Dynamoelectric machine having improved interleaved stator end turns

Disclosed is a dynamoelectric machine stator winding having a plurality of coil sides of varying lengths disposed in a plurality of slots located around the inner periphery of a tubular stator core. Top and bottom coil sides (radially inner and outer positions) of unequal length are placed within the slots and interconnected such that top coil sides are joined to bottom coil sides disposed in other slots when the top coil sides, as dictated by winding topology (for phase interspersed connector ring segments), are longer than the commonly slotted bottom coil sides. When the bottom coil side in a subject slot is longer than the commonly slotted top coil side, the top and bottom coil sides are lengthened and shortened, respectively, and the top and bottom coil sides in the subject slot are respectively joined to top and bottom coil sides on both axial ends of the stator. In all cases the coil sides are joined by connector ring segments interspersed according to phase and having a body portion with a common radius of curvature and a radially inwardly directed conductive arm of predetermined length on each end thereof. The length of the conductive arms are varied according to the position (top or bottom) occupied by the respective to-be-joined coil sides.

BRIEF DESCRIPTION OF THE PRIOR ART AND SUMMARY OF THE INVENTION 
This invention relates to multiphase dynamoelectric machines having stator 
members with multi-loop coils disposed therein constituting a stator 
winding, and more particularly to joining coil sides of different lengths 
that are positioned in radially top and bottom positions of a first stator 
slot to coil sides occupying top and bottom positions in a second and 
third slot, respectively. 
Large dynamoelectric machines designs have evolved which use a rather 
complicated stator winding disposed in axially extending slots formed in a 
stator core to handle the voltages and currents required by the loading 
demands made on the machine. A large number of stator slots, the use of 
parallel windings in each phase and the multiple turns per phase require a 
complex end connection for the winding's slot disposed coil sides. The end 
connection must be accommodated in a restricted space, be of rugged 
construction and provide the necessary electrical communication between 
the stator coil sides. 
The previous design included stator winding having "diamond" shaped coils. 
Each coil included a predetermined number of loops with each loop having 
two coil sides. The coil sides each included a straight portion which ran 
the length of the stator slots and a complexly shaped, curved portion 
situated at each end which facilitated connection with other curved 
portions. This curved portion had a complex shape which curved axially, 
radially and circumferentially. The manufacturing of this coil side 
portion required a complex shaped three-dimensional form against which the 
coil sides were bent and twisted. The stator coil sides were woven 
together and connected in the axial end regions of the machine to form the 
diamond-shaped end-basket design which has been typically used on large 
dynamoelectric machines. 
The woven together end-basket design enables completion of the necessary 
stator coil side connections and provides a compact and rugged structure. 
However, one disadvantage of the end-basket design is that the 
interweaving of the coil sides makes it impossible to remove a single coil 
side from the bottom of a stator slot without removing from twelve to 
eighteen top coil sides which obstruct its removal. 
When a machine is damaged in the field and a bottom coil side needs repair 
or replacement, many top coil sides must be removed to access the bottom 
coil. Removal of the several top coil sides is a costly and time consuming 
process. Braces and wedges in a large portion of the machine must be 
disassembled and removed. During the unbracing process and coil side 
removal, the machine is susceptible to additional damage. Subsequent to 
the machine's disassembly and coil side repair, the coil sides must be 
reassembled and the bracing system rebuilt, often under field conditions 
which are not conducive to quality control and inspection procedures. 
Copending application Ser. No. 139,083, by Mr. L. Long, filed on Apr. 10, 
1980 and assigned to the assignee of the present application, discloses a 
dynamoelectric machine having a stator winding comprising a plurality of 
stator coils each of which includes two straight coil sides which extend 
the entire length of separate stator slots with one coil side occupying a 
top or radially inner position and the other coil side occupying a bottom 
or radially outer position. The coil sides protrude rectilinearly beyond 
the stator into the end turn region of the stator. A C-shaped connector 
ring segment electrically connects the straight top and bottom coil sides. 
Additional connector ring segments electrically join the top and bottom 
coil sides to other bottom and top coil sides, respectively, to provide 
multi-loop coil. The C-shaped connector ring segments eliminate many of 
the problems encountered in coil side fabrication and reduce the time and 
labor required to repair machines having conventional diamond-shaped 
stator coils. 
