Improvements in Alternating Current Motors, applicable for Use as Transformers.
Year: 1893

page_text: και οι Αμμανατ
Complete Specification Left, 3rd July, 1893-Accepted, 3rd July, 1894
COMPLETE SPECIFICATION.
Improvements in Alternating Current Motors, applicable for Use
as Transformers.
I, OLOF DAHL, Electrician, of Paterson, in the County of Passaic and State of
New Jersey, United States of America, 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:-
The object of my invention is to provide an alternating current electric motor
which can be operated from one of the ordinary alternating currents with the two
feeding wires commonly used for electric lighting purposes and which will be
efficient in utilizing the current, as well as in running at a practically constant
speed.
Broadly speaking my invention consists in passing the alternating current from
a suitable electrical source through a commutated armature circuit and field
winding in series and when the speed of the motor has become synchronous with
that of the generator passing the alternating current uncommutated through the
armature and leading a commutated current from the armature through one or more
exciting field windings.
It is well known that certain forms of alternating current machines may be
connected up in circuit with an ordinary alternating current generator if they have
first been brought to synchronism with the generator and that they will continue to
run in synchronism with the generator as long as current is supplied up to a
certain limit of load when loaded above which limit they will stop running.
Such motors are quite efficient but they labour under the disadvantage that in
their use some outside power must be relied upon for starting them and that they
have to be excited with a continuous current.
Structurally considered my invention consists in adding to a motor of the class
described a commutator connected to the usual or to an auxiliary winding in the
same manner as in ordinary continuous current machines together with a switch
or switches so arranged that by turning the switch or switches to one position the
alternating current will be directed through the armature by means of the said
conmutator and its brushes, and also through the ordinary field-exciting winding
or an auxiliary field winding in series and secondly after the motor has torque
enough to start and when the armature has reached synchronism in changing
circuits by means of the said switch or switches so that the alternating current-
feeding wires will be connected to the collector rings only and the commutator
brushes will be connected ene to each end of the exciting field-winding and a
continuous current will be delivered from said commutator for constantly exciting
It is obvious that
the field while the motor is running as a synchronous motor.
the apparatus here described may be employed as a motor-dynamo it being necessary

page_text: to that end simply to take off current from the brushes through a branch supplying
electric lights, or other electrical translating devices.
A motor having the described structure will be entirely self-contained in that it
is self starting and self exciting and will run at a speed which is practically
constant when the motor is in synchronism with the generator.
By running in synchronism it is meant that the speed of the motor is always
in a certain fixed relation to that of the generator or that one pole of the motor is
passed by a certain point in the armature for every alternation of the current in
the feeding wires.
It is of course desirable that the starting of the motor should be accomplished
with as little sparking as possible and with an even torque. It is also desirable
there should be no dead point to interfere with the successful starting of the
apparatus. At the same time in order to maintain synchronism it is preferable to
employ a type of winding for the armature having well defined poles resulting from
aggregations of wire in compact masses which arrangement is antagonistic in a
degree to the objects just mentioned. For reconciling the conflict indicated I
provide or may provide two sets of armature windings independent of each other
and differently arranged upon the armature core. The first of these windings I
may call a distributed drum winding the arrangement being such that the starting
of the motor is accomplished with an even movement when the starting current
traverses the said winding this result being due to the fact already stated that
the winding is distributed over the face of the armature with substantial regularity
and evenness. The second winding is of the shuttle type and it may properly be
called a synchronizing shuttle winding. After the motor has been started and
brought to synchronism the drum winding is cut out of the alternating circuit and
the shuttle winding is brought into place. By reason of its well defined poles
this winding tends in an obvious manner to maintain synchronism more strongly.
By means of the distributed drum winding above described dead points are
avoided and the starting is smooth and easy. After the switch has been reversed
and the commutator brushes have been connected through the exciting field the
same character of winding that is to say the distributed drum winding brings it
about that the current used in exciting the field is less fluctuating whereby
hysteresis is avoided.
