System and method for high resistance ground fault detection and protection in power distribution systems

Patent metadata

Field	Value
Publication number	US-9046560-B2
Application number	US-201213487322-A
Country	US
Kind code	B2
Filing date	Jun 4, 2012
Priority date	Jun 4, 2012
Publication date	Jun 2, 2015
Grant date	Jun 2, 2015

Abstract

A system and method for detecting high resistance ground faults in a power distribution system is disclosed. A fault detection and protection system is provided that includes a plurality of current sensors to measure current on the three phase output of the converter-inverter arrangement of the power distribution system and a controller configured to measure the three phase current on the three phase output, extract a fundamental current component for each phase of the three phase output, extract a third harmonic component for each phase of the three phase output, compare the fundamental current component and the third harmonic component extracted from each phase to a first threshold and a second threshold, respectively, and detect a ground fault on a phase of the three phase output based on the comparisons of the fundamental current component and the third harmonic component to the first and second thresholds.

First claim

What is claimed is:

1. A power distribution system comprising:
a converter-inverter arrangement having an input connectable to a three phase AC power source and a three phase output connectable to an input terminal of a load, the converter-inverter arrangement configured to control current flow and terminal voltages in the load; and
a fault detection and protection system connected to the converter-inverter arrangement, the fault detection and protection system comprising:
a plurality of current sensors configured to measure a current on the three phase output of the converter-inverter arrangement; and
a controller configured to:
measure the three phase current on the three phase output of the converter-inverter arrangement;
extract a fundamental current component for each phase of the three phase output of the converter-inverter arrangement;
extract a third harmonic component for each phase of the three phase output of the converter-inverter arrangement;
compare the fundamental current component and the third harmonic component extracted from each phase to a first threshold and a second threshold, respectively;
detect a ground fault on a phase of the three phase output based on the comparisons of the fundamental current component and the third harmonic component to the first and second thresholds; and
declare a ground fault when one phase of the three phase output has a fundamental current component that exceeds the first threshold and a third harmonic component that exceeds the second threshold.

2. The power distribution system of claim 1 wherein the controller is configured to identify which phase of the three phase output the ground fault is present on.

3. The power distribution system of claim 1 wherein the controller is configured to generate an alarm when a ground fault is declared.

4. The power distribution system of claim 3 wherein the controller is configured to define the phase current on each phase of the three phase output as:
i=I 1 *cos θ+ I 3 *cos 3θ,

where I 1 is the amplitude of the fundamental current component, I 3 is the amplitude of the third harmonic component, and θ is the speed at which the load is commanded to run.

5. The power distribution system of claim 4 wherein the controller is configured to extract the fundamental current component without using a total fast fourier transform (FFT), the fundamental current component being extracted according to:

1

2
⁢
π

⁢

∫
0

2
⁢
π

⁢

(

I
1

⁢
cos
⁢

⁢
θ

+

I
3

⁢
cos
⁢

⁢
3
⁢
θ

)

*
cos
⁢

⁢
θ
*

ⅆ
θ

=

I
1

2

1

2
⁢
π

⁢

∫
0

2
⁢
π

⁢

(

I
1

⁢
cos
⁢

⁢
θ

+

I
3

⁢
cos
⁢

⁢
3
⁢

ⅆ
θ

)

*
sin
⁢

⁢
θ
*

ⅆ
θ

=
0

,

where I 1 is the amplitude of the fundamental current component, I 3 is the amplitude of the third harmonic component, and θ is the speed at which the load is commanded to run.

6. The power distribution system of claim 4 wherein the wherein the controller is configured to extract the third harmonic component according to:

1

2
⁢
π

⁢

∫
0

2
⁢
π

⁢

(

Assignees

• Li Huaqiang
• Eaton Corp

Inventors

• Li Huaqiang

Classifications

• G01R31/50 Primary

  Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections (testing of sparking plugs H01T13/58) · CPC title

• H02H3/52 Primary

  responsive to the appearance of harmonics · CPC title

• H02H3/165

  for three-phase systems · CPC title

• G01R19/16566

  Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 · CPC title

• H02H7/122

  for inverters, i.e. DC/AC converters · CPC title