US3728580A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Core-balance earth leakage protection
Assignee: ELECTRICAL PROTECTION CO Ltd
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Filing: 1971-04-06
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Granted: 1973-04-17
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Expires: 1991-04-06
Abstract
Abstract The core balance earth leakage protection device is improved by providing in combination with it a suitable saturable core reactor whose winding is connected in series with one primary winding of the device, usually that connected in series with the neutral conductor of the circuit. The saturable core reactor is adapted to provide an impedance of substantial value for currents below and near the rated threshold sensitivity of the device but to be saturated at the usual load current values for which the device is adapted, and to therefore offer negligible impedance to the flow of load currents. The core balance earth leakage protection device is advantageously further provided in combination with a preload impedance connected between a line conductor at a point on the load side of one winding of the device and the neutral conductor at a point on the load side of another winding of the device, adapted to draw sufficient additional current through the one winding of the device to overcome the balancing current that would flow in the other winding due to an earth short circuit. The effective impedance of the tripping core of the device must be low in comparison to the impedance of the saturable core reactor for values of current in the order of the threshold sensitivity of the device.
Inventors
- 👤 M Marot
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 00:23
CPC Classifications
H; H02; H02H; H02H3/00; H02H3/26; H02H3/32; H02H3/33; H02H3/331
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
361 words
An earth leakage protective system for protecting a load circuit from dangerous earth fault currents, comprising a source of alternating current, a load device adapted to be energized by said source and a core balance protection device interposed between said source and said load device, said core balance protection device comprising a differential transformer having a closed core which is linked by two primary windings and a secondary winding, each of said primary windings being connected in series with a line of the circuit connecting said load device to said source, a relay switch including a coil energized from said secondary winding to open the line circuit and de-energize the load device when a resultant magnetomotive force is produced in said closed core by an unbalance of the currents flowing in said primary windings as a result of a diversion of load current away from a line and its corresponding primary winding as a result of an earth leakage fault, and means for protecting said differential transformer against mal-operation in the presence of earth faults on both the source side and the load side of one of said primary windings causing a low impedance short circuit of that winding which comprises a saturable core reactor connected in series with that one of said primary windings and said load device, said saturable reactor being designed to saturate at a value of load current less than the rated current of the load device, whereby when rated current is supplied to said load device through said reactor, the impedance of said reactor is a minimum and said reactor offers minimal impedance to the flow of load current, and whereby when an earth leakage fault diverts the load current away from and effects de-saturation of said reactor and away from said series connected primary winding the impedance of said reactor is a maximum so that it is possible for a sufficient resultant magnetomotive force, to be generated in the differential transformer as a result of magnetomotive imbalance caused by an earth fault to induce a substantial current in said secondary winding to actuate said relay switch to open said line circuit and de-energize said load.
Claim 2
Dependent Claim
361 words
An earth leakage protective system for protecting a load circuit from dangerous earth fault currents, comprising a source of alternating current, a load device adapted to be energized by said source and a core balance protection device interposed between said source and said load device, said core balance protection device comprising a differential transformer having a closed core which is linked by two primary windings and a secondary winding, each of said primary windings being connected in series with a line of the circuit connecting said load device to said source, a relay switch including a coil energized from said secondary winding to open the line circuit and de-energize the load device when a resultant magnetomotive force is produced in said closed core by an unbalance of the currents flowing in said primary windings as a result of a diversion of load current away from a line and its corresponding primary winding as a result of an earth leakage fault, and means for protecting said differential transformer against mal-operation in the presence of earth faults on both the source side and the load side of one of said primary windings causing a low impedance short circuit of that winding which comprises a saturable core reactor connected in series with that one of said primary windings and said load device, said saturable reactor being designed to saturate at a value of load current less than the rated current of the load device, whereby when rated current is supplied to said load device through said reactor, the impedance of said reactor is a minimum and said reactor offers minimal impedance to the flow of load current, and whereby when an earth leakage fault diverts the load current away from and effects de-saturation of said reactor and away from said series connected primary winding the impedance of said reactor is a maximum so that it is possible for a sufficient resultant magnetomotive force, to be generated in the differential transformer as a result of magnetomotive imbalance caused by an earth fault to induce a substantial current in said secondary winding to actuate said relay switch to open said line circuit and de-energize said load.
Claim 3
Dependent Claim
32 words
A core-balance earth leakage protection device as claimed in claim 1, in which said one primary winding is that connected in series with the neutral conductor of the circuit to be protected.
Claim 4
Dependent Claim
39 words
A core-balance earth leakage protection system as claimed in claim 1, in which the saturation current of said reactor is not more than a few multiples of the rated threshold sensitivity current of said coil of said relay switch.
Claim 5
Dependent Claim
34 words
A core-balance earth leakage protection system as claimed in claim 3, in which said reactor is adapted to substantially saturate at currents near the rated threshold sensitivity of said coil of said relay switch.
Claim 6
Dependent Claim
37 words
A core-balance earth leakage protection system as claimed in claim 1, in which the impedance of said reactor at currents near saturation will be substantially larger than the effective impedance of said coil of said relay switch.
Claim 7
Dependent Claim
51 words
A core-balance earth leakage protection system as claimed in claim 1, and which further includes a pre-loading impedance connected between a line conductor at a point on the load side of a primary winding of said transformer, and a point on a neutral conductor on the load side of said reactor.
Claim 8
Dependent Claim
61 words
A core-balance earth leakage protection system as claimed in claim 6, in which said pre-loading impedance is adapteD to draw sufficient additional ampere-turns from a primary winding of said transformer to which said reactor is not connected to overcome the balancing ampere-turns that would be induced in said winding to which said reactor is connected, due to an earth short circuit.
Claim 9
Dependent Claim
18 words
A core-balance earth leakage protection system as claimed in claim 7, in which said pre-loading impedance is resistive.
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) | 1976-04-16 | 1976-10-16 | 1977-04-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-04-16 | 1980-10-16 | 1981-04-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-04-16 | 1984-10-16 | 1985-04-17 | $7700.00 | Window Closed / Lapsed |