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Description  |
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This invention relates to electric motors and generators and particularly
to motors and alternators with balanced, three-phase wave windings.
The object of the invention is to provide improved windings for such
machines capable of providing an additional voltage rating.
Accordingly, the invention provides a machine having a three-phase, wave
winding comprising a plurality of similar, but not identical,
phase-winding parts, said parts being connected together alternatively for
alternative voltages, one such connection providing the parallel
arrangement of all said phase-winding parts and said parts differing, one
from another, by the presence of a dummy coil.
By a dummy coil is meant a slot position containing no coil, or coils,
included in the circuit of the phase winding part concerned, the slot
position being bridged for the series connection of the coils of the
phase-winding part. Such dummy coil may be present, physically, in the
winding and excluded from circuit solely in the parallel connection
described, or it may be omitted physically from the winding, in which case
it is necessarily omitted in all of the alternative connections of the
windings. Advantageously the slot position devoid of coils is
substantially in the center of the corresponding phase-winding part.
In order that the invention may be clearly understood and readily carried
into practice, two conventional windings and two corresponding windings
according to the invention will now be described in detail, by way of
example, with reference to the accompanying drawings, in which:
FIG. 1 shows one phase-winding of a conventional 28-pole, three-phase wave
winding in 99 slots;
FIG. 2 shows one phase-winding of a corresponding 28-pole, three-phase wave
winding in 99 slots according to the invention;
FIG. 3 shows one phase-winding of a conventional 32-pole, three-phase wave
winding in 126 slots;
FIG. 4 shows one phase-winding of a corresponding 32-pole, three-phase wave
winding in 126 slots according to the invention.
FIG. 5 is a slot vector diagram for one phase of the 28-pole winding shown
in FIG. 1;
FIG. 6 is a slot vector diagram for one phase of the 32-pole winding shown
in FIG. 3.
FIG. 7 shows one phase-winding of an alternative 28-pole, three-phase
winding in 99 slots providing 2-parallel circuits; and
FIG. 8 shows one phase-winding of an alternative 32-pole, three-phase
winding in 126 slots providing 4-parallel circuits.
A waVe winding is characterised by the equation:
S=py.+-.a (1)
where
S is the armature slot number;
"p" is the pole-pair number;
"y" is the winding pitch;
the signs signify (+) a retrogressive winding and (-) a progressive
winding; and
"a" is the number of plexes, which determines the number of parallel paths
of the winding.
A wave winding is invariably a double-layer winding and, if single-turn
coils are used, there will thus be only two conductors per slot. Such
windings are particularly suited for low-voltage machines.
A typical, practical motor-alternator combination, frequently used in
marine service, comprises a 3-phase, 4-pole synchronous or induction motor
energised from a 3-phase, 50 HZ or 60 HZ mains supply, driving a 32-pole
or a 28-pole, 3-phase wave wound alternator to provide, respectively, a
400 HZ or 420 HZ, 3-phase output at, say, 380 volts. By using alternative
star/delta connections, the same alternator can have the dual-voltage
rating, in the example given, of 380/220 volts. Because of the wide
availability of 110 volt apparatus, it would be convenient, in the machine
combination described, to provide the further alternative output voltage
of 110 volts. This can readily be achieved in a machine according to the
present invention.
FIG. 1 is the connection diagram for phase-winding A of a conventional
28-pole, 3-phase, simplex, retrogressive wave winding in a 99-slot stator.
The letters "T" and "B" denote "T" the top coil-side slot location and "B"
the bottom coil-side slot location. Thus, the coil pitch is 3 slots (slot
1 to slot 4 and so on).
Evaluating Equation 1, above:
S=99 slots
p=14 pole-pairs
y=7
a=(+)1 and the winding is a retrogressive, single circuit winding.
Assuming unit e.m.f. for every coil, the resultant e.m.f. of the 17-coil
left-hand coil-sequence, between terminals 1 and 2, is 16.19 units. The
resultant e.m.f. of the 16-coil right-hand coil-sequence, between
terminals 3 and 4, is 15.32 units. The two resultant e.m.f.'s are
co-phasal. The layer factor is 0.955 and the pitch factor is 0.972. Phases
B and C are symmetrically displaced by 120.degree. mechanical, so that
only consideration of the one phase, phase A of FIG. 1, is necessary.
Analysis of the slot vectors on a 28-pole scale for the winding of FIG. 1,
starting with coil T1 and ending with coil T14 shows that the slot vectors
for the coil-sequence between terminals 1 and 2 are disposed
symmetrically, one half of the slot vectors on each side of the slot
vector of coil T57, the 9th coil of the coil-sequence, see FIG. 5.
