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BACKGROUND OF THE INVENTION
The present invention relates generally to dynamoelectric machines, and
winding arrangements and methods of operating the same. More particularly,
the invention is of particular value in connection with applications
wherein dynamoelectric machines are hermetically sealed within a
refrigeration system.
Induction motors used in refrigerator and freezer applications are usually
of the induction run variety, and the start or auxiliary winding is
de-energized during the running condition. Such motors are normally
connected with a current relay coil in series with the main winding. The
current relay senses the main winding current and then is operative to
open or disconnect the start winding circuit as the motor approaches
running speed. Start winding designs of this particular type of induction
motor for hermetic applications usually include additional resistance in
the form of backward-wound turns to improve the starting, accelerating,
and relay characteristics of the motor.
More recently, it has been found to be advantageous in at least some
applications to utilize the teachings of Johnson U.S. Pat. No. 3,774,062,
which issued on Nov. 20, 1973 in order to reduce, if not eliminate, the
use of backward-wound turns. The entire disclosure of this Johnson patent
is incorporated herein by reference for background purposes. Although
persons of ordinary skill in the art are familiar with the usage of
current relays for de-energizing the start windings of hermetic motors,
one publication in the art which describes such arrangements in some
detail and discusses the application of such relays in Smith et al. U.S.
Pat. No. 3,633,057, which issued Jan. 4, 1972. The disclosure of this
patent also is incorporated herein by reference.
Recently, in an effort to improve motor efficiencies, much development
effort has been dedicated to the design of capacitor run motors for those
applications in which resistance start, induction run motors have been
used heretofore. These efforst have been aimed at providing motor designs
which would result in substantially improved efficiencies compared to the
induction run design. However, capacitor run designs inherently have
relatively low starting torque. In fact, the starting torque for such
motors is usually at such low levels that it generally is inadequate for
many hermetically enclosed refrigeration applications. Because of this,
capacitor run designs intended for such applications inevitably seem to
require that an auxiliary starting aid must be utilized. One example of
such efforts is the use of an external resistor in series with the start
winding. Other examples are described in an application Ser. No. 778,335
assigned to the assignee of the present invention and filed Mar. 17, 1977
and filed in the name of William C. Rathje of Clinton, Iowa. For purposes
of background information, the disclosure of the aforementioned Rathje
application is incorporated herein by reference.
In some starting aid arrangements suggested heretofore, the external
resistor is arranged in series relationship with relay contacts external
to the hermetically enclosed motor stator. One desirable benefit with this
type of an arrangement is that the resistor is not active during running
conditions. Moreover, the resistor can serve to limit the discharge
current through the relay contacts and thus may also provide improvements
in relay reliability. Even with this approach, however, the motor would
have to be designed so that the motor main current versus speed would be
such that a usable "relay" current characteristic would be provided. One
solution for this problem would be to utilize arrangements such as those
shown in Martin U.S. Pat. No. 3,303,402, dated Feb. 7, 1967. However, it
would be even more desirable to provide improved starting torque for a
capacitor run motor without necessitating the use of any auxiliary
external starting aid. The value of avoiding the use of external resistors
or PTCRs is even greater when it is recalled that usually only finite and
discreet values of such resistors or PTCRs are commercially available at a
resonable cost. Because of this, the motor designer would have to comprise
the optimization of his winding arrangements while accommodating such
design to the discreet and finite value of a given resistor or PTCR.
It accordingly would be desirable to provide a new and improved hermetic
motor which would operate as a capacitor run motor and yet which also
would have improved starting torque characteristics without requiring the
use of an extra resistor or PTCR. More specifically, it would be desirable
to provide a new and improved motor of a type such that established and
proven high-speed winding techniques may be utilized to provide an
auxiliary winding particularly selected for capacitor run operation and
yet also having virtually any desired internal resistance during the
starting period. This type of approach would let a motor designer optimize
the auxiliary winding for capacitor run operation and yet also optimize
the winding for starting conditions and relay characteristics. It would be
further desirable to provide a motor winding arrangement such that
relatively high I.sup.2 R losses generally associated with the auxiliary
winding of a resistance split phase motor would not occur during running
conditions. Finally, it would also be desirable to provide a motor winding
arrangement wherein different types of winding materials may be utilized
in order to minimize the cost of such an arrangement.
