Improvements in and relating to Windings for Polyphase Machines.
Year: 1897

page_text: Date of Application, 22nd Dec., 1897-Accepted, 5th Feb., 1898
COMPLETE SPECIFICATION.
Improvements in and relating to Windings for Polyphase Machines.
We, THE BRITISH THOMSON-HOUSTON COMPANY, LIMITED, and HENRY METCALF
HOBART, all of 83, Cannon Street, in the City of London, 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:
-
This invention relates to windings for the armatures and fields of polyphase
machines and aims to secure certain advantages over the windings hitherto
employed.
"
Our present invention comprises methods of winding generators and motors for
polyphase currents with systems of winding which we term non-overlapping
fractional-pitch windings, these having such numbers of coils and slots as to
obtain economical proportions, convenience in mechanical arrangements, low
inductance and (in the case of motors) to avoid dead points to a considerable
extent. By a "non-overlapping" winding we mean a winding where the coils
are adjacent to each other as distinguished from a winding wherein the coils are
intermeshed or overlap each other, and by a fractional-pitch" winding we mean
one in which the pitch of the winding, i.e. the angular distance from centre to
centre of the coils, is a fraction of the polar pitch, i.e. the angular distance from
centre to centre of the F. M. poles. Non-overlapping fractional-pitch windings
are a class suitable principally for alternating polyphase current apparatus. In
the British Patent Specification No. 13503 of A.D. 1891, Michael von Dolivo
Dobrowolski has described and illustrated certain systems of winding which he
terms "doubly concatenated circuits." The present invention, so far as it relates
to the inter-connection of the windings, involves the use of doubly concatenated
circuits, but the novelty of the invention consists in the windings themselves,
which are entirely different from those described by Dobrowolski, and we would
have it understood that we do not claim as of our invention anything claimed
in his said Patent. The object of the present improvement is to construct
polyphase windings which shall have the advantages over previously arranged
windings that they are easier to construct and assemble on the core, a less
number of slots are required in the core, and the relative positions of armature
slots and F. M. poles are such as to reduce the tendency towards dead centres or
points, which have hitherto been one great obstacle to successful and economical
practice.
By our invention also, inductance of the armature winding, hitherto a source
of trouble, is reduced below the value it would have in uni-pitch windings with
equal strength of armature.
Further, by our improved method of interconnecting the windings, a wide

page_text: range of interchangeability of the connections of the different component parts
of the winding is obtained.
In fully describing our invention we will refer to the annexed figures and
diagrams illustrative thereof.
Fig. 1 diagrammatically represents Dobrowolski's system of doubly concatenated 5
circuits above referred to, as applied to three-phase work. It will be observed
that the windings A¹ and A, B and B, C and C are respectively in quadrature
with each other. Now quarter-phase, non-overlapping fractional-pitch windings
may be used with 2 coils per one, three, five or seven pole-pieces, and so on.
Placing three such windings upon one armature, we have six coils per one
pole-piece, six coils per three, five, seven, nine or eleven pole-pieces, and so on. Of.
these combinations 6 per 5, and 6 per 7 are the best proportions and give the
best results.
Take for instance, the case of six coils per five pole-pieces. It would not be
possible to use six coils per five or per seven pole-pieces for an ordinary "Delta"- }
or "Y" connected three-phase fractional-pitch winding, because the possible
numbers are limited by such combinations as: -3 coils per one pole-piece or 3
coils per two, four, five, seven, eight or ten pole-pieces, and so on.
An arrangement of six armature coils per five pole-pieces is a combination
giving very good proportions, it being hardly different from those of uni-coil 2
single-phase alternators. For example a ten-pole machine, with six coils for every
five pole-pieces would have 12 armature coils. Such a winding is shown in
Fig. 2. The light line coils 1, 2, 3, compose the three sides of the "Delta," and
the heavy line coils 4, 5, 6, compose the external coils of the "Y"-winding in
quadrature with the "Delta" coils shown in light lines. They are drawn heavy 2
because they must carry the ✓3 or say 1.73 times as great a current, and in
order to have the same armature re-action per coil, they must have only the
reciprocal, or say .577 times as many turns per coil. In order not to confuse
the diagram, only one-half of the coils shown are connected in.
-
Fig. 3 shows another combined "Delta" and "Y"- winding of the same 3
type, having 12 coils and 14 poles, that is, six coils per seven pole-pieces, only half
being shown connected.
An application of this principle to quarter-phase work yields windings of
which Figs. 4 and 5 are examples. Fig. 4 is a 12-pole machine with four armature
coils 1, 2, 3, 4 per three pole-pieces, and Fig. 5 is a 20-pole machine with 16 coils, 3
that is, four coils per five pole-pieces. Again in Fig. is shown a 10-pole
machine with four sets of coils per five pole-pieces, each set of coils consisting
of two component coils a, b, this subdivision being often desirable from electro-
magnetic conditions as reducing the reaction upon the field, and from thermal
conditions since each coil may be smaller, and therefore heat generated by the
current can easier escape.
Fig. 7 shows diagrammatically how, by our improved method, the inter-
connections of the component coils of the winding shown in Figs. 2 and 3 may
be varied. In practice the various leads would be brought to and arranged con-
veniently upon a suitable connecting board and the manner of their inter- 4
connection and operation would be controlled by switches, commutators, and so
forth as will be well understood by engineers.
In Fig. 7, A represents diagrammatically the 6 differently disposed sets of coils
of Figs. 2 and 3. In B only coils 1, 2 and 3 are shown connected up in Delta"-
and in C the same coils are in "Y"-connection.
D and E show the coils 4, 5, 6, which, it is to be remembered, have less turns
than the coils 1, 2, 3 in "Delta" and "Y"-connections respectively. F shows
all 6 sets of coils connected up in double concatenation, and G differs in that
coils 4, 5, 6 are connected in internal Y" relation to the "Delta"- connected
coils 1, 2 and 3 so that G differs from B in that it has increased current capacity,
and in having all the armature coils in service.
"

