DC ground fault detection

Claim 2

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 normally closed 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 6 cycles per second.

Claim 3

Apparatus as claimed in claim 1, 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 4

Apparatus as claimed in either of claims 1 or 2, including electronic signal conditioning means for reducing noise generated by the pulser and relay.

Claim 5

Apparatus as claimed in claim 3, 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 6

Apparatus as claimed in claim 4, including a DC battery source for the sensor, and means for minimizing DC battery voltage variation effects on said sensor.

Claim 7

Apparatus as claimed in claim 5 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 8

Apparatus as claimed in claim 5, wherein the pick up element includes a Hall effect sensing element for physical relationship about at least one conductor in the DC system.

Claim 9

Apparatus claimed in claim 6 including a switch in circuit with said pulser, said switch being normally open and being operative to closure thereby to activate the pulser.

Claim 10

Apparatus as claimed in claim 5 wherein the pulser signal is substantially a square wave with a period of substantially 6 seconds.

Claim 11

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 6 cycles per second.

Claim 12

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 6 cycles per second.

Claim 13

Apparatus as claimed in claim 10, wherein the responsive element is a ground indicator meter.

Claim 16

A method as claimed in claim 12, 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 17

A method as claimed in claim 13, including filtering from the sensor noise generated by the signal interruption.

Claim 18

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

Claim 19

Apparatus as claimed in claim 3 wherein the magnetic sensor is responsive to a leakage current of about 4 milliamps.

Claim 20

Apparatus as claimed in claim 3 wherein the magnetic sensor is responsive to a leakage current of less than about 4 milliamps.

Claim 21

Apparatus as claimed in claim 10 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 22

A method as claimed in claim 12 wherein the sensor responds to magnetic field changes at intervals of about 3 seconds.

Claim 23

A method as claimed in claim 12 wherein the magnetic sensor is responsive to a leakage current of at least less than about 4 milliamps.

Claim 24

Apparatus as claimed in claim 3 wherein the sensor is permanently located relative to the DC system.

Claim 25

A method as claimed in claim 12 including permanently locating the sensor relative to the DC system.

Claim 26

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 normally closed 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 6 cycles per second.

Claim 27

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 normally closed 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 6 cycles per second.