Improvements relating to Methods of and Means for Regulating Electric Motors.
Year: 1899

page_text: COMPLETE SPECIFICATION.
Improvements relating to Methods of and Means for Regulating
Electric Motors.
I, ROBERT LUNDELL, of No. 527 West 34th Street, New York, United States of
America, Electrician, do hereby declare the nature of this invention and in what
mauner the same is to be performed, to be particularly described and ascertained
in and by the following statement: ―
My present invention relates to methods of and means for the regulation of
electric motors.
It is customary to employ resistances in the armature circuits of motors which
are coupled in series-parallel combinations, for the purpose of avoiding too sudden
variations in speed, sparking at the brushes and excessive flashing at the con-
troller contacts. These resistances are particularly necessary while the change
from series to parallel is being effected. There are, however, serious objections
to all armature resistances, the chief objections being loss of efficiency and uneven
drop of voltage between the resistance terminals, due to variations in the load.
In fact, the resistances are only correct for one particular load upon the motor,
as a light load will cause too small a drop of voltage in the resistance itself and a
heavy load will cause a greater drop of voltage than is required for correct
variations in speed.
Many attempts have been made to return current to the mains, most of which
have proved abortive because effective only within a very limited speed range, and
because of excessive sparking at the brushes. The present invention makes it
possible to do away with all external resistance that will cause fall of potential
at the armature terminals and to effectively return current to the line, at all but
the lowest speeds, by reason of the following novel construction of the motor and
arrangement of its electric circuits.
Briefly expressed, the invention is characterized by the employment of an
electric motor furnished with two armature windings, two commutators and a
field magnet so constructed that it will be possible to run with weak field strength
without sparking at the brushes and with its electric circuits so arranged that
before a change of current from series to parallel the speed of the motor is so
increased, by reason of the weakened field, that it will approximate to the speed
obtained with strong field after the change to parallel is effected.

page_text: For a clear understanding of the invention, reference is made to the accom-
panying drawings, in which,
Figure 1 is a diagrammatic view of the circuit connections between the
stationary contacts of a controller, a motor having two armatures and two com-
mutators with a compound wound field magnet, a storage battery arranged in
two distinct groups and the resistances which are used in connection with the
field circuits of the motor.
Figure 2 illustrates the developed contacts upon the controller cylinder, the
construction of which is similar to well known forms of controller cylinders.
Figure 3 illustrates the developed contacts upon a reversing cylinder of well
known form, which serves to reverse the current through the field windings of
the motor.
Figure 4 is a diagrammatic view of the various combinations of the motor
circuits when the controller cylinder with its contacts shown in Figure 2 is
rotated over the stationary right hand contacts shown in Figure 1. The motor
in this case is supposed to be used in connection with a divided storage battery,
as indicated in Figure 1, for the propulsion of electric vehicles or for similar uses.
Figure 5 is a diagrammatic view of the various circuit combinations when a
motor having two armature windings and two commutators with a compound
wound field magnet is used in combination with another motor of like con-
struction for electric tram or railway cars, nine conditions of usage being illus-
trated.
Referring to Figures 1 and 4-C¹ and C³ represent the commutators for the
two armature windings of the motor. O represents the shunt field winding
and T the series field winding. R R R2 and R3 are resistances, the first two
named being in series with the shunt field winding or short circuited as the case
may be, and the two latter being connected in series to the terminals of the series
field winding and partly short circuited or disconnected, according to the position
of the controller. The shunt field is connected across one group of the batteries
only for all positions of the controller, as shown in Figure 1.
The first position of the controller or the first speed, causes the shunt field to
become extra strong, the resistance in series with same being short circuited. The
series field is shunted by a low resistance R³, so that the ampere turns from same
is reduced to a minimum. The storage battery, shown in Figure 1, is in this
position grouped in two parallel rows B B2, thus giving with two commutators in
series only 20 volts. per commutator, if, for example, each group of batteries is
arranged to yield 40 volts.
The second position of the controller leaves the circuit connections practically
the same, with the exception of the shunt field which is so weakened by the field
resistance that the motor has speeded up at least 50% (fifty per cent.). The
third position of the controller has changed the batteries from parallel to series,
giving 40 volts. per commutator, has caused the shunt field to again reach maxi-
mum strength and has also caused more current to flow through the series
coil by reason of an additional resistance R2 being introduced in series with R³.
This position gives to the motor a speed about 100% (one hundred per cent.) greater
than obtained at the first position. Position 4 leaves the circuits practically the
same as in the third position, with exception of the shunt field circuit, which
has been weakened by the two resistances R and R' to such an extent that
although more current is now flowing through the series coil, the total field has
been so weakened that the motor has speeded up at least 50% (fifty per cent.) from
the last position. Position 5 of the controller has changed the armature circuits
from series to parallel and is causing a strong current to flow through the series
windings by reason of the resistances R and R' being entirely cut out. The
shunt field is of the same strength as in position 2 and the total magnetization
about the same as in position 3. Each commutator is practically receiving 80
volts. and the speed is, consequently, about 100% (one hundred per cent.) greater
than at the third position.