The forces on the stator winding in the end turn region under steady state 
and short circuit conditions are extremely large. For example, a typical 
25,000 amp, 20 kV turbine generator may have forces from 70 to 100 lbs. 
per inch of coil under steady state conditions and thus create bracing 
problems for the designer. It has been found that these forces are 
comparable whether the conventional diamond-shaped end winding is used or 
the aforementioned connector ring segments. 
In copending application Ser. No. 139,082, filed on Apr. 10, 1980 and 
assigned by the same assignor to the same assignee as is the present 
application, axial interspersal of the connector ring segments according 
to phase was disclosed and found useful in reducing the forces on the 
connector rings and coil sides by approximately one-half. This force 
reduction results from current levels in the immediately surrounding coil 
sides and connector ring segments which are one-half the magnitude of 
current in the subject coil sides and connector ring segments when the 
subject connector ring segment current is at its peak. This does not 
necessarily mean that the forces on all the coil loops are halved since 
the topology of the winding varies. The peripheral currents above and 
below the subject coils are such that their fields act on the subject coil 
sides and connector ring segments and thus appear in many cases to yield 
higher forces. However, when the subject coil current is peaking, the 
current in the surrounding coils of different phase are halved. 
Calculations indicate that interspersal of connector ring segments provided 
a 48% reduction in the magnetic field when compared with the magnetic 
field of the diamond-shaped coils. This calculated reduction is regarded 
as conservative since some areas of the diamond-shaped coil have much 
higher fields than the area chosen for the calculations. As a result of 
such higher fields, estimates regarding total force reduction through the 
use of connector ring segments range up to 68%. 
Phase interspersal of the connector rings also enables the leakage 
reactance to be reduced to that contributed by the connector rings. 
Each of the stator slots have coil sides of relatively different lengths 
disposed therein in top (radially inner) and bottom (radially outer) 
positions. As such, the coil sides extend different distances beyond the 
end of the stator core. Such commonly slotted coil sides of differing 
length are typically joined to other coil sides (displaced in opposite 
circumferential directions from the commonly slotted coil sides) by 
connector ring segments. The commonly slotted top and bottom coil sides 
are electrically joined to the displaced bottom and top coil sides, 
respectively. For machines utilizing the previously mentioned interspersed 
connector rings, most top coil sides extend axially further than their 
commonly slotted, radially adjacent bottom coil sides. As such, radially 
directed conductive arms extend outward from and connect the commonly 
slotted top and bottom coil sides to separate connector rings disposed 
radially outside the stator slots. However, some slots in a machine of the 
aforementioned construction house a bottom coil side which is axially 
longer than the top coil side also housed therein. 
When the bottom coil side is longer than a commonly slotted, radially 
adjacent top coil side, the top coil side cannot be joined to a connector 
ring solely through the usual expedient of a radially outwardly directed 
conductive arm since such a conductive arm would interfere with the 
commonly slotted bottom coil side. Occurrence of such unfavorable relative 
lengths of commonly slotted top and bottom coil sides can be minimized, 
but not eliminated. A "jogged" arm which is sequentially bent from its 
connection to the top coil side in a circumferential direction to clear 
the bottom coil side and then radially to provide a solution to the 
aforementioned interference. 
The jogged arm, however, requires complex fabrication in addition to 
inducing forces per inch approximately 60% higher on the jogged arm than 
the highest force regions elsewhere in the winding. The radially directed 
portion has a large axially directed force on it and the circumferentially 
directed portion has a radial force on it above and below the intersection 
of the portions. Force analysis indicates that the forces acting on the 
radial conductive arms are approximately 40% less than the forces acting 
on the jogged arms. 
In accordance with the present invention, standard top-to-bottom coil side 
connections (the top and bottom coil sides being separated by one pole 
pitch) are used repeatedly in the winding for the cases where the top coil 
side is relatively longer (in the axial direction) than the bottom coil 
side which is housed in the same stator slot. For the other cases where 
the bottom coil side in a slot would normally be longer than the commonly 
slotted top coil, the subject top and bottom coil sides are respectively 
joined to top and bottom coil sides on both ends of the stator. 
Additionally, for the other cases, the top coil sides in the subject slots 
are lengthened and the bottom coil sides in the subject slots are 
shortened so as to be shorter than the lengthened top coils. The 
aforementioned winding technique is used in conjunction with the 
interspersed connector rings. 
In conclusion, a comparison with the short circuit force on the jogged arms 
with the radial arms of the disclosed winding indicates a 40% reduction. 
