Method for preventing a dangerous, higher-frequency earth fault current for an electrical drive system

Patent metadata

Field	Value
Publication number	US-10734800-B2
Application number	US-201716336748-A
Country	US
Kind code	B2
Filing date	Aug 17, 2017
Priority date	Sep 27, 2016
Publication date	Aug 4, 2020
Grant date	Aug 4, 2020

Abstract

A dangerous, higher-frequency (>1 kHz) earth fault current in an electrical drive system operated in an electrical grid and having a power converter and an electrical drive machine can be prevented by producing a common-mode voltage with a defined common-mode voltage component in the power converter at a selected low frequency (<1 kHz); in the event of an earth fault in the electrical drive system, flowing at the selected low frequency a common-mode current component of a common-mode current through a predominantly ohmic conductor-to-earth impedance on the basis of the defined common-mode voltage component; measuring a total common-mode current in one of several current circuits of the electrical drive system; determining from the total current the common-mode current component; and when the common-mode current component reaches a reference value, disconnecting the electrical drive system from the electrical grid.

First claim

The invention claimed is:

1. A method for preventing a dangerous higher-frequency earth fault current with a frequency of greater than 1 kH in an electrical drive system having a power converter and an electrical drive machine and operated in an electrical grid, comprising:
in a first step:
producing in the power converter a common-mode voltage having a defined common-mode voltage component at a predefined low frequency of less than 1 kHz,
measuring the common-mode voltage with a voltage sensing device at one of several current circuits of the electrical drive system at a direct voltage intermediate circuit of the power converter or at another of the current circuits a load-side power converter output, and
determining with a voltage evaluation device the defined common-mode voltage component of the produced common-mode voltage at the predefined low frequency,

in a second step:
in the event of an earth fault in the electrical drive system, flowing at the predefined low frequency through a predominantly ohmic conductor-to-earth impedance a common-mode current component of a common-mode current,

in a third step:
measuring with a current sensing device a total current of the common-mode current flowing through one of the several current circuits of the electrical drive system,

in a fourth step:
determining with a current evaluation device the common-mode current component of the common-mode current at the predefined to frequency from a total current, and

in a fifth step:
disconnecting the electrical drive system from the electrical grid with an electrical switching element, when the common-mode current component of the common-mode current reaches a reference value at the predefined low frequency.

2. The method of claim 1 , wherein the dangerous earth fault current, in particular the higher-frequency earth fault current, is detected and the electrical drive system is disconnected from the electrical grid irrespective of an operational earth leakage current flowing in the electrical drive system.

3. The method of claim 1 , wherein the predefined low frequency is an integer multiple of a supply frequency of the electrical grid, and is at the supply frequency of 50 Hz in particular 150 Hz.

4. The method of claim 1 , wherein the power converter produces the common-mode voltage having the defined common-mode voltage component at the predefined low frequency of less than 1 kHz using a rectifier or an inverter, or both.

5. The method of claim 1 , wherein the reference value has a value in a range from 0.1 times a predefined rated fault current to 1 times the predefined rated fault current.

6. The method of claim 1 , wherein when the ohmic conductor-to-earth impedance is less than or equal to 15 kΩ, the predefined common-mode voltage component at the predefined low frequency of the common-mode voltage is produced such that the common-mode current component flowing at the predefined low frequency of the common-mode current reaches the reference value.

7. A fault current protective device for preventing a dangerous higher-frequency earth fault current with a frequency of greater than 1 kHz in an electrical drive system operated in an electrical grid and having a power converter configured to produce a defined common-mode voltage component of a common-mode voltage at a predefined low frequency of less than 1 kHz, and an electrical drive machine, said fault current protective device comprising:
a voltage sensing device arranged at a direct voltage intermediate circuit of the power converter or at a load-side of the power converter;
a voltage evaluation device configured to determine the defined common-mode voltage component of the common-mode voltage at the predefined low frequency;
a current sensing device configured to measure a total current in one of several current circuits of the electrical drive system;
a current evaluation device configured to determine from the total current a common-mode current component of a common-mode current at the predefined low frequency and to compare the common-mode current component with a reference value; and
an electrical switching element configured to disconnect the electrical drive system from the electrical grid.

8. The fault current protective device of claim 7 , wherein the power converter comprises at least one of a rectifier and an inverter producing the defined common-mode voltage component of the common-mode voltage at the predefined low frequency.

9. The fault current protective device of claim 8 , wherein the rectifier is constructed as an uncontrolled rectifier or as a controlled rectifier.

10. The fault current protective device of claim 7 , further comprising a processor unit which includes the voltage evaluation device and the current evaluation device.

11. The fault current protective device of claim 10 , wherein the power converter comprises at least one of a controlled rectifier and an inverter, and wherein the processor unit is configured to control the controlled rectifier or the inverter, or both.

Assignees

• Siemens Ag

Inventors

• Schierling Hubert
• Weis Benno

Classifications

• G01R31/52

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

• G01R31/40

  Testing power supplies (testing photovoltaic devices H02S50/10) · CPC title

• H02H3/337 Primary

  avoiding disconnection due to reactive fault currents · CPC title

• H02H7/1216

  for AC-AC converters · CPC title

• H02H7/12

  for static converters or rectifiers {(for discharge lamp power supplies using static converters H05B41/2851, H05B41/2921, H05B41/2981)} · CPC title