Location of a ground fault in an IT network

Patent metadata

Field	Value
Publication number	US-11307236-B2
Application number	US-201816634048-A
Country	US
Kind code	B2
Filing date	Jun 29, 2018
Priority date	Jul 27, 2017
Publication date	Apr 19, 2022
Grant date	Apr 19, 2022

Abstract

A method for locating a ground fault in an IT network which has a converter with a rectifier connected to a power transmission network, a DC link and an inverter connected to an electrical machine includes measuring a common-mode voltage property of the converter or of the power transmission network and comparing the common-mode voltage property with an output voltage property of an output voltage of the inverter. When the IT network experiences a ground fault, the comparison of the common-mode voltage property with the output voltage property is used to determine whether a machine area of the IT network connected downstream of the converter, which includes the electrical machine and a connecting line between the electrical machine and the converter, causes the ground fault.

First claim

The invention claimed is:

1. A method for locating a ground fault in an IT network comprising a converter having a rectifier connected at an input side to a power transmission network, and an inverter connected at an output side to a rotating electrical machine, and a DC link circuit connected between the rectifier and the inverter, said method comprising:
measuring voltage pulses of a voltage between a DC link circuit potential of the DC link circuit and a ground potential or voltage pulses of a network voltage of the power transmission network and the ground potential;
comparing the measured voltage pulses with switching actions of a phase of the inverter;
specifying a count duration and a threshold value for a number of occurrences of the measured voltage pulses,
measuring within the count duration an evaluation number of simultaneous voltage pulses and switching actions; and
when the IT network experiences a ground fault and the evaluation number exceeds the threshold value for the number of occurrences, concluding that a machine area of the IT network connected downstream of the converter, which includes the electrical machine and a connecting line between the electrical machine and the converter, causes the ground fault.

2. The method of claim 1 , further comprising specifying a threshold period and defining that a voltage pulse occurs simultaneous with a switching action when a time interval between the voltage pulse and the switching action is less than the specified threshold period.

3. The method of claim 2 , wherein the specified threshold period is less than 10 μs.

4. The method of claim 1 , further comprising determining the switching actions of the phase of the inverter by measuring an output voltage of the phase against a link circuit potential of the DC link circuit.

5. The method of claim 1 , wherein the switching actions of the phase of the inverter are determined from activation signals activating the phase.

6. The method claim 1 , further comprising blocking, with a control unit, activation of the converter when it is concluded that the machine area connected downstream of the converter causes the ground fault.

7. The method of claim 1 , further comprising blocking the converter with a higher-ranking network control unit of the IT network when it is concluded that the machine area connected downstream of the converter causes the ground fault.

8. A method for locating a ground fault in an IT network comprising a converter having a rectifier connected at an input side to a power transmission network, and an inverter connected at an output side to a rotating electrical machine, and a DC link circuit connected between the rectifier and the inverter, the method comprising:
measuring a frequency spectrum of a network voltage of the power transmission network in relation to a ground potential; and
when the IT network experiences a ground fault and the frequency spectrum of the network voltage has both a spectral component matching a basic output frequency of an output voltage of the inverter and a spectral component matching a switching frequency of the inverter, concluding that a machine area of the IT network connected downstream of the converter, which includes the electrical machine and a connecting line between the electrical machine and the converter, causes the ground fault.

9. The method of claim 8 , further comprising, when the power transmission network is a multiphase power transmission network, using as the network voltage a phase voltage or a sum of all phase voltages of the power transmission network in relation to a ground potential.

10. The method of claim 8 , wherein the basic output frequency is a required basic frequency of the output voltage of the inverter.

11. The method of claim 8 , further comprising measuring the basic output frequency.

12. The method claim 8 , further comprising blocking, with a control unit, activation of the converter when it is concluded that the machine area connected downstream of the converter causes the ground fault.

13. The method of claim 8 , further comprising blocking the converter with a higher-ranking network control unit of the IT network when it is concluded that the machine area connected downstream of the converter causes the ground fault.

Assignees

• Siemens Ag

Inventors

• Weis Benno

Classifications

• G01R31/52 Primary

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

• H02H3/16 Primary

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

• H02J3/0012

  characterised by the contingency detection means in AC networks, e.g. using phasor measurement units [PMU], synchrophasors or contingency analysis · CPC title

• G01R31/086 Primary

  in power transmission or distribution networks, i.e. with interconnected conductors · CPC title

• H02H3/162

  for AC systems · CPC title