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RELATED APPLICATIONS
This application is related to my co-pending applications Ser. No. 935,009,
filed on Nov. 26, 1986 and Ser. No. 088,241, filed Aug. 24, 1987; and to
U.S. Pat. No. 4,675,565, issued on June 23, 1987.
BACKGROUND
Single phase alternating current electric motors are widely used for a
variety of different purposes and range in size from very small fractional
horsepower motors on up to multpile horsepower sizes. Single phase motors
are particularly popular since most home and business alternating current
supplies are in the form of single phase power supplies.
Single phase electric motors include a stator core, which is wound with
start windings and run windings connected to the source of operating
power. These stator windings surround and are inductively coupled to a
rotor which rotates a shaft to produce the motor output. Rotors are made
in a number of different configurations, such as squirrel cage rotors,
high resistance rotors, low resistance rotors, wound rotors or multiple
winding high and low resistance rotors. All of these configurations, along
with various stator winding arrangements, are well known in the electric
motor industry.
Typically, the start winding is made of relatively small diameter wire and
the run winding is made of relatively large diameter wire, compared to the
diameter of the start winding. These windings are physically and
electrically angularly displaced from one another on the stator.
In conventional capacitor-start and capacitor-start/capacitor-run motors, a
starting capacitor is connected in series with the starting winding and a
switch. At motor start-up the switch is closed and the capacitor, in
conjunction with the relatively small diameter starting winding, produces
a leading current in the starting winding which is approximately equal to
and approximately 90.degree. displaced in phase from the lagging current
in the main or run winding of the motor. Such arrangements produce high
values of starting torque.
Usually, the switch in a conventional capacitor start motor is a
centrifugal or thermal switch connected in series with the capacitor and
start winding across the input terminals. The run winding then is
connected in parallel with this series-connected starting circuit. In such
capacitor start motors, the starting condition is such that the
instantaneous locked rotor current is high, and the motor starting current
demand factor also is high. As a consequence, such motors undergo
relatively high operating temperatures and require some type of switch for
disconnecting or opening the starting winding circuit after a
preestablished rotational speed of the rotor is reached. Because the
starting winding of such motors generally is a relatively small diameter
wire, overheating can and frequently does occur. Such overheating results
in a relatively limited life of the starting winding due to burnout,
particularly under overload conditions of operation of the motor.
Applicant's above mentioned co-pending applications and the above mentioned
Patent all are directed to capacitor-start/capacitor-run motors which do
not use small diameter starting windings, but instead, utilize two
series-connected windings (of substantially the same diameter heavy wire)
electrically phase displaced 90.degree. from one another on the stator
core. One of these windings has a capacitor connected in parallel with it
to form a parallel resonant circuit at the operating frequency of the
motor. The motors of the above applications and Patent all are high
efficiency motors which overcome most of the disadvantages of the prior
art capacitor-start/capacitor-run motors.
For the motor of co-pending application '935, however, the starting torque
is relatively low. Thus, motors of the type disclosed in application '935
primarily are suitable for use in situations which do not require very
high starting torques, such as pumps, blowers, machines tools and many
commercial and domestic appliances. For utilization in situations where
higher starting torques are required, the motors of co-pending application
'241 and the above U.S. Pat. No. 4,674,565 are employed. These motors also
use a parallel resonant circuit at the operating frequency of the motor,
where the two windings of the motor are connected in series with one
another, and one of the windings has a capacitor across it to form a
parallel resonant circuit at the operating frequency of the motor. In
addition, a second capacitor is connected in series with a switch in
parallel with the first capacitor. This switch is closed during start up
of the motor and is opened during normal load conditions of operation of
the motor. This permits a substantial increase in the starting torque of
the motor, but during normal operating or running conditions of the motor,
the parallel resonant circuit functions in the same manner as disclosed in
the motor of copending application '935.
Applicant also has three other patents directed to single phase motors of
the capacitor start type directed to starting control circuits which
produce high starting torque. These Patents are U.S. Pat. Nos. 3,036,255;
3,573,579; and 3,916,274. The '255 Patent is directed to a capacitor motor
using a centrifugal or relay operated switch in the starting circuit to
open the capacitor starting circuit, disconnecting it and the start
winding from the motor operation during normal load conditions of
operation of the motor.
