Improvements in Electromotors for Alternating Currents.
Year: 1893

page_text: Date of Application, 31st July, 1893
Complete Specification Left, 31st May, 1894-Accepted, 7th July, 1894
PROVISIONAL SPECIFICATION.
Improvements in Electromotors for Alternating Currents.
I, JOHN AUGUSTINE KINGDON of 29 Marlborough Hill, St. John's Wood in
the County of London, Electrical Engineer do hereby declare the nature of this
invention to be as follows:-
:―
It is well known that if an ordinary electromotor is used with alternating
currents, strong secondary currents are induced in those armature coils which are
for the moment short circuited by the brushes, giving rise to excessive sparking and
heating of the commutator.
A
According to my present invention I construct the commutator of the motor with
thick plates or pieces of mica or other insulator between the bars or segments.
group of several brushes is arranged to make contact on one or more adjacent bars
of the commutator and a similar group of an equal number of brushes is arranged
to make contact on the opposite bars of the commutator. The brushes are insulated
from one another and are thiuner than the insulating material between the
commutator bars, so that a pair of adjacent commutator bars cannot be short
circuited by a brush. The brushes of each group may be arranged side by side or
one behind the other so that they make contact with the commutator bars in
succession.
To supply current to the armature I may employ a transformer wound with as
many secondaries as there are brushes in each group. Each secondary is connected
with a pair of opposite brushes, one being in each group. The secondaries are
insulated from one another except when they are connected in parallel by
commutator bars making contact with several brushes. It will be evident that as
the armature rotates each secondary supplies current to the armature as long as its
brushes make contact with commutator bars; when a brush is not in contact with
a bar, but touches one of the intermediate insulating plates, the corresponding
secondary is open circuited; but as the brushes of several other secondaries are in
contact with commutator bars, the armature current is never interrupted but
remains practically constant.
The primary of the transformer may be connected in series with the field magnet
coils of the motor or in parallel with these coils. Or the primary of the transformer
may be connected with the supply mains, another secondary winding being provided
in addition to the split secondaries for the armature, and connected in series with
the field magnet coils.
Other modifications of the circuits may be employed as for example the field
magnet coils may be split up into a number of different windings equal to the
number of secondaries and each connected in series with a secondary. The trans-
former may be attached to or form part of the motor, and the secondary coils may
be wound on the field magnets.
The armature and field magnet cores are constructed of soft iron plates of any
convenient form. In order to reduce the air gap to a minimum the armature
windings may be placed in slots or tunnels in the armature core. The armature
may be either of the drum or ring or of any other known suitable type. The field
nagnets may have two poles, or may be multipolar with any suitable number of
poles. When the armature is multipolar the windings and commutator bars may
e connected in any well known manner, and the brushes may be arranged in a
umber of groups corresponding to the number of field magnet poles.

page_text: According to another method of carrying out my invention, instead of using a
transformer with a number of split secondaries, I may split up the field magnet
windings into a number of coils equal to the number of brushes, and connect each
brush with one of these coils. The other ends of the coils are connected balf with
one supply main and the remainder with the other supply main. The coils are
arranged in two groups, each group having its outer ends connected together and
with one supply main while its inner ends are connected each to one of one group
of brushes. The armature is thus in series with two groups of split field magnet
coils, and is intermediate in position between them. The split coils may be
connected with the supply mains through additional undivided field magnet coils.
Instead of employing an armature of the ring or drum type with closed windings
I may employ one wound with a number of open coils, which are brought into use
consecutively as their commutator bars come into contact with the brushes.
The secondaries or split windings may have their resistances or number of turns
graduated so as to control the currents in the different circuits or these currents
may be regulated by means of adjustable resistances or choking coils inserted in
the circuits.
Instead of insulating the brushes one from another I may sometimes connect them
one with another through resistances or choking coils. Two or more commutators
may be fitted to the motor, or I may employ a commutator with two or more sets
of contact bars.
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1
COMPLETE SPECIFICATION.
Improvements in Electromotors for Alternating Currents.
I, JOHN AUGUSTINE KINGDON of 29 Marlborough Hill, St. John's Wood in
the County of London, Electrical 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:-—
If an ordinary electromotor is used with alternating currents of electricity
strong secondary currents are induced in those armature coils which are for the
moment short circuited by the brushes, giving rise to excessive sparking and
heating of the commutator.
In order to prevent the generation of these injurious currents, I construct the
commutator of the motor with thick plates or pieces of mica or other insulator
between the metallic segments which are connected with the armature windings.
In Fig. 1. is represented partly in section a commutator constructed in this
manner. The metallic segments S are comparatively thin and the insulating plates
are thicker than usual. A group of two or more brushes B, B, are arranged to
make contact on one or more adjacent bars of the commutator.
The brushes B₁ and B, are insulated from one another by a plate I and from
the brush holder by plates F F. The brushes are thinner than the insulating
plate M between the commutator segments S, so that a pair of adjacent
conmutator segments cannot be short circuited by a brush. The brushes of one
group B B, are connected with one another through a coil or coils of conductor,
and similar connections are provided for the brushes of the other group. The
resistances of the coil or coils connecting the brushes are so proportioned that the
currents set up in them by the action of the secondary induced electromotive
force in the armature coils, are not excessive, so that sparking at the brushes is
prevented. The conducting coils may be coils of wire provided in addition to the
ordinary windings of the motor. But I prefer to arrange the field magnet windings
of the motor so that they may be employed as resistances to check the secondary
currents induced in the armature coils, without loss of energy.

