DC ground fault detection with resistive centering

• US 20050231217A1
• Filed: 04/15/2004
• Published: 10/20/2005
• Est. Priority Date: 04/15/2004
• Status: Active Grant

• Current Assignee: BAE Systems Controls Incorporated (BAE Systems Plc)
• Original Assignee: BAE Systems Controls Incorporated (BAE Systems Plc)
• Inventors: Carruthers, Peter Alexander
• Granted Patent: US 7,049,825 B2
• Time in Patent Office: Days
• US Class Current: 324/691
• CPC Class Codes: G01R 27/18 Measuring resistance to earth , i.e. line to ground
• CPC Class Codes: G01R 31/40 Testing power supplies testing photovoltaic devices H02S50/10
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults

Abstract

A method for determining the nature of a ground fault in a floating direct voltage load powering context includes measuring the load voltage and the current at a nominal balance point, both before and after closing a circuit to the load. The fault resistance and the fault voltage are determined as the solution to an equation in two unknowns given the conditions before and after application of load voltage or at least precharge.

Claims

1. A method for sensing isolation faults in a system including a direct-voltage power supply, which direct-voltage power supply nominally floats relative to a reference conductor, and in which the system also includes a load, a first terminal of which load is connected to a first terminal of said direct voltage power supply, said method comprising the steps of:

coupling to a node, by a resistive coupling path having an equivalent resistance, a fixed proportion of the direct voltage of said direct-voltage power supply, said node being connected by a measuring path to said reference conductor;

measuring a first current flowing in said measuring path at a first time;

measuring a first voltage applied to said load at said first time;

measuring a second current flowing in said measuring path at a second time different from said first time;

measuring a second voltage applied to said load at said second time;

at a time between said first and second times, coupling a second terminal of said direct-voltage power supply to a second terminal of said load, for energization thereof; and

determining, from said equivalent resistance, and said first and second voltages and currents, at least one of fault voltage and resistance.

2. A method according to claim 1, wherein said step of determining said fault resistance, R_fault is performed by

$\begin{array}{c}{R}_{\mathrm{fault}}=\frac{V_{\mathrm{link2}}-V_{\mathrm{link1}}}{2}\end{array}$

( Ig f1 - Ig f2 ) - Rg 2 ( 1 )

where;

V_link1 is the voltage at load at said first time;

V_link2 is the voltage at said load at said second time;

Ig_f1 is the current in said measurement path at said first time;

Ig_f2 is the current in said measurement path at said second time; and

Rg is said equivalent resistance.

3. A method according to claim 1, wherein said step of determining said fault voltage V_fault is established by

$\begin{array}{c}{V}_{\mathrm{fault}}=\frac{V_{\mathrm{link2}}}{}\end{array}$

Ig f1 - V link1 ⁢

Ig f2 2 ⁢

( Ig f1 - Ig f2 ) ( 2 )

where;

V_link1 is the voltage at said load at said first time;

V_link2 is the voltage at said load at said second time;

Ig_f1 is the current in said measurement path at said first time;

Ig_f2 is the current in said measurement path at said second time; and

Rg is said equivalent resistance.

4. A method according to claim 1, wherein said steps of measuring a first voltage at said load, and measuring a second voltage at said load, are performed by measuring voltage across said load.

5. A method according to claim 3, wherein the voltage Vfault is referenced to the negative terminal of the load.