U.S. Pat. Nos. '579 and '274 both are directed to solid state motor
starting control circuits which do not employ mechanical switches. As a
consequence, arcing, which is associated with mechanical switches, and
other inherent shortcomings of mechanical switches, such as centrifugal
switches, are overcome by the solid state circuitry used in the starting
control circuit of these two patents. These patents, like other prior
capacitor start motors, however, have starting capacitors connected in
series with a start winding and the switch; so that starting current is
applied through the start winding only during the start up portion of
operation and the motor. Once the motor reaches or nears operating running
speed, the solid state switch creates an open circuit condition in the
starting circuit; and the starting winding is removed from further
operation. Consequently, such a solid state motor starting control circuit
functions in a manner similar to the mechanical switch circuits of the
prior art to control the connection and disconnection of the starting
winding from the power input terminals, in accordance with the particular
state of operation of the motor.
It is desirable to provide an efficient motor which is capable of producing
a high starting torque while still retaining the advantages of the
above-identified co-pending applications.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide an improved
alternating current motor.
It is another object of this invention to provide an improved alternating
current motor operated from a single phase alternating current power
supply.
It is an additional object of this invention to provide an improved single
phase alternating current motor which operates at high efficiency and
which develops high starting torque.
It is a further object of this invention to provide a high efficiency
alternating current motor operating with a series resonant circuit.
It is still another object of this invention to provide an alternating
current motor employing a run winding of relatively large wire size
connected in series with a capacitor having a large capacitance to provide
series resonant operating conditions with improved efficiency.
In accordance with a preferred embodiment of the invention an alternating
current motor is operated from a source of single phase alternating
current power. The motor has first and second windings electrically
angularly displaced from one another by substantially 90.degree. on a
stator core and inductively coupled to a rotor. The first winding is
connected in series with a capacitor to a source of alternating current
power. The second winding is connected in parallel with the series circuit
of the first winding and the capacitor. The capacitor and the first
winding form a series resonant circuit at the frequency of the alternating
current power supply, and the wire size of the first winding is relatively
large to permit it to carry the full load operating current. The capacitor
has a large capacitance; and the circuit operates such that, during normal
load operating conditions, little or no current flows through the second
winding. The motor produces a relatively high starting torque; and if
increased starting torque is desired, a switched capacitor is connected in
parallel with the series-connected capacitor during the start up
conditions of operation of the motor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 thorugh 6 are schematic diagrams of preferred embodiments of motors
according to the invention;
FIG. 7 is a curve illustrating the relative starting and running torques of
the motor of FIG. 1;
FIGS. 8A through 8D are vector diagrams of operating conditions of the
motor shown in FIG. 1;
FIGS. 9A through 9D are vector diagrams of additional operating conditions
of the motor shown in FIG. 1;
FIGS. 10 through 13 are vector diagrams of the the operating conditions of
the motor shown in FIG. 2; and
FIG. 14 is another embodiment of the invention.
DETAILED DESCRIPTION
Reference now should be made to the drawings where the same reference
numbers are used in the different figures to designate the same or similar
components.
FIG. 1 is a schematic diagram of a single phase capacitor run motor capable
of developing either moderate or high starting torque. Conventional split
capacitor motors or capacitor run motors develop very low starting
torques, so they typically are used for applications such as fans and
blowers which do not require high starting torques. The circuit of FIG. 1
essentially comprises two motors in one, namely a motor which, in one mode
of operation, is capable of producing high motor starting torque of the
type associated with known capacitor start motors. In another mode the
mode operates as a switchless motor which develops a moderate starting
torque developing rapidly to a high torque following initial start, so
that the motor is capable of use in a wide variety of applications.
In the circuit of FIG. 1, single phase alternating current power is
supplied from a suitable source 9 through a double-pole single-throw
switch 10/12. A center tapped run winding 13A, 13B is wound on the stator
core and is connected in series with a run capacitor 17 across the switch.
