Ground-fault-responsive electrical protective systems

Claim 2

A sensitive protective circuit breaker system for detecting a high-resistance line-to-ground short circuit or an abnormal leakage current to ground from conductors forming at least one path in an electrical circuit connected to supply conductors from a source of electricity, one of the supply conductors being grounded at the source of electricity, comprising: current-interrupting means adapted to be connected into the supply conductors; impedance means connectable in each of said supply conductors for developing electrical potentials thereacross in response to currents of different magnitudes in said supply conductors; signal comparator means having a plUrality of input ports, each coupled to a separate one of said impedance means to receive potentials developed thereacross as a result of currents in said supply conductors, and an output port for developing an output signal responsive to the potentials applied to said input ports, said signal comparator means being so constructed that normal load currents flowing in said supply conductors give rise to a net output signal, the magnitude of which varies with such differential currents; and means responsive to the attainments by said output signal of a predetermined threshold value for causing said currentinterrupting means to interrupt current flow through said supply conductors.

Claim 3

The system of claim 1 wherein each of said impedance means has an absolute value of impedance substantially less than that of the corresponding input port coupled thereto, such that most of the currents in said line conductors pass through said impedance means rather than through said input ports.

Claim 4

The system of claim 1 wherein each of said impedance means has an absolute value of impedance substantially less than that of the corresponding input port coupled thereto, such that most of the currents in said line conductors pass through said impedance means rather than through said input ports.

Claim 5

The system of claim 1 wherein said impedance means comprises a highly permeable magnetic core structure having a plurality of impedance windings thereon, each connected in series circuit with a respective one of said supply conductors, and so connected that the fluxes induced in said core structure by said windings due to normal load currents in said supply conductors are in opposition.

Claim 6

The system of claim 3 wherein said core structure comprises a single closed magnetic circuit on which each of said impedances windings is wound.

Claim 7

The system of claim 1 in which said signal comparator means comprises a summing transformer with a highly permeable magnetic core structure wherein each of said input ports comprises a separate input winding on said core structure and wherein said output port comprises winding turns inductively coupled to a portion of said core structure to be linked by a net flux developed herein by said primary windings.

Claim 8

The system of claim 5 wherein said input windings are loosely coupled to each other on said summing transformer core structure.

Claim 9

The system of claim 6 wherein said summing transformer core structure comprises a plurality of separate legs on each of which is positioned a respective one of said input windings.

Claim 10

A sensitive protective system for an electrical circuit for providing power to a load from at least two supply conductors, one of said conductors being grounded at the source, comprising: signal-generating impedance means connectable in each of such supply conductors for developing electrical potentials in response to currents of different magnitudes in such supply conductors; and signal comparator means having a plurality of input ports, each coupled to a respective one of said impedance means to receive signals as a result of currents in said supply conductors, and an output port for developing output signals responsive to the potentials applied to said input ports, said signal comparator means being so constructed that normal load currents flowing in said supply conductors give rise to a net output signal of substantially zero, and that differential currents flowing in said supply conductors give rise to a net output signal, the magnitude of which represents the magnitude of imbalance of currents in said supply conductors.

Claim 11

A sensitive protective system for an electrical circuit for providing power to a load from at least two supply conductors, one of said conductors being grounded at the source, comprising: signal-generating impedance means connectable in each of such supply conductors for developing electrical potentials in response to currents of different magnitudes in such supply conductors; and signal comparator means having a plurality of input ports, each coupled to a respective one of said impedance means to receive signals as a result of currents in said supply conductors, and an output port for developing output signals responsive to the potentials applied to said input ports, said signal comparator means being so constructed that normal load currents flowing in said supply conductors give rise to a net output signal of substantially zero, and that differential currents flowing in said supply conductors give rise to a net output signal, the magnitude of which represents the magnitude of imbalance of currents in said supply conductors.

Claim 12

The system of claim 8 wherein each of said impedance means has an absolute value of impedance substantially less than of the corresponding input port coupled thereto, such that most of the currents in said line conductors pass through said impedance means rather than through said input ports.

Claim 13

The system of claim 8 wherein said impedance means comprises a highly permeable magnetic core structure having a plurality of impedance windings thereon, each connected in series circuit with a respective one of said supply conductors, and so connected that the fluxes induced in said core structure by said windings due to normal load currents in said supply conductors are in opposition.

Claim 14

The system of claim 10 wherein said core structure comprises a single closed magnetic circuit on which each of said impedance windings is wound.

Claim 15

The system of claim 8 in which said signal comparator means comprises assuming transformer with a highly permeable magnetic core structure, herein each of said input ports comprises a separate input winding on said core structure and wherein said output port comprises winding turns inductively coupled to a portion of said core structure to be linked by a net flux developed therein by said primary windings.

Claim 16

The system of claim 12 wherein said input windings are loosely coupled to each other on said summing transformer core structure.

Claim 17

The system of claim 13 wherein said summing transformer core structure comprises a plurality of separate legs on each of which is positioned a respective one of said input windings.

Claim 18

A sensitive protective system for an electrical circuit for providing power to a load from at least two supply conductors, one of said conductors being grounded at the source, comprising: signal-generating impedance means comprising a highly permeable magnetic core structure defining at least one closed magnetic circuit and having a plurality of impedance windings thereon, each connected in series circuit with a respective one of said supply conductors and so wound on said core structure that the fluxes induced in said core structure due to normal load currents in said supply conductors are in flux opposition; summing transformer means having a highly permeable magnetic core structure with a plurality of input windings therein loosely coupled to each other, each of said input windings being connected across a separate one of said impedance windings to receive input signals therefrom, said summing transformer also having an output winding on said core structure to interrupt a net flux developed therein by said primary windings, the impedance presented by each of said input windings to normal load currents in said supply conductors being substantially less than that of the corresponding impedance winding connected thereto, such that most of the currents in said line conductors pass through said impedance windings, whereby said secondary winding has induced therein a fault-characterizing output signal in response to unbalanced current flow in said input windings, such fault-characterizing signal representing the magnitude of current imbalance in said supply conductors.

Claim 19

A sensitive protective system for an electrical circuit for providing power to a load from at least two supply conductors, one of said conductors being grounded at the source, comprising: signal-generating impedance means comprising a highly permeable magnetic core structure defining at least one closed magnetic circuit and having a plurality of impedance windings thereon, each connected in series circuit with a respective one of said supply conductors and so wound on said core structure that the fluxes induced in said core structure due to normal load currents in said supply conductors are in flux opposition; summing transformer means having a highly permeable magnetic core structure with a plurality of input windings therein loosely coupled to each other, each of said input windings being connected across a separate one of said impedance windings to receive input signals therefrom, said summing transformer also having an output winding on said core structure to interrupt a net flux developed therein by said primary windings, the impedance presented by each of said input windings to normal load currents in said supply conductors being substantially less than that of the corresponding impedance winding connected thereto, such that most of the currents in said line conductors pass through said impedance windings, whereby said secondary winding has induced therein a fault-characterizing output signal in response to unbalanced current flow in said input windings, such fault-characterizing signal representing the magnitude of current imbalance in said supply conductors.

Claim 20

The sensitive protective system of claim 15 wherein said primary windings are arranged so that under normal current conditions the total magnetomotive force produced in the summing transformer core structure is substantially balanced out so that the net flux linking said secondary winding is zero and under current-flowing-to-ground conditions a net flux results which produces an output signal in the secondary winding of said summing transformer.

Claim 21

The sensitive protective system of claim 16 further comprising: circuit-interrupting means responsive to said fault-characterizing output signal for opening the circuit through said supply conductors when said output signal exceeds a predetermined threshold value.