DC ground fault detection

Claim 3

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being between about 1/6 to about 1/11 cycles per second.

Claim 4

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being between about 1/6 to about 1/11 cycles per second.

Claim 5

Apparatus as claimed in claim 2, wherein said sensor includes at least one of a meter indicator, LED display or sound indicator and said sensor indicates a presence of said pulse interrupted ground fault signal by said meter indicator, LED display or sound indicator.

Claim 6

Apparatus as claimed in either of claims 2 or 3, including electronic signal conditioning means for reducing noise generated by the pulser and relay.

Claim 7

Apparatus as claimed in claim 4, including a signal pick-up element, and wherein the electronic signal conditioning means includes a DC amplifier and a low pass filter and means for biasing the output of the DC amplifier between a selected voltage range.

Claim 8

Apparatus as claimed in claim 5, including a DC battery source for the sensor, and means for minimizing DC battery voltage variation effects on said sensor.

Claim 9

Apparatus as claimed in claim 6 wherein the means for minimizing DC battery voltage variation includes a first voltage regulator to detect variations in battery supply voltage, and a second voltage regulator to minimize transients.

Claim 10

Apparatus as claimed in claim 6, wherein the pick up element includes a Hall effect sensing element for physical relationship about at least one conductor in the DC system.

Claim 11

Apparatus claimed in claim 7 including a switch in circuit with said pulser, said switch being normally open and being operative to closure thereby to activate the pulser.

Claim 12

Apparatus as claimed in claim 6 wherein the pulser signal is substantially a square wave with a period in a range of substantially 6 to 11 seconds.

Claim 13

Apparatus as claimed in claim 4 wherein the indicator response in the sensor is indicated at about 6 second intervals.

Claim 14

Apparatus as claimed in claim 4 wherein the magnetic sensor is responsive to a leakage current of about 4 milliamps.

Claim 15

Apparatus as claimed in claim 4 wherein the magnetic sensor is responsive to a leakage current of less than about 4 milliamps.

Claim 16

Apparatus as claimed in claim 4 wherein the sensor is permanently located relative to the DC system.

Claim 17

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being less than about 2 times per second.

Claim 18

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being less than about 2 times per second.

Claim 19

Apparatus as claimed in claim 15, wherein said sensor includes at least one of a meter indicator, LED display or sound indicator and said sensor indicates a presence of said pulse interrupted ground fault signal by said meter indicator, LED display or sound indicator.

Claim 20

Apparatus as claimed in either of claims 15 or 16, including electronic signal conditioning means for reducing noise generated by the pulser and relay.

Claim 21

Apparatus as claimed in claim 17, including a signal pick-up element, and wherein the electronic signal conditioning means includes a DC amplifier and a low pass filter and means for biasing the output of the DC amplifier between a selected voltage range.

Claim 22

Apparatus as claimed in claim 18, including a DC battery source for the sensor, and means for minimizing DC battery voltage variation effects on said sensor.

Claim 23

Apparatus as claimed in claim 19 wherein the means for minimizing DC battery voltage variation includes a first voltage regulator to detect variations in battery supply voltage, and a second voltage regulator to minimize transients.

Claim 24

Apparatus as claimed in claim 19 wherein the pick up element includes a Hall effect sensing element for physical relationship about at least one conductor in the DC system.

Claim 25

Apparatus as claimed in claim 20 including a switch in circuit with said pulser, said switch being normally open and being operative to closure thereby to activate the pulser.

Claim 26

Apparatus as claimed in claim 19 wherein the pulser signal is substantially a square wave with a period in a range of substantially 6 seconds.