A start winding 14 also is wound on the stator and is connected to the
center tap between the winding sections 13A and 13B.
To permit instantaneous reversal of operation of the motor, a three-pole
double-throw reversing switch 19 is employed to reverse the direction of
the current flow through the winding 14 with respect to the current flow
through the winding sections 13A and 13B. If this reversing feature is not
desired, however, the switch 19 may be eliminated, with the winding 14
being connected directly between the junction of the winding sections 13A
and 13B and the terminal of the switch 12. From an examination of FIG. 1,
it can be seen that when the poles of the switch 19 are in the right hand
position, the upper end of the winding 14 is connected to the junction
between the winding sections 13A and 13B and the lower end to the switch
12. When the poles of the switch 19 are in the left hand position, this
interconnection is reversed; so that the lower end of the winding 14 is
connected to the junction between the winding sections 13A and 13B and the
upper end is connected to the switch 12. During the running of the motor
of FIG. 1, the switch 19 can be switched from one position to the other,
causing instantaneous reversal of the rotation of a rotor 15 which is
surrounded by the stator on which the windings 13 and 14 are placed.
The capacitor 17, which is connected in series with the winding section
13B, has a large value of capacitance in contrast with the typical
starting capacitor used in capacitor start or split capacitor motors. In
addition, the wire size of the winding sections 13A and 13B is relatively
large. Typically, for a one horsepower motor, the wire size of the winding
sections 13A and 13B is number 16 or number 17 wire while the wire size of
the winding 14 is number 18 or number 20 wire. The capacitance of the
capacitor 17, operating at 370 volts, is approximately 80 microfarads.
These values are not to be considered limiting, but are representative of
values which have been found to provide the desired operating
characteristics of the motor shown in FIG. 1.
During the operation of the motor from start through no load and/or full
load conditions, the capacitor 17 in series with the winding section 13B
forms a series resonant circuit, the resonance of which is selected to be
at or near the 60 Hz frequency of the power supply 9. Obviously if power
supplies of different frequencies, such as 50 Hz or 120 Hz are used, the
resonance of the series resonant circuit consisting of the winding section
13B and the capacitor 17, is selected to match the frequency of the
particular alternating frequency source 9. The capacitor 17 is an
alternating current non-polarized capacitor and may be an electrolytic
capacitor, a metallized foil capacitor, or a metallized polypropylene
capacitor.
The motor of FIG. 1 causes a substantial portion of the total current at
start up to flow through the winding 14. This current, however, rapidly
drops to near zero, with essentially all of the operating current flowing
through the run winding sections 13A and 13B. This shift of the current
flow occurs automatically as a result of the characteristics of the series
resonant circuit, so that the start winding 14 may be made of relatively
small diameter wire. There is no danger of burnout of the starting winding
since it never carries any high current for any prolonged period of time.
In fact, during normal run operation of the motor, the start winding 14
could be switched entirely out of the circuit, if desired. This is not
necessary, however, since the current automatically drops to zero or near
zero due to the inherent operating characteristics of the motor.
The circuit described thus far produces a moderate starting torque which
develops to substantially full or maximum torque at approximately 50of the
rated RPM value of the motor. When the motor reaches full operating speed
at full load, the torque drops down to a point which is near the starting
torque.
If, however, a high starting torque is desired, a starting capacitor 27 may
be connected in parallel with the capacitor 17 through a pair of switches
21 and 23. The switch 21 is used to optionally connect the starting
capacitor 27 into or out of the circuit on a semi-permanent basis. This
permits use of the motor as "two motors in one". When the switch 21 is
open, obviously the capacitor 27 is never connected into the circuit and
has no effect on the circuit operation. The motor then exhibits moderate
starting torque, as described. When the switch 21 is closed, however, the
capacitor 27 is connected in parallel with the capacitor 17 during motor
start up. The second capacitor 27, in parallel with the capacitor 17,
causes the phase displacement of the currents through the windings 13 and
14 to be in the vicinity of a 90.degree. displacement during motor
starting conditions. This produces a high starting torque in the motor
which is considerably greater than when the capacitor 27 is not used in
the circuit. Once the rotor 15 of the motor attains or approaches its
normal operating speed, a centrifugal switch 25 coupled to the rotor 15
opens the contacts 23 and removes the capacitor 27 from the circuit.
