Improved Means for Controlling the Induced Currents in Short- circuited Windings of the Armatures of Electro Motors Worked with Rotary Phase Alternating Currents.
Year: 1894

page_text: Date of Application, 3rd Nov., 1894
Complete Specification Left, 1st Aug., 1895-Accepted, 14th Sept., 1895
PROVISIONAL SPECIFICATION.
[Communicated from abroad by Messrs. SIEMENS & HALSKE, of Berlin, in the
German Empire, Electrical Engineers.]
Improved Means for Controlling the Induced Currents in Short-
circuited Windings of the Armatures of Electro Motors Worked
with Rotary Phase Alternating Currents.
We, SIEMENS BROTHERS & Co. LIMITED, of 12 Queen Anne's Gate,
Westminster, in the County of Middlesex, Electrical Engineers, do hereby
declare the nature of this invention to be as follows:-
-
For starting electro motors worked by rotary phase alternating currents, whose
armatures only work with induced currents, it is necessary to provide special
devices for preventing sudden and considerable changes of potential difference.
The present invention relates to a device whereby a too rapid increase of the
current in the armature circuit on starting is effectually prevented.
For this purpose several separate windings are provided on the armature, these
being so connected on starting that the electro motive forces therein neutralise
each other to a greater or less' extent. As soon as the motor has attained a
sufficient speed, the separate windings are so connected that the full electro motive
force of each winding is utilised for producing current.
According to one arrangement for this purpose as applied for simplicity's sake
to a bipolar motor, the armature has two windings for rotary phase currents which
are arranged for star connection.
Both windings are arranged in exactly the same manner on the armature; they
only differ in the one having more turns than the other.
Referring to Fig. 1 of the accompanying drawing, the commencements of the
windings are situated at exactly the same point of the armature. If therefore the
commencement A' of the one winding be connected with the commencement a¹ of
the other winding and in the same manner, A' with a' and A³ with a' the electro-
motive forces of each two windings will be opposed to each other, and would
completely neutralise each other if the number of turns were exactly the same in
each. With unequal turns a difference of electromotive force exists, the extent of
which can be greatly varied, according to the difference in the number of turns.
Not only is the strength of the currents reduced thereby, but still more so the
ampère turns, because only the difference of the number of ampère turns comes
into account.
1
If now, after the motor has attained a sufficient speed, the three com-
mencements A A' A³ be connected with each other, as also a a' a³, as at Fig. 3,
the electromotive forces in' each winding will produce the full strength of current,
and the motor will now work with only a small loss of speed.
The conditions would not be altered if the first mentioned connections A¹ a',
A a², A' a be allowed to remain; these connections might therefore be made
permanent, and only the connections A¹ A' A³ be made to open and close as
at Fig. 2. It is also immaterial whether the neutral or zero points D and d be
connected with each other or not.

page_text: The arrangement may also be used with a greater number of steps, as indicated
at Fig. 4.
The first winding with most turns is A¹ B¹, A' B³, A' B', whose ends are
connected to a common zero point D.
The second winding with less turns is a¹ b¹, a² 3, a 6; the ends b¹³ ³ are also
connected to the zero point D.
The second winding is divided into a series of steps that are in connection with
a row of contacts opposite which are three contact rails that are connected with
each other.
A moveable brush serves to convey the current from a contact of each row to
the corresponding rail, and the three brushes are connected together so as to be
simultaneously shifted from one contact to another. On starting the electromotor,
the brushes are situated at b¹³; the connections are then as described with
reference to Fig. 1.
If now the three brushes are moved to the next contacts, one section of the
second winding will be closed on itself and thus be suitably connected for rotary
phase currents, the other parts of the second winding remain connected in
opposition to the first one.
In this section therefore the total electromotive forces must be greater. The
farther the brushes are mored towards a¹ a² a³, the greater will be the number of
sections of the second winding that are closed on themselves and thus suitably
connected for rotary phase currents, and the greater will be the action of the
electromotive force in the first winding.
In the foregoing it has been assumed that the two windings are situated exactly
one over the other, and are consequently identical with the exception of the
number of turns.
According to another modification, the two windings may have an equal number
of turns, but are shifted relatively to each other, so that the phases of the induced
electromotive forces are also shifted relatively to each other; then according as
the connections are made between the ends of the two windings, a greater or less
number of ampère turns may be produced.
In like manner other modifications may be made for carrying out the essential
feature of the invention namely, providing separate windings on the armature and
so connecting these that at starting, the electromotive forces of the two windings
are caused to more or less neutralise each other, while when the motor has attained
full speed the full electromotive force of each winding is made available for
producing current.
Dated this 3rd day of November 1894.
ABEL & IMRAY,
Agents for the Applicants.
COMPLETE SPECIFICATION.
Improved Means for Controlling the Induced Currents in Short-
circuited Windings of the Armatures of Electro Motors Worked
with Rotary Phase Alternating Currents.
We, SIEMENS BROTHERS & Co. LIMITED of 12 Queen Anne's Gate,
Westminster, in the County of Middlesex, Electrical Engineers, 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 :-
For starting electro motors worked by rotary phase alternating currents, whose
armatures only work with induced currents, it is necessary to provide special devices
for preventing sudden and considerable changes of potential difference.

