Apparatus and method for locating ground faults

Claim 1

An apparatus for precisely locating unintentional grounds on electric cables or ungrounded direct current power control systems, including in combination, a low frequency electric current generator having a variable output voltage for generating a low frequency current signal and which is to be operatively connected to the cables of an ungrounded direct current power control system; a Hall-effect current probe having a split magnetic core for positioning about and around the cables of said control system for detecting a low frequency current signal in the cables produced by said generator; a narrow band-pass filter connected to the output of said Hall-effect current probe for substantially blocking all signal frequencies except the low frequency signal transmitted on said cables in said signal generator; a signal amplifier connected to the output of said band-pass filter for amplifying said low-frequency signal; a first current connecting lead having a first and second end of which the first end of said first conducting lead is connected to a faulted cable of the ungrounded direct current power control system; a variable capacitor having a first and second terminal wherein said first terminal is connected to the second end of said first conducting lead; and a second current conducting lead having a first and second end of which the first end is connected to said second terminal of said variable capacitor and said second end of said first conducting lead is passed through said magnetic core and connected to ground such that the direction of the low frequency current in said second conducting lead is in a direction to oppose the effect of the low frequency current in the faulted cable, and readout means connected to the output of said amplifier for indicating the relative magnitude of said low frequency signal to identify the precise location of the ground fault.

Claim 2

An apparatus for precisely locating unintentional grounds on electric cables or ungrounded direct current power control systems, including in combination, a low frequency electric current generator having a variable output voltage for generating a low frequency current signal and which is to be operatively connected to the cables of an ungrounded direct current power control system; a Hall-effect current probe having a split magnetic core for positioning about and around the cables of said control system for detecting a low frequency current signal in the cables produced by said generator; a narrow band-pass filter connected to the output of said Hall-effect current probe for substantially blocking all signal frequencies except the low frequency signal transmitted on said cables in said signal generator; a signal amplifier connected to the output of said band-pass filter for amplifying said low-frequency signal; a first current connecting lead having a first and second end of which the first end of said first conducting lead is connected to a faulted cable of the ungrounded direct current power control system; a variable capacitor having a first and second terminal wherein said first terminal is connected to the second end of said first conducting lead; and a second current conducting lead having a first and second end of which the first end is connected to said second terminal of said variable capacitor and said second end of said first conducting lead is passed through said magnetic core and connected to ground such that the direction of the low frequency current in said second conducting lead is in a direction to oppose the effect of the low frequency current in the faulted cable, and readout means connected to the output of said amplifier for indicating the relative magnitude of said low frequency signal to identify the precise location of the ground fault.

Claim 7

A method for locating ground faults on ungrounded direct current power control cables, including the steps of: applying a low frequency voltage to ground to each of the positive and negative cables of a normally ungrounded direct current power system, whereby a low frequency current signal is caused to flow in the cables of said power system; creating a second current conducting path through a variable capacitor and flexible current conducting leads to ground; detecting the value of the minimum current in the ground faulted cable by utilizing the cancelling effect of the opposing low frequency currents through the power system cables and said second current conducting path with an adjustment of said variable capacitor; and locating the ground fault by noting the point on the faulted cable where said value of minimum detected current is substantially reduced.

Claim 8

A method for locating ground faults on ungrounded direct current power control cables, including the steps of: applying a low frequency voltage to ground to each of the positive and negative cables of a normally ungrounded direct current power system, whereby a low frequency current signal is caused to flow in the cables of said power system; creating a second current conducting path through a variable capacitor and flexible current conducting leads to ground; detecting the value of the minimum current in the ground faulted cable by utilizing the cancelling effect of the opposing low frequency currents through the power system cables and said second current conducting path with an adjustment of said variable capacitor; and locating the ground fault by noting the point on the faulted cable where said value of minimum detected current is substantially reduced.