US3787709A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Ground fault-sensitive detector and circuit breaker device
Assignee: Sanmina Corp
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Filing: 1971-12-13
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Granted: 1974-01-22
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Expires: 1991-12-13
Abstract
Abstract The device detects ''''ground faults'''' (short circuits to ground) in electrical wiring systems such as those used in household or factory wiring. The device causes disconnection of power if the fault current exceeds a relatively low value such as 5 milliamperes so as to minimize shock damage to the human being or other object causing the short circuit. Means are provided for detecting the grounding of the ''''hot'''' wire and/or the neutral wire at a point between the device and the load. A transformer with oppositely-wound primary windings, each connected in one of the lines, is connected in a bridge circuit in which the transformer normally is unbalanced. A ground fault adds the fourth leg to the bridge, balances the bridge, and a detector circuit causes the circuit breaker to open the line. The device also includes means for making it relatively insensitive to quadrature leakage currents; i.e., leakage currents which either lead or lag the alternating line current by 90*. This reduces the likelihood of ''''false tripping'''' of the device. A current transformer with its secondary winding in the neutral line and an independent source for energizing the primary winding helps make the device quite small in size and relatively inexpensive to manufacture.
Inventors
- 👤 R Coe
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 04:04
CPC Classifications
H; H01; H01R; H01R13/00; H01R13/648; H02; H02H; H02H3/00; H02H3/26; H02H3/32; H02H3/33; H02H3/331; H02H3/337
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
82 words
A ground fault-indicator device for indicating ground faults in an A.C. power line, said device including detecting means For detecting and indicating a predetermined difference between the currents flowing towards and away from a load on said line, said detecting means including control means for substantially eliminating quadrature signals from said difference, said control means comprising means for enabling said detecting means only during alternate half-cycles of the A.C. line voltage, and means for averaging the output signals of said detecting means.
Claim 2
Dependent Claim
82 words
A ground fault-indicator device for indicating ground faults in an A.C. power line, said device including detecting means For detecting and indicating a predetermined difference between the currents flowing towards and away from a load on said line, said detecting means including control means for substantially eliminating quadrature signals from said difference, said control means comprising means for enabling said detecting means only during alternate half-cycles of the A.C. line voltage, and means for averaging the output signals of said detecting means.
Claim 3
Dependent Claim
178 words
A ground fault-indicator device for indicating ground faults in an A.C. power line, said device including detecting means for detecting and indicating a pre-determined difference between the currents flowing towards and away from a load on said line, said power line having at least two conductors, a transformer with two oppositely-wound primary windings on a core, each primary winding being connected in series with one of said conductors, and a secondary winding on said core, at least one of said conductors being grounded adjacent the A.C. source, a current transformer having a primary winding and a secondary winding, said secondary winding being connected in series with one of said conductors so as to change the balance of the first-named transformer when said one conductor is grounded at a location between the first-named transformer and a load, said detecting means being adapted to detect said change in balance, a current-limiting impedance connected in series with the primary winding of said current transformer, and means for connecting the combination of said impedance and the latter primary winding between said conductors.
Claim 4
Dependent Claim
178 words
A ground fault-indicator device for indicating ground faults in an A.C. power line, said device including detecting means for detecting and indicating a pre-determined difference between the currents flowing towards and away from a load on said line, said power line having at least two conductors, a transformer with two oppositely-wound primary windings on a core, each primary winding being connected in series with one of said conductors, and a secondary winding on said core, at least one of said conductors being grounded adjacent the A.C. source, a current transformer having a primary winding and a secondary winding, said secondary winding being connected in series with one of said conductors so as to change the balance of the first-named transformer when said one conductor is grounded at a location between the first-named transformer and a load, said detecting means being adapted to detect said change in balance, a current-limiting impedance connected in series with the primary winding of said current transformer, and means for connecting the combination of said impedance and the latter primary winding between said conductors.
Claim 5
Dependent Claim
29 words
A device as in claim 2 in which said impedance and primary winding combination are connected to said conductors at locations between said first-named transformer and said A.C. source.
