IMPROVEMENTS IN AND RELATING TO ELECTRO-DYNAMIC MOTORS
Year: 1885

page_text: I THOMAS JOHN HANDFORD of 42 Southampton Buildings in the County of
Middlesex, Patent Agent do hereby declare the nature of this invention for
"IMPROVEMENTS IN AND RELATING TO ELECTRO-DYNAMIC MOTORS"
a communi-
cation to me from abroad by Frank Julian Sprague of New York, in the County
and State of New York, United States of America, Electrical Engineer to be as
follows:-
This invention relates mainly to a mode of constructing electro-dynamic motors
by which the necessity of shifting the commutator brushes upon the commutator
cylinder when the armature current varies, to avoid spark, is obviated.
The necessity for shifting the commutator brushes of a motor ordinarily arises
from the fact that when the armature current varies there is a distortion of the
magnetic field and a shifting of the magnetic resultant of the armature and field
magnetism so that the line of parallel-cutting of the lines of force and the points
of least spark on the commutator cylinder are changed and the brushes have to be
shifted accordingly.
By the construction which forms this invention, this distortion of the magnetic
field due to variations of armature current is opposed by a counter distortion
dependent upon such variations, so that the magnetic resultant is unchanged and
the position of the non-sparking points never varies.
In carrying the invention into effect my foreign correspondent employs main
field magnet coils in shunt relation to the armature, differential field magnet coils
in series with the armature and additional cumulative field magnet coils, also in
series with the armature. The main field coils may be shunted upon the armature
alone, or upon the armature and both the cumulative and differential series coils,
or upon the armature and either of the said series coils, the other series coil
remaining outside the terminal of the main field shunt.
The proportions of the winding of all the field magnet coils are preferably such
as are set forth in the provisional specification accompanying my application for

page_text: '
Letters Patent dated the 17th March 1885 N° 344685 that is to say, so that a zero
field is produced if circuit is closed to the shunt and series coils when the motor is
at rest.
This necessitates the employment of means for varying the magnetizing effect
of the differential coils. Such means are set forth in the said former provisional
specification and may consist of a short circuiting and reversing switch.
In accomplishing the counter distortion of the field the motor used is one in
which field magnet cores extend in different directions from the field of force in
which the armature revolves. The differential series coils are wound or arranged
so that their greatest effect is produced on diagonally opposite parts of the magnetic
field, and the cumulative series coils so that their greatest effect is produced on the
other diagonally opposite parts.
The differential coils are arranged to have a greater magnetizing effect than the
cumulative coils.
A decrease of load causing a decreased armature current tends to shift the
magnetic resultant of the armature and field magnet. But this also decreases the
magnetizing effect of all the series coils and therefore the parts of the field
principally affected by the cumulative coils are weakened and those principally
affected by the differential coils are strengthened whereby a distortion of field is
produced opposed to that produced by the decrease of armature current and hence
the magnetic resultant, the line of parallel cutting and the points of least .spark
remain unchanged. Thus no shifting of the commutator brushes is ever required
except on account of wear.
At the same time as the differential series coils predominate over the cumulative
the whole field magnet strength is increased and the speed of the motor is brought
down to compensate for the decreased load.
The arrangement of two sets of series field coils, one differential the other
cumulative, may be employed simply as a means of field regulation where it is not
desired to produce the counter distortion. In such case the coils may be evenly
wound on all the legs of the field magnet and used only to regulate the motor,
being wound in the proportions above set forth. The differential and cumulative
series coils have a differential effect which as the differential coils predominate
over the cumulative coils produces a weakening of the total strength of the field
magnet when the armature current, increases and a strengthening of the field
magnet when the armature current decreases and so maintains constant the speed
of the motor.

page_text: Improvements in and relating to Electro-dynamic Motors.
I THOMAS JOHN HANDFORD of 42 Southampton Buildings in the County of
Middlesex, Patent Agent 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:-
This invention relates mainly to a mode of constructing electro-dynamic motors
by which the necessity of shifting the commutator brushes upon the commutator
cylinder, when the armature current varies, to avoid spark, is obviated.
The necessity for shifting the commutator brushes of a motor ordinarily arises
from the fact that when the armature current varies there is a distortion of the
magnetic field and a shifting of the magnetic resultant of the armature and field
magnetism, so that the line of parallel-cutting of the lines of force and the points
of least spark on the commutator cylinder are changed, and the brushes have to be
shifted accordingly.
By the construction which forms this invention, this distortion of the magnetic
field due to variations of armature current is opposed, by counter distortion
dependent upon such variations, so that the magnetic resultant is unchanged and
the position of the non-sparking points never varies.
In carrying the invention into effect, my foreign correspondent employs main
field magnet coils in shunt relation to the armature, differential field magnet coils
in series with the armature, and additional cumulative field magnet coils, also in
series with the armature. The main field coils may be shunted upon the armature
alone, or upon the armature and both the cumulative and differential series coils,
or upon the armature and either of the said series-coils, the other series coil
remaining outside the terminal of the main field shunt.
The proportions of the winding of all the field magnet coils are preferably such
as are set forth in the complete specification to my Letters Patent dated the
17th March 1885 N° 34465, that is to say so that a zero field is produced if circuit
is closed to the shunt and series coils when the motor is at rest:
This necessitates the employment of means for varying the magnetizing effect of
the differential coils. Such means are set forth in the said former specification,
and may consist of a short circuiting and reversing switch.
In accomplishing the counter distortion of the field, the motor used is one in
which field magnet cores extend in different directions from the field of force in
which the armature revolves. The differential series coils are wound or arranged
so that their greatest effect is produced on diagonally opposite parts of the
magnetic field, and the cumulative series coils so that their greatest effect is
produced on the other diagonally opposite parts.
The differential coils are arranged to have a greater magnetizing effect than the
cumulative coils.
A decrease of load causing a decreased armature current tends to shift the
magnetic resultant of the armature and field magnet. But this also decreases the
magnetizing effect of all the series coils and therefore the parts of the field
principally affected by the cumulative coils are weakened and those principally