An energy dissipating resistor 26 is connected across the capacitor 27 for
the purpose of dissipating any energy stored in the capacitor 27 at the
time the switch 23 opens. A similar energy dissipating resistor 18 is
connected across the series resonant capacitor 17 for the same purpose
whenever the switch contacts 10 and 12 are opened to turn off the motor or
disconnect it from the source of alternating current power 9.
A significant feature of the motor which is shown in FIG. 1 is its
capability of instantaneous or nearly instantaneous reversal, under either
light load or heavy load, without the necessity of first stopping the
rotation of the rotor 15. This is accomplished, as mentioned previously,
by changing the position of the reversing switch 19 from the right hand
position to the left hand position or vice-versa. This reverse the very
light current flow through the winding 14 a sufficient amount to reverse
the phase of operation of the entire circuit to rapidly and instantly
reverse the direction of rotation of the rotor 15. This can be
accomplished at full operating RPMs, if desired.
FIG. 2 is another embodiment of the invention employing a single run
winding 13 (not center-tapped as in FIG. 1) and which has the reversing
switch 19 connected to the run winding 13 instead of to the start winding
14. In all other respects, the system of FIG. 2 operates the same as the
circuit of FIG. 1. The winding 13 is made of heavy wire (number 16 or
number 17 wire has been found to be suitable) and is connected in series
with the capacitor 17 to form a series resonant circuit at the operating
frequency of the motor. When the reversing switch 19 has the poles moved
to the right, the left-hand end of the winding 13 is connected to the
switch 10, and the lower terminal of the capacitor 17 is connected in
common with the lower end of the winding 14 to the bottom or return side
of the power supply 9 by way of the switch 12. When the poles of the
reversing switch 19 are moved to the left, as viewed in FIG. 2, the left
hand end of the winding 13 is connected through the poles of the switch 19
to the lower end of the winding 14 and the switch 12. The lower terminal
of the capacitor 17 then is connected through the switch 19 (the upper
pole thereof) to the switch 10, thereby reversing the connections of the
series resonant circuit 13, 17 with respect to the winding 14. This
provides the capability of instant reversal of the operation of the rotor
15 of the motor whenever the poles of the switch 19 are moved from their
far right position to the far left position and vice-versa.
Thus, it can be seen that the reversing switch 19 may be connected with
either one of the windings 13 or 14 to effect the reversal of direction of
rotation of the rotor 15. In all other respects the circuit of FIG. 2
operates in the same manner as the circuit of FIG. 1 which has been
described above.
FIGS. 3, 4 and 5 illustrate motor with moderate starting torque, which have
a further provision for varying the speed of operation of the rotation of
the rotor 15. The winding arrangements of the circuits of FIGS. 3, 4 and 5
for the run winding 13 and start winding 14 essentially are the same as
the arrangement shown in FIG. 2. In each of these circuits, the capacitor
17 is in series with the run winding 13 (having large diameter wire) to
form a series resonant circuit at the operating frequency of the
alternating current power supply from the source 9. In the circuit of FIG.
3, the start winding comprises a two section winding, 14A and 14B. The
winding 14A is comparable to the winding 14 of FIGS. 1 and 2. This
winding, however, is connected in series with a winding 14B which has a
slide tap on it to vary the number of turns of the winding 14B which are
connected in series with the winding 14A. This tap, in turn, is connected
to the switch 12; so that by varying the position of the tap on the
winding 14B, different number of turns (and therefore a different
inductance) is provided for the composite start winding. This varies the
speed of operation of the rotor 15 of the motor under load conditions.
