Ground fault detector and circuit interrupter by magnetic flux storage method

Claim 2

In apparatus for detecting leakage currents in a system having a plurality of conductors carrying electrical current between a source and a load, a differential transformer having a magnetic core and primary windings formed by at least two of said conductors passing through said core to produce zero net magnetic flux in said core during normal conditions and a nonzero net flux signal in said core when leakage occurs, magnetic flux storage means coupled to said differential transformer for storing the flux signal produced by a leakage current, and means connected to said flux storage means for reading the stored flux signal out of said storage means.

Claim 3

Apparatus as in claim 1 together with current-interrupting means having contacts movable between open and closed states and adapted to be connected into said conductors, said current-interrupting means also having an operating coil controlling the state of said contacts, and electrical signal-conditioning means intermediate said flux storage means and said operating coil for tripping said coil and opening said contacts to interrupt the current flow in said conductors in response to the flux signal read out of said storage means.

Claim 4

Apparatus as in claim 2 wherein said electrical signal-conditioning means includes electronic switching means for controlling the flow of current in said operating coil.

Claim 5

Apparatus as in claim 2 wherein said electrical signal-conditioning means includes counting means for delaying the opening of said contacts until a predetermined number of flux signals have been read out of said flux storage means.

Claim 6

Apparatus as in claim 2, together with pulsating power supply means connected for supplying pulsating operating power to said signal-conditioning means.

Claim 7

Apparatus as in claim 2, together with direct current power supply means connected to said conductors for providing operating power for the apparatus from the alternating current supplied by said source.

Claim 8

Apparatus as in claim 6 together with capacitor means connected for receiving energy from said direct current power supply means and storing said energy for delivery to the operating coil of said current-interrupting means.

Claim 9

Apparatus as in claim 7 together with means for inhibiting the operation of the means for reading the stored flux out of the storage means until said capacitor has been charged to a predetermined level.

Claim 10

Apparatus as in claim 1 wherein said flux storage means includes at least one indicator core adapted for changing between states of high and low permeability in accordance with the magnetomotive force applied thereto.

Claim 11

Apparatus as in claim 9 wherein said inductor core is fabricated of a material having a high nickel content.

Claim 12

Apparatus as in claim 9, together with at least one additional transformer core coupled to the magnetic core in said differential transformer and to said reactor core.

Claim 13

In a miniaturized protective device for detecting fault currents to ground from conductors forming a path for electrical current between a source and a load, a differential transformer having a magnetic core of high-permeability material and having at least two of said conductors passing through said core to form single-turn primary windings adapted for producing zero net magnetic flux in said core during normal current conditions and for producing a nonzero flux signal in said core when a ground fault occurs, said differential transformer also having a secondary winding of at least one turn on said core, at least one inductor core coupled to said magnetic core through said secondary winding and adapted to change from a first state of permeability to a second state of permeability in reSponse to the magnetomotive force produced by a fault current, thus providing means for storing the signal produced by a fault current as a flux signal, pulse generator means coupled to said inductor core for reading the stored flux signal out of said core by delivering a current pulse to said inductor core for causing it to change back to its first state of permeability, a tertiary winding on the magnetic core of said differential transformer adapted for receiving the flux signal read out of said inductor core, current interrupter means having normally closed contacts connected in said conductors and having an operating coil adapted for opening said contacts when energized, and electrical signal-conditioning means connected intermediate said tertiary winding and said operating coil for energizing said coil to interrupt the flow of current in said conductors in response to a fault current.