Accordingly, it is an object of the present invention to provide improved
dynamoelectric machine winding arrangements for hermetically sealed
applications whereby capacitor-run performance may be obtained and yet
wherein adequate starting and accelerating torque may also be provided
without requiring the use of external resistors or PTCRs, and yet wherein
desired main winding current characteristics will also be established for
proper current relay operation.
It is a more specific object of the present invention to provide a motor
having a main winding phase and an auxiliary winding phase wherein the
auxiliary winding phase includes multiple sections that may be selectively
energized depending upon whether the motor is in a starting and
accelerating mode or in a normal running mode, wherein desired running and
starting performance is provided, and yet wherein normal duty relays may
be reliably used to control the selective energization of such multiple
sections.
It is yet another object of the present invention to provide improved
motors and winding circuit arrangements therefor wherein, during starting
conditions, the effective "a" ratio of the auxiliary and main windings is
of a first relatively low value (and the resistance of the auxiliary
winding phase is relatively high) so that a suitable relay current will
flow through the main winding of the motor and so that relatively good
starting torque will be provided; and wherein, during running conditions,
the effective "a" ratio of the auxiliary and main windings is higher than
it was during starting so that effective utilization of a run-capacitor
will result, and the auxiliary winding resistance is relatively low (as
compared to starting) so that improved running efficiencies may be
attained.
It is a more specific object of the present invention to provide an
arrangement of the type described in the immediately preceding paragraph
wherein the auxiliary winding is devised so that at least part of this
winding will act as a protective impedance for the contacts of a current
relay.
It is still another object of the present invention to provide a resistance
start-capacitor run motor wherein an auxiliary winding circuit is devised
so that the motor designer will have one more degree of design freedom
than has generally been recognized heretofore; all with the result that
the resistance start motor may be designed having desirable features
previously recognized for resistance start motors, and yet wherein such
motor may also be design optimized for good capacitor-run running
performance.
SUMMARY OF THE INVENTION
In carrying out the present invention in one form thereof, I provide a
motor that is particularly designed and adapted for operation during
starting conditions as a resistance split phase motor having a primary
winding phase with a preselected number of effective winding turns
n.sub.le ; a first section of an auxiliary winding phase for carrying
current in a first instantaneous relative reference direction and having a
first preselected number of effective winding turns n.sub.lesr ; and a
second section of an auxiliary winding phase for carrying current in a
second instantaneous relative direction opposite to the reference
direction in the first section; and wherein the first and second sections
of such auxiliary winding phase have, when energized at the same time, a
second preselected number of effective winding turns n.sub.less.
The number of effective winding turns of the auxiliary winding phase are
selected so that the ratio of n.sub.less to n.sub.le (herein defined as
"a.sub.s ") is in a first predetermined range; and so that the ratio of
n.sub.lesr to n.sub.le (herein defined as "a.sub.r ") is in a second
predetermined range. These predetermined ranges are selected so that
during running conditions when the first section of the auxiliary winding
phase remains energized with a capacitor connected in series therewith
good running performance results; and so that during starting conditions
when both sections of the auxiliary winding phase are energized good
starting and accelerating performance (as compared to a permanent
capacitor motor) will result. During starting conditions, the main winding
current is influenced by the ratio "a.sub.s " and the current
characteristic is such that it will cause proper operation of a relay
having its relay coil connected in series with the main winding. Thus, the
relay is operable to open its contacts at a desired main winding current
condition corresponding at least approximately to a predetermined motor
speed.
The auxiliary winding is provided with connecting points that are
interrelated with the relay contacts and a power supply line so that
during starting conditions, both of the auxiliary winding sections are
energized; but only the first winding section of the auxiliary winding is
energized after the relay contacts open. At this time, the capacitor
provides good running performance because the ratio "a.sub.r " has been
selected to be in a desirable range.
In preferred embodiments of the present invention, the ratio "a.sub.s " is
in the range of from about 0.7 to about 1.0; and the ratio "a.sub.r " is
in the range of from about 1.0 to about 1.7--in more preferred forms,
"a.sub.r " is from about 1.1 to 1.5. Furthermore, the numerical ratio of
"a.sub.r " to "a.sub.s " is less than 2. When the ratio "a.sub.r " is in
the range just mentioned, improved motor operating efficiency will result
with a capacitor connected in series with the first section of the
auxiliary winding phase.
