Improvement in Method of and Means for Varying the Speed of Direct Current Motors.
Year: 1899

page_text: Date of Application (in United Kingdom), 23th Mar., 1899
Complete Specification Left, 22nd Dec., 1899-Accepted, 17th Mar., 1900
Improvement in Method of and Means for Varying the Speed of Direct
Current Motors.
I, BENJAMIN GARVER LAMME, of 230, Stratford Avenue, Pittsburg, in the
County of Allegheny, and State of Pennsylvania U.S.A., Electrical Engineer,
do hereby declare the nature of this invention to be as follows:-
My invention relates to the utilization of direct electric currents and it has
for its object to provide a method and means whereby the speed of direct current
electric motors may be varied without varying the electromotive force supplied
to such motor and without any changes in the field-magnet windings.
According to my invention i accomplish these objects by varying the armature
reaction and consequently the field magnet strength of the motor by connecting
one or more auxiliary alternating current circuits to the armature winding and
varying or adjusting the phase relation between the current and electromotive
force of such circuit or circuits.
It has been determined that if the current and electromotive force waves
supplied by an alternating current generator are in step the armature reaction
will be substantially zero, hence the field magnet strength will not be altered;
if, however, the current lags, the armature reaction will be increased and the
field magnet strength correspondingly decreased. If, on the other hand, the
current leads the electromotive force the armature reaction will be such as to
strengthen the field magnet. It is clear, therefore, that the field magnet strength
depends upon the armature reaction, hence by varying the armature reaction the
speed of the armature may also be varied.
In the accompanying drawings:-
-
Figure 1 is a diagram of a direct current motor having two out-of-phase alter-
nating current circuits connected to its armature winding, said circuits being
provided with variable self-inductive devices, and
Figure 2 is a similar diagram in which the alternating current circuits have
valiable capacity.
1 is a direct current generator provided with mains 3 and 4. which supply
through a commutator 5 the armature 6. The field magnet coils are indicated
at as being.connected as a shunt to the armature, and this type of winding is
Paine &

page_text: preferred since the field produced by it should be relatively weak, as compared
with that produced by the armature winding, A series field magnet winding
may, however, be used if desired.
Referring now to Figure 1, the motor armature is furnished with two pairs
of collecting rings, 8, 9 on which bear brushes 10 and 11. To these brushes are
connected auxiliary circuits 12 and 13 which are provided with inductive re-
sistances illustrated as being choke coils, 14 and 15. Each of these coils is shewn
as provided with an adjustable core 16 and 17 respectively, and with a series of
leads to which are connected switches 18 and 19 for varying the active length of
the choke coil, or cutting it out of the circuit altogether. It will be clear that
the self-induction in the alternating current circuits may be varied by adjusting
the movable cores or varying the active length of the coils, or by the use of both
these means in combination. In fact, any suitable device may be utilized for
varying the self-induction of the alternating current circuits.
-
The operation of the system of circuits shewn in Fig. 1 is as follows:-
If the switches 18 and 19 are all open, the motor will run at a normal speed,
corresponding to its winding, the number of field-magnet poles, and the electro-
motive force supplied from the mains 3, 4. If, however, each of the circuits 12,
13 be closed by operating the proper switches 18, 19, so as to include one section
of the choke coils 14, 15, therein, a current lag will be effected in said circuits
which will serve to increase the armature action of the motor, and consequently
the field-magnet strength, so that the speed of rotation of the motor will increase.
The speed will obviously increase according to the number of sections of the
choking coils which are included in circuit. Further, the self-induction in cir-
cuits may be varied if desired by adjusting the cores 16, 17, with reference to
the choking coils and by this means a further variation in the speed of the motor
may be obtained.
In Fig. 2 which shews a modification, the alternating current circuits 12, 13,
are provided with condensers 20, the number of which in circuit may be varied
by means of the proper switches 21. By this means considerable variation in
the capacity included in the alternating current circuit may be produced, which
variation in capacity will vary the amount by which the current in said circuit
leads the electromotive force. It will be understood of course that such a lead
of the current will so affect the armature reaction that the field-magnet strength
will be increased and the speed of the motor will thereby be decreased.
I wish it to be understood that synchronous motors may be employed in place
of either the choke coils of Fig. 1, or the condensers of Fig. 2, since the phase
relations between the current and electromotive force may be adjusted by ad-
justing the field-magnet strength of such synchronous motor.
Although I have shewn two-phase alternating current circuits joined to the
armature 6, it will be obvious that the invention is not restricted in this respect,
as circuits of any desired number of phases may be utilised.
Furthermore, I do not restrict myself to any specific construction of direct
Jurrent motor either as regards the armature or field-magnet of the machine.
Dated the 28th day of March 1899.
Improvement in Method of and Means for Varying the Speed of Direct
Current Motors.
I, BENJAMIN GARVER LAMME, of 230, Stratford Avenue, Pittsburg, in the
County of Allegheny, and State of Pennsylvania U.S.A., Electrical Engineer,

