DC ground fault detection

Claim 2

Apparatus for the detection of ground leakage in a normally ungrounded DC 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 (16, 17) for connection across the DC power supply, a tapping point (18) to the resistor element, a connector (21) between the tapping point and a ground point (23) such that a ground leakage in the system completes a ground circuit, characterised in that a normally closed relay (122) is provided between the tapping point and ground, there being a pulser (22) 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 pulse interrupted ground fault signal, and in that a sensor 24 is provided for location relative to the DC system for sensing said pulse interrupted ground fault signal and thereby providing for detecting the location of the ground leakage, said DC system remaining substantially closed and operational during the ground leakage detection.

Claim 3

Apparatus as claimed in claim 1, characterised in that said sensor includes at least one (55) 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, characterised in that it includes electronic signal conditioning means (34) for reducing noise generated by the pulser and relay.

Claim 5

Apparatus as claimed in claim 3, characterised in that a signal pick-up element (25) is provided, and in that the electronic signal conditioning means (34) includes a DC amplifier (56, 57, 58) and a low pass filter and means (36) for biasing the output of the DC amplifier between a selected voltage range.

Claim 6

Apparatus as claimed in any of claims 1 to 4 characterised in that a DC battery source (30) is provided for the sensor, and in that means (31, 33, 39) are provided for minimising DC battery voltage variation effects on said sensor.

Claim 7

Apparatus as claimed in claim 5 characterised in that the means for minimising DC battery voltage variations includes a first voltage regulator (31) to detect variations in battery supply voltage, and a second voltage regulator (33) to minimise transients.

Claim 8

Apparatus as claimed in any preceding claim, characterised in that the sensor or pick up element includes a Hall effect sensing element (25) for physical relationship about at least one conductor in the DC system.

Claim 9

Apparatus as claimed in any preceding claim characterised in that a switch (222) is provided 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 any preceding claim characterised in that the pulser signal is substantially a square wave with a period in a range of substantially 6 to 11 seconds.

Claim 11

Apparatus, for the detection of ground leakage in a normally ungrounded DC system including a DC power supply and conductors from the supply for supplying power to a load connected in the DC system, comprising a resistor element (16,17) for connection across the DC power supply, a tapping point (18) to the resistor element, a responsive element (19) connected between the tapping point and a ground point (23) such that a ground leakage in the system completes a ground circuit to activate the responsive element, characterised in that a relay is provided between the responsive element and ground, and in that a pulser is provided 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 pulse interrupted ground fault signal, said pulser being incorporated in a circuit with a normally open switch (222), whereby on the occurrence of a ground fault condition, said switch is closed and said pulser operates said relay, in that a sensor (24) is provided for location relative the DC system for sensing said pulse interrupted ground fault signal whereby solely said interrupted ground fault signal provides the necessary signal for ground fault detection, and in that electronic signal conditioning means are provided for reducing noise generated by the pulser and relay, said conditioning means includes an amplifier and filter for the noise.

Claim 12

Apparatus, for the detection of ground leakage in a normally ungrounded DC system including a DC power supply and conductors from the supply for supplying power to a load connected in the DC system, comprising a resistor element (16,17) for connection across the DC power supply, a tapping point (18) to the resistor element, a responsive element (19) connected between the tapping point and a ground point (23) such that a ground leakage in the system completes a ground circuit to activate the responsive element, characterised in that a relay is provided between the responsive element and ground, and in that a pulser is provided 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 pulse interrupted ground fault signal, said pulser being incorporated in a circuit with a normally open switch (222), whereby on the occurrence of a ground fault condition, said switch is closed and said pulser operates said relay, in that a sensor (24) is provided for location relative the DC system for sensing said pulse interrupted ground fault signal whereby solely said interrupted ground fault signal provides the necessary signal for ground fault detection, and in that electronic signal conditioning means are provided for reducing noise generated by the pulser and relay, said conditioning means includes an amplifier and filter for the noise.

Claim 13

Apparatus as claimed in claim 10, characterised in that the responsive element (19) is a ground indicator meter.

Claim 16

A method as claimed in claim 12, further characterised by the step of closing a switch to a pulser which controls 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, further characterised by the step of filtering from the sensor output, noise generated by the signal interruption.