Patent US3835356A successfully refreshed from Google Patents.
US3835356A
Expired / Lapsed
US
⏱️ 0.0 years remaining
System for operating three-phase induction motor under balanced conditions for changing loads
Assignee: United States Department of Agriculture
•
Filing: 1973-04-23
•
Granted: 1974-09-10
•
Expires: 1993-04-23
Abstract
Abstract Improvements are made to an autotransformer-capacitor static phase converter for energizing a three-phase induction motor from a single-phase source which enable the motor to operate under balanced conditions for various loads. The amplitude of the derived phase voltage is changed to equalize the voltage of the two other phases, and the capacitance in the derived phase is increased as a function of load current.
Inventors
- 👤 L Soderholm
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 02:03
CPC Classifications
H; H02; H02P; H02P27/00; H02P27/02
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
178 words
In a static phase converter for supplying a three-phase voltage to an induction motor from a single-phase voltage source including an autotransformer for generating an artificial phase voltage and first capacitor means connected in circuit with said artificial phase and one terminal of said motor, an improvement for balancing the phase currents during normal operation as the load on said motor changes, said improvement comprising: current sensing means for generating a signal representative of the normal operating load current in said motor; second capacitor means adapted to be connected in parallel with said first capacitor means; comparison circuit means responsive to said load current signal for connecting said second capacitor means in parallel with said first capacitor means when said normal operating load current signal exceeds a predetermined value; and feedback circuit means responsive to two of the phase voltages of said motor for changing the magnitude of said voltage of said artificial phase to cause said sensed phase voltages to be equal during operation of said motor and as a function of the load on said motor.
Claim 2
Dependent Claim
178 words
In a static phase converter for supplying a three-phase voltage to an induction motor from a single-phase voltage source including an autotransformer for generating an artificial phase voltage and first capacitor means connected in circuit with said artificial phase and one terminal of said motor, an improvement for balancing the phase currents during normal operation as the load on said motor changes, said improvement comprising: current sensing means for generating a signal representative of the normal operating load current in said motor; second capacitor means adapted to be connected in parallel with said first capacitor means; comparison circuit means responsive to said load current signal for connecting said second capacitor means in parallel with said first capacitor means when said normal operating load current signal exceeds a predetermined value; and feedback circuit means responsive to two of the phase voltages of said motor for changing the magnitude of said voltage of said artificial phase to cause said sensed phase voltages to be equal during operation of said motor and as a function of the load on said motor.
Claim 3
Dependent Claim
61 words
The system of claim 1 further comprising third capacitor means adapted to be connected in parallel with said first capacitor; and third comparison circuit means responsive to Said load current signal for switching said third capacitor in series with said first capacitor when said load current signal exceeds a second predetermined value higher than said first predetermined value of load current.
Claim 4
Dependent Claim
87 words
The system of claim 1 wherein said feedback circuit means comprises first circuit means for generating a signal representative of one phase of the three phases of voltage energizing said motor; second circuit means for generating a signal representative of the amplitude of the second phase voltage fed to said motor; comparison circuit means responsive to said signals representative respectively of the magnitudes of said first and second phase voltages; and means for varying the input voltage of said autotransformer in response to said comparison circuit means.
Claim 5
Dependent Claim
124 words
In a static phase converter for supplying a three-phase voltage to an induction motor from a single-phase source, a first phase being derived from the secondary of said autotransformer and further including a capacitor connected in series with said first phase voltage, the improvement comprising: A plurality of additional capacitors adapted to be connected in parallel with said first capacitor; circuit means responsive to normal operating load currents for individually connecting each of said plurality of capacitors in parallel with said first capacitor at predetermined levels of increasing load current during normal operation of said motor; and control means for varying the amplitude of said first phase voltage during normal operation under varying loads to equalize the magnitude of voltages at said induction motor.
Claim 6
Dependent Claim
124 words
In a static phase converter for supplying a three-phase voltage to an induction motor from a single-phase source, a first phase being derived from the secondary of said autotransformer and further including a capacitor connected in series with said first phase voltage, the improvement comprising: A plurality of additional capacitors adapted to be connected in parallel with said first capacitor; circuit means responsive to normal operating load currents for individually connecting each of said plurality of capacitors in parallel with said first capacitor at predetermined levels of increasing load current during normal operation of said motor; and control means for varying the amplitude of said first phase voltage during normal operation under varying loads to equalize the magnitude of voltages at said induction motor.
Claim 7
Dependent Claim
75 words
The system of claim 4 wherein said control means includes a variable voltage transformer having its variable output lead connected across the primary of said autotransformer, one of said first and second phases being derived from the primary of said variable voltage transformer and the other of said first and second phases being derived between the terminal common to the autotransformer and the primary of said variable transformer, and the output terminal of said autotransformer.
Claim 8
Dependent Claim
45 words
The apparatus of claim 5 wherein said control means further comprises comparison circuit means sensing the voltage at said first and second phases to vary the output voltage of said variable transformer means to equalize the magnitude of voltage at said first and second phases.
Claim 9
Independent Claim
103 words
A method of equalizing the phase currents in a three-phase induction motor energized by a single phase source by means of a statis autotransformer-capacitor converter during normal operation of said motor, comprising: sensing the operating load current in said motor; increasing the value of series capacitance in said converter with increasing operating load current during normal operation with varying load; comparing the amplitude of voltages at two phases of said motor; and changing the amplitude of the voltage at the third phase to cause the amplitudes at said first and second phases to be equal as normal operating loads on said motor vary.
Claim 10
Independent Claim
103 words
A method of equalizing the phase currents in a three-phase induction motor energized by a single phase source by means of a statis autotransformer-capacitor converter during normal operation of said motor, comprising: sensing the operating load current in said motor; increasing the value of series capacitance in said converter with increasing operating load current during normal operation with varying load; comparing the amplitude of voltages at two phases of said motor; and changing the amplitude of the voltage at the third phase to cause the amplitudes at said first and second phases to be equal as normal operating loads on said motor vary.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-09-09 | 1978-03-11 | 1978-09-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-09-09 | 1982-03-11 | 1982-09-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-09-09 | 1986-03-11 | 1986-09-10 | $7700.00 | Window Closed / Lapsed |