torque of the slipping motor as well as to strengthen the torque of the
other motor. The specific mechanism which has been devised for this purpose,
consists of a pair of electro magnets connected in series around the two motors
with a lead from the wire between the magnets to a point between the motors.
These magnets are balanced in their action so long as the drop around the two
motors or current flow in them is equal. An armature under the influence of the
magnets controls a switch which when thrown to one side or to the other,
establishes a new current path around one or the other of the two motors the
current path preferably includes a moderate resistance, for reasons presently to
be explained. This description of the device is taken as being typical of any
which may be devised embodying this invention.
The accompanying drawing is a diagram showing the invention in one form
which it may take, in which the particular mechanism just briefly described is
employed but of course many other means might be used to carry out the method.
In the drawing, T is the trolley, R is the resistance, M; M² are the motors,

page_text: and G is the ground wire. We do not show any special means for regulating the
motors, in the ordinary sense of the term, because any controlling device whatever
may be employed, as for example a series parallel controller. A is the device
embodying this invention consisting of the balanced magnets A1, A2, in a circuit
around the motors, with a lead B from a point between them to a point between
the motors. The switch-blade A³ is controlled by the action of the magnets and
reciprocates between contacts a¹, a in circuit respectively with the resistance R1, R2.
The winding of the magnets is of high resistance as it must exhaust the entire
potential across the circuit without taking an unreasonably large current.
The action of the device is as follows; assume for instance that motor M races,
and its counter electro-motive force rises so that the current in the circuit of the
two motors is cut down and the torque of the motor M2 falls off. Under these
conditions the drop around the motor M' will be so great that the magnet A' will
over-power the magnet A² and draw up the armature throwing the switch A³ to
the dotted line position, thus establishing a circuit by way of the resistance R¹,
contact a and lead B to the terminal of the motor M2. The resistance R¹ acts to
steady the motor against the sudden rise of potential, and prevents a jerky action.
Owing to the resistance and counter electro-motive force of the motor M³, the
greater part of the current will be diverted around it to the motor M2, the torque
of the inotor M will be greatly cut down, and the torque of the motor M²
increased. Under these conditions the motor M will slow down until the wheel
which it drives against adheres to the track. When the motors are again in step,
so to speak, the magnets a', a will be balanced, and the switch will open. Theo-
retically, as soon as the switch-blade touches the contact al, the magnet A¹ is short-
circuited; but owing to the high resistance winding, it takes a short time for its
magneto-motive force to run down, the action being thus prolonged for a moment.
In practice the switch-blade A³ will vibrate from one contact to the other in
accordance with the relative speeds of the motors M, M. No difficulty occurs
on account of sparking at these contacts inasmuch as only half the line voltage is
broken at them at any time; but as an additional precaution, we may make the con-
tacts a¹² of carbon and, if preferred any usual or suitable arc-extinguishing
means, such as a blow out magnet, may also be employed. The springs S $ are
used to prevent the action from being produced by mere accidental differences in
the counter electro-motive forces of the two motors, such as might be produced
by differences in their characteristic curves. Our invention is in no manner
limited to two motors, though it will be most generally thus applied; its applica-
tion to other numbers of machines is apparent and requires no illustration or
description.
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-The art of regulating two or more motors in series, which consists in simul-
taneously cutting down the current in any motor the electro-motive force of which
rises above that of the other or others, and increasing the current in that or those
of lower electro-motive force.
2 The art of regulating electro-motors connected in series, which consists in
simultaneously cutting down the current in any motor which slips and increasing
it in that or those of lower speed.
3-The art of regulating motors in series, which consists in shunting any
motor the electro-motive force of which exceeds that of another in the same
circuit, so as to divert current from the machine of higher electro-motive force
to that of lower.
4-The art of regulating motors in series, which consists in increasing the
current and torque in any motor of lower electro-motive force, and diminishing
the same factors in that or those of higher electro-motive force.
5-The art of regulating motors in series, which consists in establishing a shunt

page_text: path around any motor when it slips, thus diverting current to the motor or motors
of normal speed.
6-The art of regulating motors in series, which consists in automatically
shunting current from any motor which tends to slip to that or those which main-
tain their normal speed.
7 The combination of motors in series with means actuated by an increase
in electro-motive force of any motor above that of others, for diverting current
from such motor to the other or others.
8 The combination of motors in series, with means for shunting as a whole,
any motor which tends to slip.
9 The combination of motors in series, with means for closing a shunt path
around any motor which tends to slip, and thus increasing the current in the
non-slipping motor or motors.
10 The combination of motors in series, with an electromagnetic switch acting
automatically to shunt any motor which tends to slip.
11 The combination of two motors in series, with an electro-magnetically-
operated switch having windings in shunt to. each motor, the two windings being
opposed in effect so that when the current flow in the two motors is equal, the
switch is in a neutral position, with contacts upon the switch for closing a shunt
path around either motor; whereby when the drop around one motor exceeds that
around the other, the switch will be actuated to close a shunt path around the
motor the circuit of which has the greater drop.
12 The combination of a pair of motors driving a common load but not
mechancally geared together, with means for increasing the torque of one of the
motors when the other tends to slip.
13 The combination of a pair of motors driving a common load but so geared
that one or the other of the motors may slip or race, with an electro-magnetically
operated switch automatically acting to divert current from the slipping motor
to the circuit of the motor at normal speed.
14 The combination of motors in series, with an electro-magnetic_switch
acting automatically to shunt any motor which tends to slip and means for pre-
venting the action from taking place by mere accidental difference of counter-
electro-motive force.
THE BRITISH THOMSON-HOUSTON CO. LTD.
J. J. MANHEIM,
A. R. MONKS,
}
ALFRED CLEMENTS,
Directors.
Assistant Secretary.