Improvements in Alternating Current Motors.
Year: 1898

page_text: Date of Application, 10th Nov, 1000
Complete Specification Left, 17th Aug., 1899-Accepted, 7th Oct., 1899
Date of Application, rou! HUF 100U
Complete Specification Left, 17th Aug., 1899-Accepted, 7th Oct., 1899
Improvements in Alternating Current Motors.
I, WALTER LANGDON-DAVIES, of 101, Southwark Street, in the County of Surrey,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
The object of my invention is to produce an alternating current motor from
which a large starting effort can be obtained, and the speed of which can be
continuously regulated electrically and is not entirely dependent on the
periodicity of the current.
The motor has two elements, one fixed which I call the field magnet, and one
rotating which I call the armature. Each element is wound with coils, the
coils on one element are energized by the supply current and induce current in
the coils on the other element.
When the coils on the field magnet are energized by the supply current, the
armature is wound with coils in which currents are induced by the field magnet,
the coils are connected to a suitable commutator and their direction is controlled
by suitable brushes in contact with one another, and with portions of the com-
mutator.
It is not essential that the armature winding, commutator and brushes should
constitute the induced circuit but the brushes may be suitably joined to the
electro motive source, and the field magnet coils may be short circuited per-
manently, the same result will be obtained.
The principle upon which the motor works is illustrated in the drawing
annexed.
In this drawing a are the field magnet windings, & the armature, o commutator
bars and d d brushes connected to the mains e
The arrow 1 indicates the magnetic axis of the field magnets and the arrow 2
the magnetic axis of the armature.
The induced currents in the field magnet winding produce an alternating
magnetic field the axis of which is shown as being vertical.
If the axis of the fields of the field magnets and armature do not coincide,
the field of the field magnet and the field of the armature will repel one another
and a continuous rotation will result.
I wind the field on a continuous ring of iron (which may be laminated) pro-
vided with suitable slots or holes to receive the windings, so that the field
magnet has no projecting pole pieces, and to produce a suitable distribution of
the field I wind my field magnet in sections as described in my Patent
No. 18870. In some cases I prefer to make the magnetism in the central por-
tion denser than the sides.
This motor may be controlled as to speed and power by introducing choke or
resistance, into the induced or inducing winding, either or both, or a transformer
may be used to reduce the volts and therefore current in the machine.

page_text: The brush or brushes may be carried upon any suitable adjustable support
and by adjusting the position in one direction or the other the speed and effort
of the motor may be regulated and also the direction or rotation may be reversed.
To change the direction of rotation of such a motor I may provide the field
magnet with two sets of windings, set at an angle to one another, such that the
axis of the field produced by one set of windings lies at a suitable angle to the
axis of the other field to produce rotation in one direction, and the field set up
by the other field winding produces an opposite rotation, the direction of rotation
is then controlled by a suitable switch exterior to the motor, which connects
one or other set of windings.
Or I may provide two sets of brushes, set in different positions and connect
the brushes of one or other 'set, according to the direction in which the motor is
to be run.
T
____ 1800
.Improvements in Alternating Current Motors.
I, WALTER LANGDON-DAVIES, of 101, Southwark Street, in the County of Surrey,
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 :-
The object of my invention is to produce an alternating current motor from
which a large starting effort can be obtained, and the speed of which can be
continuously regulated electrically and is not entirely dependent on the
periodicity of the current.
My improvements are illustrated in the drawings annexed.
Figure 1 is an end elevation of a motor of the class to which my improvements
apply.
.
Figure 2 is an end view of a field magnet continuous ring with closed slots for
receiving the windings but if desired the inner ends of the slots might be open..
Figure 3 is a diagram end view of a motor constructed according to my in-
vention.
Figures 4, 5 and 6 are similar diagrammatic views illustrating the effect of
three different distributions of the field windings.
Figure 7 is a diagram view shewing how a magnetic field similar to that
shewn in Figure 3 may be produced by a different disposition of the field windings
to that shewn in that figure.
Figure 8 is a diagram view of a motor such as shewn at Figure 3 but provided
with two sots of field windings one to be used for running in one direction the
other in the other direction.
The motor has two elements, one fixed which I call the field magnet, and one
rotating which I call the armature. Each element is wound with coils, the
coils on one element are energized by the supply current and induce current in
the coils on the other element.
When the coils on the field magnet are energized by the supply current, the
armature is wound with coils in which currents are induced by the field magnet,
the coils are connected to a suitable commutator and their direction is controlled
by suitable brushes in contact with one another, and with portions of the com-
mutator.
-
It is not essential that the armature winding, commutator and brushes should.
constitute the induced circuit but the brushes mav be joined to the

