Improvements in the Regulation of Dynamo Electric Machines and Motors.
Year: 1898

page_text: Date of Application, 18th Jan., 1898-Accepted, 12th Mar., 1898
COMPLETE SPECIFICATION.
Improvements in the Regulation of Dynamo Electric Machines and
Motors.
I, FREDERIC AYRES JOHNSON, of No. 4, Chapin Street, in the City of Bingham-
ton, County of Broome, and State of New York, United States of America,
Engineer, 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 regulation of dynamo electric machines, and com-
prises a new and useful method of and apparatus for effecting such regulation.
It is particularly designed for electric motors, and will be described with refer-
ence thereto, but the same principles are equally applicable to electric generators
whose voltage is to be varied within wide limits.
When an electric motor is to be run on a constant potential circuit, it is well
known that efficient speed regulation is exceedingly difficult. In practice it is
very common to use two or more small motors instead of one large one, and to
control them by the series-parallel method. This system gives fairly good results,
but greatly increases the first cost and weight of the installation.
It is also common to insert variable resistances in series with the armature,
but this is obviously an exceedingly wasteful practice. It has also been proposed
to secure the required speed regulation by weakening the field-magnets, but in
commercial work this has been found out of the question except within a narrow
range of speed, for the reason that if the field is weakened the neutral line shifts
and the motor sparks excessively, unless the brushes are also shifted. If this
weakening of the field is carried beyond a certain limit, it may happen that there
is no point at which the brushes may be set in order that the motor may run
without sparking, on account of the great distorting effect of the armature reaction
upon the comparatively weak field.
When the machine is to be used as a generator producing different voltages,
the same difficulties occur.
In order to avoid sparking, it is necessary that at the instant of commutation the
short circuited coil be passing through a field of such strength that when it
pases out from under the brush, and is placed in its new relation on the other
side of the armature circuit, it shall be the seat of a current practically equal
to the current which it must carry in the new relation. In practice, a stiff field
is provided, and the brushes are so set that commutation takes place on the edge
of this field.
I am able to secure the proper commutation field at all strengths, and at the
same time to permit wide variations in the total flux through the armature, by my
improved method and apparatus.
Particular embodiments of my invention are illustrated in the accompanying
drawings, in which:
Fig. 1 is a view, partly in section, of a machine constructed according to my
invention, in which the regulation is effected by varying the reluctance of a
portion of the magnetic circuit. Figs. 2 to 6 are diagrammatic views of machines

page_text: in which the regulation is effected by varying the magneto-motive force acting
upon a portion of the magnetic circuit.
In Fig. 1 is shown a motor consisting of the field magnet 1, excited by coils 2, 3,
and the armature 4, with commutator 5, and brushes 6, 7. The armature may be
of any preferred type, and is illustrated in diagram only.
The pole-pieces are hollow, and the cavities are fitted with the soft iron
masses 8, 9, whose position may be adjusted by the screws 10, 11. If these masses
are forced as far as possible into the poles of the field-magnet, the flux through the
armature will be a maximum, and the motor will run at its lowest speed. If,
however, these masses are wholly or partially removed from the cavities in which
they slide, the flux through the center of each pole-piece will be greatly reduced,
and the speed of the motor will be increased. But the flux through the polar
tips will not be reduced, but will on the contrary tend to be strengthened.
The commutated coils, therefore, are still in a stiff field, and the motor does not
spark. But as the total flux through the armature is reduced, the total counter-
electromotive force of the motor is also reduced, and the speed rises.
Fig. 2 shows another form, in which a similar result is accomplished by purely
electrical means. In this figure, 1 is the field-magnet, of a common consequent
pole type, with main exciting coils 2, 3, as before: and 4, is the armature, with
the commutator 5, and brushes 6, 7. The brushes are in multiple with the
mains 30, 31, and the main field coils are connected in multiple with the same
mains through the adjustable resistance 12.
Wound in slots in the field-magnet structure, are auxiliary field coils 81, 91,
connected in multiple with the mains through the reversing switch 13, and adjust-
able resistances 14, 14¹, as shown. It will be seen that these coils are so wound as
to send lines of force through the center of the pole-pieces only, and that their
effect upon the polar tips is small. With the switch 13, on the point 15, these
coils are cut out, and have no effect upon the action of the motor.
If now the switch 13, be moved to the point 16, as shown, the current will pass
from the mains through the switch, through resistance 141, to the coils 81 and 9¹,
segment 22, switch 13, to main 31, magnetizing the coils 81, 91, in such a way
that the flux in the center of each pole-piece is increased, without seriously
affecting the flux through the polar tips. The speed of the motor will therefore
fall. As the switch is moved to the points 17 and 18, the resistance 14¹ is cut
out, and the total flux through the armature of the motor is still further increased.
But the commutated coils are in practically the same field as before and the motor
does not spark.
If on the other hand the switch 13 be moved to the contacts 19 and 23, the
current in the coils 8 and 9¹ is reversed, and the field at the center of each polar
projection is weakened. As the switch passes to the points 20, 21, this effect
becomes still more pronounced. But as the flux through the polar tips is not
weakened, the neutral line is not shifted, and the motor still runs sparklessly.
By properly adjusting the resistances 12, 14 and 14', it is possible to secure any
desired speed within wide limits, and at the same time to maintain the commutated
coils in such a field that the motor shall still be quite sparkless.
Fig. 3 shows a slightly different arrangement. The main field coils 2 and 3
are connected in series with the auxiliary coils 24, 25, 26, 27, with shunting
switches 28, 29, whose action will be described below. The relative directions
of the windings are indicated by the N, S, marks upon the poles. It will be seen
that the effect of the coils 24, 25, 26, 27, is to strengthen the poles at the tips
without greatly affecting the strength of the poles at the centers of the polar ex-
tensions. At the same time, the resistance of these coils is such as to materially
cut down the current in the main field coils.
If, however, both of the switches are closed, the main field coils are connected
directly across the mains, and the auxiliary coils are de-energized. The field
excitation is then a maximum. But if the switch 28, be opened, as shown, the
auxiliary coils 26, 27, will be connected in series with the main field coils 2 and 3,