In applications utilizing the present invention in preferred forms thereof,
a motor circuit is provided that utilizes motors particularly designed and
constructed according to the invention and wherein a capacitor is
connected between one side of the power supply and the electrical junction
of the first and second sections of the auxiliary winding phase. During
starting and accelerating conditions, the second section of the auxiliary
winding phase is connected through closed relay contacts in parallel
circuit relation with the capacitor. However, when the contacts open, the
second section of the auxiliary winding phase is disconnected from the
power supply, and power to the first section of the auxiliary winding
phase is supplied only through the capacitor.
With this arrangement, the second section of the auxiliary winding phase
provides a protective impedance for the relay contacts and prevents arcing
and associated damage to the relay contacts. Accordingly, relatively slow
acting, state of the art relays may be used.
In preferred applications, both sections of the auxiliary winding phase are
energized during starting conditions and the total auxiliary winding phase
presents a relatively high resistance load to the power source while the
second section of the auxiliary winding phase shunts the capacitor. Thus,
relatively good starting torque associated with resistance split phase
motors is provided. Then, when the relay contacts drop out, the second
section of the auxiliary winding phase is de-energized, and the relatively
lower resistance first section of the auxiliary winding phase continues to
be energized--but through the capacitor. In this mode, efficient running
performance usually associated with capacitor motors is attained.
When carrying out the present invention, the first and second sections of
the auxiliary winding phase may be made of the same winding material and
may be of the same size (i.e., diameter). Alternatively, higher resistance
per turn materials-for example, such as smaller diameter copper, or EC
aluminum (of suitable diameter) or material having a particular
characteristic ratio "R" (and also of suitable diameter) as described in
the above-referenced Johnson U.S. Pat. No. 3,774,062 may be used for the
second winding section. Preferably, relatively good conductor material,
such as EC aluminum or copper will be utilized for the first section of
the auxiliary winding phase. The ability to select different materials
and/or sizes of winding material for the two winding sections gives the
motor designer still further flexibility and freedom in designing a motor
for a particular application-all as will now be understood by persons
skilled in the motor art.
One of the preferred modes of establishing the first and second winding
sections of the auxiliary phase winding is to arrange and energize the
winding turns of the first section on a magnetic core so that they conduct
current in a first instantaneous reference direction; and to arrange and
connect the winding turns of the second section in such a manner that they
would conduct (at the same instant in time) current in a sense opposite to
the reference direction. Thus, the second winding section is in bucking
relation with respect to the first winding section. The net result of this
arrangement is that energization of the entire auxiliary winding results
in less effective turns (i.e., n.sub.less) than the effective turns
n.sub.lesr which result when only the first section is energized.
Moreover, this results in a relatively high resistance winding with a low
number of effective turns (which is analogous to what occurs with
"blacklash" winding arrangements), while the auxiliary winding resistance
is relatively low when the number of effective turns is "high".
As is known, the "a" ratio of a motor at any given time is a function of
the relative number of effective turns in the auxiliary and main windings.
In carrying out the present invention, a higher "a" ratio during running
conditions is desirable for capacitor run operation, and a lower "a" ratio
is desirable for resistance start and relay current characteristics.
With the arrangements taught herein, it is now possible for a motor
designer to optimize his motor design by optimizing the capacitor voltage
as a result of being able to design for a relatively high "a" ratio during
running conditions. With prior approaches, attempts to do this would
result in degrading the needed relay-main winding current characteristics.
The backward or reverse turns in the second auxiliary winding section now
permit the attainment of good relay-main winding current characteristics
and, moreover, the reverse turns establish a protective impedence for the
relay contacts.
The subject matter which I regard as my invention is set forth in the
appended claims. The invention itself, however, together with further
objects and advantages thereof may be better understood by referring to
the following more detailed description taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified schematic diagram for one type of motor that has
been known heretofore in the prior art; wherein an auxiliary winding is
provided with two winding sections, and a centrifugal mechanism is
utilized to selectively by-pass a capacitor and one of the auxiliary
winding sections connected in series therewith;
FIG. 2 is a simplified schematic diagram of a motor embodying the present
invention in one preferred form thereof; and
FIG. 3 is a schematic representation of a stator assembly embodying the
invention in one specific form and wherein windings are disposed on a
magnetic core.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to the drawings in more detail, and more particularly to FIG.