Claim 27

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a distribution system having a relatively high capacitive reactance, including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a responsive element connected between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit to activate the responsive element, a relay between the responsive element and ground pulser for periodically opening and closing said relay, while the ungrounded DC system remains operational, the opening and closing of said relay interrupting said ground circuit effectively to generate a DC pulse interrupted ground fault signal to produce proportional periodic changes in a magnetic field associated with the system, said pulser being incorporated in a circuit with a normally open switch, whereby on the occurrence of a ground fault condition, said pulser operates said relay, and a magnetic sensor for location relative the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal whereby solely said interrupted ground fault signal provides the necessary signal for the low level ground fault current in the relatively high capacitive reactance system detection, and including electronic signal and conditioning means for reducing noise generated by the pulser and relay wherein said conditioning means includes an amplifier and filter for the noise, the pulse interruption rate being less than about 2 times per second.

Claim 28

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a distribution system having a relatively high capacitive reactance, including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a responsive element connected between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit to activate the responsive element, a relay between the responsive element and ground pulser for periodically opening and closing said relay, while the ungrounded DC system remains operational, the opening and closing of said relay interrupting said ground circuit effectively to generate a DC pulse interrupted ground fault signal to produce proportional periodic changes in a magnetic field associated with the system, said pulser being incorporated in a circuit with a normally open switch, whereby on the occurrence of a ground fault condition, said pulser operates said relay, and a magnetic sensor for location relative the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal whereby solely said interrupted ground fault signal provides the necessary signal for the low level ground fault current in the relatively high capacitive reactance system detection, and including electronic signal and conditioning means for reducing noise generated by the pulser and relay wherein said conditioning means includes an amplifier and filter for the noise, the pulse interruption rate being less than about 2 times per second.

Claim 31

A method as claimed in claim 25, including closing a switch to a pulser whereby the pulser effectively signals the opening and closing of a relay thereby to generate said pulse interrupted ground fault signal.

Claim 32

A method as claimed in claim 26, including filtering from the sensor noise generated by the signal interruption.

Claim 33

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal being substantially a square wave, and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being less than about 2 times per second.

Claim 34

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal being substantially a square wave, and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being less than about 2 times per second.

Claim 37

apparatus as claimed in claim 17 wherein the indicator response in the sensor is indicated at about 3 second intervals.

Claim 38

Apparatus as claimed in claim 17 wherein the magnetic sensor is responsive to a leakage current of about 4 milliamps.

Claim 39

Apparatus as claimed in claim 17 wherein the magnetic sensor is responsive to a leakage current of less than about 4 milliamps.

Claim 40

Apparatus as claimed in claim 24 wherein the DC pulse interrupted ground fault signal has a period of at least about 6 seconds and wherein the magnetic sensor is responsive to a leakage current of less than about 4 milliamps.

Claim 41

A method as claimed in claim 25 wherein the sensor responds to magnetic field changes at intervals of about 3 seconds.

Claim 42

A method as claimed in claim 25 wherein the magnetic sensor is responsive to a leakage current of at least less than about 4 milliamps.

Claim 43

Apparatus as claimed in claim 17 wherein the sensor is permanently located relative to the DC system.

Claim 44

A method as claimed in claim 25 including permanently locating the sensor relative to the DC system.

Claim 45

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being between about 2 to about 1/6 cycles per second.

Claim 46

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being between about 2 to about 1/6 cycles per second.

Claim 47

Apparatus as claimed in claim 38, wherein said sensor includes at least one of a meter indicator, LED display or sound indicator and said sensor indicates a presence of said pulse interrupted ground fault signal by said meter indicator, LED display or sound indicator.

Claim 48

Apparatus as claimed in either of claims 38 or 39, including electronic signal conditioning means for reducing noise generated by the pulser and relay.

Claim 49

Apparatus as claimed in claim 40, including a signal pick-up element, and wherein the electronic signal conditioning means includes a DC amplifier and a low pass filter and means for biasing the output of the DC amplifier between a selected voltage range.

Claim 50

Apparatus as claimed in claim 41, including a DC battery source for the sensor, and means for minimizing DC battery voltage variation effects on said sensor.

Claim 51

Apparatus as claimed in claim 42 wherein the means for minimizing DC battery voltage variation includes a first voltage regulator to detect variations in battery supply voltage, and a second voltage regulator to minimize transients.