Reversal of the typical coil sides eliminates the problems of difficult 
mechanical construction and high forces while at the same time providing 
symmetrically arranged coil side connections on both ends of the 
dynamoelectric machine so as to leave the voltage per winding per phase 
unchanged.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, FIG. 1 shows a partial sectional view of a 
dynamoelectric machine 10 having an outer casting 12, a rotor 14, and a 
stator structure 16 including a generally tubular stator core 17 which has 
multiloop coils 18 disposed therein constituting a multiphase stator 
winding. Each loop of the multiloop coils includes two coil sides 20 which 
are housed in slots, not shown, formed around the inner periphery of the 
stator core 17 and are joined by annular connector ring segments 22. The 
connector ring segments 22 are held in place by a plurality of mounting 
brackets 24. On each end of the stator structure 16 there are three 
parallel rings 26A, 26B, and 26C which are part of the machine's coolant 
system and are connected to the stator coils 18 by insulated tubing 28. 
A multiphase stator winding normally has a plurality of multiloop coils 
each having a number of loops distributed in an even number of stator 
slots and in the end turn regions of the stator. Each loop of each 
multiloop coil has two parallel coil sides 20 which are circumferentially 
separated on the inner periphery of the stator core 17 and a connector 
ring segment 22 which joins the ends of coil sides 20 and is disposed on a 
first end of stator structure 16. End turn connections of two coil loops 
64 and 66 are shown in FIG. 2. Coil loop 64 includes two straight coil 
sides 20 disposed in slots 58 of the stator core 17 and connector ring 
segment 22. The straight coil sides 20 are connected by connector ring 
segment 22. Several such loops, when joined together on a second end of 
stator structure 16 by a plurality of connector ring segments 22, form a 
multiloop coil having parallel sides and end connections. Coil sides 20 
which occupy top or radially inner positions in stator slots 58 are 
generally connected to bottom coil sides which occupy radially outer 
positions in stator slots 58. FIG. 2 illustrates a coil loop 66 which 
includes two straight coil sides 20 disposed in slots 58 of the stator 16. 
As illustrated in FIGS. 2 and 3, coil sides 20 in coil loop 64 extend 
axially beyond coil sides 20 of loop 66 for a distance represented by 
reference numeral 68. 
FIG. 2 further illustrates the connector ring segments 22 connected to the 
coil sides 20 which are disposed in the stator slots 58. As can be seen in 
FIG. 2, top coil sides are generally connected to circumferentially 
separated bottom coil sides. Each connector ring 22 illustrated has two 
conductor arm portions 23 which extend radially inwardly from a C-shaped 
body portion to the respective coil sides 20. It is to be understood that 
while only two coil loops 64 and 66 are illustrated, many coil loops are 
usually provided in typical stator windings. Two coil sides 20 (one from 
each loop) occupy radially adjacent positions in a first slot 58 and are 
connected to circumferentially separated coil sides housed in second and 
third slots. For purposes of clarity, only one coil side 20 is illustrated 
as occupying a top or bottom slot position in the second and third set. 
However, in actual practice, the radially adjacent or complemental slot 
position in the second and third slots are each occupied by another coil 
side 20. Connector ring segments 22 are disposed in planes at discrete 
axial displacements from stator structure 16 and are axially interspersed 
according to phase such that a connector ring segment 22 of one phase is 
axially surrounded by connector ring segments 22 of different phases as 
better shown in FIG. 6. For example, in a three-phase machine, connector 
ring segments carrying a particular phase are axially interleaved with 
connector ring segments carrying the other two phases such that the 
subject phase connector ring segments occupy every third discrete axial 
position from stator structure 16. As indicated in commonly assigned 
copending Ser. No. 139,082, filed Apr. 10, 1980, axial interspersal of the 
connector ring 22 according to phase drastically reduces the operational 
electromagnetic forces thereon. 
Commonly slotted coil sides 20 of different phase must have different axial 
lengths if phase interspersed connector ring segments 22 are to be used 
since all connector ring segments 22 in each displaced axial plane must be 
at the same phase. For most cases where phase interspersed connector ring 
segments 22 are used, commonly slotted coil sides (having the same and 
different phase) include top coil sides 20 which have relatively long and 
short lengths, respectively. Connection of the commonly slotted coil sides 
to circumferentially separated bottom and top coil sides 20, respectively, 
is provided by connector ring segments 22 illustrated in FIGS. 2 and 3. 