page_text: The sixth and last position of the controller opens the shunt field entirely, (or
practically so) but leaves the other circuits as they were in the fifth position, thus
causing the motor to speed up and to become a plain series wound motor.
Assuming now that the motor is used in connection with an electric vehicle,
the following points will be clear from the above description of the circuits.
First, as the motor is gradually converted from practically a shunt wound motor
at the lowest speed to a series wound motor at the top speed, it follows that the
speed of the vehicle will be practically constant at the lower speeds, no matter
what the load happens to be, but that the top speeds will greatly depend upon
the load. In other words, the motor will, at the lower speeds, show a disposition
to "fight" or take current through its armature windings in proportion to the
required torque. An excessive current will not cause sparking at the brushes:
for the reason that at the first and second positions of the controller, the difference
of potential between consecutive commutator bars is only one-quarter of that at
top speed.
Second, should the speed of the vehicle materially exceed the speed correspond-
ing to a certain position of the controller No. 1, No. 2 or No. 3, by reason of
running down hill, it follows that the motor will automatically become a dynamo
and will thus restore energy to the battery.
Third, should the vehicle happen to be running at top speed and the controller
to be rather quickly returned to positions No. 2 or No. 1, it follows that a rather
excessive current will flow through the armature windings, charging the battery,
but that the same will be kept within safe limits on account of the weakening
effect of the series field which, by reason of weakening of the field strength, will
correspondingly reduce the electro-motive force of the armature. The charging
of the battery is in a measure regulated automatically viz., a heavy charging
current will weaken the field and thus reduce the E.M.F. and a small charg-
ing current will strengthen the field and thus increase the E.M.F.
Referring to Figure 5: 0¹ represents the shunt winding, T¹ the series winding,
C¹ C² the commutators for the armature windings of one motor. 02 T² C³ C¹
represent the corresponding windings and the commutators of the other motor.
Each armature combination yields three different speeds by reason of a varied field
strength.
The first three speed combinations, 1st, 2nd and 3rd give 125 volts. per com-
mutator (with a line voltage of 500) and the motors are practically working as
shunt motors, owing to the very strong shunt and the weak series field winding.
The next three speeds 4th, 5th and 6th give 250 volts. per commutator. The
series fields have now become considerably stronger, owing to an increase of
current through their windings, and the shunt fields have been somewhat weakened
by the introduction of one or more resistances in series with the same. The three
last speed combinations, 7th, 8th and 9th, give 500 volts. per commutator, not
counting the drop due to the series field winding. The series field at the 7th
position is four times as strong as at the 1st position and at the 8th and 9th
positions it is furthermore strengthened, by reason of more current flowing
through the armature. The shunt field has been so reduced by reason of
additional resistances in series with the same that the motors at the top speed
are practically working as plain series wound motors. As there is no external
resistance in the armature circuits to cause a considerable drop of potential, and
as the internal resistances of the motors themselves are comparatively small, it
follows that the speed of the motors will principally depend upon their counter
electro-motive forces, which in turn, depend upon the series-parallel grouping of
the armature windings and upon the field strength. It also follows, from the
above description of the various circuit combinations, that the motors will not
accelerate more rapidly when the controller is moved from the 3rd to the 4th
and from the 6th to the 7th positions, than between any other two positions (the
speed at the 3rd and 6th positions being so increased by reason of the weakened
field, that it approximates the speed at the 4th and 7th positions). The controller

page_text: with its contacts shown in Figures 1, 2 and 3 forms no part of the present invention
and is only shown in order that the circuits may be traced.
I do not limit this invention to the particular details of construction and
arrangement of circuits and circuit connections hereinbefore described and illus-
trated in the accompanying drawings for practicing the methods of operation
hereinafter claimed.'
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. The method of regulating one or more compound wound electric motors
which consists in grouping the armature circuits in series-parallel combinations
and in changing the field magnets strength from a strong shunt and weak series
for the lower speed combinations to a weak shunt and strong series for the higher
speed combinations.
2. The described method of increasing the speed of one or more electric motors
which consists in changing the armature circuits from series to parallel and in
increasing the ratio of series ampere turns to shunt ampere turns upon the field
after such a change is effected.
3. An electric motor or motors provided with means such as variable resistances
for diverting part of the field current before the armature circuits are changed
from series to parallel and for increasing the field currents before the armature
circuits are changed from parallel to series, so that the speed obtained with weak
field and armature circuits in series will closely approximate the speed obtained
with strong field and armature circuits in parallel, substantially as described.
4. An electric motor provided with multiple field and armature windings, in
combination with variable resistances, in a shunt around one set of field windings,
and additional variable resistances adapted to be placed in series relation with
the other set of field windings, substantially as described.
5. An electric motor or motors having compound wound field magnets in com-
bination with means, such as variable resistances, for reducing the field strength
before the armature circuits are changed from series to parallel and for increasing
the ratio of series ampere turns to shunt ampere turns after such a change is
effected, substantially as described.
6. An electric motor provided with double field magnet and double armature
windings, the armature windings being in series relation with one set of field
windings having variable resistances located in shunt relation thereto; the other
set of field windings being located in series relation with variable resistances,
together with circuit connections whereby the field magnet strength may be varied
in such manner that the armature will restore or return electrical energy to the
source of current supply for the lower speed combinations of the motor, and will
cause it to retain the qualities of a series wound motor for the higher speed com-
bination thereof, substantially as described.
7. Two or more electric motors provided each with multiple field and armature
windings, in combination with two sets of variable resistances, one of which is
adapted to be connected in series relation with one set of the field windings of
each motor, and the other in shunt relation to the other sets of field windings of
all of the motors, together with circuit connections for connecting the armature
windings of all of the motors to the last named field windings in any desired
order, substantially as described.
1
1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.