Claim 52

Apparatus as claimed in claim 42, wherein the pick up element includes a Hall effect sensing element for physical relationship about at least one conductor in the DC system.

Claim 53

Apparatus claimed in claim 43 including a switch in circuit with said pulser, said switch being normally open and being operative to closure thereby to activate the pulser.

Claim 54

Apparatus as claimed in claim 42 wherein the pulser signal is substantially a square wave with a period of substantially 6 seconds.

Claim 55

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a distribution system having a relatively high capacitive reactance, including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a responsive element connected between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit to activate the responsive element, a relay between the responsive element and ground pulser for periodically opening and closing said relay, while the ungrounded DC system remains operational, the opening and closing of said relay interrupting said ground circuit effectively to generate a DC pulse interrupted ground fault signal to produce proportional periodic changes in a magnetic field associated with the system, said pulser being incorporated in a circuit with a normally open switch, whereby on the occurrence of a ground fault condition, said pulser operates said relay, and a magnetic sensor for location relative the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal whereby solely said interrupted ground fault signal provides the necessary signal for the low level ground fault current in the relatively high capacitive reactance system detection, and including electronic signal and conditioning means for reducing noise generated by the pulser and relay wherein said conditioning means includes an amplifier and filter for the noise, the pulse interruption rate being between about 2 to about 1/6 cycles per second.

Claim 56

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a distribution system having a relatively high capacitive reactance, including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a responsive element connected between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit to activate the responsive element, a relay between the responsive element and ground pulser for periodically opening and closing said relay, while the ungrounded DC system remains operational, the opening and closing of said relay interrupting said ground circuit effectively to generate a DC pulse interrupted ground fault signal to produce proportional periodic changes in a magnetic field associated with the system, said pulser being incorporated in a circuit with a normally open switch, whereby on the occurrence of a ground fault condition, said pulser operates said relay, and a magnetic sensor for location relative the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal whereby solely said interrupted ground fault signal provides the necessary signal for the low level ground fault current in the relatively high capacitive reactance system detection, and including electronic signal and conditioning means for reducing noise generated by the pulser and relay wherein said conditioning means includes an amplifier and filter for the noise, the pulse interruption rate being between about 2 to about 1/6 cycles per second.

Claim 57

Apparatus as claimed in claim 47, wherein the responsive element is a ground indicator meter.

Claim 60

A method as claimed in claim 49, including closing a switch to a pulser whereby the pulser effectively signals the opening and closing of a relay thereby to generate said pulse interrupted ground fault signal.

Claim 61

A method as claimed in claim 50, including filtering from the sensor noise generated by the signal interruption.

Claim 62

Apparatus as claimed in claim 40 wherein the indicator response in the sensor is indicated at about 3 second intervals.

Claim 63

Apparatus as claimed in claim 40 wherein the magnetic sensor is responsive to a leakage current of about 4 milliamps.

Claim 64

Apparatus as claimed in claim 40 wherein the magnetic sensor is responsive to a leakage current of less than about 4 milliamps.

Claim 65

Apparatus as claimed in claim 47 wherein the DC pulse interrupted ground fault signal has a period of at least about 6 seconds and wherein the magnetic sensor is responsive to a leakage current of less than about 4 milliamps.

Claim 66

A method as claimed in claim 49 wherein the sensor responds to magnetic field changes at intervals of about 3 seconds.

Claim 67

A method as claimed in claim 49 wherein the magnetic sensor is responsive to a leakage current of at least less than about 4 milliamps.

Claim 68

Apparatus as claimed in claim 40 wherein the sensor is permanently located relative to the DC system.

Claim 69

A method as claimed in claim 49 including permanently locating the sensor relative to the DC system.

Claim 70

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal being substantially a square wave, and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being between about 2 to about 1/6 cycles per second.