page_text: electro motive source, and the field magnet coils may be short circuited per-
m'anently.
The general principle upon which the motor works is illustrated in Figure 1.
In this drawing a are the field magnet windings connected to the mains, & the
armature, commutator bars to which the armature winding is coupled at
intervals, and ad brushes connected to one another.
The arrow 1 indicates the magnetic axis of the field magnets, it is shown as
being horizontal, and the arrow 2 the magnetic axis of the armature, it is in
a line with the points of contact of the brushes.
If the axis of the fields in the field magnet and armature do not coincide,
the field of the field magnet and the field of the armature will repel one another
and a 'continuous rotation will result.
Motors on the general principles above described have been made but are
inefficient.
In such an arrangement as that shown in Figure 1 the reluctance in the path
of a field having its axis on the line shown by the arrow 2 is greater than that
of a field having its axis on the line shown by the arrow 1 therefore one of the
fields would be weaker than would be the case if reluctance was the same for each
field. And as the power is derived from the reaction of these two fields upon
one another there would be less power obtainable and therefore an arrangement
such as shown in Figure 1 must necessarily be very imperfect.
In motors working upon the above general principle I according to my in-
vention wind the field on a continuous ring of iron having no projecting pole
pieces and suitably laminated and provided with open or closed slots in the
polar faces to receive the windings and for the reasons hereinafter 'stated I
also so dispose the windings as to make the magnetic density strongest at the
centre of each pole face.
"
It may be assumed in such a machine of fixed dimensions as has been described
that the "torque or turning effort with a given strength of inducing field is
proportional to the amount of current flowing in the induced windings provided
the brushes are fixed in position.
I find that the amount of current induced in the induced windings by a given
total strength of inducing field may vary considerably with the way in which
the inducing field is distributed over the pole faces, and that the best results
are obtained by so distributing the field windings as to make the magnetic density
strongest in the centre of the pole face, and decreasing at the outer edges as
indicated by Figure 3 in which the dotted lines represent diagrammatically the
lines of force.
To produce this result I wind my inducing field in sections so that the iron
of each polar face is surrounded by different numbers of turns, which increase
the magnetic density towards the centre.
The field winding required to produce such a field will vary more or less for
different sizes and varied forms of the motor-but generally to produce such a
magnètic field one turn of the field winding may for example be passed through
slots marked No. 1 in Figure 3 and be available for more or less magnetizing
the whole of the iron in the space between these slots, another turn of the winding
may be carried through the slots No. 2 and be available for increasing the
magnetization of the iron in tlie space between them and so on to the slots No. 8
near the centre of the pole face.
The induction density can then be tested by means of an exploring coil in the
known way or the armature itself may be used as the exploring coil and the
voltage for different positions of the brushes be taken.
The information so obtained will indicate what corrections have to be made
in the proportioning of the field windings to produce the field required.
To illustrate the effect of different forms of windings I have in the diagrams
Figures 4, 5 and 6 illustrated approximately the electrical and magnetic. condi-
tions produced by various forms of winding.