I have taken the drum and the shuttle winding as types especially adapted to
the needs of my apparatus but other types might be chosen and they would be
equivalent to those above described provided they accomplished the same results in
substantially the same manner.
Besides the advantages for power purposes of a machine constructed according
to the principle of my invention it has other advantages in that it may be used as
a transformer for converting for example alternating currents into continuous
currents or for transforming single-phase alternating currents into multiphase
currents of the same class.
I have illustrated my invention in the accompanying drawings in which
Fig. 1 is a diagram of an apparatus embodying my invention showing two field
windings and one armature winding in the motor.
Fig. 2 is a diagram of a motor and switch apparatus the motor having two field
windings as in Fig. 1 and two armature windings.
Fig. 3 is a diagram of a motor and switch showing one field winding and two
armature windings.
Fig. 4 is a similar diagram showing one field winding and one armature winding.
Fig. 5 is a diagram of a motor and switch the motor having a single field with
two windings and a double armature each of which has a single winding.
Fig. 6 is a similar diagram of a motor having two fields and two armatures.
Fig. 7 is a diagram of a multipolar motor having two field windings and one
armature winding.
Fig. 8 is a similar diagram in which the field of the motor is represented as
having two windings and in which the armature also is shown with two windings

page_text: of different types one of the last named windings being an exciting winding and
the other being for the purpose of starting, and
Fig. 9 shows a similar arrangement of armature windings adapted to be used
with a two-pole field.
For the sake of simplicity the motor is shown in most of the figures of the
drawing as a bi-polar motor the armature of which is a so-called Siemens shuttle
armature and the commutator a two-part commutator. An alternating current
motor constructed in this way would with the number of alternations per minute
commonly used in the United States of America run at a speed of 7,500 revolutions
per minute. Such a speed would generally be too high but by increasing the
number of poles say to six as shown in Figs. 7 and 8 the motor would have a
proportionately smaller number of revolutions that is in the case mentioned 2,500
revolutions per minute. I shall therefore ordinarily employ motors having a
larger number of poles than two but I may where the conditions are favourable
use that number only and for the sake of clearness as already stated I have
illustrated a two-pole motor.
Referring to the drawings by letter A represents a converter or other source of
alternating currents connected by wires 1 and 2 to the terminals 3 and 5 of a
switch B at c is shown a special switch by means of which the alternating current
can be cut off from the motor. The switch B has three pivotal terminals 3, 5
and 4 and six terminals 9, 10, 11, 12, 13, 14, in the range of movement of the
switch-bars 6, 8 and 7, which constitute the moving parts of the switch. The
switch is moved by means of an operating bar of insulating material.
The arrangement of the parts is such that while the switch-bars are always iu
contact with the pivotal terminals 3, 5, and 4, they may rest at the opposite ends
either upon the terminals 10, 12, and 14, simultaneously or when reversed upon the
terminals 9, 11 and 13. The former position is shown in full lines in Fig. 1, the
latter in dotted lines in the same figure.
The motor shown at D is provided in the form illustrated in Fig. 1 with two
On the
windings 15 and 16 on its field and a single winding 17 on its armature.
shaft of the armature is mounted a two-part commutator 18, pressed upon by the
usual commutator brushes 19 and 20 while upon the opposite end of the armature
shaft are mounted two collector rings 21 and 22 the former being pressed upon by
a brush 23 and the latter by a brush 24. The armature winding 17 is joined at
one end to the two parts of the commutator 18 and at the other end on the one
side to the collector 21 and on the other to the collector 22. The armature shaft is
represented in Fig. 1 as carrying a loose pulley 25 and a tight pulley 26 for
transmitting the power developed in the motor. While the use of a loose and a
tight pulley is not absolutely essential yet I prefer to employ this construction the
belt being run on the loose pulley until synchronism is attained and afterwards
shifted to the tight pulley.
