US3868665A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Ground fault current detector
Assignee: Amerace Corp
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Filing: 1974-02-08
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Granted: 1975-02-25
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Expires: 1994-02-08
Abstract
Abstract A ground fault current monitoring and limiting circuit is connected between an isolated electrical power distribution system and ground. Means are included for connecting the power lines alternately to fault current monitoring and detection means. The last-named means provides a low impedance from a line to ground for low values of fault current. The impedance increases sharply for values of fault current above a predetermined magnitude and a warning is provided when the fault current exceeds such predetermined magnitude.
Inventors
- 👤 Edward M Treglown
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 22:13
CPC Classifications
G; G01; G01R; G01R27/00; G01R27/02; G01R27/16; G01R27/18
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
181 words
A detector for sensing ground currents above a predetermined magnitude in either of a pair of isolated power lines and for limiting said ground current, said detector comprising, means providing a variable impedance path to ground for said ground currents, said variable impedance means providing a low impedance path at low values of ground current and increasing with increasing magnitude of ground current to a maximum at values of ground current slightly above said predetermined magnitude, alarm means responsive to values of ground current in said variable impedance path above said predetermined magnitude for providing an alarm indicating excessive ground current, switch means between each of said power lines and said variable impedance path, and bistable means synchronized to the frequency of said power lines for providing signals to trigger said switch means alternately into conduction on alternate cycles of the power line frequency, whereby said power lines are connected alternately on alternate cycles of the power line frequency to said variable impedance means to cause ground currents from either power line above said predetermined magnitude to be detected and limited.
Claim 2
Dependent Claim
181 words
A detector for sensing ground currents above a predetermined magnitude in either of a pair of isolated power lines and for limiting said ground current, said detector comprising, means providing a variable impedance path to ground for said ground currents, said variable impedance means providing a low impedance path at low values of ground current and increasing with increasing magnitude of ground current to a maximum at values of ground current slightly above said predetermined magnitude, alarm means responsive to values of ground current in said variable impedance path above said predetermined magnitude for providing an alarm indicating excessive ground current, switch means between each of said power lines and said variable impedance path, and bistable means synchronized to the frequency of said power lines for providing signals to trigger said switch means alternately into conduction on alternate cycles of the power line frequency, whereby said power lines are connected alternately on alternate cycles of the power line frequency to said variable impedance means to cause ground currents from either power line above said predetermined magnitude to be detected and limited.
Claim 3
Dependent Claim
80 words
A detector as claimed in claim 1 wherein said variable impedance means includes a full wave rectifier having its input connected between the common output of said switching means and ground, a first transistor connected to said rectifier to provide a normally low impedance path for ground currents and a second transistor coupled to said first transistor so as to decrease the conductive bias on said first transistor in response to increasing values of ground current in said first transistor.
Claim 4
Dependent Claim
105 words
A detector as claimed in claim 2 wherein said first transistor has its collector coupled to one output terminal of said rectifier and its emitter coupled through a resistance to the other output terminal of said rectifier, said first transistor being normally biased into conduction, said second transistor having its base coupled to the emitter of said first transistor and its collector coupled to the base of said first transistor, whereby increasing values of ground current in said first transistor increase the conductive bias on said second transistor and cause it to divert conductive biasing current from said first transistor and thereby increase its impedance.
Claim 5
Dependent Claim
41 words
A detector as claimed in claim 1 wherein the low impedance provided by said variable impedance means at low values of ground current is no greater than one-tenth of the minimum fault impedance at which an alarm is to be produced.
Claim 6
Dependent Claim
26 words
A detector as claimed in claim 1 wherein said switch means includes a triac connected between each of said power lines and said variable impedance means.
Claim 7
Dependent Claim
53 words
A detector as claimeD in claim 1 wherein said bistable means includes a bistable multivibrator and circuit means triggering said multivibrator from one to another stable state on each cycle of the power line frequency, said multivibrator triggering one and the other of said switch means into conduction on alternate changes of state.
Claim 8
Dependent Claim
19 words
A detector as claimed in claim 1 further comprising a meter for reading the peak values of ground current.
Claim 9
Dependent Claim
100 words
A detector as claimed in claim 1 wherein said alarm means includes audible alarm means and visual alarm means, said visual alarm means having a first state providing a periodic visual alarm indication and a second state providing a steady visual alarm indication, said audible alarm means and said periodic state of said visual alarm means being produced initially in response to detection of a ground current exceeding said predetermined magnitude, and means for turning-off said audible alarm means and switching said visual alarm means to said second state to limit said alarm means to a steady visual alarm indication.
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) | 1978-02-24 | 1978-08-26 | 1979-02-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-02-24 | 1982-08-26 | 1983-02-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-02-24 | 1986-08-26 | 1987-02-25 | $7700.00 | Window Closed / Lapsed |