page_text: affected by the differential coils are strengthened, whereby a distortion of field is
produced, opposed to that produced by the decrease of armature current, and hence
the magnetic resultant, the line of parallel cutting and the points of least spark
remain unchanged. Thus no shifting of the commutator brushes is ever required
except on account of wear,
At the same time as the differential series coils predominate over the cumulative,
the whole field magnet strength is increased and the speed of the motor is brought
down to compensate for the decreased load.
The arrangement of two sets of series field coils, one differential the other
cumulative, may be employed simply as a means of field regulation where it
is not desired to produce the counter distortion. In such case the coils may be
evenly wound on all the legs of the field magnet and used only to regulate the
motor, being wound in the proportions above set forth. The differential and
cumulative series coils have a differential effect which as the differential coils
predominate over the cumulative coils, produces a weakening of the total strength
of the field magnet when the armature current increases and a strengthening of
the field magnet when the armature current decreases and so maintains constant
the speed of the motor.
And in order that the said invention may be perfectly understood, I shall now
proceed more particularly to describe the same and for that purpose shall refer to
the several figures on the accompanying sheet of drawings the same letters of
reference indicating corresponding parts in all the figures.
Figures 1 to 8 are diagrams illustrating various arrangements of the motor
circuits which may be employed.
and
Figure 9, is a view of a motor embodying the invention;
Figures 10, 11 and 12, are diagrams illustrating the distortion of the magnetic
field.
In all these figures, A. is the armature, B the main or shunt field coils, C the
differential series field coils, and D the cumulative series field coils. 1, 2, are the
mains of a constant potential circuit with which it is preferred to employ
the invention: 3, 4, are the motor terminals, and 5 is a terminal of the armature
or main field coils shunt.
In figure 1 the main field coils are shunted around the armature alone. In
figure 2 the main coils are shunted around the armature and the cumulative series
coils alone, the differential coils being outside the shunt terminal. In figure 3 the
shunt is around the armature and both the series sets. Figure 4 is similar to
figure 1 except that the positions of the two series sets are reversed. In figure 5
the shunt is around the armature and the differential series coils, the cumulative
series coils being outside the terminals of the shunt.
Figure 6 is similar to figure 3 with the series coils reversed in position.
Figure 7 shows means for varying the magnetizing effect of the differential series
coils. Such means here consist of a short circuiting and reversing switch E. In
starting the motor this switch has the position shown, the current in the
differential coils being thus reversed and the field being therefore very strong
when the motor starts. The position of the switch is then changed, to short-
circuit the series coil and so weaken the field magnet, and finally the coils are
thrown in direct so as to exert their usual effect.
In figure 8 the terminal 5 of the armature shunt is shown shifted to a different
point of the main field coils. This may be done by any suitable commutator, and
the difference of potential at the armature shunt terminals and the current in the
armature are thereby varied, and also, if the series coils are inside the shunt
terminals as in this figure, the magnetizing effect of such coils is varied.
In figure 9, F is an electro-dynamic motor, like that represented in figure 6, the
two sets of series coils being both inside the shunt terminals The differential
series coils are wound on two diagonally opposite legs of the field magnet and the
cumulative series coils on the other two legs. These coils act to regulate the speed
of the motor under variable loads and also to produce the counter distortion and

page_text: maintain the non-sparking point constant in the manner which has been above
explained. This is seen in figures 10, 11 and 12 wherein xx, is the line of the
magnetic resultant. In figure 10 this line is at its normal position In figure 11,
it is shifted as shewn by a change in the armature current due to a variation in
load, while in figure 12 the line is brought back to its original position by the
counter-distortion as has been fully explained.
For convenience of illustration the armature shown in these three figures is a
Gramme ring-N, S, are the field magnet poles. The dotted lines in the interpolar
space represent the magnetic lines of force."
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. An electro-dynamic motor having differential field magnet coils and cumulative
field magnet coils both in series with the armature, and main field magnet coils
shunted upon the armature alone or upon the armature and either or both of the
said sets of series coils, substantially as herein before described.
2. In an electro-dynamic motor, the combination with the armature and main
field magnet coils in shunt relation with the armature, of differential field magnet
coils and cumulative field magnet coils both in series with the armature, the said
differential coils being arranged to produce their greatest effect on diagonally
opposite parts of the magnetic field, and the said cumulative coils arranged to
produce their greatest effect on other diagonally opposite parts of the magnetic
field, substantially as herein before described.