FIGS. 4 and 5 are additional speed control configurations. The circuit of
FIG. 4 is similar to the one of FIG. 3, except that the tap on the winding
14B is connected between the junction of the winding 14A and the winding
14B instead of with the switch 12 as in the circuit of FIG. 3. This
circuit of FIG. 4, however, operates to control the speed of rotation of
the rotor 15 in the same manner as the circuit of FIG. 3. FIG. 4, however,
illustrates an alternative wiring interconnection between the winding
sections 14A and 14B.
The circuit of FIG. 5 employs a reactor (auto transformer) in series with
the series-connected run winding 13 and capacitor 17. Instead of returning
the lower terminal of the capacitor 17 directly to the switch 12, the
reactor 20 is connected between switch 12 and the capacitor 17. The
variation of the reactance of the reactor 20, as established by the
setting of the slide point, functions to change the voltage across the
capacitor 17, which in turn operates to change the power of the motor.
The circuit of FIG. 6 is similar to the circuit of FIG. 2, except the run
winding 13 has been broken into two sections 13A and 13C which are
inductively coupled together in a transformer like relationship to
increase the voltage across the capacitor 17. This has the effect of
increasing the starting and running torque of the motor.
It should be understood that a reversing switch 19 arranged either as shown
in FIG. 1 or FIG. 2, also can be used with the embodiments shown in FIGS.
3 through 6. In addition, the starting capacitor circuit consisitng of the
second or starting capacitor 27, centrifugal switch 25, 23 and the switch
21, also may be connected in parallel with the series-resonant capacitor
17 in the circuits of FIGS. 3 through 6, if desired. These features have
not been repeated in FIGS. 3 through 6 since the function of both the
reversing switch 19 and the second or additional starting capacitor
circuit, including the capacitor 27, is the same for all of the circuits
and operates in the same manner in the circuits of FIGS. 3 through 6 as in
the embodimetns shown in the circuits of FIGS. 1 and 2.
In the operation of all of the embodiments of FIGS. 1 through 6, a
significant difference exists between these circuits and conventional
capacitor run circuits. In conventional circuits, the capacitor is
connected in series with a relatively small wire size start winding. In
the circuits of FIGS. 1 through 6, this circuit interconnection is
reversed. The run winding is made of relatively heavy wire and is
connected in series with a large capacitance capacitor so that the major
current flow (essentially all of the current flow) which takes place
during the operation of the motor flows through the capacitor 17 and the
run winding 13, with current through the start winding 14 automatically
inherently dropping to near zero upon attainment of the full load and no
load operating conditions of the motor.
In all of the embodiments of FIGS. 1 through 6, the starting winding 14
briefly carries practically all of the current at initial startup. Because
the two windings are electrically dephased by 90.degree. on the stator,
high starting torque is developed, but the current flow through the
winding 14 rapidly drops off as the rotation of the rotor 15 increases.
The final running current through the winding 13 is controlled by the size
of the capacitor 13. The series resonance of the circuit consisting of the
winding 13 and the capacitor 17 builds a maximum current through the run
winding 13 to an amount which is limited by the capacitance of the
capacitor and the voltage applied across the capacitor 17. This series
resonance takes place immediately upon motor starting and throughout full
load and no load running conditions of operations.
Upon motor start conditions, the start winding 14 carries the full wattage
load of the given motor horsepower, while the run winding with its
capacitor 17 in series is dephased from the start winding 14 by
substantially 90.degree. electrically. At full load or near full load
operation, a change takes place where the run winding, with the capacitor
17 in series, has the full wattage of the horsepower of the motor across
it; and the start winding 14 leads or lags isolated current dephased from
the run winding 13 in the vicinity of 90 electrical degrees. Since the run
winding 13 of all of the different embodiments of FIGS. 1 through 6
carries substantailly all of the power developed by the motor as a result
of the operation of the series resonant circuit, consisting of the winding
13 and the capacitor 17, there is no danger of burnout of the start
winding 14, even if the start winding is wound of relatively small size
wire (such as number 18 or number 20 wire).
