Detector of backfeed electrical currents

Claim 2

Apparatus for detecting, in a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant but having the three lines connected together by short-circuiting means of negligible impedance, the current flow in any one of said lines adjacent to said short-circuiting means, said apparatus comprising: coupling means including three transformers which may be magnetically each coupled to a respective one of said lines adjacent said short-circuiting means for providing an alternating current output whenever alternating current flows in any of said lines; combining means having an input and an output and having its input connected to said transformers for combining the alternating current output of the latter and providing an alternating voltage at its output whenever there is alternating current flowing in any of said lines; and indicating means connected to said output of said combining means and responsive to an alternating voltage at said output.

Claim 3

Apparatus as set forth in claim 1, wherein said short-circuiting means comprises a switch for interconnecting said lines and wherein said transformers are current transformers, each having core means for the passage of one of said lines therethrough.

Claim 4

Apparatus as set forth in claim 1, wherein said indicating means comprises alarm means.

Claim 5

Apparatus as set forth in claim 3, wherein said alarm means comprises a light source energized by the presence of a voltage at the output of said combining means.

Claim 6

Apparatus as set forth in claim 3, wherein said alarm means comprises an audible signal generator energized by the presence of a voltage at the output of said combining means.

Claim 7

In a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant, testing and detecting apparatus comprising: switch means for interconnecting said lines with negligible impedance therebetween; three current transformers magnetically coupled to said lines at portions thereof which are adjacent said switch and which are substantially the same voltage as the voltage on said switch, one transformer being coupled to each line, for providing an alternating voltage after said switch is closed and current flows in the line to which a transformer is coupled; voltage responsive means connected to said transformers for providing an output after said switch is closed and said alternating voltage is provided by at least one of said transformers; and indicating means connected to said voltage responsive means and responsive to said output thereof whenever it is present.

Claim 8

In a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant, testing and detecting apparatus comprising: switch means for interconnecting said lines with negligible impedance therebetween; three current transformers magnetically coupled to said lines at portions thereof which are adjacent said switch and which are substantially the same voltage as the voltage on said switch, one transformer being coupled to each line, for providing an alternating voltage after said switch is closed and current flows in the line to which a transformer is coupled; voltage responsive means connected to said transformers for providing an output after said switch is closed and said alternating voltage is provided by at least one of said transformers; and indicating means connected to said voltage responsive means and responsive to said output thereof whenever it is present.

Claim 9

Apparatus as set forth in claim 6, wherein said indicating means comprises alarm means.

Claim 10

In a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant, testing and detecting apparatus comprising: switch means for interconnecting said lines with negligible impedance therebetween, said switch means comprising energizable means for opening said switch means and thereby disconnecting said lines from each other; three current transformers magnetically coupled to said lines adjacent said switch, one transformer being coupled to each line, for providing an alternating voltage when current flows in the line to which a transformer is coupled; voltage responsive means connected to said transformers for providing an output when said alternating voltage is provided by at least one of said transformers; and circuit means for energizing said energizable means including control means connected to said voltage responsive means for preventing energization of said energizable means and thereby preventing opening of said switch when said voltage responsive means provides said output.

Claim 11

In a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant, testing and detecting apparatus comprising: switch means for interconnecting said lines with negligible impedance therebetween, said switch means comprising energizable means for opening said switch means and thereby disconnecting said lines from each other; three current transformers magnetically coupled to said lines adjacent said switch, one transformer being coupled to each line, for providing an alternating voltage when current flows in the line to which a transformer is coupled; voltage responsive means connected to said transformers for providing an output when said alternating voltage is provided by at least one of said transformers; and circuit means for energizing said energizable means including control means connected to said voltage responsive means for preventing energization of said energizable means and thereby preventing opening of said switch when said voltage responsive means provides said output.

Claim 12

Testing and detecting apparatus as set forth in claim 8, wherein said energizable means is a solenoid and said control means comprises a relay connected to said voltage responsive means.

Claim 13

Apparatus for detecting, in a three wire, three phase, alternating current electrical system having three lines, one for each phase, which normally are at different voltages at any given instant but having a switch of negligible impedance for interconnecting said lines, the current flow in any one of said lines adjacent to said short-circuiting means, said apparatus comprising: coupling means including three current transformers each having core means for the passage of one of said lines therethrough adjacent said switch for providing an alternating current output when alternating current flows in any of said lines; combining means comprising a further transformer having three inputs and an output and means connecting a first one of said inputs to a first one of said three transformers, a second one of said inputs to a second one of said three transformers with the same polarity as said first one of said inputs and connecting the third one of said inputs to the remaining one of said three transformers with a polarity opposite to that of the first and second inputs for combining the alternating current output of said three transformers and providing an alternating voltage at its output; and indicating means connected to said output of said combining means and responsive to an alternating voltage at said output.

