US4381531A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Alternating current motor protection system
Assignee: Carrier Corp
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Filing: 1981-07-02
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Granted: 1983-04-26
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Expires: 2001-07-02
Abstract
Abstract A system for protecting a three-phase motor is disclosed. The system includes a signal conditioning circuit which senses the magnitude of current flowing through each motor phase and generates a single-line, three-phase voltage output signal having each of its phases corresponding to a single motor current phase. This three-phase voltage output signal is efficiently utilized by a microcomputer system to detect motor current overload and motor current imbalance. The microcomputer system instructs a motor controller to shut down the motor in response to a motor current overload or motor current imbalance.
Inventors
- 👤 Virgil E. Eisenhauer
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 05:17
CPC Classifications
H; H02; H02H; H02H3/00; H02H3/08; H02H3/083
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
173 words
A system for protecting a three-phase alternating current motor from current overload and from current imbalance comprising: means for sensing the current magnitude of each phase of the alternating current supplied to the motor; signal conditioning means for generating a three-phase electrical output signal in response to the current magnitudes sensed by the current sensing means, the magnitude of the first, second and third phase of said output signal being proportional to the magnitude of the first, second and third phase, respectively, of the alternating current; signal processing means for monitoring the magnitude of each phase of the output signal to determine the absolute magnitude of each phase of the alternating current and to determine the relative magnitude of each phase of the alternating current relative to the magnitude of each of the other phases of the alternating current; and means for terminating the operation of the motor when the absolute magnitude of a current phase exceeds a preselected value or when the relative magnitude of a current phase exceeds a preselected value.
Claim 2
Independent Claim
173 words
A system for protecting a three-phase alternating current motor from current overload and from current imbalance comprising: means for sensing the current magnitude of each phase of the alternating current supplied to the motor; signal conditioning means for generating a three-phase electrical output signal in response to the current magnitudes sensed by the current sensing means, the magnitude of the first, second and third phase of said output signal being proportional to the magnitude of the first, second and third phase, respectively, of the alternating current; signal processing means for monitoring the magnitude of each phase of the output signal to determine the absolute magnitude of each phase of the alternating current and to determine the relative magnitude of each phase of the alternating current relative to the magnitude of each of the other phases of the alternating current; and means for terminating the operation of the motor when the absolute magnitude of a current phase exceeds a preselected value or when the relative magnitude of a current phase exceeds a preselected value.
Claim 3
Dependent Claim
158 words
A control system as recited in claim 1 wherein the signal conditioning means comprises: means for generating separate first, second and third voltage signals in response to the first, second, and third current phases, respectively, each of said voltage signals having a magnitude which is proportional to the magnitude of the sensed current phase to which it corresponds; switching means, for connecting either the first, second or third voltage signal to a common load while disconnecting the other voltage signals from the load when the switching means is activated to a first, second, or third state, respectively; and means for detecting a zero cross point of each voltage signal and activating the switching means in response to these points to sequentially connect and disconnect the first, second and third voltage signals to the common load to form a three-phase electrical output signal having first, second and third phases corresponding to the first, second, and third voltage signals, respectively.
Claim 4
Dependent Claim
52 words
The signal conditioning circuit as recited in claim 2, further comprising: means for adjusting the magnitude of each of the three voltage signals, after these signals are generated by the current sensing means, to a scale which is suitable for proper operation of the switching means and the zero cross detection means.
Claim 5
Dependent Claim
74 words
The signal conditioning circuit as recited in claims 2 or 3 further comprising means for generating an electrical pulse when the zero cross detection means detects a zero cross point; and, wherein the signal processing means includes a timing means for responding to the pulses to enable the signal processing means to monitor each phase of the output signal at substantially the same fixed time interval after the occurrence of a zero cross pulse.
Claim 6
Dependent Claim
37 words
The signal conditioning circuit as recited in claims 2 or 3 wherein the current sensing means comprises three current pickups each of which responds to a separate phase of the three-phase alternating current supplied to the motor.
Claim 7
Dependent Claim
85 words
The signal conditioning circuit as recited in claims 2 or 3 wherein the switching means comprises three PNP transistors having their emitters connected in parallel to the common load, having their collectors connected to the current sensing means to apply the first, second and third voltage signal at the collector of the first, second and third transistor, respectively, and having their bases connected to the zero cross detection means to activate the transistors by properly biasing the bases to provide the desired sequential switching sequence.
Claim 8
Dependent Claim
110 words
The signal conditioning circuit as recited in claim 6 wherein the zero cross detection means comprises: a first operational amplifier means for providing an activating biasing signal to the base of the third PNP transistor only when the first voltage signal is below the zero cross level; a second operational amplifier means for providing an activating biasing signal to the base of the first PNP transistor only when the second voltage signal is below the zero crossing level; and a third operational amplifier means for providing an activating biasing signal to the base of the second PNP transistor only when the third voltage signal is below the zero cross level.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1986-04-25 | 1986-10-25 | 1987-04-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-04-25 | 1990-10-25 | 1991-04-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-04-25 | 1994-10-25 | 1995-04-26 | $7700.00 | Window Closed / Lapsed |