page_text: In Figure 4 the magnetic density is shown as being greater towards the ends
of each pole face than at the centre.
In Figure 5 the density is uniform or approximately so over the pole face,
directions for so proportioning the windings as to produce a uniform magnetic
density are given in the Specification of a former Patent granted to me No. 18870
in the year 1895. In Figure 6 it is greater at the centre than at the ends and
this is effected by passing a greater number of turns of winding through the
slots which are near to the centre of the pole face than would be required to
produce uniform density as described in my former patent. If an equal number
of turns be passed through each slot this will approximately produce the result
desired, but will vary somewhat in different machines with different widths of
air gap
The figures diagrammatically represent a 2 pole motor. In each of the figures
a is a field magnet ring formed in the way illustrated at Figures 2 and 3. b is
the armature having sixteen teeth. The armature is shown wound with a con-
tinuous ring winding having one turn wound in each notch between the teeth,
this winding is shown connected in the usual manner to a sixteen part com-
mutator c.
The dotted lies from the field magnet through the armature and
back to the field magnet represent the magnetic field. The different numbers of
lines entering each tooth of the armature are intended to graphically represent
the density of the magnetic field over the pole faces.
The whole upper half of the inside face of the field magnet is considered as one
pole face, and the lower half as the other pole face. There is no gap in the iron
between them, in other words these are not what are to be understood as pro-
jesting poles.
It is assumed in the following deductions that one magnetic line of force
alternating in one turn of the armature winding produces a potential difference
of one volt at the terminals of that turn, that is to say in the winding shown
having one turn between each commutator segment the volts between each pair
of commutator segments are equal to the number of magnetic lines alternating
through the turn of winding between them.
The volts between the pairs of commutator segments are written above the
commutator in each of the figures, and the directions of the arrows show the
relative directions in which current would flow.
In each of the figures the same total number of magnetic lines is assumed
to be produced by the field magnet, and to pass through the armature.
By adding the volts between the sectors, giving them their position or negative
values as shown by the direction of the arrows, the volts between a pair of
brushes placed at the ends of any diameter of the commutator can be calculated.
The maximum volts obtainable in Figure 4 are 44, in Figure 5 are 64, and in
Figure 6 are 84. As the only difference in the construction of the three figures
consists of the different distribution of the inducing magnetic field it is obvious
that the greatest induced current and therefore torque can be obtained from the
arrangement shown in Figure 6.
A practically similar magnetic field having the lines of force concentrated to
the central portion of each pole face can as shown at Figure 7 be produced by.
winding the central portion only of the pole face with a single coil. In such
a case it will not be necessary to wind the inducing coila in sections but as shown
the central portion only not exceeding or much exceeding one half of the pole
face may be wound with a single coil.
The magnetic distribution obtained by such a field magnet as that shown in
Figure 1 may effectively resemble that shown in Figure 7 but owing to the gaps
in the magnetic circuit the gain by distribution will have to be set off against
the losses arising from the reluctance of the path of the field set up by the
induced current.
If the armature windings are connected to the source of supply by means of
the brushes the distribution of the field set up by the armature will be similar

page_text: to the inducing field shown in Figure 6, since the armature windings are dis-
tributed over the pole face, though the position of its axis will depend on the
position of the brushes. Hence it is apparent that to produce the same results
the same construction must be used whether the fixed or rotating part or both
of them be energized by the supply current.
The proportions of turns in the sections and the most suitable distribution
for the field may as above stated be found by experiment, and will vary for
different sizes of motor and for the different kinds of work they are required
to perform, but the field should always be banked to the centre as in Figure 7
by means of the winding, and without projecting poles.
Although I have only shown my improvements applied to a two pole machine
it is evident that they may be applied to machines having a greater number of
poles.
The motor may be controlled as to speed and power by introducing choke or
resistance into the induced or inducing winding, either or both.
To change the direction of rotation of a motor I in some cases wind the field
magnet ring as illustrated at Figure 8 with two sets of windings ef set at an
angle to one another such that the axis of the field produced by one set of
windings e lies at a suitable angle to the axis of the other or armature field to
produce rotation in one direction-and the field set up by the other field winding f
produces a rotation in the opposite direction. In this way the direction of
rotation can be controlled by a suitable switch exterior to the motor bringing
into action one or the other set of windings as required.
"
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. An alternating current motor having its field magnets formed in a drum
wound slotted continuous ring with no projecting pole pieces and their windings
so distributed as to make the magnetic density strongest at the centre of each
pole face and having its armature wound with a continuous winding coupled at
intervals to commutator bars and also having brushes bearing against the com-
mutator on a line inclined to the magnetic axis of the field magnets, which
brushes are short circuited if the field magnet windings are supplied with current
or have current supplied to them if the field magnet windings are short cir-
ouited.
2. An alternating current motor having its field magnets formed in a drum
wound slotted continuous ring with no projecting pole pieces and having the
central portion only not exceeding or much exceeding one half of each pole face
magnetized by the field windings and having its armature windings coupled at
intervals to the bars of a commutator and brushes bearing against the com-
mutator on a line inclined to the magnetic axis of the field magnets which
brushes are short circuited if the field windings are supplied with current or
have current supplied to them if the field windings are short circuited.
8. An alternating current motor having armature windings coupled at intervals
to commutator bars and brushes bearing on the commutator and having its field
magnets formed in a drum wound slotted continuous ring having no projecting
pole pieces and provided with two sets of windings in such position relatively
to the brushes that when one set is used the motor will run in one direction and
when the other is used the motor will run in the opposite direction.
4. Alternating current motors constructed
substantially as hereinbefore
described and illustrated in Figures 3, 6, 7 and 8 of the drawings annexed.
AL 1
1000