FIG. 2 shows phase A of a 3-phase 28-pole wave winding in 99 slots of
generally similar form to that of FIG. 1 but differing in that, firstly,
coil T57 is excluded from the coil-sequence and, secondly, the left hand
coil-sequence between terminals 1 and 2, is connected in parallel with the
right-hand coil sequence, between terminals 3 and 4.
For the winding of FIG. 2, the coil-pitch is 3 slots (slot 1 to slot 4 and
so on) as for the winding of FIG. 1. Assuming unit e.m.f. for each coil,
the resultant e.m.f. of the left-hand coil-sequence, between terminals 1
and 2, is 15.19 units and the resultant e.m.f. of the right-hand
coil-sequence, between terminals 3 and 4, is 15.32 units. The two
resultant e.m.f.'s are co-phasal and the average e.m.f. if 15.26 units.
The layer factor os 0.925, the pitch factor is 0.972 and the winding factor
is 0.899. Phases B and C are symmetrically displaced by 120.degree.
mechanical with respect to phase A shown.
In a practical alternator, connections from all terminals 1, 2, 3 and 4 are
brought out to switching terminals to permit of the further alternative
parallel (delta) connection shown in FIG. 2. Together with the series
star/series delta connections used for the winding of FIG. 1, the
arrangement of FIG. 2 provides alternative voltage outputs in the ratios
2.sqroot.3:2:1, that is 380/220/110 volts in the specific instance. Thus,
a series star/series delta/parallel delta connection can be provided (not
shown).
FIG. 3 shows phase A of a conventional 32-pole, 3-phase wave winding in 126
slots.
Evaluating Equation 1, above:
S=126 slots
p=16 pole-pairs
y=8
a=(-)2 and the winding is thus a progressive winding with 2 circuits per
phase.
The coil-pitch is 4 slots (slot 1 to slot 5 and so on). Assuming unit
e.m.f. per coil, the resultant e.m.f. of the left half coil-sequence,
between terminals 1 and 2 and terminals 4 and 3 in series, is 20.06 units.
The resultant e.m.f. of the right half coil-sequence, between terminals 5
and 6 and terminals 8 and 7 in series, is also 20.06 units. The two
resultant e.m.f.'s are co-phasal. The layer factor is 0.955, the pitch
factor is 1.0 and the winding factor is 0.955. Phases B and C are
symmetrically disposed at 120.degree. mechanical separation with respect
to phase A, so that only phase winding A of FIG. 3 need be considered.
In the 2 circuit per phase arrangement of FIG. 3, four coil-sequences in
all are shown, respectively between terminals 1, 2; terminals 5, 6;
terminals 3, 4 and terminals 7, 8. These coil-sequences contain,
respectively 10 coils, 10 coils, 11 coils and 11 coils.
Analysing, now, the slot-vectors of the two 11-coil coil-sequences on a
32-pole scale, it will be seen that the slot-vectors of five coils are
each symmetrically disposed with respect to the slot-vectors of five other
coils about the slot-vector corresponding to coil T37 and coil T100,
respectively, see FIG. 6.
FIG. 4 shows phase A of a modified 3-phase, 32-pole wave winding in 126
slots, according to the present invention, wherein the coils T37 and T100
of the FIG. 3 arrangement are omitted from circuit in the respective
11-coil coil-sequences, reducing them to 10-coil coil-sequences.
As in the earlier figures, the letters "T" and "B" represent "T"--top
coil-sides and "B"--bottom coil-sides. The two dummy coils are represented
by rectangular blocks enclosing the coil-side slot numbers. The winding of
the invention provides the additional 4-circuit connection shown in FIG. 4
and the four circuits are indicated by the Circuit No. numerals 1 to 4
beneath the respective coil-sequences.
Assuming unit e.m.f. per coil, the resultant e.m.f. of each of circuits No.
1 and No. 3 is 9.59 units. The resultant e.m.f. of each of circuits No. 2
and No. 4 is 9.46 units. The resultant e.m.f.'s of all four circuits are
co-phasal and the average resultant e.m.f.'s are 9.53 units.
The layer factor is 0.907, the pitch factor is 1.0 and the winding factor
is 0.907.
The three permissible connections of the windings: 2-parallel
star/2-parallel delta/4-parallel delta provides output, or supply rating,
voltages in the ratios 2.sqroot.3:2:1 or, in the specific case, 380
volts/220 volts/110 volts.
