Method and apparatus for monitoring capacitor bushings for a three-phase AC system

Patent metadata

Field	Value
Publication number	US-9759761-B2
Application number	US-201415027772-A
Country	US
Kind code	B2
Filing date	Nov 11, 2014
Priority date	Nov 15, 2013
Publication date	Sep 12, 2017
Grant date	Sep 12, 2017

Abstract

A three-phase alternating current mains has capacitor bushings that each have a conductor connected with one of the mains lines of the alternating current mains and an electrically conductive lining surrounding the conductor. These bushings are monitored by first determining an upper capacitance and a lower capacitance for each bushing and then detecting a measured voltage between the respective lining and a ground potential at each capacitor bushing. An actual capacitance for each capacitor bushing is calculated that depends on the respective measured voltage and the respective lower capacitance as well as on the measured voltage, the lower capacitance, and the upper capacitance of one of the other capacitor bushings. For each capacitor bushing the respective upper capacitance is compared with the respective actual capacitance and a monitoring signal is generated that is dependent on the results of the capacitance comparison.

First claim

The invention claimed is:

1. A method of monitoring capacitor bushings for a three-phase alternating current mains, where each capacitor bushing comprises a conductor connected with one of the mains lines of the alternating current mains, and an electrically conductive lining surrounding the conductor, the method comprising the steps of:
determining an upper capacitance and a lower capacitance for each capacitor bushing;
detecting a measured voltage present between the respective lining and a ground potential at each capacitor bushing;
calculating an actual capacitance for each capacitor bushing, the actual capacitance depending on the respective measured voltage and the respective lower capacitance as well as on the measured voltage, the lower capacitance, and the upper capacitance of one of the other capacitor bushings;
for each capacitor bushing comparing the respective upper capacitance with the respective actual capacitance; and
generating a monitoring signal dependent on the results of the capacitance comparison.

2. The method according to claim 1 , further comprising the steps of:
detecting the mains voltage for each phase;
comparing the detected mains voltages with one another; and
if the voltage comparison has the result that the mains voltages differ from one another by not more than a predetermined amount carrying out the calculation of the actual capacitances, the comparison of the capacitances and the generation of the monitoring signal.

3. The method according to claim 2 , wherein effective values and/or peak values and/or amplitudes of the mains voltages are used in the voltage comparison.

4. The method according to claim 3 , further comprising the steps of:
determining tolerance values UAB>0, UBC>0, UCA>0 for the voltage comparison; and
carrying out the voltage comparison to check whether |Uae−Ube|≦UAB and |Ube−Uce|≦UBC and |Uce−Uae|≦UCA.

5. The method according to claim 1 , wherein
the actual capacitance of the first capacitor bushing is calculated according to the following formula:

C

0
⁢
a

′

=

C

1
⁢
a

×

U

1
⁢
a

×

K
a

U

1
⁢
b

×

C

1
⁢
b

C

0
⁢
b

+

U

1
⁢
b

-

U

1
⁢
a

×

K
a

where Ka is a correction value for which Ka=1 or Ka=Ub/Ua; and/or
the actual capacitance of the second capacitor bushing is calculated according to the following formula:

C

0
⁢
b

′

=

C

1
⁢
b

×

U

1
⁢
b

×

K
b

U

1
⁢
c

×

C

1
⁢
c

C

0
⁢
c

+

U

1
⁢
c

-

U

1
⁢
b

×

K
b

where Kb is a correction value for which Kb=1 or Kb=Uc/Ub; and/or
the actual capacitance of the third capacitor bushing is calculated according to the following formula:

C

0
⁢
c

′

=

C

1
⁢
c

×

U

1
⁢
c

Assignees

• Reinhausen Maschf Scheubeck

Inventors

• Wu Junliang
• Viereck Karsten
• Sundermann Ulrich

Classifications

• G01R31/1245 Primary

  of line insulators or spacers, e.g. ceramic overhead line cap insulators; of insulators in HV bushings · CPC title

• G01R15/16

  using capacitive devices · CPC title

• G01R19/16576

  comparing DC or AC voltage with one threshold (G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533 and G01R19/1659 take precedence) · CPC title

• G01R27/2605

  Measuring capacitance (capacitive sensors G01D5/24) · CPC title

• G01R19/02

  Measuring effective values, i.e. root-mean-square values · CPC title