FIG. 7 illustrates the differences in starting torque versus motor RPMs
which are provided by (a) the switchless versions of the circuit (such as
shown in FIGS. 3 through 6 and which occur when the switch 21 of FIGS. 1
and 2 is open) and (b) the operation of the system when the switch 21 is
closed to employ the separate starting capacitor 27, described above in
conjunction with FIGS. 1 and 2. In the circuits of FIGS. 3 through 6 and
the circuits of FIGS. 1 and 2 with the switch 21 open, the plot of torque
versus RPMs is illustrated by the curve 30. It can be seen that the
starting torque of curve 30 is a relatively moderate torque which builds
to a maximum amount approximately at a speed of rotation which is 50% of
the final or full load rotational speed of the motor. This fulll load
speed is shown at the point 33 on FIG. 7. This is a switchless version of
the motors such as shown in FIGS. 3 through 6.
If a starting capacitor 27 of the type shown in FIGS. 1 and 2 is employed,
the motor exhibits a very high starting torque as shown on the curve 31 of
FIG. 7. This starting torque is in excess of 300% and exceeds the full
load torque at the point 33, as is readily apparent from an examination of
FIG. 7.
FIGS. 8A through 8D illustrate, respectively, the vector diagrams for the
motor of FIG. 1 at start (with switch 21 closed), at start (with switch 21
open), full load and no load conditions of operation. In FIG. 8A, the
current vectors for the motor at start up are dephased by substantially
97.degree. to produce a high starting torque. This dephasing is a result
of the combined capacitance of the capacitors 17 and 27. The relative
capacitance of the capacitors 17 and 27 is such that the capacitance of
the start capacitor 27 is higher than that of the capacitor 17 (for
example 175 microfarads for capacitor 27 and 50 to 80 microfarads for the
capacitor 17). The composite effect of this capacitance upon the starting
current is illustrated in FIG. 8A. The vector OA constitutes the current
through the start winding 14, and the vector AB constitutues the current
through the run winding 13. Line current is shown by vector OB.
FIG. 8B illustrates the start conditions for the motor of FIG. 1 with the
switch 21 open. This means that the capacitor 27 is not in the circuit and
only the series resonant capacitor 17 is in the circuit. It can be seen
that the phase displacement between the two windings in this mode of
operation is approximately 112.degree. and that a greater proportion of
the current flows through the winding 14 (as shown by the vector OA') than
flows through the winding 13B (as shown by the vector A'B').
FIGS. 8C and 8D illustrate, respectively, the current vectors for the motor
of FIG. 1 at full load and no load operating conditions. It is readily
apparent from an examination of these figures that the current vectors of
the windings 14 and 13B are approximately 180.degree. out of phase; and
consequently, the capacitor current controls the motor operation. It also
is apparent from an examination of FIGS. 8C and 8D that the current
through the starting winding 14 falls in the second or negative cosine
quadrant, which cause in the current through the winding 14 to be a
lagging current. This causes the motor operation to be at a near unity
power factor.
FIGS. 9A through 9D are vector diagrams of the operating characteristics of
the motor of FIG. 1 which have the voltage vector diagrams superimposed
over the current diagrams of FIGS. 8A through 8D. The current vectors are
the same as those shown in FIGS. 8A through 8D, and the voltage vectors
constitute the vectors AV/BV (for winding 13A) and BV/CV (for the run
winding section 13B). The vector O/BV constitutes the voltage across the
start winding 14, adn the vector O/CV constitutes the line voltage.
FIG. 9B illustrates the moderate torque starting conditions of operation
which exist when the switch 21 of FIG. 1 is opened. The various vectors
are shown with a prime (') but otherwise the designations are the same as
those given in conjunction with FIG. 9A. The various voltages, however,
and the relationships of the voltages and currents to one anther are
considerably different from the starting conditions with the switch 21
closed, as illustrated in FIG. 9A.
FIG. 9C shows the full load current and voltage vectors for the motor of
FIG. 1. The full load operating conditions are the same, whether the
starting capacitor 27 is or is not used since at full load, the capacitor
27 always is switched out of the circuit in the manner described
previously in conjunction with the description of the operation of the
circuit of FIG. 1. The vectors shown in FIG. 9C are the same as those
described previously in conjunction with FIGS. 9A and 9B except that each
of the vectors is provided with a double prime (") in this figure.