The full lines at the switch in Fig. 1 represent the position of the parts when it
is desired to start the motor. Tracing the circuit from the source A it goes over
the following course; wire 1, switch c, terminal 3, switch bar 6, terminal 10, field
winding 15, brush 20, commutator 18, and armature winding 17, the other side of
the commutator, brush 19, terminal 4, switch-bar 7, terminals 14 and 12, switch-bar 8
and wire 2.
Under the conditions described one of the field windings is in series with the
armature and it is evident that the motor will start up and run as a series motor.
The number of turns in the field winding 15 is so proportioned that the motor will
be capable of running when started at a speed higher than synchronism. Now the
switch B is kept in the position shown in the full lines until the speed of the motor
has risen to or somewhat above the point of synchronism after which the switch is
thrown over to its reverse position shown in dotted lines. The current now passes
by way of the wire 1, switch c, terminal 3, switch-bar 6, terminal 9, and brush 24,
to the collecting ring 22, whence it goes through the armature winding to the
collector 21, and is led off by the brush 23, and its connected wire, to the

page_text: terminal 11, switch-bar 8, terminal 5, and wire 2. At the same time a circuit is
made from the commutator brush 19, terminal 4, switch-bar 7, terminal 13, through
the winding 16, of the field magnet, to the brush 20, thereby causing the output
from the armature to traverse the field coils in series producing alternate north and
south poles with a constant field of force. The motor will then fall into step and
will continue to run synchronously with the generator and load may be thrown on
by means of the loose and fixed pulleys 25 and 26 or by friction clutches, or any
other preferred means.
The principle of operation is precisely the same in the apparatus illustrated in
Fig. 2 as in that shown in Fig. 1 and already described. The only point of
difference is that the armature in the apparatus illustrated in Fig. 2 has two
windings the terminals of one of which are joined to the two parts of the
commutator while the terminals of the other are connected to the collector rings.
Fig. 3 illustrates a motor designed to carry out the principle of my invention
and having one field winding and two armature windings. With this apparatus the
form of the switch is modified by the addition of switch-bars 27, and 28 and
terminals 29, 30, 31, 32, 33, 34, 35 and 36.
The original course of the current from the generator is by way of wire 1,
switch-bar 6, terminal 10, brush 19, commutator 18, on one side one of the armature
windings opposite side of commutator, brush 20, switch-bar 7, beyond which the
current divides, and passes in multiple through the upper and lower field windings
from the terminals 32 and 33 with which the switch-bar 7 is originally in contact
to the terminals 30 and 29, respectively with both of which the switch bar 8 is
originally in contact, and thence by way of switch-bar 8, terminals 5, and wire 2,
back to the source from which it emanates. The alternating current employed in
starting this type of apparatus is divided between the coils of the field magnet
passing through them in multiple after traversing the armature. The start is
made in this way, and after synchronism has been reached the switch is reversed
with the result that the current from the alternating source passes in at the
terminal 3, switch-bar 6, and terminal 9 to the ring 21, through one winding of
the armature to the ring 22, and thence back by way of the terminal 11, switch-
bar 8, terminal 5, and wire 2. Simultaneously with the reversal of the switch,
the external circuit of the armature is completed as follows; From brush 19 to
terminal 35, switch-bar 28, terminal 34, upper magnet coil, terminal 30, switch-
bar 27, terminal 31, lower magnet coil terminal 13, switch-bar 7, terminal 4 and
brush 20. The field magnet coils are connected up in series with the brushes, so
that there is a constant excitation of the field, with alternate north and south
polarization, requiring only synchronism with the exciting source, in order to
produce an efficient motor.