The windings according to the invention, as exemplified by the
parallel-connected windings of FIG. 2 and FIG. 4 provide not only the
additional output, or supply, voltage rating described but, in common with
known multi-parallel circuit windings, provide harmonic suppression,
reduction of magnetic noise, and enhancement of starting and running
torque, when used as motor windings, or provide improvement of transient
performance and of output waveform, when used as generator windings.
The use of dummy coils, as described, to permit of doubling of the number
of parallel circuits, reduces the winding factors by some 5% in each of
the two examples given with reference to FIGS. 2 and 4.
The dummy coils described may also be included in the Series star/Series
delta and 2-parallel star/2-parallel delta connections of FIG. 2 and FIG.
4 respectively. The voltage ratings of the winding with all coils in
circuit are modified in consequence, so that the obtainable ratings are in
the ratios (1.05.times.2.sqroot.3):(1.05.times.2):1 or, in the specific
case, 400 volts:230 volts:110 volts, which may often be a more
advantageous voltage rating.
The 28-pole winding in 99 slots of FIG. 2 and the 32-pole winding in 126
slots of FIG. 4 both have co-phasal induced e.m.f.'s in the parallel
branches of each phase-winding, as has been explained with reference to
FIG. 5 and FIG. 6, respectively, but slightly different magnitudes.
There is an alternate multi-parallel circuit connection wherein the
fundamental e.m.f's induced in all the branches of each phase-winding are
equal in magnitude but differ slightly in phase.
FIG. 7 shows the alternate arrangement by comparison with FIG. 2 and FIG. 8
shows the alternative arrangement by comparison with FIG. 4.
In FIG. 7, as in FIG. 1 and FIG. 2, "T" denotes the Top and "B" denotes the
Bottom coil-side slot location. The pitch is 3 slots.
In the arrangement of FIG. 7, the connection of the left-hand coil sequence
are: terminal 1 to coil-side T1, coil side B53 to terminal 2, terminal 2
to terminal 4 omitting the slot position T.57 as the 9th coil, terminal 4
to coil side B63 and coil side T11 to terminal 3. The connections of the
right-hand coil sequence are: terminal 5 to coil side T64, coil side B17
to terminal 6, terminal 6 to terminal 8, terminal 8 to coil side B7 and
coil side T54 to terminal 7, there being no dummy coil. The two phase
winding parts are parallel between terminals 1/5 and terminals 3/7, as
shown.
Assuming unit e.m.f. for every coil of the phase-winding, the resultant
e.m.f.'s of the left-hand and right-hand coil sequences are both 15.26
units, but they differ in phase by 1.82.degree. electrical. The winding
factor is 0.899.
Parallel connection of the phase winding parts between terminals 1, 2, 4
and 3 and between terminals 5, 6, 8 and 7 is electrically permissible, the
resultant induced e.m.f. being no greater than that arising from
manufacturing tolerances in coil-side location or lamination dissymmetry.
In the arrangement of FIG. 8, the connections of the first of the four
circuits are: terminal 1 to coil side T1, coil side B37 to terminal 2,
terminal 2 to terminal 4, terminal 4 to coil side B81 and coil side T45 to
terminal 3. The connections of the second circuit are: terminal 5 to coil
side T41, coil side B77 to terminal 6, terminal 6 to terminal 8 omitting
slot position T37, terminal 8 to coil side B33 and coil side T123 to
terminal 7. The connections of the third circuit are: terminal 9 to coil
side T64, coil side B100 to terminal 10, terminal 10 to terminal 12,
terminal 12 to coil side B18 and coil side T108 to terminal 11. The
connections of the fourth circuit are: terminal 13 to coil side T104, coil
side B14 to terminal 14, terminal 14 to terminal 16 omitting the slot
position T100, terminal 16 to coil side B96 and coil side T60 to terminal
15.
Again assuming unit e.m.f. for every coil, the induced e.m.f. in each of
the four circuits is 9.53 units. The e.m.f.'s of circuit 1 and 3 are
co-phasal and the e.m.f.'s of circuits 2 and 4 are co-phasal but the first
pair (circuits 1 and 3) differ in phase from the second pair (circuits 2
and 4) by 2.86.degree. electrical. Again, parallel connection of all four
circuits between terminals 1/5/9/13 and terminals 3/7/11/15 is
permissible. Such a connection can be thus used to provide a 2-parallel
star/2-parallel delta/4-parallel delta configuration (not shown).
The slot-numbers, 99 slots and 126 slots, of the examples given herein are
low compared with slot-numbers which may be used in practice. As a rule,
the greater the slot-number, the smaller the induced e.m.f. differences
between parallel branches.
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