1, a motor 10 has been schematically illustrated which has been
manufactured and sold by the assignee of the present invention long prior
to the present invention. The motor 10 includes a conventional squirrel
cage rotor 11 and a centrifugal switch mechanism 12 which opens a switch
13 as the rotor 11 approaches running speed. During starting conditions,
the switch 13 is in the closed condition as shown in FIG. 1.
The motor 10 includes a main winding phase 14 of any desired number of
poles and an auxiliary winding that includes a first winding section 16
and a second winding section 17. The winding section 17, along with a run
capacitor 18, is short circuited by line 19 and the switch 13 under
starting conditions. Thus, during starting conditions, the auxiliary
winding section 16 alone is energized from lines L1 and L2. As the motor
10 approaches running speed, however, the switch 13 opens and winding
sections 16 and 17 both then are connected in series with the capacitor 18
and across lines L1 and L2. The winding sections 16 and 17 are, as will be
understood, disposed on a magnetic core in aiding relationship and thus
both contribute to the development of positive torque during running
conditions. During starting conditions, the "a" ratio of effective turns
of the winding 16 to the main winding 14 would be on the order of about
0.7 to 0.9, and the resistance of the auxiliary winding 16 is relatively
low. However, when the switch 13 opens, the combined or total resistance
of windings 16 and 17 is anywhere from two to five times the resistance of
the winding 16 when considered alone. Moreover, the "a" ratio of the
auxiliary winding to main winding (with both windings 16 and 17 energized)
typically is in the range of from about 2 to 2.5. Thus, the "a" ratio is
changed (i.e., increased from starting to running conditions) by a factor
of about 2 to 0.7 or about 2.8:1. The description of the prior art
typified by FIG. 1 is presented herein for background purposes, but it is
noted that other patents in the art have also discussed approaches where
relays or centrifugal switches have been used for selectively energizing
only part of an auxiliary winding during running conditions. These types
of arrangements are shown for example in: Kingston U.S. Pat. No. 1,948,037
(Feb. 20, 1934); Lyden U.S. Pat. No. 2,028,230 (Jan. 21, 1936); and
Kennedy U.S. Pat. No. 1,780,881 (Nov. 4, 1930), to name but a few.
Kennedy U.S. Pat. No. 1,780,881 also illustrates an arrangement where an
extra auxiliary winding section is added to a basic auxiliary winding
section only during starting conditions. In the Kennedy arrangement,
however, a capacitor is always connected in circuit with the auxiliary
winding regardless of whether all or only part of the auxiliary winding is
being energized. Another patent--i.e., Bailey U.S. Pat. No. 1,707,424
(Apr. 2, 1929)--does discuss arrangements wherein an external resistance
may be selectively switched into series circuit arrangement with all or
part of an auxiliary winding. Bailey also teaches that the auxiliary
winding may be energized through a capacitor when the external resistor is
"switched out".
It now will be appreciated that many different approaches have been
suggested heretofore for providing resistance split-phase induction start
and capacitor run motors. However, utilizing such prior teachings would
result in one or more of the problems or difficulties that have been
discussed hereinabove.
In FIG. 2, a motor 20 embodying the present invention in one form thereof
is illustrated in schematic form. The motor 20 includes a conventional
squirrel cage rotor 21, a primary or main winding 22, and an auxiliary
winding which includes a first winding section 23 and a second winding
section 24.
It will be noted that the schematic representation for the winding sections
23 and 24 shows that they are in the opposite "sense" because the
instantaneous magnetic effect of winding section 24, when energized, is in
bucking relationship to the instantaneous magnetic effect of winding
section 23. It should be understood that the present invention may be
applied to motors of any desired number of poles or multi-speed motors,
and that such motors may be supplied with single phase power of any
suitable voltage and frequency.
When stator assembly embodying the present invention are to be utilized in
hermetically sealed refrigeration systems--for example in hermetically
sealed compressors--the stator assembly and a rotor usually are
transferred from one location to another where the stator assembly is
assembled within a hermetically sealable container. The rotor (usually
comprising a magnetic core with a die cast squirrel cage winding) normally
is then assembled with a compressor shaft, crank, and so forth.
Subsequently, the container is hermetically sealed. The stator assembly is
energized by connections or leads that extend through a seal in the
compressor housing which are interconnected with the four motor leads
26-29. In FIG. 2, the leads that are external are identified as leads 30,
31, 32 and 33. These leads may extend from the compressor to a location
that is either closely proximate to the compressor or remote therefrom,
and these leads in turn are interconnected with other components as will
now be described with continued reference to FIG. 2.
