Method and device for monitoring capacitor bushings for an alternating-current grid

Patent metadata

Field	Value
Publication number	US-11054486-B2
Application number	US-201816488617-A
Country	US
Kind code	B2
Filing date	Feb 22, 2018
Priority date	Feb 28, 2017
Publication date	Jul 6, 2021
Grant date	Jul 6, 2021

Abstract

A method monitors capacitor bushings of a three-phase AC mains, which has first, second, and third mains lines respectively associated with first, second, and third: phases, capacitor bushings, and mains voltages. Each of the capacitor bushings has: a conductor connected with the associated mains line, and an electrically conductive foil enclosing the conductor. The method includes, for each of the phases: determining, at a predetermined initial instant for a characteristic variable, which is characteristic for the respective capacitor bushing, a corresponding characteristic value; determining, at a predetermined later instant after the initial instant for the characteristic variable, a corresponding normalised characteristic value in dependence on the respective characteristic value and/or on at least one of remaining characteristic values; and checking whether the normalised characteristic value has impermissibly changed.

First claim

The invention claimed is:

1. A method of monitoring capacitor bushings for an alternating current mains, the alternating current mains having phases, the phases comprising a first phase, a second phase, and a third phase, the alternating current mains comprising:
a first mains line of a plurality of mains lines, with which the first phase and a first capacitor bushing of the capacitor bushings are associated and at which a first mains voltage of a plurality of mains voltages is present,
a second mains line of the mains lines, with which the second phase and a second capacitor bushing of the capacitor bushings are associated and at which a second mains voltage of the mains voltages is present, and
a third mains line of the mains lines, with which the third phase and a third capacitor bushing of the capacitor bushings are associated and at which a third mains voltage of the mains voltages is present;
each of the capacitor bushings comprising:
a conductor connected with the associated one of the mains lines, and
an electrically conductive foil enclosing the conductor, and the method comprising, for each of the phases:

determining, at a predetermined initial instant for a characteristic variable, which is characteristic for the respective one of the capacitor bushings, a corresponding characteristic value;
determining, at a predetermined later instant after the initial instant for the characteristic variable, a corresponding normalised characteristic value in dependence on the respective characteristic value and/or on at least one of remaining characteristic values; and
checking whether the normalised characteristic value has impermissibly changed.

2. The method according to claim 1 , wherein for each of the phases:
at the predetermined later instant after the initial instant for the characteristic variable, a corresponding later characteristic value is determined; and
determination of the normalised characteristic value additionally depends on the respective later characteristic value and/or on at least one of the remaining later characteristic values.

3. The method according to claim 1 , wherein for each of the phases:
at the initial instant, for a reference voltage, a corresponding initial reference voltage value is determined; and
determination of the normalised characteristic value additionally depends on the respective initial reference voltage value and/or on at least one of the remaining initial reference voltage values.

4. The method according to claim 3 , wherein the reference voltage of each of the phase depends on the respective one of the mains voltages.

5. The method according to claim 4 , wherein for each of the phases:
the reference voltage is the respective one of the mains voltages;
at the initial instant the respective one of the mains voltages is detected and a corresponding initial mains voltage value is determined; and
the initial mains voltage value forms the respective initial reference voltage value.

6. The method according to claim 4 , wherein:
a first parallel capacitor bushing of a plurality of parallel capacitor bushings is associated with the first mains line;
a second parallel capacitor bushing of the capacitor bushings is associated with the second mains line;
a third parallel capacitor bushing of the parallel capacitor bushings is associated with the third mains line;
each of the parallel capacitor bushings comprises:
a conductor connected with the associated one of the mains lines, and
an electrically conductive foil enclosing this the conductor;

each reference voltage is a parallel foil voltage present between the foil and ground potential of the respective one of the parallel capacitor bushings; and
for each of the phases:
at the initial instant the parallel foil voltage is detected and a corresponding initial parallel foil voltage value is determined; and
the initial parallel foil voltage value forms the respective initial reference voltage value.

7. The method according to claim 1 , wherein for each of the phases the reference voltage is a constant voltage for which a corresponding constant voltage value is predetermined.

8. The method according to claim 1 , wherein for each of the phases:
at the initial instant a foil voltage present between the respective foil and ground potential is detected and a corresponding initial foil voltage value is determined; and
determination of the normalised characteristic value additionally depends on the respective initial foil voltage value and/or on at least one of the remaining initial foil voltage values.

9. The method according to claim 1 , wherein:
a measuring device is coupled to the foil of each of the capacitor bushings, and for each of the phases a foil voltage present between the respective foil and ground potential can be detected; and
for each of the phases:
an outer capacitor is formed by the respective foil and a ground potential;
a lower-voltage capacitor is formed by a parallel circuit, which comprises the measuring device and the outer capacitor;
at the initial instant for the lower capacitance of the lower-voltage capacitor a corresponding lower capacitance value is determined; and
determination of the normalised characteristic value additionally depends on the respective lower capacitance value and/or on at least one of the remaining lower capacitance values.

10. The method according to claim 1 , wherein:
for each of the phases:
an upper-voltage capacitor is formed by the respective foil and the respective conductor;
the respective characteristic variable is the upper capacitance of the respective upper-voltage capacitor and the respective characteristic value is a corresponding upper capacitance value;
at the later instant for each of the phases
the foil voltage is detected and a corresponding later foil voltage value is determined;

the normalised upper capacitance value of the first capacitor bushing is calculated in accordance with the following equation:

C
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=

B
a

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V
a

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(

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N
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K
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V
b

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(

t
n

Assignees

• Reinhausen Maschf Scheubeck

Inventors

• Viereck Karsten
• Wu Junliang
• Hertel Udo

Classifications

• H01G4/35

  Feed-through capacitors or anti-noise capacitors · CPC title

• G01R31/12

  Testing dielectric strength or breakdown voltage {; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing (G01R31/08, G01R31/327 and G01R31/72 take precedence; measuring in plasmas G01R19/0061; measuring dielectric constants G01R27/2617; ESD, EMC or EMP testing of circuits G01R31/002)} · CPC title

• G01R15/16

  using capacitive devices · CPC title

• G01R31/64 Primary

  Testing of capacitors · CPC title

• G01R15/06

  having reactive components, e.g. capacitive transformer · CPC title