Improvements in or connected with Alternating Current Electric Motors.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
Improvements in or connected with Alternating Current Electric
Motors.
I, ALEXANDER HEYLAND, of 57, Wasserstrasse, Frankfort-on-the-Main, in the
German Empire, Electrical Engineer, do hereby declare the nature of my invention
to be as follows:-
"
In changing the pole-number of alternating current motors (for the purpose of
varying the speed of rotation)-(with the exception of motors with "ring-wound
coils and a simple short circuit armature which are however rarely now used)
considerable difficulty has hitherto been experienced.
"
In modern drum-wound" motors with a wound short-circuiting armature the
pole number is changed by winding the motor for a given maximum pole number
and by so shunting part of the pole winding, when it becomes necessary to pass
from a greater to a less pole-number, that two or more poles of the same sign or
polarity in all cases are situated in juxtaposition, so as always jointly to form one
pole only. This enables the maximum number of poles to be readily reduced
to, or some other fraction of it.
This method of operation is, however, attended by two main drawbacks, which
alone may be said to preclude it from being successfully applied to practical
purposes.
In the first place the diminution of the pole number in this case is only owing to
the fact that, by reason of the partial shunting of the poles, currents, flowing side
by side, neutralize each other's action, which means that the space allotted for the
winding is not fully taken advantage of and that the distribution of the magnetic
field is defective.
Secondly the rotary short-circuiting armature may be shunted or reversed only
through the medium of a comparatively great number of sliding rings; but from
practical considerations the number of these should not exceed a somewhat narrow
limit.
The present invention consists of certain winding arrangements which when it
is desired to change the number of poles, render any shunting on the short circuit
armature superfluous, and obviate the drawbacks above stated in the shunting of
the exciting armature.
The requisite change in the pole number of the exciting armature is to be
effected first and foremost by winding it for a small number of poles and by so
shifting certain parts of the windings or coils as to develope successive or
"follower" poles, whereby the pole number may subsequently be increased at
will.
Taking for example a single double-pole monophase winding, the poles being N
and S.
Ru dividing this winding into halves and shunting one half by means of an

page_text: invertor or alternator the polarity of that half will be reversed and between the
two halves there will form the "follower" poles so that a four-pole motor will be
thus obtained.
By dividing the windings into three parts and only shunting the central part,
there will be obtained two "follower" poles, and a six-pole motor will be the
result.
Thus it will readily be seen that by further subdividing the, winding, the
number of poles may be increased at will, without any of the herein before
mentioned disadvantages.
The short-circuiting armature should be so wound that the several phase-windings
shall consist of a number of branches switched parallel to each other; which will
then take up such a position in relation to each other that, when the pole number
is that at which the short circuiting armature is supposed to be controllable the
electro motive forces will be induced in all branches in the same direction, so
that the circuits will only close through the action of the rings and may be
connected to meet "starting" resistances; while when the number of poles of the
exciting armature is different, all or part of the parallel branches will be short-
circuited in themselves.
Where a double-pole motor has to be dealt with, the electro-motive forces of the
several branches at all times follow the identical direction and the circuits can
only close through the conductors to the aforesaid rings.
In four-pole motors, the electro-motive forces will circle round in one half of the
coil and the circuits will close without passing through the conductors.
By arranging the several coils so as to make them partly overlap each other, the
circuits may be caused partially to neutralize each other and partially to join or be
added together.
Especially by this latter method, and by the employment of a number of parallel
branches, such short-circuit armatures may be caused to influence a very large
number of different pole numbers.
Of course the winding may also be so arranged that the electro-motive forces of
the different branches never neutralize each other altogether, whatever the numbers
of poles; hereby minimizing the wear of the sliding rings.
Again, these sliding rings and other shunting devices or switches may be dis-
pensed with altogether, by the employment, in starting, of that number of poles at
which all the electro-motive forces in the short-circuiting armature for the most
part neutralize each other; and if desired, the starting resistances attached to the
short-circuiting armature direct, may be utilized; the pole-number-whilst the
motor is in operation-being changed to that, at which the short-circuiting
armature is short-circuited.
All the above arrangements apply equally well to monophase and polyphase
alternating current motors.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.
Improvements in or connected with Alternating Current Electric
Motors.
I, ALEXANDER HEYLAND, of 57, Wasserstrasse, Frankfort on the Main, in the
German Empire, Electrical Engineer, do hereby declare the nature of this invention