page_text: and the result will be to reduce the current in the main coils, and to weaken
the field of the motor. But the coils 26, 27, produce additional magneto-motive
force acting upon these coils of the armature which are under-going commutation,
and a stiff commutating field is provided. The total flux through the armature
is, however, greatly reduced, both by the weakening of the exciting current of the
coils 2, 3, and also by the tendency of the lines of force flowing from the polar
tips on which the coils 26, 27, are wound to return through the centers and
opposite tips of the same pole-pieces, neutralizing at those points partially or
wholly the flux due to 2, 3. These shunting switches 28, 29, may, if preferred,
be replaced with variable resistances to give a larger number of changes of speed.
If the motor is run in the opposite direction, the switch 28, may be opened when
an increase of speed is desired, which will strengthen the field at the polar tips
on which the coils 26, 27, are wound, and weaken the field at all other points.
Fig. 4 shows a motor of a similar structure, arranged to run in one direction
only. The coils 271, 281, are in this case also wound so as to strengthen the field
on those tips on which they are placed, and are connected in multiple with the
line through the switch 38, and resistance 39. The main field coils 2, 3, are also
connected in multiple with the line, through the same resistance, and the connec-
tions are so made that as the switch 38, is moved, it cuts resistance out of one of
the branch circuits and into the other. When the switch is thrown to the right,
the result will be to cut out the resistance in series with 2, 3, and to place all of the
resistance in series with 261, 27. The main field coils will then exert a very
powerful magnetizing effect, and the auxiliary coils will be partially de-energized.
This position corresponds to the slowest speed.
If now the switch 38, be moved to the left, the current in the main field coils
will be gradually reduced, and the flux through the armature weakened. But
at the same time the current in 26¹, 271, is increased, and the flux through the
commutated coils maintained or even increased, according to the proportions of
the various coils. It will be obvious that with this arrangement I am enabled
to run a motor sparklessly at a number of different speeds, but in one direction
only.
In Fig. 5 I have shown an arrangement very similar to that shown in Fig. 2.
The auxiliary coils 81, 91, are wound to oppose the flux produced by the
main coils 2, 3, at the centers of the polar faces; while at the tips they tend to
strengthen the original field. Adjustable resistances 32, 33, are inserted in series
with the auxiliary coils and with the main field coils, respectively.
While in the above construction the result is produced by varying the reluctance
of a portion of the magnetic circuit of the machine or by superposing upon the main
magneto-motive force in a part of the magnetic circuit only an additional magneto-
motive force or counter-magneto-motive force, I accomplish the same result by
exciting those portions of the magnetic field under which commutation takes place
by a magneto-motive force independent of the magneto-motive force which excites
the other portions of the field. Such a construction is shown in Fig. 6, where some
of the parts are lettered as above.
The field structure is shown as consisting of a ring, provided with two pole-pieces
40, 41, connected with the ring by necks 56, 57, 58, 59, on which are wound
the exciting coils 42, 43, 44, 45. The coils 42, 45, are connected across the mains
in series with the adjustable resistance 49, while the coils 43, 44, are connected
across the mains in series with the adjustable resistance 48.
It will be seen that the flux through the coils under commutation is furnished
by the coils 43, 44, and can be maintained at such a value that the machine will
run sparklessly, without reference to the excitation of the necks 56, 57.
In the condition of slowest speed, if the machine is running as a motor, both
resistances 48, 49, are cut out entirely, that is to say, the switches 52 and 53, are
pushed to the extreme left and to the extreme right respectively. The field strength
is then a maximum. If now the arm 53, be pushed to the left, the current in the
exciting coils 42, 45, will be weakened, and the flux through the necks 56, 57, will

