Cross-field ground fault sensor
First Claim
1. A ground fault sensing circuit, comprising:
- a first magnetic core having an air gap therein;
a first primary winding connected between one terminal of an A.C. source and one terminal of a load, a second primary winding connected between a second terminal of said A.C. source and a second terminal of said load, said primary windings being coupled to said first core in such a manner as to produce oppositely directed fluxes in said first core;
a secondary winding coupled to said first core to have induced therein a voltage related to the difference in magnitude of the currents flowing in said first and second primary windings;
a second magnetic core magnetically coupled to said first core in parallel magnetic circuit relationship with said air gap so as to provide an alternate magnetic path for said oppositely directed fluxes induced in said first core whenever said second core is not saturated;
a control winding coupled to said second core;
means for periodically energizing said control winding so as to periodically drive said second core into saturation at a relatively rapid rate whereby said oppositely directed fluxes induced in said first core change at a relatively rapid rate thereby increasing the magnitude of said voltage induced in said secondary winding.
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Accused Products
Abstract
A differential transformer having a core of low permeability ferromagnetic material, a pair of identical primary windings and a secondary winding of relatively few turns capable of producing a large voltage output for a small magnitude ground fault current. A cross-field winding is utilized to periodically saturate a portion of the flux path in the transformer core to produce sudden changes in magnetic flux, which flux changes vary in magnitude proportional to the amount of fault current. During the time interval when the cross-field portion of the sensor is not saturated by a pulse of sampling current, a second pulse of current is introduced into the sensor secondary winding for detecting a grounded neutral wire by sensing the output voltage produced in response thereto.
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Citations
24 Claims
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1. A ground fault sensing circuit, comprising:
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a first magnetic core having an air gap therein; a first primary winding connected between one terminal of an A.C. source and one terminal of a load, a second primary winding connected between a second terminal of said A.C. source and a second terminal of said load, said primary windings being coupled to said first core in such a manner as to produce oppositely directed fluxes in said first core; a secondary winding coupled to said first core to have induced therein a voltage related to the difference in magnitude of the currents flowing in said first and second primary windings; a second magnetic core magnetically coupled to said first core in parallel magnetic circuit relationship with said air gap so as to provide an alternate magnetic path for said oppositely directed fluxes induced in said first core whenever said second core is not saturated; a control winding coupled to said second core; means for periodically energizing said control winding so as to periodically drive said second core into saturation at a relatively rapid rate whereby said oppositely directed fluxes induced in said first core change at a relatively rapid rate thereby increasing the magnitude of said voltage induced in said secondary winding. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A ground fault sensing circuit, comprising:
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a differential transformer including a magnetic core having a saturable section; said magnetic core including a first generally toroidal core portion having a radial width extending from the bore of said first toroidal core portion to the exterior edge of said first toroidal core portion furthest from a center axis of rotation thereof and having an axial length extending between a front and a back plane lying perpendicular to said center axis of rotation of said first toroidal core portion; said first generally toroidal core portion including at least one radial slot cut therein, each said slot having a radial length substantially equal to said radial length of said first toroidal core portion; said saturable section including a second generally toroidal core portion having a center axis of rotation which is perpendicular to said center axis of rotation of said first generally toroidal core portion, said second generally toroidal core portion formed between said front and back planes of said first toroidal core portion and partially radially exterior to the periphery of said first toroidal core portion, said second toroidal core portion partially including the cross-sectional portion of said main section adjacent either side of each said slot, whereby a magnetic field induced to flow through said second toroidal core portion is in a direction generally transverse to a direction of a magnetic field induced to flow in said first toroidal core portion; a first primary winding connected between one terminal of an A.C. source and one terminal of a load, a second primary winding connected between a second terminal of said A.C. source and a second terminal of said load, said primary windings being coupled to said first toroidal core portion in such a manner as to produce oppositely directed fluxes in said first toroidal core portion, said fluxes normally flowing through said saturable section; a secondary winding coupled to said first toroidal core section to have induced therein a voltage related to differential currents flowing in said primary windings; a control winding coupled to said second toroidal core portion; means for periodically energizing said control winding so as to periodically drive said second toroidal core portion into saturation at a relatively rapid rate whereby said oppositely directed fluxes induced in said first toroidal core portion change at a relatively rapid rate thereby increasing the magnitude of said voltage induced in said secondary winding. - View Dependent Claims (16, 17, 18)
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19. A ground fault sensing circuit, comprising:
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a magnetic core having a saturable section; a first primary winding connected between one terminal of an A.C. source and one terminal of a load, a second primary winding connected between a second terminal of said A.C. source and a second terminal of said load, said primary windings being coupled to said magnetic core in such a manner as to produce oppositely directed fluxes in said magnetic core which normally flow through said saturable section; a secondary winding coupled to said magnetic core to have induced therein a voltage related to differential currents flowing in said primary windings; a control winding coupled to said saturable section; means for periodically energizing said control winding so as to periodically drive said saturable section into saturation at a relatively rapid rate whereby said oppositely directed fluxes induced in said magnetic core change at a relatively rapid rate thereby increasing the magnitude of said voltage induced in said secondary winding; said first primary winding on said source side being connected to ground through a neutral conductor; additional means for detecting the presence of a ground connection between said load and said first primary winding, said additional means being coupled to said secondary winding and being adapted to detect the presence of a ground connection between the load and said first primary winding by energizing said secondary winding during time intervals between the spaced time intervals during which said control winding is energized whereby the same magnetic core is utilized for detection of a ground fault in either load line connected to said primary windings. - View Dependent Claims (20, 21, 22, 23, 24)
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Specification