Power lines L1 and L2 are connectable to lines 25 and 30 and, for
simplicity of discussion, line 30 will be considered as a common line for
a 110 volt application. Line 25 on the other hand is connected to one side
of a capacitor 36, to one terminal 37 of a relay, and to one side of a
relay coil 39. The other relay contact 41 is connected to line 32, and
depending upon how much current is flowing through relay coil 39, relay
arm 42 will be in a circuit making position (as shown), or in a circuit
breaking position.
When power is initially supplied to the motor 20, the current supplied to
the main winding 22 through relay coil 39 will be sufficiently great to
close the relay contacts and power will then also be applied across lines
27 and 29, with current flowing serially through the auxiliary winding
sections 24 and 23.
The total auxiliary winding comprising the sections 23 and 24, in
conjunction with the main winding 22, causes the rotor 21 to rotate and
accelerate, all as will be understood by persons skilled in the art.
Satisfactory starting and acceleration of rotor 21 is accomplished only
when the second auxiliary winding section 24 is energized with section 23,
and when capacitor 36 is shunted by winding section 24. As the rotor 21
accelerates and approaches a predetermined speed, (e.g., in the
neighborhood of 3,000 rpm for a two pole, 60 Hz energized motor) the
current through the main winding 22 decreases to a level such that the
relay coil 39 "drops out" and opens contacts 37, 41. Thereafter, power is
no longer supplied to lead 27 and the second auxiliary winding section 24
is de-energized.
As the relay contacts open, the second auxiliary winding section 24 acts as
a protective impedence and prevents arcing across the contacts (and thus
damage to the contacts) which otherwise would occur. After the relay drops
out, the auxiliary winding 23 continues to be energized, but through
capacitor 36 and lead 28.
Thereafter, the motor 20 operates as if it were a capacitor run motor, and
its operation is characterized by desirable features, such as good
efficiency, that normally are expected from capacitor run motors. It, of
course, will be understood that during running conditions the main winding
current is not of sufficient magnitude to cause reclosure of the relay
contacts.
As has been mentioned hereinabove, since the motor 20 is used in
conjunction with a current relay, the main winding current versus rotor
speed must be such that the relay will pull in at standstill but drop out
before running speed (e.g., about 3,450 rpm for a two-pole, 60 Hz motor)
is reached. In order to provide the desired current characteristics in the
main winding, it is necessary to hold a particular relationship between
the auxiliary winding and main winding in terms of, among other things,
the effective turns ratio for the windings. On the other hand, for
capacitor run operation, it is generally desirable for the auxiliary
winding to have a relatively low resistance (as compared to that of a
resistance start-split phase motor) and also have an effective turns ratio
vis-a-vis the main winding which is considerably different from that which
would provide satisfactory relay operation.
The ratio of effective turns of an auxiliary winding to effective turns of
a main winding is called the "a" ratio for the motor, but motors (or
stator assemblies) embodying the present invention must have two
distinctly different "a" ratios--a ratio "a.sub.s " for resistance-split
phase starting and accelerating conditions, and a ratio "a.sub.r " for
capacitor-run conditions.
My work to date has shown that the ratio "a.sub.s " preferably should be in
the range of from about 0.7 to about 1.0; and that the ratio "a.sub.r "
will most preferably be in the range of from about 1.0 to about 1.5.
The ratio "a.sub.s " and "Q.sub.s " ratio are both of concern vis-a-vis
proper relay operation, where "Q.sub.s " is defined as:
##EQU1##
where "r.sub.s " is the resistance of the start winding, "r.sub.m " is the
resistance of the main winding, and "a.sub.s " is as defined hereinabove.
Generally speaking, for normal resistance-split phase hermetic motor
applications and for satisfactory relay operation, Q.sub.s should have a
value greater than 6, and "a.sub.s " will be from about 0.7 to 0.9,
although "a.sub.s " may be as low as 0.55 for some applications. However,
for these same types of applications where the motor is to be operated as
a capacitor run motor, the running "a" ratio should generally or usually
be from about 1.0 to about 1.7. Moreover, the auxiliary winding energized
while "running" preferably will have relatively low resistance in order to
improve efficiency of the motor. Motors embodying the invention, however,
must still have resistances r.sub.s and r.sub.m such that a satisfactory
"Q.sub.s " ratio will result.
