Improvements in Alternating Current Motors.
Year: 1897

page_text: PROVISIONAL SPECIFICATION.
Improvements in Alternating Current Motors.
I, WALTER LANGDON-DAVIES, of 16, Red Lion Street, Clerkenwell, E.C.,
Electrical Engineer, do hereby declare the nature of this invention to be as
follows:-
In self starting alternating current motors having distributed magnetic field
such for example as is obtained by a winding similar to that described in my
Patent No. 18870 of 1895, in order to obtain a better starting effect I set the bars
of the armature, instead of in a plane parallel to the axis of rotation, in a plane
at an angle to the axis. I find that in many cases this angle may be equivalent
to one bar pitch i.e. that the end of one bar may be in the same axial plane as the
beginning of the next one, but we do not confine ourselves to this particular angle.
I am aware that such skewed winding has been used before but not in conjunction
with a distributed field. This form of skewed winding in combination with the
distributed field enables us to obtain an equally good effect even when the rotor
bars are wound in open slots instead of in tunnels in the iron of the rotor thereby
cheapening the construction. By bars I mean conductors on the face of the arma-
ture nearest the field magnet. I sometimes obtain a like result by skewing the
field instead of the armature.
Improvements in Alternating Current Motors.
I, WALTER LANGDON-DAVIES, of 16, Red Lion Street, Clerkenwell, E.C.,
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:-
In self starting alternating current motors having distributed magnetic field
such for example as is obtained by a winding similar to that described in
Patent No. 18870 of 1895, in order to obtain a better starting effect I set the bars
of the armature, instead of in a plane parallel to the axis of rotation, in a plane
at an angle to the axis. I find that in many cases this angle may be equivalent
to one bar pitch i.e. that the end of one bar may be in the same axial plane as the
beginning of the next one, but I do not confine myself to this particular angle.
I am aware that such skewed winding has been used before but not in conjunction
with a distributed field. This form of skewed winding in combination with the
ונ...D

page_text: distributed field enables me to obtain a good effect even when the rotor bars are
wound in open slots instead of in tunnels in the iron of the rotor thereby cheapen-
ing the construction. By bars I mean the armature conductors nearest the field
magnet. I sometimes obtain a like result by skewing the field windings instead
of the armature windings.
Figure 1 of the drawings annexed shews an alternating current motor con-
structed in the above manner. Figures 2 and 3 shew a plan and end view of part
of one form of skew wound armature and Figures 4 and 5 similar views of an
open slot form.
In Figure 1 A A are the field windings disposed as described in the hereinbefore
mentioned patent in such a way as to produce a uniformly distributed magnetic
field. A¹ A¹ are starting coils used in conjunction with the field windings for
producing a rotating magnetic field for starting the armature from rest and bring
it up to a speed at which it will be kept running by current passing through the
coils A only the coils A¹ being then switched out of use. The arrangements
for producing the rotating magnetic field may be such as described in the Specifi-
cation of a Patent to Walter Langdon-Davies No. 7772 of 1897. B is the revolv-
ing armature having its rotor bars inclined to the armature axis. The armature
is as usual formed of a number of thin iron discs or rings held together side by side.
The windings may either be passed through holes formed through the discs or
rings near their outer circumference as shewn at Figures 2 and 3 or they may as
above stated be made to lie in radial grooves made to extend inwards from the
outer circumference as shewn at Figures 4 and 5. The winding for each rotor
bar may be a closed circuit winding independent of the windings for the other
rotor bars or the winding for one rotor bar at one part of the circumference of
the armature may be continued to form other rotor bars at equal distances apart
from one another the distance apart being governed by the number of field magnet
poles as is well understood.
In Figures 2 and 4 the rotor bars are shewn to be set at one bar pitch, the end of
one bar being in the same axial plane as the beginning of the next but the angle
at which the bars are set might vary somewhat from this angle and yet a good
result be obtained.
Alternating current motors formed as above described with a skew wound arma-
ture in combination with a distributed magnetic field will start from rest smoothly
and uniformly and not with a succession of jerks as in other self starting alter-
nating current motors heretofore constructed.
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 a uniformly distributed magnetic field
and either the field windings or the armature windings set askew substantially
as described.
2. The construction of alternate current motors substantially as hereinbefore
described and illustrated in the drawing annexed.