Claim 71

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal being substantially a square wave, and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being between about 2 to about 1/6 cycles per second.

Claim 72

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a distribution system having a relatively high capacitive reactance, including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a responsive element connected between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit to activate the responsive element, a relay between the responsive element and ground pulser for periodically opening and closing said relay, while the ungrounded DC system remains operational, the opening and closing of said relay interrupting said ground circuit effectively to generate a DC pulse interrupted ground fault signal to produce proportional periodic changes in a magnetic field associated with the system, said pulser being incorporated in a circuit with a normally open switch, whereby on the occurrence of a ground fault condition, said pulser operates said relay, and a magnetic sensor for location relative the Dc system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal whereby solely said interrupted ground fault signal provides the necessary signal for the low level ground fault current in the relatively high capacitive reactance system detection, and including electronic signal and conditioning means for reducing noise generated by the pulser and relay wherein said conditioning means includes an amplifier and filter for the noise, the pulse interruption rate being between about 1/6 to about 1/11 cycles per second.

Claim 73

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a distribution system having a relatively high capacitive reactance, including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a responsive element connected between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit to activate the responsive element, a relay between the responsive element and ground pulser for periodically opening and closing said relay, while the ungrounded DC system remains operational, the opening and closing of said relay interrupting said ground circuit effectively to generate a DC pulse interrupted ground fault signal to produce proportional periodic changes in a magnetic field associated with the system, said pulser being incorporated in a circuit with a normally open switch, whereby on the occurrence of a ground fault condition, said pulser operates said relay, and a magnetic sensor for location relative the Dc system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal whereby solely said interrupted ground fault signal provides the necessary signal for the low level ground fault current in the relatively high capacitive reactance system detection, and including electronic signal and conditioning means for reducing noise generated by the pulser and relay wherein said conditioning means includes an amplifier and filter for the noise, the pulse interruption rate being between about 1/6 to about 1/11 cycles per second.

Claim 74

Apparatus as claimed in claim 61, wherein the responsive element is a ground indicator meter.

Claim 77

A method as claimed in claim 63, including closing a switch to a pulser whereby the pulser effectively signals the opening and closing of a relay thereby to generate said pulse interrupted ground fault signal.

Claim 78

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal being substantially a square wave, and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being between about 1/6 to about 1/11 cycles per second.

Claim 79

Apparatus for the detection of low level ground leakage current in a normally ungrounded DC system in a multifeeder distribution system having a relatively high capacitive reactance and being associated with a relatively strong electromagnetic and electrostatic field, said system including a DC power supply, conductors from the supply for supplying power to a load connected in the DC system comprising a resistor element for connection across the DC power supply, a tapping point to the resistor element, a connector between the tapping point and a ground point such that a ground leakage current in the system completes a ground circuit, a relay between the tapping point and ground, a pulser for periodically opening and closing said relay while the ungrounded DC system remains substantially closed and operational, the opening and closing of said relay interrupting said ground circuit effectively thereby to generate a DC pulse interrupted ground fault signal being substantially a square wave, and a magnetic sensor for location relative to the DC system for sensing said magnetic field changes and thereby said DC pulse interrupted ground fault signal and thereby providing for detecting the location of the low level ground leakage current in the relatively high capacitive reactance system, said DC system remaining substantially closed and operational during the ground leakage current detection, the pulse interruption rate being between about 1/6 to about 1/11 cycles per second.

Claim 82

Apparatus as claimed in claim 61 wherein the DC pulse interrupted ground fault signal has a period of at least about 6 seconds and wherein the magnetic sensor is responsive to a leakage current of less than about 4 milliamps.

Claim 83

A method as claimed in claim 63 wherein the sensor responds to magnetic field changes at intervals of about 6 seconds.

Claim 84

A method as claimed in claim 63 wherein the magnetic sensor is responsive to a leakage current of at least less than about 4 milliamps.

Claim 85

A method as claimed in claim 63 including permanently locating the sensor relative to the DC system.