page_text: be decreased, which will increase the speed of the motor. This may be carried
so far as to allow the lines of force from 57, to return through the neck 56, and
the lines of force from 58 to return through 59; which will cause the electromotive
forces induced in certain portions of the armature to be opposite in direction to
those in other portions, and still further decrease the counter-electromotive force
of the armature, and increase the speed.
In this case, however, and in any case in which the magneto-motive forces of
the two necks of either pole-piece are unequal, there will be a certain tendency
for a portion of the flux to return through the pole-pieces 40 and 41, without
cutting the armature, that is to say, 56 and 59, will form magnetic shunts for the
magneto-motive forces of 57 and 58. To avoid this, I prefer to cut slots 55, in
the pole-pieces, as shown, of sufficient width and sufficient depth to prevent this
effect from becoming unduly large.
If in any of the conditions above supposed, the machine is running in such a
direction that the brushes are set under the necks 56 and 59, it is obvious that
the manipulations would be opposite. The machine is thus adapted to act both
as a generator and as a motor, and to run in either direction, with a wide range
of voltages and speeds.
The variable resistances 48, 49, may be of any preferred type, but are shown
as continuous coils, connected at intervals to the segments over which sweep the
arms 52, 53. It is preferable to make these arms of such width that the circuit
is not opened in passing from one plate to the other.
It will be obvious that my invention is not limited to shunt wound machines,
nor to any particular type or structure, and that various changes may be made
without departing from the spirit of my invention.
Having now particularly described and ascertained the nature of the said in-
vention and in what manner the same is to be performed, I declare that what I
claim is:
1st. The method of producing and varying the magnetic flux in a dynamo-electric
machine, which consists in creating a magneto-motive force in a magnetic circuit
composed, at one or more points, of several branches, generating, in one or more of
said branches, a second magneto-motive force, and varying said second magneto-
motive force at will to vary the total flux through the machine, while maintaining
a strong flux through those branches of the magnetic circuit which furnish the
field for the coils under commutation.
2nd. The method of regulating the speed of an electric motor, which consists
in varying the total flux through the armature at will within wide limits to vary
the speed of the motor, and maintaining at all speeds a strong field at those portions
of the pole-pieces under which the commutation takes place, substantially as
described.
3rd. The method of varying the speed of an electric motor, which consists in
varying the total flux through the armature at will within wide limits, to vary the
speed of the motor, and maintain at all speeds a strong and approximately constant
field at those portions of the pole-pieces under which the commutation takes place,
substantially as described.
4th. The method of varying the speed of an electric motor, which consists in
generating a flux nassing through the coils under commutation by a practically
constant magneto-motive force, and generating a second flux passing through
other coils of the armature, by an independent magneto-motive force, and varying
said second flux at will independent of the conditions of the main circuit.
5th. The method of avoiding sparking in a dynamo electric machine, which
consists in exciting those portions of the field-magnets under which commutation
takes place with a magnetism independent of the magnetism exciting the remaining
portions of the field-magnets, and varying the said independent magnetism at
will, independent of the conditions of the circuit, to vary the total flux of the
armature,

page_text: 6th. In an electric motor, the combination with the field-magnets and armature,
of means for adjusting and varying at will the magnetic flux passing through a
portion of each or any pole-piece, without greatly affecting the quantity passing
through the portion of the pole-pieces furnishing the field for the coils under
commutation.
7th. In an electric motor, in combination with the armature and field-magnet, a
switch for increasing the flux passing through one tip of one of the pole-pieces,
and for at the same time diminishing the flux through the center of the pole-pieces
to vary the speed of the motor without causing sparking.
8th. In an electric motor, the combination of a field-magnet and armature,
main field-magnet windings, an auxiliary field-magnet winding wound in a slot
in one or more of the pole-pieces in such a way as to embrace only a portion
thereof, and a switch for varying the current in the auxiliary winding, substantially
as described.
9th. In an electric motor, the combination of a field-magnet and armature, main
field-magnet windings, an auxiliary field-maguet winding surrounding a part only
of one or more of the pole-pieces, and a switch for varying and reversing the
current in the auxiliary winding, substantially as described.
10th. In an electric motor, the combination of a field-magnet, an armature,
main field-magnet windings, auxiliary field-magnet windings, and a switch adapted
to strengthen the field acting upon the coils under commutation and at the same
time to weaken the total flux through the armature.
11th. In an electric motor, the combination of a field-magnet, an armature,
main field-magnet windings, auxiliary field-magnet windings, and a switch and a
resistance adapted to gradually strengthen the field acting upon the coils under
commutation and at the same time to weaken the total flux through the armature,
substantially as described.
12th. In an electric motor, the combination of two sources of magneto-motive
force, acting upon separate magnetic circuits terminating in a common pole-piece,
and means for varying at will within wide limits that one of the two sources of
magneto-motive force which does not furnish the flux for the coils under commuta-
tion to vary the speed of the motor without materially decreasing the flux through
the coils under commutation, substantially as described.
וד
A T 1000
PHILIP M. JUSTICE,
Chartered Patent Agent, London, For the Applicant.