US3584282A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Current limiting system for motor control
Assignee: Westinghouse Electric Corp
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Filing: 1969-04-01
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Granted: 1971-06-08
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Expires: 1989-04-01
Abstract
Abstract A system is disclosed for limiting the current to a motor operative with the controlled power supply including controlled rectifier devices for converting an AC input to a DC output wherein a firing circuit is provided which generates firing pulses for controlling the conductive period of the controlled rectifiers when a base voltage having a sawtooth voltage superimposed thereon exceeds a predetermined value. A current indicative of the magnitude of the actual current through the motor is sensed and is utilized to control the magnitude of the base voltage whenever the sensed current exceeds a preselected magnitude so that the current through the motor is limited to safe values. Whenever the sensed current exceeds the preselected value by a predetermined larger amount, a fast response circuit is utilized to remove quickly the overcurrent condition from the motor.
Inventors
- 👤 John R Reeves
- 👤 Bruce R Dow
- 👤 Francis T Thompson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 19:31
CPC Classifications
H; H02; H02H; H02H7/00; H02H7/08; H02H7/0833; H02P; H02P7/00; H02P7/06; H02P7/18; H02P7/24; H02P7/28; H02P7/285; H02P7/292; H02P7/293; Y; Y10; Y10S; Y10S388/00; Y10S388/90; Y10S388/903; Y10S388/907; Y10S388/917
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
231 words
In a system for limiting the current to a motor operative with a controlled power supply including controlled switching devices for converting an AC input to a DC output, the combination of: firing circuit means for generating firing pulses for controlling the conductive period of said controlled switching devices so that a selected current is normally supplied to said motor, said firing circuit means including means for generating a base voltage, means for generating a sawtooth voltage and means for combining said base and sawtooth voltages, said firing pulses being generated when the combined base and sawtooth voltages exceed a predetermined level; sensing means for sensing a current related to the actual magnitude of the current through said motor; and current responsive means responsive to the actual magnitude of the current through said motor when it exceeds a preselected magnitude for varying said base voltage in response thereto so that said firing pulses are generated in such a fashion to limit the actual current magnitude, said current responsive means comprising a limiting capacitor operative to limit the magnitude of said base voltage and a limiting device operatively connected to said limiting capacitor and being operative when said preselected magnitude of current is exceeded to discharge said limiting capacitor to decrease thereby the magnitude of said base voltage and thereby delay the generation of said firing pulses by said firing circuit means.
Claim 2
Dependent Claim
231 words
In a system for limiting the current to a motor operative with a controlled power supply including controlled switching devices for converting an AC input to a DC output, the combination of: firing circuit means for generating firing pulses for controlling the conductive period of said controlled switching devices so that a selected current is normally supplied to said motor, said firing circuit means including means for generating a base voltage, means for generating a sawtooth voltage and means for combining said base and sawtooth voltages, said firing pulses being generated when the combined base and sawtooth voltages exceed a predetermined level; sensing means for sensing a current related to the actual magnitude of the current through said motor; and current responsive means responsive to the actual magnitude of the current through said motor when it exceeds a preselected magnitude for varying said base voltage in response thereto so that said firing pulses are generated in such a fashion to limit the actual current magnitude, said current responsive means comprising a limiting capacitor operative to limit the magnitude of said base voltage and a limiting device operatively connected to said limiting capacitor and being operative when said preselected magnitude of current is exceeded to discharge said limiting capacitor to decrease thereby the magnitude of said base voltage and thereby delay the generation of said firing pulses by said firing circuit means.
Claim 3
Dependent Claim
36 words
The combination of claim 1 wherein: said sensing means includes a current transformer for sensing the AC current flow from said AC input which is indicative of the actual magnitude of the current through said motor.
Claim 4
Dependent Claim
72 words
The combination of claim 1 wherein said firing circuit means includes a clamping device, a base capacitor, a sawtooth capacitor, and means for establishing the clamping level of said clamping device, said base capacitor charging until said clamping level is reached wherein said clamPing device is operative to clamp to that voltage and establish said base voltage, said sawtooth capacitor charging to establish said sawtooth voltage until said predetermined level is exceeded.
Claim 5
Dependent Claim
37 words
The combination of claim 3 wherein said firing circuit means includes a unijunction transistor device which is operative to be fired and provide said firing pulses whenever the combined base and sawtooth voltages exceed said predetermined level.
Claim 6
Dependent Claim
27 words
The combination of claim 4 includes: a discharge circuit for discharging said base and sawtooth capacitors at the end of each half cycle of said AC input.
Claim 7
Dependent Claim
83 words
The combination of claim 3 wherein: said sensing means includes a current transformer for sensing the AC current flow from said AC input which is indicative of the actual magnitude of the current through said motor and providing an output in response thereto, and said current responsive means includes rectifier means for receiving the output of said current transformer and providing a unidirectional control output, and load means for controlling the magnitude of said control output for determining said preselected magnitude of current.
Claim 8
Dependent Claim
103 words
The combination of claim 1 wherein: said current responsive means includes a slow response circuit and a fast response circuit respectively operatively connected to said limiting device, said slow response circuit responsive to activate said limiting device when said preselected magnitude of current is exceeded to discharge said limiting capacitor to a degree necessary to limit said current to a predetermined overcurrent level, said fast response circuit responsive to activate said limiting device when said preselected magnitude of current is exceeded by a certain amount to discharge rapidly said limiting capacitor so that no firing pulses are generated by said firing circuit means.
Claim 9
Dependent Claim
72 words
The combination of claim 7 wherein said firing circuit means includes a clamping device, a base capacitor, a sawtooth capacitor, and means for establishing the clamping level of said clamping device, said base capacitor charging until said clamping level is reached wherein said clamping device is operative to clamp to that voltage and establish said base voltage, said sawtooth capacitor charging to establish said sawtooth voltage until said predetermined level is exceeded.
Claim 10
Dependent Claim
83 words
The combination of claim 8 wherein: said sensing means includes a current transformer for sensing the AC current flow from said AC input which is indicative of the actual magnitude of the current through said motor and providing an output in response thereto, and said current responsive means includes rectifier means for receiving the output of said current transformer and providing a unidirectional control output, and load means for controlling the magnitude of said control output for determining said preselected magnitude of current.
Claim 11
Dependent Claim
27 words
The combination of claim 8 includes: a discharge circuit for discharging said base and sawtooth capacitors at the end of each half cycle of said AC input.
Claim 12
Dependent Claim
37 words
The combination of claim 8 wherein said firing circuit means includes a unijunction transistor device which is operative to be fired and provide said firing pulses whenever the combined base and sawtooth voltages exceed said predetermined level.
Claim 13
Dependent Claim
83 words
The combination of claim 1 wherein: said sensing means includes a current transformer for sensing the AC current flow from said AC input which is indicative of the actual magnitude of the current through said motor and providing an output in response there, and said current responsive means includes rectifier means for receiving the output of said current transformer and providing a unidirectional control output, and load means for controlling the magnitude of said control output for determining said preselected magnitude of current.
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) | 1974-06-07 | 1974-12-07 | 1975-06-08 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-06-07 | 1978-12-07 | 1979-06-08 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-06-07 | 1982-12-07 | 1983-06-08 | $7700.00 | Window Closed / Lapsed |