The present invention, as thus far generally described herein, teaches a
way of resolving the conflicting requirements for resistance-start motors
as compared to capacitor run motors, and one specific reduction to
practice of the invention will now be described in more detail. In this
description, the same reference numerals used in connection with FIG. 2
will be used in order to avoid confusion.
In one particular reduction to practice, the main winding 22 had a number
of effective winding turns "n.sub.le " of 106.10 (on a per pole or per
coil group basis) and a resistance "r.sub.m " of 1.4 ohms when the two
coil groups of the two pole main winding were connected in parallel. The
auxiliary winding section 23, on the other hand, had a total resistance of
6.85 ohms when the two poles thereof were connected in series and the (per
pole or per coil group) number of effective turns of the auxiliary winding
section 23 (i.e., n.sub.lesr) was 130.1. The second section 24 of the
auxiliary winding had a total resistance, when the two poles or coil
groups thereof were connected in series with each other (and also in
series with the auxiliary winding section 23) of 2.78 ohms. The number of
effective winding turns (on a per pole or per coil group basis) of the
winding section 23, was 52.81 in a negative sense because they have a
negative magnetic effect as compared to section 24. When the winding
sections 23 and 24 were both energized, the net or resultant number
(n.sub.less) of effective winding turns for the auxiliary winding was
77.29 (i.e., 130.1 minus 52.81), and the total resistance (r.sub.s) was
9.63 ohms. Thus, "a.sub.s " equaled 77.29/106.10, or 0.728; and "a.sub.r "
equaled 130.1/106.10, or 1.226.
With reference now to FIG. 3, the constructional details of this particular
reduction to practice will be discussed in even more detail with reference
to the stator assembly 51.
The stator assembly comprises, or course, a slotted magnetic core having a
bore extending through the center thereof, with the bore being defined by
the tips 52 of a plurality of teeth 53. These teeth, in turn, established
therebetween axially extending slots which accommodated the turns of the
main and auxiliary windings.
The magnetic core 54 was made up of a plurality of common iron laminations
as known in the art, and a sufficient number of these laminations were
stacked together to establish a core having a stack height or length of
about 1.75 inches. The rotor (not shown in FIG. 3) had a shaft receiving
bore of about three-quarters of an inch, the squirrel cage rotor bars were
skewed at a nominal angle of about 15.5.degree., and the air gap between
the rotor outer diameter and the bore of the stator assembly was about
0.0115 inches.
FIG. 3 is a full size representation of the core 51, and it will be noted
from reviewing FIG. 3, that the core included 24 uniformly, angularly
spaced apart slots of uniform size and shape. However, it will be
understood, that the present invention may be practiced with cores having
a number of slots other than 24 and/or wherein different slots may be of
different sizes or shapes. The main winding 22 was formed with two coil
groups disposed on the core to establish two primary or main poles; the
winding sections 23, 24 of the auxiliary winding were also each formed
with two coil groups as a two pole winding; and the motor utilizing the
stator assembly 51 had a rated speed of 3,450 rpm when energized from a 60
Hz, 115 volt single phase source.
The particular winding distribution and winding materials utilized to
produce a one quarter horsepower version of the motor 20 will now be
presented. With regard first to the main winding 22, it will be noted that
each coil group thereof comprises five coils. The number of turns in each
of these coil groups, commencing from the innermost coil 61 to the
outermost coil 62 was 39, 47, 52, 66, and 67 winding turns respectively,
and on a "per pole" basis, the number of effective turns in each main
winding coil group (n.sub.le) was 106.10. The wire used to make the main
winding 22 was 0.0320 inch diameter copper wire, with a total weight of
1.711 pounds of copper being used for the main winding.
With regard to the auxiliary winding, a total of 0.585 pounds of 0.0213
inch diameter copper wire was used in making the auxiliary winding
sections 23, 24. When the same diameter is used to make the sections 23
and 24, all of the turns for a given slot could be wound continuously and
taps then brought out and interconnected to establish the sections 23 and
24 in bucking relationship. However, this would be very inconvenient.
Accordingly, it is preferred that the winding sections 23 and 24 be wound
separately and then placed on the core (either concurrently or
sequentially) with modern coil placing equipment. In the event that wire
of different diameters or wire of different materials (as discussed
hereinabove) is used for each of the auxiliary winding sections 23 and 24,
it will be obvious that the sections must be wound as separate and
distinct coil groups.
With contin | | |