Claim 14

In a miniaturized protective device for detecting fault currents to ground from conductors forming a path for electrical current between a source and a load, a differential transformer having a magnetic core of high-permeability material and having at least two of said conductors passing through said core to form single-turn primary windings adapted for producing zero net magnetic flux in said core during normal current conditions and for producing a nonzero flux signal in said core when a ground fault occurs, said differential transformer also having a secondary winding of at least one turn on said core, at least one inductor core coupled to said magnetic core through said secondary winding and adapted to change from a first state of permeability to a second state of permeability in reSponse to the magnetomotive force produced by a fault current, thus providing means for storing the signal produced by a fault current as a flux signal, pulse generator means coupled to said inductor core for reading the stored flux signal out of said core by delivering a current pulse to said inductor core for causing it to change back to its first state of permeability, a tertiary winding on the magnetic core of said differential transformer adapted for receiving the flux signal read out of said inductor core, current interrupter means having normally closed contacts connected in said conductors and having an operating coil adapted for opening said contacts when energized, and electrical signal-conditioning means connected intermediate said tertiary winding and said operating coil for energizing said coil to interrupt the flow of current in said conductors in response to a fault current.

Claim 15

A miniaturized protective device as in claim 12 wherein said pulse generator means comprises a blocking oscillator.

Claim 16

A miniaturized protective device as in claim 12 wherein said electrical signal-conditioning means includes detector means connected for receiving the signal from said tertiary winding and electronic switch means connected to said operating coil and triggered by the output from said detector means for energizing said coil in response to the signal read out of said inductor core.

Claim 17

A miniaturized protective device as in claim 14 together with amplifier means connected intermediate said tertiary winding and said detector means.

Claim 18

A miniaturized protective device as in claim 15 wherein said electrical signal-conditioning means further includes accumulator capacitor means and a unilateral switch connected intermediate said detector means said electronic switch means for delaying the interruption of the current in said conductors until a predetermined number of ground fault flux signals have been read out of said reactor core.

Claim 19

In a miniaturized protective device for detecting fault currents to ground from conductors forming a path for electrical current between a source and a load, a differential transformer having a toroidal magnetic core of high-permeability material and having at least two of said conductors passing through said core to form single-turn primary windings adapted for producing zero net magnetic flux in said core during normal current conditions and for producing a nonzero net flux signal in said core when a ground fault occurs, an inductor core adapted to be changed from a first state of permeability to a second state of permeability by the magnetomotive force produced by a fault current, thus providing means for storing the flux signal produced by a fault current, a coupling core coupled to said magnetic core and to said inductor core, pulse generator means coupled to said reactor core through said coupling core for reading the stored flux signal out of said inductor core, and an output winding on said coupling core adapted for receiving the stored flux signal from the inductor core.

Claim 20

In a miniaturized protective device for detecting fault currents to ground from conductors forming a path for electrical current between a source and a load, a differential transformer having a toroidal magnetic core of high-permeability material and having at least two of said conductors passing through said core to form single-turn primary windings adapted for producing zero net magnetic flux in said core during normal current conditions and for producing a nonzero net flux signal in said core when a ground fault occurs, an inductor core adapted to be changed from a first state of permeability to a second state of permeability by the magnetomotive force produced by a fault current, thus providing means for storing the flux signal produced by a fault current, a coupling core coupled to said magnetic core and to said inductor core, pulse generator means coupled to said reactor core through said coupling core for reading the stored flux signal out of said inductor core, and an output winding on said coupling core adapted for receiving the stored flux signal from the inductor core.

Claim 21

A miniaturized protective device as in claim 17 together with current-interrupting means having normally closed contacts connected in said conductors and having an operating coil adapted for opening said contacts when energized and electrical signal-conditioning means contacted intermediate said output winding and said operating coil for energizing said coil to interrupt the flow of current in said conductors in response to a fault current.

Claim 22

A miniaturized protective device as in claim 18 wherein said electrical signal-conditioning means includes a silicon-controlled rectifier.

Claim 23

A miniaturized protective device as in claim 19 together with temperature compensation means connected to said silicon-controlled rectifier.

Claim 24

A miniaturized protective device as in claim 19 together with capacitor means connected to said silicon-controlled rectifier and to said operating coil, said capacitor means being adapted for storing electrical eneRgy for energizing said operating coil on triggering of said silicon-controlled rectifier.

