Monitoring apparatus and method for electrical protection systems

Abstract

.Iadd. 1. Apparatus for increasing the security of an electrical protection system in which a protected location is conductively coupled to a central station which comprises at least two conductive means for coupling said protected location to said central station, at said central station, a first supervisory circuit and a second supervisory circuit, each supervisory circuit including a source of supervisory current coupled to a corresponding one of said conductive means and current-sensitive means coupled to said corresponding conductive means to detect predetermined changes in supervisory current therein, and at said protected location, a first protection circuit and a second protection circuit respectively corresponding to said first and second supervisory circuits at said central station, wherein each protection circuit is provided with an input terminal, a shunt terminal and an output terminal, and wherein at least one of said protection circuits is provided with at least one detection device connected between said input terminal and said output terminal so that operation of said detection device alters the flow of supervisory current in said protection circuit, Means for connecting the input terminal of each of said protection circuits to a corresponding one of said conductive means to couple each protection circuit to a corresponding supervisory circuit at said central station, so that supervisory current is directed to each protection circuit, a ground point, switching means interposed between said ground point and said output terminals of said first and second protection circuits, said switching means including: first relay means and second relay means respectively corresponding to said first and second protection circuits, wherein each of said relay means is provided with a winding having first and second terminals, an armature, and a contact, means for connecting the second terminal of each relay means to said ground point, means for connecting the armature of each relay to the first terminal of the winding of the other relay, two first conductor means for connecting the output terminals of said first and second protection circuits to said respective first terminals of said windings of said correspondingly first and second relay means, and two second conductor means for connecting the shunt terminals of each of said first and second protection circuits to said contacts of said second and first relay means, respectively, wherein each of said shunt terminals is located in said respective first and second protection circuits at a point selected to shunt a predetermined portion of the respective protection circuit in response to the energizing of the relay means corresponding to the other protection circuit.

What is claimed is: 
     
       1. Apparatus for increasing the security of an electrical protection system in which a protected location is conductively coupled to a central station which comprises at least two conductive means for coupling said protected location to said central station, at said central station, a first supervisory circuit and a second supervisory circuit, each supervisory circuit including a source of supervisory current coupled to a corresponding one of said conductive means and current-sensitive means coupled to said corresponding conductive means to detect predetermined changes in supervisory current therein, and   at said protected location, a first protection circuit and a second protection circuit respectively corresponding to said first and second supervisory circuits at said central station, wherein each protection circuit is provided with an input terminal, a shunt terminal and an output terminal, and wherein at least one of said protection circuits is provided with at least one detection device connected between said input terminal and said output terminal so that operation of said detection device alters the flow of supervisory current in said protection circuit,   means for connecting the input terminal of each of said protection circuits to a corresponding one of said conductive means to couple each protection circuit to a corresponding supervisory circuit at said central station, so that supervisory current is directed to each protection circuit,   a ground point,   switching means interposed between said ground point and said output terminals of said first and second protection circuits, said switching means including: first relay means and second relay means respectively corresponding to said first and second protection circuits, wherein each of said relay means is provided with a winding having first and second terminals, an armature, and a contact,   means for connecting the second terminal of each relay means to said ground point,   means for connecting the armature of each relay to the first terminal of the winding of the other relay,   two first conductor means for connecting the output terminals of said first and second protection circuits to said respective first terminals of said windings of said corresponding first and second relay means, and   two second conductor means for connecting the shunt terminals of each of said first and second protection circuits to said contacts of said second and first relay means, respectively, wherein each of said shunt terminals is located in said respective first and second protection circuits at a point selected to shunt a predetermined portion of the respective protection circuit in response to the energizing of the relay means corresponding to the other protection circuit.     
     
     
       2. The method of detecting attempts to compromise an electrical protection system including a central station connected to a protected location by at least two conductors, at least two protection circuits at said protected location, and at least two supervisory circuits at said central station individually connected to supply separate supervisory current to each of two corresponding protection circuits by means of two of said conductors, which comprises the step of: shunting a portion of either of said protection circuits in response to a predetermined change in supervisory current in the other one of said protection circuits so that a predetermined change in supervisory current in either one of said protection circuits is accompanied by a selected change in supervisory current in the other one of said protection circuits.   
     
     
       3. An electrical protection system in which a protected location is conductively coupled to a central station which comprises: first conductive means and second conductive means for coupling said protected location to said central station,   at said central station, a first supervisory circuit and a second supervisory circuit corresponding to said first and second conductive means, wherein each supervisory circuit includes a source of supervisory current coupled to said corresponding conductive means and current-sensitive means coupled to said corresponding conductive means to detect predetermined changes in said supervisory current therein, and   at said protected location, a first protection circuit and a second protection circuit respectively coupled to said first and second conductive means to carry supervisory current supplied by said corresponding supervisory circuit to a ground point, and   switching means interposed between said ground point and said first and second protection circuits for shunting a portion of either of said protection circuits in response to a predetermined change in supervisory current in the other one of said protection circuits so that a predetermined change in supervisory current in either one of said protection circuits is accompanied by a change in supervisory current in the other one of said protection circuits.   
     
     
       4. Apparatus as defined in claim 3 wherein said first protection circuit comprises at least two current-adjusting resistors so that said switching means shunts one of said current-adusting resistors in response to said predetermined change in supervisory current in the other one of said protection circuits. 
     
     
       5. Apparatus as defined in claim 3 wherein said second protection circuit comprises at least one detection device so that operation of said detection device alters said supervisory current carried by said first protection circuit. 
     
     
       6. Apparatus as defined in claim 3 wherein each of said first and second protection circuits includes at least one detection device so that operation of said detection device in either one of said protection circuits alters said supervisory current carried by the protection circuit including said operated detection device. 
     
     
       7. Apparatus as defined in claim 3 wherein said switching means comprises: a first relay means including an armature, a contact, and a winding with an input terminal and a ground terminal,   a second relay means including an armature, a contact, and a winding with an input terminal and a ground terminal,   means for connecting said armature of said first relay means to the input terminal of said winding of said second relay means,   means for connecting said armature of said second relay to said input terminal of said winding of said first relay means, and   means for connecting said ground terminals of said windings of said first and second relay means to said ground point. .Iadd. 8. Apparatus as defined in claim 1 wherein at least one of said first and second protection circuits includes at least one additional shunt terminal beyond that connected by the second conductor means to the contact of the relay means, and wherein said apparatus further includes   switch means corresponding in number to the number of said additional shunt terminals, each of said switch means having a first and second terminal,   third conductor means for connecting the first terminal of each of said switch means to one of said additional shunt terminals, and   fourth conductor means for connecting the second terminal of each of said switch means to the second conductor means connected to the shunt terminal of the protection circuit which contains the additional shunt terminal to which the first terminal of the switch is connected by said third conductor means,   whereby the elements of either of the protection circuits included in the shunted portion of the protection circuits can be varied..Iaddend..Iadd. 9. Apparatus as defined in claim 8 wherein the first and second protection circuits each include at least one additional shunt terminal..Iaddend..Iadd. 10. Apparatus as defined in claim 3 further including means for varying the portion of either of the protection circuits which is shunted..Iaddend..Iadd. 11. Method as defined in claim 2 further including varying the portion of either of the protection circuits which is shunted..Iaddend.