Method and detection device for detecting a high-impedance ground fault in an electrical energy supply network with a grounded neutral point

Patent metadata

Field	Value
Publication number	US-10768243-B2
Application number	US-201816161348-A
Country	US
Kind code	B2
Filing date	Oct 16, 2018
Priority date	Oct 27, 2017
Publication date	Sep 8, 2020
Grant date	Sep 8, 2020

Abstract

A method detects a high-impedance ground fault in an electrical energy supply network with a grounded neutral point. A test signal is fed via a detection device into the energy supply network, the test signal has a frequency which differs from the network frequency of the energy supply network. To enable a reliable detection, with low equipment costs, of high-impedance ground faults in energy supply networks with a grounded neutral point, a three-phase test signal is fed into the phase conductors of the energy supply network as the test signal. A measuring signal which indicates the residual voltage of the test signal is generated with the detection device. The residual voltage is compared with a threshold value using a test device of the detection device, and the presence of a high-impedance ground fault is detected if the residual voltage exceeds the threshold value.

First claim

The invention claimed is:

1. A method for detecting a high-impedance fault having a presence of a fault current in a three-phase electrical energy supply network with a grounded neutral point, which comprises the steps of:
feeding a test signal, via a detection device, into the three-phase electrical energy supply network, the test signal having a frequency differing from a network frequency of the three-phase electrical energy supply network, the test signal being a three-phase test signal injected into phase conductors of the three-phase electrical energy supply network;
generating a measuring signal indicating a residual voltage, the residual voltage is vector sum of the voltages to ground of the several phrase wires of an electrical supply circuit, of the test signal induced in three-phases of the three-phase electrical energy supply network via the detection device;
comparing the residual voltage with a threshold value using a testing device of the detection device; and
detecting a presence of the high-impedance fault if the residual voltage exceeds the threshold value.

2. The method according to claim 1 , which further comprises forming the three-phase test signal such that a symmetrical three-phase network with an isolated neutral point is simulated with a signal-generating device of the detection device.

3. The method according to claim 1 , which further comprises selecting the frequency of the test signal within a range in which transformers present in the three-phase electrical energy supply network have a high impedance.

4. The method according to claim 1 , which further comprises injecting the test signal by means of a coupling device into the three-phase electrical energy supply network, the coupling device is configured as a capacitive coupling, as an analog amplifier or as an inverter.

5. The method according to claim 1 , which further comprises determining the residual voltage of the test signal with the detection device in relation to a ground potential of the three-phase electrical energy supply network.

6. The method according to claim 1 , which further comprises performing, via the testing device, a separation of the measuring signal from signals having the network frequency of the three-phase electrical energy supply network.

7. The method according to claim 1 , which further comprises comparing either an absolute amplitude of the residual voltage or a deviation of the residual voltage from a stationary value of the residual voltage with the threshold value.

8. The method according to claim 1 , which further comprises forming the test signal in a form of a sinusoidal wave, a pulsed signal or a pseudo-random binary signal.

9. A detection device assembly for detecting a high-impedance fault having a presence of a fault current in a three-phase electrical energy supply network with a grounded neutral point, the detection device assembly comprising:
a detection device configured to:
connect to phase conductors of the three-phase electrical energy supply network;
inject a test signal into the three-phase electrical energy supply network, the test signal having a frequency which differs from a network frequency of the three-phase electrical energy supply network, said detection device configured to inject the test signal as a three-phrase test signal into phase conductors of the three-phase electrical energy supply network; and
generate a measuring signal which indicates a residual voltage, the residual voltage is vector sum of the voltages to ground of the several phrase wires of an electrical supply circuit, of the test signal induced in three-phases of the three-phase electrical energy supply network;

said detection device having a testing device configured to compare the residual voltage with a threshold value; and
said testing device is configured to detect a presence of a high-impedance ground fault if the residual voltage exceeds the threshold value.

Assignees

• Siemens Ag

Inventors

• Englert Heiko
• Jurisch Andreas

Classifications

• G01R31/52 Primary

  Testing for short-circuits, leakage current or ground faults · CPC title

• G01R31/085

  in power transmission or distribution lines, e.g. overhead · CPC title

• H02H3/17

  by means of an auxiliary voltage injected into the installation to be protected {(using summation current transformers H02H3/33)} · CPC title

• H02H1/0007

  concerning the detecting means (in general G01R or other subclasses of G01; reed switches H01H71/2445) · CPC title

• H02H3/16

  responsive to fault current to earth, frame or mass (with balanced or differential arrangement H02H3/26 {; monitoring earth connection H02H5/105}) · CPC title