Method, electrical circuit arrangements and insulation monitoring devices for an interference-resistant insulation monitoring of an ungrounded power supply system having a converter

Patent metadata

Field	Value
Publication number	US-11705715-B2
Application number	US-201816030918-A
Country	US
Kind code	B2
Filing date	Jul 10, 2018
Priority date	Jul 11, 2017
Publication date	Jul 18, 2023
Grant date	Jul 18, 2023

Abstract

The invention relates to a method, electrical circuit arrangements and insulation monitoring devices for an interference-resistant insulation monitoring of an ungrounded power supply system having a converter.
Switching-frequent interfering signals, which are caused by operating the converter, are identified and assessed in a measured displacement voltage independently of the detection of a measuring signal in order to derive a switching (off) signal if required.
Complementary thereto, an interfering resistance with respect to low-frequency interfering portions generated by the converter is attained by these low-frequency interfering portions being generated from a replica of a pulse width modulation signal of the converter and being suppressed sufficiently via subtraction that a monitoring without gaps (frequency) of the insulation resistance becomes possible.

First claim

The invention claimed is:

1. A method for an interference-resistant insulation monitoring of an ungrounded power supply system having a converter, comprising the method steps:
applying a measuring voltage between an active conductor of the power supply system and ground and detecting a measuring signal driven by the measuring voltage,
detecting a displacement voltage between an active conductor of the power supply system and ground on an input side of the converter,
filtering a switching-frequent signal portion, which is generated by the converter, from the detected displacement voltage,
evaluating the filtered, switching-frequent signal portion,
triggering a switching signal should the evaluation of the switching-frequent signal portion yield that the switching-frequent signal portion surmount a critical amplitude value.

2. The method according to claim 1 , characterized by separating the converter from the power supply system should the switching signal be triggered.

3. A method for an interference-resistant insulation monitoring of an ungrounded power supply system having a converter, comprising the method steps:
applying a measuring voltage between an active conductor of the power supply system and ground and detecting a measuring signal driven by the measuring voltage,
replicating a pulse width modulation signal of the converter,
assessing the replicated pulse width modulation signal using filter characteristics corresponding to a filtering of the detected measuring signal in order to obtain a low-frequency interfering signal,
subtracting the low-frequency interfering signal from the detected measuring signal.

4. The method according to claim 3 , characterized in that a frequency and a duty factor of the pulse width modulation signal are provided by the converter via a digital interface.

5. The method according to claim 3 , characterized in that a frequency and a duty factor of the pulse width modulation signal are calculated using signal processing methods.

6. The method according to claim 3 , characterized in that an amplitude of the pulse width modulation signal is directly predetermined as an amplitude of an intermediary-circuit direct voltage of the converter.

7. The method according to claim 3 , characterized in that the amplitude of the pulse width modulation signal is metrologically detected via a direct voltage measurement at the intermediate circuit of the converter or via a conductor voltage measurement having a correction factor.

8. An electrical circuit arrangement for an interference-resistant insulation monitoring of an ungrounded power supply system having a converter, having a coupling device for applying a measuring voltage between an active conductor of the power supply system and ground and for detecting a measuring signal driven by the measuring voltage; having a detection device for detecting a displacement voltage between an active conductor of the power supply system and ground on an input side of the converter and for filtering a switching-frequent signal portion, which is generated by the converter, from the detected displacement voltage; and having an evaluation circuit for evaluating the filtered switching-frequent signal portion and for triggering a switching signal should the evaluation of the switching-frequent signal portion yield that the switching-frequent signal portion surmounts a critical amplitude value.

9. The electrical circuit arrangement according to claim 8 , characterized in that the detection device is realized as an analogous RC high-pass filter circuit.

10. The electrical circuit arrangement according to claim 8 , characterized in that the detection device for filtering the switching-frequent signal portion comprises a digital signal processing circuit.

11. The electrical circuit arrangement according to claim 8 , characterized by a separating device connected to the evaluation circuit via a signal line for forwarding the switching signal.

12. An insulation monitoring device for monitoring an insulation resistance in an ungrounded power supply system having a converter, characterized by an electrical circuit arrangement for an interference-resistant insulation monitoring according to claim 8 .

13. An electrical circuit arrangement for an interference-resistant insulation monitoring of an ungrounded power supply system having a converter, having a coupling device for applying a measuring voltage between an active conductor of the power supply system and ground and for detecting a measuring signal driven by the measuring voltage;
having a reconstruction unit for replicating a pulse width modulation signal of the converter; having an assessment circuit for assessing the replicated pulse width modulation signals, said assessment circuit having filter characteristics corresponding to a filtering of the detected measuring signal in order to obtain a low-frequency interfering signal; and having a subtraction circuit for subtracting the low-frequency interfering signal from the detected measuring signal.

14. The electrical circuit arrangement according to claim 13 , characterized by a digital interface via which a frequency and a duty factor of the pulse width modulation signal are provided by the converter.

15. The electrical circuit arrangement according to claim 13 , characterized by a computing unit for computing a frequency and a duty factor of the pulse width modulation signal using signal processing methods.

16. An insulation monitoring device for monitoring an insulation resistance in an ungrounded power supply system using a converter, characterized by an electrical circuit arrangement for an interference-resistant insulation monitoring according to claim 13 .

Assignees

• Bender Gmbh & Co Kg

Inventors

• Hackl Dieter

Classifications

• H02H3/17 Primary

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

• G01R27/18

  Measuring resistance to earth {, i.e. line to ground} · CPC title

• G01R27/025 Primary

  Measuring very high resistances, e.g. isolation resistances, i.e. megohm-meters · CPC title

• G01R31/1272 Primary

  of cable, line or wire insulation, e.g. using partial discharge measurements (locating faults in cables G01R31/083) · CPC title

• H02H3/165

  for three-phase systems · CPC title