In Fig. 4 both the armature and the field have a single winding each. The
switch is identical with that shown in Fig. 3. It should be observed that the
switch-bars 8, 34, and 7 in both instances are shaped at their free ends so as to
bridge at need two adjoining terminals. The circuit traversed by the starting
current is the same as that already described for Fig. 3 with the difference that
the armature winding included in the circuit is the only winding the armature has
whereas in Fig. 3 it is one of two armature windings. The difference is substan-
tially identical with that which exists between the apparatus shown in Fig. 1 and
that shown in Fig. 2.
In Fig. 5 the arrangement is identical with that shown in Fig. 2 except that in
Fig. 5 there are two independent armatures corresponding to the two windings
in Fig. 2.
Fig. 6 is substantially identical with Fig. 2 also the main difference between the
motors illustrated in the two figures being one of structure and consisting in using
two armatures and two field magnets in place of the doubly wound armature and
field magnet of Fig. 2.
Referring now to Fig. 7 and the multipolar motor there illustrated it will be
seen by tracing the circuit from point to point, that its course is precisely identical

page_text: with that of the circuit in Fig. 1. Instead of a two-pole field Fig. 7 shows a field
aving six poles and a corresponding change is made in the number of commutator
sections. For clearness of illustration the collector rings are represented as
surrounding the commutator but these differences are manifestly no departures from
the essential structure of the apparatus first described in this Specification.
In Fig. 8 is shown a machine having six poles with double field windings and
with two independent armature windings of different types. The outer winding
of the armature (designated by the character 46) is a distributed winding of the
drum type corresponding to the usual winding for the six-pole machine having a
drum armature. The inner winding is of the shuttle type and is indicated at the
cylindrical gaps or openings 47. In order to make the arrangement of the circuits
perfectly clear I may say that the original circuit is by way of wire 1, terminal 3,
switch-bar 6, terminal 10, the outer winding of the field magnets as far as the
point 45 thence to the brush 19, through the outer winding of the armature,
brush 20, terminal 4, switch-bar 7, terminals 14 and 12, switch-bar 8, terminal 5,
and wire 2. By reason of the fact that the outer armature winding is spread in the
manner illustrated the tendency to rotation is evenly distributed and the armature
begins to rotate with a very even torque. When synchronism has beeu attained the
switch B is reversed whereupon a new circuit is made as follows:-wire 1, terminal 3,
switch-bar 6, terininal 9, ring 21, and the shuttle windings of the armature, ring 22,
terminal 11, switch-bar 8, terminal 5, and wire 2.
It is obvious that the alternating current traverses the shuttle windings of the
armature which being aggregated bodies of wire at fixed intervals are subject to a
more pulsating action than the outer winding 46 for which reason the tendency of
the motor is now strongly synchronizing which is the effect I am seeking to
produce.
Simultaneously with the closing of the new circuit through the armature I have
an exciting circuit passing from brush 19, through the inner coils of the field
magnets successively and out to the terminal 13, switch-bar 7, terminal 4, back to
the brush 20. Manifestly a magnetic field with alternate north and south polarity
is now excited by the motor current. Consequently as long as synchronism is
maintained the motor will do its work.
Fig. 9 illustrates the two types of armature winding applied to a bi-polar motor.
The distributed drum winding is shown at 46, and the synchronizing shuttle
winding at 48.
The action is identical in principle with that of the six-pole motor
shown in Fig. 8.
The rectifying commutator shown in Figs. 1, 2, 3, 4, 5 and 6 is represented as a
two-part commutator and the winding of the armature as an ordinary shuttle
winding mainly for the purpose of avoiding complications in the diagrams. In
practice I should prefer to use other types of winding and a commutator having
many segments connected to such windings so as to get advantage of distribution
which has already been referred to in the foregoing Specification. It will be
observed that Figs. 7, 8, and 9 represent commutators with a larger number of
segments than two and in order to secure the best results I propose to multiply the
number beyond the limits indicated in the drawings on a principle which is well
understood in the art of dynamo electric machinery.