Claim 6
Dependent Claim
198 words
A ground fault-sensitive circuit breaker device for opening an A.C. line having at least two conductors, said device including circuit breaker contacts in one of said conductors, electromagnet means for disconnecting said contacts from one another, a balanceable transformer having a core, first and second primary windings wound oppositely on said core, each such primary winding being connected in series with one of said conductors, a secondary winding on said core, means for detecting a pre-determined balance condition in said core, said balance condition being the result of a ground fault on one of said conductors, said detecting means including a high-gain differential operational amplifier for amplifying signals from said secondary winding and means for detecting a pre-determined output level from said amplifier and means for energizing said electromagnet means in response to detection of said level, gating means for gating ''''on'''' the output of said amplifier only during alternate half-cycles of line voltage, integrator means for integrating and smoothing the output from the gating means, means for turning on a semiconductor switch when the integrator output reaches zero, said switch providing a low impedance connection of said electromagnet means to said conductors to open said breaker contacts.
Claim 7
Dependent Claim
198 words
A ground fault-sensitive circuit breaker device for opening an A.C. line having at least two conductors, said device including circuit breaker contacts in one of said conductors, electromagnet means for disconnecting said contacts from one another, a balanceable transformer having a core, first and second primary windings wound oppositely on said core, each such primary winding being connected in series with one of said conductors, a secondary winding on said core, means for detecting a pre-determined balance condition in said core, said balance condition being the result of a ground fault on one of said conductors, said detecting means including a high-gain differential operational amplifier for amplifying signals from said secondary winding and means for detecting a pre-determined output level from said amplifier and means for energizing said electromagnet means in response to detection of said level, gating means for gating ''''on'''' the output of said amplifier only during alternate half-cycles of line voltage, integrator means for integrating and smoothing the output from the gating means, means for turning on a semiconductor switch when the integrator output reaches zero, said switch providing a low impedance connection of said electromagnet means to said conductors to open said breaker contacts.
Claim 8
Dependent Claim
54 words
A device as in claim 4 including a current transformer with a secondary winding of relatively large gauge wire connected in series with said other conductor, and a primary winding of relatively small gauge wire, a current-limiting impedance connected to said primary winding, and means for supplying current through said impedance and primary winding.
Claim 9
Dependent Claim
17 words
A device as in claim 5 in which said impedance comprises a portion of said detecting means.
Claim 10
Dependent Claim
84 words
A device as in claim 5 in which said electromagent means is connected in series with said impedance and said primary winding, and, with no ground fault present, the current flowing through said primary winding is substantially greater than that which must be developed in the secondary winding of said current transformer in order to ensure operation of said detecting means when said other conductor is grounded adjacent a load connected to said line, whereby said current transformer can be relatively inefficient and inexpensive.
Claim 11
Dependent Claim
75 words
A device as in claim 4 including a gating transistor for conducting the output of said amplifier through its collector-emitter path during alternate half-cycles of line voltage, a Miller integrator circuit connected to receive signals from said gating transistor, said integrator including an emitter-base diode, a temperature-compensating diode connected in a bridge circuit with said amplifier, gating transistor and integrator transistor in a sense such that temperature-induced resistance changes in aid compensating diode integrator transistor.
Claim 12
Dependent Claim
50 words
A device as in claim 4 including a resistor connected between the input said of the first primary winding and the output side of the second primary winding so as to form a bridge circuit with a grounding impedance when the first conductor is connected through a fault to ground.
Claim 13
Dependent Claim
43 words
A device as in claim 2 in which the value of said current-limiting impedance is such as to provide the primary winding of said current transformer with an energizing current of approximately twice the value of the ground fault current to be detected.
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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) | 1977-01-21 | 1977-07-23 | 1978-01-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-01-21 | 1981-07-23 | 1982-01-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-01-21 | 1985-07-23 | 1986-01-22 | $7700.00 | Window Closed / Lapsed |