page_text: The present invention relates to a device whereby a too rapid increase of the
current in the armature circuit on starting is effectually prevented.
For this purpose several separate windings are provided on the armature, these
being so connected on starting that the electro motive forces therein neutralise each
other to a greater or less extent. As soon as the motor has attained a sufficient
speed, the separate windings are so connected that the full electro motive force of
each winding is utilised for producing current.
According to one arrangement for this purpose as applied for simplicity's sake
to a bipolar motor, the armature has two windings for rotary phase currents which
are arranged for star connection.
Both windings are arranged in exactly the same manner on the armature; they
only differ in the one having more turns than the other.
armature.
Referring to Fig. 1 of the drawing accompanying the Provisional Specification,
the commencements of the windings are situated at exactly the same point of the
If therefore the commencement A' of the one winding be connected
with the commencement a¹ of the other winding and in the same manner, A³ with a²
and As with a³, the electromotive forces of each two windings will be opposed to
each other, and would completely neutralise each other if the number of turns were
exactly the same in each. With an unequal number of turns a difference of
electromotive force exists, the extent of which can be greatly varied, according to
the difference in the number of turns. Not only is the strength of the currents
reduced thereby, but still more so the ampère turns, because only the difference
of the number of ampère turns comes into account.
If now,
after the motor has attained a sufficient speed, the three commence-
ments A' A' A' be connected with each other, as also a¹ a² a³ with each other as
in Fig. 3, the electromotive forces in each winding will produce the full strength
of current, and the motor will now work with full power.
:
The conditions would not be altered if the first mentioned connections A¹ to a',
A² to a², A' to a', were allowed to remain these connections might therefore be
made permanent, and only the connections A' to A' to A³ be made to open and
close as in Fig. 2. It is also immaterial whether the neutral or zero points D and d
be connected with each other or not.
The arrangement may also be used with a greater number of steps, as indicated
in Fig. 4.
The first winding with the greatest number of turns is A' B', A² B³, A³ B³, the
ends B₁ B, B, of which are connected to a common zero point D.
The second winding with fewer turns is a b', a' b³, a³ ³; the ends b¹³ ³ are
also connected to the zero point D.
The second winding is divided into a series of steps that are in connection with
a row of contacts opposite which are three contact bars that are connected with
each other.
A moveable brush serves to convey the current from a contact of each row to
the corresponding bar, and the three brushes are connected together so as to be
simultaneously shifted from one contact to another. On starting the electro motor,
the brushes are situated at 1; the connections are then as described with
reference to Fig. 1.
If now the three brushes are moved to the next contacts, one section of the
second winding will be closed on itself and thus be suitably connected for rotary
phase currents, the other parts of the second winding remain connected in opposition
to the first winding.
In this section therefore the total electro motive forces must be greater. The
farther the brushes are moved towards a' a' a' the greater will be the number of
sections of the second winding that are closed on themselves and thus suitably
connected for rotary phase currents, and the greater will be the action of the
electromotive force in the first winding.
Figs. 5 and 7 of the accompanying drawings are longitudinal sections of machines
adapted for carrying out this invention, Figs 6 and 8 shewing the respective