Finally, FIG. 9D shows the operating current and voltage vectors for the
motor of FIG. 1 under no load conditions of operation. In the operation of
the motor which is represented by the vectors of FIGS. 9C and 9D, the
operating speed essentially is the full operating RPM of the motor as
illustrated by the point 33 on the curves of FIG. 7.
An actual motor modified to have the winding configuration illustrated in
FIG. 1 and from which the information providing the basis for the vector
diagrams of FIGS. 8A through 8D and 9A through 9D has been constructed.
The motor used was a standard Dayton motor, frame 56, model Number 5K4310.
This was a one horsepower motor, 1725 RPM, 230 volts, 7.4 amps. The stator
was rewound in accordance with the configuration of FIG. 1, with number 16
wire for the winding sections 13A and 13B and with number 18 wire for the
start winding 14. In addition, the winding which was used as the run
winding in the original motor is employed as the start winding 14 and the
rewound start winding is used as the run winding 13A, 13B. The table below
indicates measurements taken at start (both with the switch 21 closed and
with it open), full load and no load conditions of operation (allowing
approximately 2% to 5% plus or minus meter accuracy readings):
TABLE I
______________________________________
Wind- Wind- Wind-
Single Phase ing ing ing Cap Cap
Power Input 14 13A 13B 27 17
______________________________________
Start Peak
23 A 16 A 23.0 A
19 A 19 A 6.6 A
A*
(21 closed)
Start Peak A
14 A 15 A 14.0 A
6.5 A 0 6.5 A
(21 open)
Full Load A
5.5 A 3.1 A 5.5 A 8.5 A 0 8.5 A
No Load A
3.2 A 6.0 A 3.2 A 9.0 A 0 9 A
Start V* 240 V 190 V 100 V 80 V 230 V 230 V
(21 closed)
Start V 240 V 190 V 60 V 25 V 0 200 V
(21 open)
Full Load V
240 V 230 V 125 V 135 V 0 295 V
No Load V
240 V 240 V 125 V 145 V 0 305 V
PF* Start
99% 90% 80% 87% 0 03%
(21 closed)
PF Start 97% 89% 73% 73% 0 03%
(21 open)
PF Full 90% 02% 69% 80% 0 01%
PF No Load
30% 02% 70% 75% 0 01%
______________________________________
Key:
A* Amperes
V* Volts
PF* Power Factor
From the measured currents of the motor shown in the above table and
illustrated in FIGS. 8 and 9, it can be seen that the motor is capable of
producing a relatively high starting torque (moderate when the switch 21
is open and very high when the switch 21 is closed). The starting torque
with the switch open is 3.1 foot pounds. With the switch 21 closed, the
starting torque is approximately 14.1 foot pounds. At full load or running
conditions of operation, the motor developed one horsepower at 3.0 foot
pounds of torque at 5.5 amperes of current at 1,750 RPM. The breakdown
torque from the motor full load to stalling is in the vicinity of 9 foot
pounds. The motor, as originally designed, draws 7.4 amperes for a one
horsepower output; so that the modified winding configuration employing
the series resonant circuit of the combination of the windings 13A, 13B
and capacitor 17 results in significantly higher efficiency during the
full load or running condition of operation of the motor.
FIGS. 10 through 13 illustrate the current and voltage vectors for a motor
constructed in accordance with the circuit configuration of FIG. 2. FIG.
10 is the full load vector diagram, FIG. 11 is the start condition vector
diagram with the switch 21 closed, FIG. 12 is the start condition vector
diagram with the switch 21 open, and FIG. 13 is the no load vector
diagram. The different phase angles are shown and the current vector
designations and voltage vector designations which are employed in FIGS.
10, 11, 12 and 13 are comparable to the ones which have been used in FIGS.
9A through 9D. The current vectors simply use letter designations (ABC)
with an origin "O", whereas the voltage vectors use the designations AV,BV
in conjunction with the origin "O". The current vector OA of Figure 11
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