page_text: 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 the utilisation of direct electric currents and it has
for its object to provide a method and means whereby the speed of direct current
electric motors may be varied without varying the electromotive force supplied
to such motor and without any changes in the field-magnet windings.
According to my invention 1 accomplish these objects by varying the armature
reaction and consequently the field magnet strength of the motor by connecting
one or more auxiliary alternating current circuits to the armature winding and
varying or adjusting the phase relations between the current and electromotive
force of such circuit or circuits.
It has been determined that if the current and electromotive force waves supplied
by an alternating current generator are in step the armature reaction will be
substantially zero, hence the field magnet strength will be at a maximum, if,
however, the current lags, the armature reaction will be increased and the field
magnet strength correspondingly decreased. If, on the other hand, the current
leads the electromotive force the armature reaction will be such as to strengthen
the field magnet. It is clear, therefore, that the field magnet strength depends
upon the armature reaction, hence by varying the armature reaction the speed
of the armature may also be varied.
In the drawings accompanying my Provisional Specification:-
Figure 1 is a diagram of a direct current motor having two out-of-phase alter-
nating current circuits connected to its armature winding, said circuits being
provided with variable self-inductive devices, and
Figure 2 is a similar diagram in which the alternating current circuits have
variable capacity.
1 is a direct current generator provided with mains 3 and 4, which supply
through a commutator 5 the armature 6 of the motor. The field magnet coils
of the motor are indicated at 7 as being connected as a shunt to the armature,
and this type of winding is preferred since the field produced by it should be
relatively weak compared with that produced by the armature winding. A series
field magnet winding may, however, be used if desired.
Referring now to Figure 1, the motor armature is furnished with two pairs
of collecting rings, 8, 9, on which bear brushes 10 and 11. To these brushes are
connected auxiliary circuits 12 and 13 which are provided with inductive re-
sistances illustrated as being choke coils, 14 and 15. Each of these coils is
shewn as provided with an adjustable core 16 and 17 respectively, and with a series
of leads to which are connected switches 18 and 19 for varying the active length
of the choke coil, or cutting it out of the circuit altogether. It will be clear
that the self-induction in the alternating current circuits may be varied by
adjusting the movable cores or varying the active length of the coils, or by the
use of both these means in combination. In fact, any suitable device may be
utilized for varying the self-induction of the alternating current circuits.
The operation of the system of circuits shewn in Figure 1 is as follows:-
If the switches 18 and 19 are all open, the motor will run at a normal speed,
corresponding to its winding, the number of field magnet poles and the electro-
motive force supplied from the mains 3, 4. If, however, each of the circuits 12,
13 be closed by operating the proper switches 18, 19, so as to include one section
of the choke coils 14, 15, therein, a current lag will be effected in said circuits
which will serve to increase the armature re-action of the motor, and consequently
to decrease the field-magnet strength so that the speed of rotation of the motor
will increase. The speed will obviously increase according to the number of
sections of the choking coils which are included in circuit. Further, the self-
induction in the circuits may be varied if desired by adjusting the cores 16, 17,
with reference to the choking coils and by this means a further variation in the
speed of the motor may be obtained.

page_text: In Figure 2 which shews a modification, the alternating current circuits 12,
13 are provided with condensers 20, the number of which in circuit may be
varied by means of the proper switches 21. By this means considerable variation
in the capacity included in the alternating current circuit may be produced, which
variation in capacity will vary the amount by which the current in said circuit
leads the electromotive force. It will be understood of course that such a lead
of the current will so affect the armature reaction that the field-magnet strength
will be increased and the speed of the motor will thereby be decreased.
I wish it to be understood that synchronous motors may be employed in place
of either the choke coils of Fig. 1, or the condensers of Fig. 2, since the phase
relations between the current and electromotive force may be adjusted by ad-
justing the field-magnet strength of such synchronous motor.
Although I have shewn two-phase alternating current circuits joined to the
armature 6, it will be obvious that the invention is not restricted in this respect,
as circuits of any desired number of phases may be utilised.
Furthermore, I do not restrict myself to any specific construction of direct
current motor either as regards the armature or field-magnet of the machine.
Having now particularly described and ascertained the nature of my said in-
vention and in what manner the same is to be performed, I declare that what I
claim is: :-
1. The method of varying the speed of a direct current electric motor which
consists in varying the phase relation between current and electromotive force
in the armature circuit whereby the armature reaction is varied.
2. A direct current electric motor having connected to its armature winding
an auxiliary alternating current circuit including means for adjusting the phase
relation between the current and the electromotive force therein, for the purpose
specified.
3. The arrangements for operating direct current motors at a variable speed,
shewn in Figures 1 and 2 of the drawings, substantially as described.
Dated the 22nd day of December 1899.
W. P. THOMPSON & Co.,
Of London, Liverpool, Manchester and Birmingham.