Claim 14

Apparatus for detecting, in a three wire, three phase, alternating current electrical system having three lines, one for each phase, which normally are at different voltages at any given instant but having a switch of negligible impedance for interconnecting said lines, the current flow in any one of said lines adjacent to said short-circuiting means, said apparatus comprising: coupling means including three current transformers each having core means for the passage of one of said lines therethrough adjacent said switch for providing an alternating current output when alternating current flows in any of said lines; combining means comprising a further transformer having three inputs and an output and means connecting a first one of said inputs to a first one of said three transformers, a second one of said inputs to a second one of said three transformers with the same polarity as said first one of said inputs and connecting the third one of said inputs to the remaining one of said three transformers with a polarity opposite to that of the first and second inputs for combining the alternating current output of said three transformers and providing an alternating voltage at its output; and indicating means connected to said output of said combining means and responsive to an alternating voltage at said output.

Claim 15

Apparatus for detecting, in a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant but having the three lines connected together by a switch of negligible impedance, the current flow in any one of said lines adjacent to said short-circuiting means, said switch having energizable means for opening said switch and circuit means for energizing said energizable means, said apparatus comprising: coupling means including three transformers which may be magnetically each coupled to a respective one of said lines adjacent said switch for providing an alternating current output when alternating current flows in any of said lines; combining means having an input and an output and having its input connected to said transformers for combining the alternating current output of the latter and providing an alternating voltage at its output; and indicating means connected to said output of said combining means and responsive to an alternating voltage at said output, said indicating means comprising control means responsive to the presence of a voltage at the output of said combining means and further comprising means for interconnecting said control means and said circuit means for preventing opening of said switch when a voltage is present at the output of said combining means.

Claim 16

Apparatus for detecting, in a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant but having the three lines connected together by a switch of negligible impedance, the current flow in any one of said lines adjacent to said short-circuiting means, said switch having energizable means for opening said switch and circuit means for energizing said energizable means, said apparatus comprising: coupling means including three transformers which may be magnetically each coupled to a respective one of said lines adjacent said switch for providing an alternating current output when alternating current flows in any of said lines; combining means having an input and an output and having its input connected to said transformers for combining the alternating current output of the latter and providing an alternating voltage at its output; and indicating means connected to said output of said combining means and responsive to an alternating voltage at said output, said indicating means comprising control means responsive to the presence of a voltage at the output of said combining means and further comprising means for interconnecting said control means and said circuit means for preventing opening of said switch when a voltage is present at the output of said combining means.

Claim 17

In a three wire, three phase, alternating current electrical system having three lines, one for each phase, which normally are at different voltages at any given instant, testing and detecting apparatus conprising: switch means for interconnecting said lines with negligible impedance therebetween; three current transformers magnetically coupled to said lines adjacent said switch, one transformer being coupled to each line, for providing an alternating voltage when current flows in the line to which a transformer is coupled; voltage responsive means comprising a further transformer having three inputs and an output and means connecting a first one of said inputs to a first one of said three transformers, a second one of said inputs to a second one of said three transformers with the same polarity as said first one of said inputs and connecting the third one of said inputs to the remaining one of said three transformers with a polarity opposite to that of the first and second inputs for providing an output when said alternating voltage is provided by at least one of said current transformers; and indicating means connected to said voltage responsive means and responsive to said output thereof.

Claim 18

In a three wire, three phase, alternating current electrical system having three lines, one for each phase, which normally are at different voltages at any given instant, testing and detecting apparatus conprising: switch means for interconnecting said lines with negligible impedance therebetween; three current transformers magnetically coupled to said lines adjacent said switch, one transformer being coupled to each line, for providing an alternating voltage when current flows in the line to which a transformer is coupled; voltage responsive means comprising a further transformer having three inputs and an output and means connecting a first one of said inputs to a first one of said three transformers, a second one of said inputs to a second one of said three transformers with the same polarity as said first one of said inputs and connecting the third one of said inputs to the remaining one of said three transformers with a polarity opposite to that of the first and second inputs for providing an output when said alternating voltage is provided by at least one of said current transformers; and indicating means connected to said voltage responsive means and responsive to said output thereof.

Claim 19

In a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant, testing and detecting apparatus comprising: switch means for interconnecting said lines with negligible impedance therebetween, said switch means comprising energizable means for opening said switch means for disconnecting said lines from each other and circuit means for energizing said energizable means; three current transformers magnetically coupled to said lines adjacent said switch, one transformer being coupled to each line, for providing an alternating voltage when current flows in the line to which a transformer is coupled; voltage responsive means connected to said transformers for providing an output when said alternating voltage is provided by at least one of said transformers; indicating means connected to said voltage responsive means and responsive to said output thereof; and control means responsive to said output of said voltage responsive means and connected to said circuit means for preventing opening of said switch means when said voltage responsive means provides said output.

Claim 20

In a three wire, alternating current electrical system having three lines which normally are at different voltages at any given instant, testing and detecting apparatus comprising: switch means for interconnecting said lines with negligible impedance therebetween, said switch means comprising energizable means for opening said switch means for disconnecting said lines from each other and circuit means for energizing said energizable means; three current transformers magnetically coupled to said lines adjacent said switch, one transformer being coupled to each line, for providing an alternating voltage when current flows in the line to which a transformer is coupled; voltage responsive means connected to said transformers for providing an output when said alternating voltage is provided by at least one of said transformers; indicating means connected to said voltage responsive means and responsive to said output thereof; and control means responsive to said output of said voltage responsive means and connected to said circuit means for preventing opening of said switch means when said voltage responsive means provides said output.