page_text: windings for the primary currents, the stationary outer windings being of kind
suitable for producing rotary fields. Such windings are in the first place all
polyphase current windings (for two phase and three phase currents) but moreover
an ordinary second winding may be used which by itself generates only poles of
alternating sign at fixed points of the annular iron core, since in this case also a
rotation of the magnetic field is produced by the action of the secondary currents
induced in the rotating armature so that the magnetic behaviour of this motor in
its normal motion differs very little from that of polyphase current motors.
In Figs. 6 and 8 is shewn that part of the winding which is marked in
Fig. 1, A, A, A, D). It may be supposed that in this winding diagram each line
represents two wires. The second winding a₁ a, a, d in Fig. 1 lies exactly as the
winding shewn in Figs. 6 and 8. It may now be supposed that in this winding
diagram each line represents one wire, that is to say, this winding has only half the
number of turns of the former winding. As already stated the neutral points D d
are connected, also A, to a₁, A₂ to a₂, A3 to a. In the arrangement shewn in
Figs. 5 and 6 the three points A, A, A, are connected to three contact
rings R₁ R, R, which are fixed on the shaft and on which bear three insulated
brushes F, F, F, (of which F, only is shewn in Fig. 5) for leading off the induced
current. These brushes are connected to three contacts C₁ C, C, of a switch
having a handle attached and carrying three metallically connected rubber springs
by which the contacts can be short circuited. When the contacts are disconnecte:l,
the motor runs with opposed currents, when the contacts are connected, the
motor runs with currents normally acting together. The switch for this purpose
can be situated in any convenient place and may be connected to the switch for
the primary windings of the motor.
1
2
In the form of motor shown in Figs. 7 and 8 three insulated contacts P₁ P, P,
(of which P, only is shewn in Fig. 7) are connected respectively to the ends A, A, A,
of the windings. On the axis, is fitted with a feather, a sliding sleeve H so that
it revolves with the axis, but can, while the motor runs, be slid to and fro by the
lever J, screw spindle K and band wheel L. This sleeve carries insulated from
it a metal ring with three springs which, on pushing the sleeve towards the
armature; come on the contacts P₁ P, P, and short circuit them on one another.
When they are not short circuited, the motor operates with opposing currents, but
when they are short circuited, it works with normal currents. Instead of the three
contacts P P P rotating with the armature, 3n contacts might be used, these
being connected to the winding as in Fig. 4 and short circuited by springs on a
sliding sleeve as above described. On putting the motor in circuit the three
brushes stand in the positions b₁ b, b, (Fig. 4), the connections being then as in
Fig. 1. When the brushes are pushed on to the nearest contacts, one step of the
second winding is closed on itself to form a rotary current connection, the rest of
it remaining opposed to the first winding. In this portion the total of the electro-
motive forces is increased. The farther the brushes are moved towards a₁ a, a, so
much the more are the portions of the second winding closed on themselves to form
a rotary current connection, and so much the more does the electromotive force of
the first winding come into action. An example may shew this increase. Assuming
that the winding A B has 3 times 8 turns all connected in series, that ab has
If the resistance of each
3 times turns forming the steps mentioned above.
convolution is always 1 ohm and its electromotive force 1 volt, the five positions
of the brushes give the following values.

page_text: In position 1 the brushes are at the zero points and the two windings are con-
nected in opposition to each other. The first winding has 8 turns per branch
with 8 ohms resistance and 8 volts E.M.F. The second has 4 turns, with
4 ohms R, and 4 volts E.M.F. In the two together there are 12 ohms R, but
the total E.M.F. is only 4 volts so that the current strength is amp. In the
first winding of 8 turns there are
are
4 × 4
12
difference
8 × 4
12
12
ampere turns in the second of 4 turns
ampere turns; in the two, which are opposed, there is therefore the
4 x 4 16
12
12
=
ampere turns. In this position of the brushes, there is no
second circuit. When the brushes are moved by one step of the contacts there
are 3 turns of the second connected in opposition to 8 of the first winding. The
resistance is then 8+ 3 = 11 ohms, the total E.M.F. is 8 35 volts, the
current strength is therefore 5/11 amperes; there are
one and
25
5 x 3
11
ampere
being ampere turns.
11
5 x 8
11
1
ampere turns in the
turns in the other winding, the difference due to opposition
This arrangement is marked I II in the table. Now,
1
however there is a second circuit formed in each of the three branches of a turn
of the second winding as shown by Fig. 4. It is distinguished in the table by IIa.
In this coil there being 1 ohm R, 1 volt E.M.F. there is 1 ampere current
strength, so that there is 1 ampère turn in this circuit. When the brush is in this
place there are therefore
25 11 36
+ =
11
11
ampère turns. In a similar way, the other
lines of the table are calculated. It will be seen how the ampère turns increase
until in position 5 all the 12 windings count.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that
what we claim in respect of electromotors worked with rotary phase alternating
currents is
The subdivision of the armature windings into two or more portion's so combined
with connecting and disconnecting switches that the electromotive force can be
raised step by step, thus avoiding excessive strength of induced currents, whilst in
regular work the energy of all the portions is utilized.
Dated this 1st day of August 1895.
ABEL & IMRAY,
Agents for the Applicants.