It lies within the scope of the present invention to couple up two machines
mechanically and electrically in such a manner that one shall serve the purposes of
starting and exciting and the other those of synchronous operation. In this case
one of the machines would be provided with the distributed winding and multiple
art commutator and the other with the concentrated winding and the collector
rings. It would not be necessary that the two machines should have the same
number of poles but one machine could be say a bi-polor machine while the other
might have six or any other convenient number of poles.
To illustrate the employment of my machine as a motor dynamo I show in
Fig. 2 a derived circuit including electric lamps 50, 50. Any kind of electrical
translating devices might be employed in place of the lamps.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
-claim is :-
1. The method of operating synchronous alternating current electric motors
which consists in passing the alternating current through a commutated armature
circuit and field winding in series and when the speed becomes synchronous with
that of the generator passing the alternating current uncommutated to the armature
and passing commutated currents through one or more exciting field windings
substantially as set forth.
2. The method of operating synchronous alternating current electric motors
which consists in passing the alternating current through the armature and field
winding in series and afterwards passing the alternating current through the
armature alone and leading commutated current through an exciting field
substantially as set forth.
3. The method of operating synchronous alternating current electric motors
which consists in first passing alternating currents through the armature winding
by means of a commutator connected as in the ordinary continuous current
armatures having greater number of segments than the number of field poles of the
motor and afterwards passing alternating currents uncommutated to the armature
for synchronous running.
4. A dynamo electric machine consisting of a field magnet an armature having a
rectifying commutator with more segments than number of poles of the motor and
a pair of collector rings connected into the armature winding or winding brushes
for said commutator and said collector rings and means for directing current
alternately through the commutator to the armature and field in series and to the
collector rings and the armature circuit alone as and for the purposes set forth.
5. A dynamo electric machine consisting of a field magnet having a winding or
windings included in the external circuit of the armature in combination with the
said armature having a rectifying commutator and a pair of collector rings
connected to the armature winding or windings a source of alternating currents and
a switch and connections from the switch in one position to the field winding on one
side and commutator brushes on the other and in the other position to the collector
brushes the reversal of the switch serving also to complete the circuit of the
armature from the commutator through the field winding as and for the purpose set
forth.
6. A dynamo electric machine consisting of field magnet armature having
rectifying commutator and collector rings connected to its winding and a switch
serving to direct first alternating current through the commutator to the armature
and field in series and afterwards alternating current through the collector rings to
the armature and continuous current through the field-magnet winding substantially
as and for the purpose set forth.
7. In a dynamo electric machine or alternating current electric motor an
armature having two sets of windings one being a distributed winding for purposes
of starting and the other a concentrated winding for purposes of synchronism as
and for the purpose set forth.
8. In a dynaino electric machine or electric motor a field magnet having a winding
included in the external circuit of the armature in combination with the said
armature having independent windings one of which is distributed and the other
concentrated substantially as described a source of alternating currents and a switch
for closing the circuit of the said source first through the distributed armature
winding and a portion or all of the field windings in series and then by a
reversal of the switch through the concentrated windings as and for the purposes
set forth.
9. A source of alternating current and an electric motor connected therewith and
an intermediate switch the said motor having a circuit through its commutator and
amature and one or more field windings in series another circuit through its

page_text: armature alone and a third circuit from the commutator brushes through a field
winding or windings the said switch being adapted to control the said circuits as.
and for the purpose set forth.
10. A source of alternating current and an electric motor provided with the
usual field magnet and armature the said armature being provided with a rectifying
commutator and a pair of collector rings the said motor having a circuit through
the commutator brushes including the armature and a field winding in series.
another circuit through the collector brushes and the armature and a third circuit
from the commutator brushes through a field winding or windings and a switch
intermediate between the said source and the said motor the said switch being
adapted to control the said circuit as and for the purpose set forth.
Dated this 2nd dow of Iul 1802
TONGUE & BIRKBECK,
34, Southampton Buildings, Chancery Lane, London, W.C.,
Agents for the Applicant.