page_text: and in what manner the same is to be performed to be particulary described and
ascertained in and by the following statement:-
In changing the pole number of alternating current-motors, for the purpose of
varying the speed of rotation, (with the exception of motors with "ring-wound
coils and a simple short circuit armature which are however rarely now used)
considerable difficulty has hitherto been experienced.
"
In modern drum-wound" motors with a wound short-circuited armature the
pole number is changed by winding the motor for a given maximum pole number
and by so reversing part of the pole winding, when it becomes necessary to pass
from a greater to a less pole-number, that two or more poles of the same sign or
polarity in all cases are situated in juxtaposition, so as always jointly to form one
pole only. This enables the maximum number of poles to be readily reduced
to 2/3 or some other fraction of it.
This method of operation is, however, attended by two main drawbacks, which
alone may be said to preclude it from being successfully applied to practical
purposes.
In the first place the diminution of the pole number in this case is only owing to
the fact that, by reason of the partial reversing of the poles, currents, flowing side
by side, neutralize each other's action, which means that the space allotted for the
winding is not fully taken advantage of and that the distribution of the magnetic
field is defective.
Secondly, the rotary short-circuited armature may be reversed only through
the medium of a comparatively great number of sliding rings; but from practical
considerations the number of these should not exceed a somewhat narrow limit.
The present invention consists of certain winding arrangements which, when it
is desired to change the number of poles, render any reversal of the winding on the
short-circuited armature superfluous, and obviate the drawbacks above stated in the
reversal of the field armature.
The requisite change in the pole number of the field armature is to be effected
first and foremost by winding it for a small number of poles and by so shifting
certain parts of the windings or coils as to develop successive or follower "-poles;
whereby the pole number may subsequently be increased at will.
Referring to the accompanying drawings Fig. 1 shews a double-pole monophase
winding, the poles being N and S.
By dividing this winding into halves as shown in Fig. 2 and reversing one half
by means of an invertor or switch u, the polarity of that half will be reversed and
between the two halves there will form the poles S, S; so that a four-pole motor
will be thus obtained.
By dividing the windings into three parts as shown in Fig. 3 and reversing only
the central part, there will be obtained two "follower" poles S, S, and N, N, and
a six-pole motor will be the result.
Thus it will readily be seen that by further subdividing the winding, the number
of poles may be increased at will, without any of the hereinbefore mentioned
disadvantages.
The short-circuited armature should be so wound that the several phase-windings
shall consist of a number of branches parallel to each other; which will then take
up such a position in relation to each other that, when the pole-number is that at
which the short-circuited armature is supposed to be controllable, the electromotive
forces will be induced in all branches in the same direction, so that the circuits
will only close through the action of the rings and may be connected to meet
starting" resistances; while when the number of poles of the field armature is
different, all or part of the parallel branches will be short-circuited in themselves.
Figs. 4 and 5 of the drawings illustrate such connections of the several phases.
Where a double-pole motor has to be dealt with, the electro-motive forces of the
several branches at all times follow the identical direction and the circuits can only
close through the conductors a and b leading to the aforesaid rings.
"

page_text: In four-pole motors, the electro-motive forces will circle round in one half of the
coil (as indicated in Fig. 6 by dotted lines) and the circuits will close without
passing through the conductors a and b.
By arranging the several coils so as to make them partly overlap each other, as
shown in Fig. 5, the circuits may be caused, partially to neutralize each other and
partially to join or be added together.
Especially by this latter method, and by the employment of a number of
parallel branches, such short-circuited armatures may be caused to influence a
very large number of different pole-numbers.
Of course the winding may also be so arranged that the electro-motive forces of
the different branches never neutralize each other altogether, whatever the number
of poles; thereby minimizing the wear of the sliding rings.
Again, these sliding rings and other reversing devices or switches may be
dispensed with altogether, by the employment, in starting, of that number of poles
at which all the electro-motive forces in the short-circuited armature for the most
part neutralize each other; and if desired, the starting resistances indicated
at W W in Fig. 6, attached to the short-circuited armature direct, may be utilized
as shown; the pole number-whilst the motor is in operation-being changed to
that, at which the short-circuited armature is short-circuited.
All the above arrangements apply equally well to monophase and poly-phase
alternating current motors.
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. A device for changing the pole-number in alternating-current electric motors,
the main feature of which is that the winding for the smaller number of poles
consists of individual coils by the partial reversion of which "successive" poles
are formed, so that the number of winding poles is increased by the number of these
successive poles substantially as described.
2. A device for changing the pole number of alternating-current electric motors,
the main feature of which is that the short-circuit winding consists of a number of
separate branches connected parallel to each other, their relative position being
such that when the number of poles of the field armature is that at which the
short-circuited armature should be controllable, all the electro-motive forces induced
in the several branches of the short-circuiting armature take a parallel direction,
whereas when the pole number is not that which is above specified, all or part of
the parallel branches are short-circuited in themselves, substantially as described.
3. A device for altering the pole-number of alternating current motors, the main
feature of which is that the short-circuit winding consists of branches, so wound,
that at one or a set of predetermined pole-numbers in the motor, all or part of the
induced electro-motive forces neutralize each other or close through the medium of
suitably arranged resistances substantially as described.
1000
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.