Claim 25

A miniaturized protective device as in claim 21 together with regulated power supply means connected for charging said capacitor to a predetermined voltage and a network of resistors and capacitors connected intermediate said conductors and said power supply means, said network being adapted for providing said power supply means with an AC voltage smaller than the voltage across said conductors and for filtering out transients and other spurious changes in the voltage across said conductors to isolate the protective device from such transients and changes to prevent false tripping of the interrupting means in response thereto.

Claim 26

A miniaturized protective device as in claim 17 together with low-pass filter means connected intermediate said differential transformer and said reactor core.

Claim 27

A miniaturized protective device as in claim 17 together with means for timing the output of said pulse generator means relative to the phase of the ground fault current.

Claim 28

In a method for detecting fault currents to ground from conductors forming a path for electrical current between a source and a load, passing the current in at least two of said conductors through the primary windings of a differential transformer to produce zero net flux in the core of said transformer during normal current conditions and to produce a nonzero flux signal upon the occurrence of a ground fault, storing a flux signal corresponding to the nonzero flux signal from said differential transformer in an inductor core, and reading the stored flux signal out of said inductor core.

Claim 29

In a method for detecting fault currents to ground from conductors forming a path for electrical current between a source and a load, passing the current in at least two of said conductors through the primary windings of a differential transformer to produce zero net flux in the core of said transformer during normal current conditions and to produce a nonzero flux signal upon the occurrence of a ground fault, storing a flux signal corresponding to the nonzero flux signal from said differential transformer in an inductor core, and reading the stored flux signal out of said inductor core.

Claim 30

A method as in claim 25 together with the additional steps of connecting current-interrupting contacts into said conductors, said contacts being adapted to be opened by energizing an operating coil, and energizing said operating coil with a signal derived from said stored flux signal.

Claim 31

A method as in claim 25 together with the additional step of delaying the energizing signal by means of an accumulator capacitor to prevent energizing said coil until a predetermined number of flux signals have been stored in said inductor core, thereby preventing interruption of the current in said conductors except when a ground fault of predetermined duration occurs.

Claim 32

A method as in claim 25 together with the additional step of delaying the coil-energizing signal until a signal of predetermined magnitude has been stored in said inductor core, thereby preventing interruption of the current in said conductors except when a ground fault of predetermined amplitude and energy content per pulse occurs.

Claim 33

In apparatus for indicating the occurrence of ground fault currents forming a path for electrical current between a source and a load, a differential transformer having a magnetic core and a plurality of single-turn primary windings passing through said core and adapted for connection in series with said conductors for producing zero net magnetic flux in said core during normal current conditions and for producing a nonzero flux signal in said core when a ground fault occurs, magnetic flux storage means coupled to said differential transformer for storing the flux signal produced by a ground fault, pulse-generating means connected to said flux storage means for reading stored flux signal out of said storage means, and means connected for receiving the flux signal read out of said storage means and producing a visual indication in response thereto.

Claim 34

In apparatus for indicating the occurrence of ground fault currents forming a path for electrical current between a source and a load, a differential transformer having a magnetic core and a plurality of single-turn primary windings passing through said core and adapted for connection in series with said conductors for producing zero net magnetic flux in said core during normal current conditions and for producing a nonzero flux signal in said core when a ground fault occurs, magnetic flux storage means coupled to said differential transformer for storing the flux signal produced by a ground fault, pulse-generating means connected to said flux storage means for reading stored flux signal out of said storage means, and means connected for receiving the flux signal read out of said storage means and producing a visual indication in response thereto.

Claim 35

Apparatus as in claim 29 wherein said means connected for receiving the flux signal and producing a visual indication includes a transformer winding coupled to said storage means, and electrically actuated visual display element, and a switching element connected for controlling the actuation of said display element, said switching element being connected to said transformer winding in such manner that its conductivity is controlled by the flux signal from said storage means.

Claim 36

Apparatus as in claim 29 wherein said pulse generating means includes a bilateral switching element.

Claim 37

Apparatus as in claim 29 wherein said differential transformer includes a secondary winding having a plurality of turns and clamping diode means connected across said winding for limiting the signal produced by large fault currents.

Claim 38

Apparatus as in claim 30 wherein said switching element is a bilateral switching element.