page_text: 3"
In Fig. 2 is illustrated a method in which there are two brushes in each group.
One pair B, and B, belonging to one group, are connected together through a pair
of field magnet coils F, and F, wound on the same magnet core and having their
outer ends connected together at T₁. The brushes B3 and B. belonging to the
other group are similarly connected through the coils F, and F, wound on the same
magnet core and having their outer ends connected at T. T₁ and T, are connected
each with one supply main. 1 and 2 are segments of the commutator connected
with the armature coil A. The alternating currents passing in the coils F, F, F, 1
', F₁
set up an alternating magnetic flux in the iron of the field magnets and armature.
The result is that a secondary electromotive force is set up in the coils A, and A..
As the currents due to these electromotive forces have to traverse the resistances.
of the coils F, and F,, F3 and F, respectively, they are much smaller than would
be the case if the coils A, and A, were short circuited by brushes touching simul-
taneously the commutator segments 1 and 2, and the corresponding segments
connected with the coil A.. Sparking at the commutator of the motor is thus
prevented. The coils F, and F, are wound side by side, or with twin wire or
sandwiched one with another on the same iron core and in the same direction so as
to have a strong inductive action, one on the other. The brushes B, B., and the
insulation separating them are so spaced that one brush is always in contact with a
commutator bar, and so that the armature current is never interrupted, and current
passes in one or other of the coils F, and F2. The brushes B, and B, are arranged
in a precisely similar manner.
According to a modification of my invention illustrated in Figs. 3 and 4, I
employ in connection with the electromotor an auxiliary transformer having two-
or more secondary windings S₁ and S2. Each secondary has one end connected
with a brush in one group and the other end connected with a brush in the other
group. The secondary S, is connected with the brushes B, and B, and the
secondary S with the brushes B, and B. The primary of the transformer P
is connected with a source of alternating current supply. In Fig. 4. the
secondaries S, and S, are connected with the respective brushes through the field
coils F, F, F, F.
2 3
Instead of splitting up the field magnet coils or the secondary coils of the
transformer into only two windings in each group I may split each group of
windings up into three or any higher number of windings.
In Fig. 5 is illustrated an arrangement in which each group of field coils is split. "
up into five separate windings Fi and F, each connected with one brush B.
A is the arinature. C is the commutator with metallic segments S separated by
insulating pieces i. The commutator C, as also in Figs. 3 and 4 is shown outside
the armature A merely for the purpose of clearness in the diagrams.
The five outside ends of the windings F, constituting one group of coils are all
connected together and to one supply main M₁. The other five windings F, are
connected in a similar manner to the other supply main M₂.
In Fig. 6 the secondary windings of the transformer are wound on the field
magnets of the motor. The field magnet coil P is the primary winding and is
connected with the source of alternating current. The secondary coils S, S₂ are
connected with the brushes B, B, B, B, as shown in the figure.
The motors described and illustrated in the drawings have but two field magnet
poles, and two groups of brushes, but it will be evident that any higher even
number of field poles may be employed in combination with an armature wound
so as to have a corresponding number of poles.
Both the armature and field magnets of the motor have their cores constructed
of thin sheet iron. As it is important to reduce the air gap between the magnet
iron and the armature core to a minimum the armature coils are wound in slots in
the armature core.
The armatures may be wound ring or drum or in any known suitable manner.
Adjustable resistances or choking coils may be employed in addition to the field
magnet or transformer coils.

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. An electromotor having more than one brush at each of its poles, such
brushes being insulated from one another, and connected with the supply mains
through the split windings of the field magnet coils substantially as described.
2. Splitting up the field magnet windings of an electromotor and utilising the
resistances of the split coils for checking the secondary currents induced in the
armature coils under the brushes.
3. Connecting the brushes of an electromotor with the split windings of an
auxiliary transformer as and for the purpose described.
4. An electromotor having groups of brushes insulated from one another at
the brush holders, but connected through conducting coils wound on the motor or
elsewhere.
5. The combination in an electromotor of a commutator having insulating bars
thicker than the brushes with two or more brushes at the poles insulated from one
another and with split windings of the field magnet coils.
6. Constructing an electromotor with primary and secondary coils on the field
magnets, the secondary coils being split up into two or more windings connected
with the brushes substantially as and for the purpose described.
7. In an electromotor having two or more separate brushes at each pole, insulated
from one another, utilising the resistance of conductors forming part of the windings
of the motor or of apparatus connected therewith to check secondary currents set
up in the armature coils and prevent sparking.
J. A. KINGDON.