However, as dictated by winding topology, troublesome cases arise where 
the top coil side 20 is axially shorter than the commonly slotted bottom 
coil side. The troublesome cases arise because the connector ring segments 
standard radial arm portions 23 joined to the top coil side 20 interferes 
with the radially outwardly adjacent bottom coil side. The troublesome 
cases can be minimized for any machine having phase interspersed connector 
ring segments 22, but they cannot be eliminated. 
FIG. 4 is a pictorial view of one end of stator structure 16 illustrating a 
connection solution for the troublesome cases. A modified connector ring 
segment 22' having circumferential clearance portion 25 disposed between 
radial arm portion 23 and the top coil side 20 provides a structure 
suitable for overcoming the connection problems for the aforementioned 
troublesome cases. Circumferential clearance portion 25 extends 
peripherally a distance sufficient for the connected radial arm portion 23 
to clear the commonly slotted bottom coil side 20. Disadvantages of such 
modified connector ring segment 22' include complex fabrication and 
operational force levels per inch of connector ring segment significantly 
higher than elsewhere in the winding. 
It should be understood that FIGS. 2 and 3 represent the coil side 
interconnections (i.e. each radially outer coil is electrically connected 
to a radially inner coil) presently utilized in turbine generator stator 
coil systems and that FIG. 4 illustrates the circumferential clearance 
portion 25 of certain coil sides which is necessitated by the 
above-mentioned interconnection scheme. It is the elimination of this 
clearance portion 25 to which the present invention is directed. 
FIGS. 5 and 6 illustrate the present invention winding in pictorial and 
schematic views, respectively. Generally, coil sides 20 in all slots 
having axially longer bottom coil sides 20 than top coil sides 20 should 
be interchanged. In other words, connections to those coil sides 20 should 
be reversed such that the top coil side in the subject slot connected at 
both ends of the stator to top coil sides 20 in different slots rather 
than the typical top-to-bottom connections. Likewise, the bottom coil side 
20 in the subject slot is connected at both ends of the stator to bottom 
coil sides 20 in different slots. Thus, commonly slotted top and bottom 
coil sides (labeled T and B) 20 are respectively joined to other top and 
bottom coil sides circumferentially displaced therefrom in different 
slots. As can be seen, the standard connector ring segments 22 can then be 
used for joining coil sides 20 throughout the winding. 
FIG. 6 is a radial view of one stator end turn region in which the 
invention is embodied. In contradistinction to the typical top coil side 
to bottom coil side connections described above and illustrated in FIGS. 
2, 3 and 4, the present invention connects preselected top coil sides to 
other preselected top coil sides and also connects preselected bottom coil 
sides to other preselected bottom coil sides as shown pictorially in FIG. 
5 and schematically in FIG. 6. In FIG. 6, a thirty-six slot machine is 
represented as it would appear in a radially outward view laid flat. Each 
slot, S1 through S36, has two coil sides 20 disposed therein. In each 
slot, the upper of the two coil sides 20 is the bottom coil side B and the 
lower of the two coil sides 20 is the top coil side T. As can further be 
seen in FIG. 6, eighteen axial end turn positions, 1 to 18, are 
represented with phases A, B and C being interleaved. These axial 
positions are the physical locations in which the C-shaped connector rings 
22 are disposed. For purposes of clarity, only selected coil sides 20 and 
connector rings 22 have been labeled. As can be seen in FIG. 6, many of 
the connections provide electrical communication between top and bottom 
coils (e.g. the top coil of slot 17 connected to the bottom coil of slot 
34 and the bottom coil of slot 27 connected to the top coil of slot 10). 
However, in order to avoid the necessity of specially shaped coils (e.g. 
reference numeral 25 of FIG. 4), certain preselected top coil sides are 
electrically connected to other top coil sides and preselected bottom coil 
sides. By example, the top coil sides 20 rather than the bottom coil sides 
in slots 1, 7, 13, 19, 25, and 31 are connected to top coil sides in slots 
20, 26, 32, 2, 8, and 14, respectively. The bottom coil sides in slots 1, 
7, 13, 19, 25, and 31 are likewise connected to bottom coil sides in slots 
18, 24, 30, 36, 6 and 12, respectively. Similar interchanging of coil side 
connections is required on the exciter end (turbine end is shown) for the 
slots where the top coil side is shorter than the radially adjacent bottom 
coil side. Although the invention is shown embodied in a 36 stator slot 
machine, it is to be understood that the connections for any number of 
slots may be provided in the aforementioned prescribed manner.