page_text: To
Fig. 8 shows the same method of interconnection adapted with reference
Figs. 4 and 5.
A represents diagrammatically the 8 differently disposed sets of coils of Figs. 4
and in C the
and 5. In B only coils 1, 3, 1, 3, are shown connected in "mesh"
same coils are in "star" connection. D and E show the heavy coils of fewer
turns 2, 4, 2, 4, in "mesh" and "star connection respectively. F shows all
the 8 sets of coils connected up in double concatenation and in G they are again
all shown, the heavy coils 2, 4, 2, 4, however being connected in internal
connection to the "mesh connected coils 1, 3, 1, 3.
"
"
66
star"
The chief advantages accruing from the use of the windings constituting the
subject of this invention are:-
a. A relative number of coils and poles may be selected, which will be much
more nearly prime (i.e. having no common factor) than could be obtained with
the connections heretofore used in the art of winding. This is of particular
importance in the case of synchronous and induction motors since one of the
chief difficulties met with in these is dead centres, which are, by this invention.
largely avoided. As an instance of this, referring to Fig. 4 the left hand side
of coil 1 at the top of the figure is directly under the field pole F and is conse-
quently in the position of maximum inductance, if the other or right hand side
of the same coil were in the corresponding position with respect to the next
adjacent pole on the right (as would be the case with ordinary windings) it
also would be in the position of maximum inductance and hence would tend to
hold the armature at rest in this position, but since the right hand side of 1 is
not under the pole F¹ it is in a position of much less than maximum inductance,
and hence the coil 1 as a whole has less inductance than in the ordinary con-
struction, and the whole armature has less marked dead points.
b. The range of choice of relative widths of coils and pole-pieces is greatly
increased, and this choice has an important bearing on the design of a machine.
c. By simple switches and commutating devices (well understood in the art)
a change may be effected from one to the other of the six arrangements described
in reference to Figs. 7 and 8, whereby the particular connection best adapted to
the conditions of starting or of continuous running, or to the degree of load which
the machine may be handling, or the voltage at which it may be desired to run,
may be readily secured. We know that it has already been suggested to change
from simple Delta" to simple "Y"-windings for purposes of adapting a
machine to diverse conditions, but the extent or range of these possible trans-
formations is considerably increased by the present invention, for, as has been
shown, the heavy windings with the fewer turns may be independently connected
in either "Delta" or "Y," as well as the light windings with the many turns,
and also the combination of these two.
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 is:-
1. The improved windings for polyphase machines, disposed and connected up
and adapted for use substantially in the several manners herein set forth.
2. The improved windings for three-phase machines, consisting of 6 coils per
5 pole-pieces, and 6 coils per 7 pole-pieces substantially as herein set forth respec-
tively in reference to Figures 2 and 3.
3. The improved windings for quarter-phase machines consisting of 4 coils
per 3 pole-pieces and 4 coils per 5 pole-pieces substantially as herein set forth
respectively in reference to Figures 4, 5 and 6.
4. The method of varying the interconnections of the component parts of the
several improved windings for polyphase machines as above described in reference
to and represented diagrammatically in Figs. 7 and 8 of the drawings.
5. In armature and field windings for polyphase machines the several com-
binations with doubly concatenated windings of non-overlapping fractional-pitch

page_text: windings substantially as herein set forth in reference to and shown respectively
in Figs. 1, 2, 3, 4, 5 and 6 of the drawings.
1
3
10.1
1
. T
1007
windings substantially as herein set forth in reference to and shown respectively
in Figs. 1, 2, 3, 4, 5 and 6 of the drawings.
18th day of December
windings substantially as herein set forth in reference to and shown respectively
in Figs. 1, 2, 3, 4, 5 and 6 of the drawings.
10.1
December
For the Applicants,
J. C. CHAPMAN.
Chartered Patent Agent, 70, Chancery Lane, London, W.C.
For the Applicants,
J. C. CHAPMAN.
Chartered Patent Agent, 70, Chancery Lane, London, W.C.