US3644789A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Overcurrent relays
Assignee: English Electric Co Ltd
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Filing: 1968-08-05
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Granted: 1972-02-22
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Expires: 1988-08-05
Abstract
Abstract This invention relates to an overcurrent relay in which a voltage is developed proportional to the current in an AC circuit, a two-state switch is responsive to an overcurrent condition in which the monitored voltage periodically exceeds a reference level whereby to assume one state for the duration of these periods during which this level is exceeded, a storage circuit progressively accumulates a voltage from a datum level during each period for which the switch is in its other state, and a timer is operable whenever the switch assumes its one state to actuate an output device after a predetermined delay, the timer being reset by the storage circuit each time its voltage attains a predetermined magnitude. The maximum ''''overshoot'''' of the relay, i.e., the effect which could cause the output device to operate and effect protective action even with an unsustained overcurrent, may be contained within a period just in excess of one cycle, or even less, and the pickup/dropoff ratio of the output device can practically approach the optimum value of 100 percent.
Inventors
- 👤 Michael Charles Stephe Simpson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 10:58
CPC Classifications
H; H02; H02H; H02H3/00; H02H3/08; H02H3/093; H02P; H02P29/00; H02P29/40
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
114 words
A definite time protective relay comprising; monitoring means for monitoring at least one alternating quantity in an AC circuit to be protected and producing a peak excess signal whenever a monitored quantity exceeds a predetermined level; a first delay circuit fed by the peak excess signals and which produces an output for the duration of and for a predetermined time (in excess of the maximum interval between successive peak excess signals due to a sustained fault) after the end of an input signal; and a second delay circuit fed with the output of the first delay circuit and which produces an output indicating a fault if the input to it exceeds a predetermined duration.
Claim 2
Dependent Claim
114 words
A definite time protective relay comprising; monitoring means for monitoring at least one alternating quantity in an AC circuit to be protected and producing a peak excess signal whenever a monitored quantity exceeds a predetermined level; a first delay circuit fed by the peak excess signals and which produces an output for the duration of and for a predetermined time (in excess of the maximum interval between successive peak excess signals due to a sustained fault) after the end of an input signal; and a second delay circuit fed with the output of the first delay circuit and which produces an output indicating a fault if the input to it exceeds a predetermined duration.
Claim 3
Dependent Claim
54 words
A definite time protective relay according to claim 1, wherein the first delay circuit includes a capacitor which is charged to a first state by an input signal and towards a second state when no input signal is present, the circuit producing an output signal when the capacitor is not in the first state.
Claim 4
Dependent Claim
39 words
A definite time protective relay according to claim 2, wherein the first delay circuit includes a transistor which is turned on by an input signal and is connected to charge the capacitor to the first state when turned on.
Claim 5
Dependent Claim
51 words
A definite time protective relay according to claim 1, wherein the second delay circuit includes a capacitor which is normally held in a first state and is charged towards a second state while an input signal is present, the circuit producing an output signal when the capacitor reaches the second state.
Claim 6
Dependent Claim
39 words
A definite time protective relay according to claim 4, wherein the second delay circuit includes a transistor which is turned off by an input signal and is connected to charge the capacitor to the first state when turned on.
Claim 7
Dependent Claim
49 words
A definite time protective relay according to claim 5, wherein the secOnd delay circuit includes a voltage-responsive element subjected to the voltage on the capacitor in the second delay circuit and adapted to break down and produce an output signal in response to this voltage attaining a preset level.
Claim 8
Dependent Claim
44 words
A definite time protective relay according to claim 1, including also an auxiliary circuit fed by the monitoring means and operable to produce an output signal indicating a fault substantially instantaneously if the monitored quantity is of a magnitude indicating an excessive fault condition.
Claim 9
Dependent Claim
75 words
A definite time protective relay according to claim 1, including: a current transformer having a primary winding connected in the AC circuit and a secondary winding; rectifying means connected to the secondary winding of the transformer for producing a rectified waveform of the derived voltage; and a voltage-responsive element fed by the rectifying means and adapted to breakdown and produce a peak excess signal in response to the rectified waveform exceeding the said predetermined level.
Claim 10
Dependent Claim
96 words
A definite time protective relay according to claim 1, including: a current transformer having a primary winding connected in the AC circuit and a secondary winding; rectifying means connected to the secondary winding of the transformer for producing a rectified waveform of the derived voltage; and a sensing circuit fed by the rectifying means and operable to develop a DC bias voltage, proportional to the voltage subsisting in the AC circuit, which serves as the said predetermined level, and to produce a peak excess signal in response to the rectified waveform exceeding the said predetermined level.
Claim 11
Dependent Claim
37 words
A definite time protective relay according to claim 8, adapted for multiphase operation, the current transformers and rectifying means corresponding in number to the number of phases and being connected in common to the voltage responsive element.
Claim 12
Dependent Claim
24 words
The invention according to claim 1, wherein said monitoring means produces a peak excess signal whenever a monitored quantity instantaneously exceeds a predetermined level.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-02-21 | 1975-08-23 | 1976-02-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-02-21 | 1979-08-23 | 1980-02-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-02-21 | 1983-08-23 | 1984-02-22 | $7700.00 | Window Closed / Lapsed |