Ground fault interrupter circuit with excited secondary winding on differential transformer

Claim 2

A circuit for detecting a fault condition in a power distribution system and for producing in response to a detected fault a signal that is useful in the operation of current interrupter means in said system to interrupt current flow therein, said circuit comprising at least first and second current carrying conductors for connecting a source of current for said system to respective load terminals, the first one of said conductors being grounded at said source, transformer means having first and second like windings in series connection, respectively, with each of said two conductors, said first and second windings being wound in balanced relationship, said transformer means including a multi-turn third winding inductively coupled to said first and second windings, output means connected to said third winding for providing an output signal useful in the operation of a current interrupter means in said system, means connecting said third winding to said source for passing a predetermined magnitude of current from said source through the third winding to establish at said output means, in the absence of a fault on one of said conductors, a signal of predetermined finite magnitude, said third winding being wound to produce magnetic flux in the transformer means in opposition to flux produced by the second one of said windings.

Claim 3

The combination claimed in claim 1 wherein said first and second windings are single turn windings and said third winding has many more turns than the primary windings.

Claim 4

The combination claimed in claim 1 wHerein all three of said transformer windings are multi-turn windings.

Claim 5

The circuit claimed in claim 1 wherein the means connecting the third winding to said source is proportioned to pass a current through said third winding sufficient in magnitude to establish in said transformer means a magnitude of magnetic flux approximately equal to that produced by a differential current flowing in said first and second conductors when a fault current of minimum unacceptable magnitude is flowing in said system.

Claim 6

The combination claimed in claim 4 wherein the means connecting said third winding to said source comprises a shunt circuit between said two conductors including impedance means in series connection with the third winding for establishing said predetermined magnitude of current flow through the third winding.

Claim 7

The combination claimed in claim 1 wherein said first and second windings comprise single turn windings and said third winding has many more turns than the first and second windings, said impedance means and the turns of said third winding being proportioned to produce an ampere turns value which is equal to the ampere turns value associated with said first and second windings when a differential fault current flows therethrough which has been predetermined to be of undesired magnitude, whereby the current in the third winding is less than said differential current by a large multiple.

Claim 8

A circuit for detecting a fault condition in a power distribution system and for producing in response to a detected fault a signal that is useful in the operation of current interrupter means in said system to interrupt current flow therein, said circuit comprising at least first and second current carrying conductors for connecting a source of current for said system to respective load terminals, the first one of said conductors being grounded at said source, transformer means having first and second like windings in series connection, respectively, with each of said two conductors, said first and second windings being wound in balanced relationship, said transformer means including a multi-turn secondary winding inductively coupled to said first and second conductors, output means connected to said secondary winding, means connecting said secondary winding between said first and second conductors for passing a predetermined magnitude of current from said source through the secondary winding to establish at said output means, in the absence of a fault on one of said conductors, a signal of predetermined finite magnitude, said secondary winding being wound on the transformer means to produce therein a magnetic flux in opposition to magnetic flux produced by a differential current flowing in said conductors when a fault is present in said system, whereby the occurrence of a fault in said system causes a change in the finite magnitude of said signal at said output means.

Claim 9

A circuit for detecting a fault condition in a power distribution system and for producing in response to a detected fault a signal that is useful in the operation of current interrupter means in said system to interrupt current flow therein, said circuit comprising at least first and second current carrying conductors for connecting a source of current for said system to respective load terminals, the first one of said conductors being grounded at said source, transformer means having first and second like windings in series connection, respectively, with each of said two conductors, said first and second windings being wound in balanced relationship, said transformer means including a multi-turn secondary winding inductively coupled to said first and second conductors, output means connected to said secondary winding, means connecting said secondary winding between said first and second conductors for passing a predetermined magnitude of current from said source through the secondary winding to establish at said output means, in the absence of a fault on one of said conductors, a signal of predetermined finite magnitude, said secondary winding being wound on the transformer means to produce therein a magnetic flux in opposition to magnetic flux produced by a differential current flowing in said conductors when a fault is present in said system, whereby the occurrence of a fault in said system causes a change in the finite magnitude of said signal at said output means.

Claim 10

The circuit claimed in claim 7 wherein the means connecting said secondary winding between said first and second conductors is proportioned to pass a current through the secondary winding sufficient in magnitude to establish in said transformer means a magnitude of magnetic flux which, when opposed by magnetic flux produced by a differential current flowing in said first and second conductors as a result of a fault current of minimum unacceptable magnitude flowing in said system, causes a decrease in said signal of predetermined finite magnitude at said output means.

Claim 11

The combination claimed in claim 8 wherein said means for connecting said secondary winding to said source comprises a shunt circuit between said two conductors including impedance means in series connection with the secondary winding for permitting a given value of source current to flow through the secondary winding.

Claim 12

The combination claimed in claim 9 wherein said primary windings comprise single turn windings and said secondary wiNding has many more turns than the primary windings, said impedance means and the turns of said secondary winding being proportioned to produce an ampere turns value which is equal to the ampere turns value associated with said primary windings when a differential fault current flows therethrough which has been predetermined to be of minimum undesired magnitude whereby the current in the secondary winding is less than said differential fault current by a large multiple.

Claim 13

The combination claimed in claim 8 wherein said primary windings and said secondary winding all are multiple-turn windings.