Monitoring system for high-voltage switches

• US 7,405,569 B2
• Filed: 11/30/2006
• Issued: 07/29/2008
• Est. Priority Date: 11/30/2005
• Status: Expired due to Fees

• Current Assignee: ABB Technology AG (ABB Limited)
• Original Assignee: ABB Technology AG (ABB Limited)
• Inventors: Hagel, Marek, Fehlmann, Patrick
• Primary Examiner(s): Nguyen; Vincent Q.
• Assistant Examiner(s): NGUYEN, HOAI AN D
• Application Number:
  US11/606,234
• Publication Number:
  US 20070120567A1
• Time in Patent Office: 607 Days
• Field of Search: 324/421, 324/415, 324/418, 324/419, 324/420, 324/422, 324/423, 324/424, 324/537, 324/538, 324/700, 324/71.2, 324/71.1, 324/76.11, 73/86
• US Class Current: 324/421
• CPC Class Codes: G01R 31/3271 of high voltage or medium voltage devices G01R31/333 takes precedence

Abstract

A method and an apparatus are disclosed for measuring contact erosion in an electrical switching device by a dynamic resistance measurement (DRM). To determine an overlap time and a contact erosion in an exemplary switching device, a change in current across the switching device can be measured indirectly by a measurement current being passed across the switching device and a parallel conductor, the change in current in the parallel conductor being measured. Exemplary embodiments relate, to the following: detection of a differential current measurement signal in the parallel conductor with the aid of a Rogowski coil; and selection of a parallel conductor resistance on an order of the switch resistance.

Claims

1. A method for measuring contact erosion in an electrical switching device, which has a rated current path having a rated current contact system, and a consumable contact current path having a consumable contact system, an overlap time between the separation of the rated current contacts and of the consumable contacts being measured from a change in resistance when the rated current contacts and the consumable contacts are separated, and erosion of the consumable contacts being determined from this, comprising:

a) branching a first current and a second current from a feed current of a measurement current source;

b) passing the first current through the switching device, and passing the second current in parallel with the switching device; and

c) detecting the second current with the aid of a measurement system, and determining the overlap time from a change in the second current as a function of time.

2. The method for measuring contact erosion as claimed in claim 1, wherein a current measurement signal, which characterizes the second current, is detected as a function of time with the aid of a current sensor.

3. The method for measuring contact erosion as claimed in claim 1, comprising:

a) owing to changes in resistance when the rated current contacts are separated, measuring a first signature in the current measurement signal; and

owing to changes in resistance when the consumable contacts are separated, measuring a second signature in said current measurement signal; and

b) determining the overlap time from a difference between points in time of the first and second signature.

4. The method for measuring contact erosion as claimed in claim 1, comprising:

a) measuring a differential current measurement signal proportional to a time derivative of the second current by the measurement system.

5. The method for measuring contact erosion as claimed in claim 1, comprising:

a) measuring a differential current measurement signal proportional to the first time derivative of the second current by a Rogowski coil.

6. The method for measuring contact erosion as claimed in claim 4, wherein

a) the differential current measurement signal is evaluated without any prior integration for determining the overlap time;

and/or

b) the differential current measurement signal is integrated and then evaluated for determining the overlap time.

7. The method for measuring contact erosion as claimed in claim 1, wherein:

a) the total feed current is split into the first current and the second current; and

/or

b) a constant direct current on an order of magnitude of a few amperes is fed in by the measurement current source.

8. The method for measuring contact erosion as claimed in claim 1, wherein during a measurement phase prior to separation of the consumable contacts:

a) the first current is subjected to a switch resistance via the switching device, and the second current is subjected to a parallel conductor resistance through a parallel conductor connected in parallel to the switching device; and

b) a ratio between the parallel conductor resistance and the switch resistance is selected to be less than 100; and

c) the parallel conductor resistance is selected to be less than 10 mΩ

.

9. The method of claim 8, wherein the ratio between the parallel conductor resistance and the switch resistance is less than 5.

10. The method of claim 8, wherein the parallel conductor resistance is selected to be equal to a maximum of the switch resistance.

11. A measurement system for measuring contact erosion in an electrical switching device, which has a rated current path having a rated current contact system, and a consumable contact current path having a consumable contact system, the measurement system, comprising:

a measurement current source, a sensor, and an evaluation unit, which serve for measuring resistance across the switching device as a function of time, for determining an overlap time between a separation of rated current contacts and consumable contacts, and for determining erosion of the consumable contacts; and

a parallel conductor provided in parallel with the switching device, the sensor being arranged on the parallel conductor, wherein

the measurement current source is connected to the switching device for feeding a first current, and to the parallel conductor for feeding a second current; and

the sensor detects the second current, the evaluation unit having means for determining the overlap time from a change in the second current as a function of time.

12. The measurement system as claimed in claim 11, wherein:

a) the sensor detects a current measurement signal, which characterizes the second current, as a function of time and is a current sensor; and

b) the current sensor measures a differential current measurement signal which is proportional to a time derivative of the second current.

13. The measurement system as claimed in claim 12, wherein:

a) the current sensor is a Rogowski coil and measures a differential current measurement signal which is proportional to the first time derivative of the second current; and

b) to determine the overlap time, the differential current measurement signal is evaluated without any prior integration and/or after integration over time.

14. The measurement system as claimed in claim 12, wherein:

a) the evaluation unit has means for detecting a first and second signature in the current measurement signal, which signatures occur owing to changes in resistance when the rated current contacts and the consumable contacts are separated; and

b) the evaluation unit has means for determining the overlap time from a difference between points in time of the first and second signature.

15. The measurement system as claimed in claim 11, wherein:

a) the total feed current is equal to a sum of the first and second current; and

/or

b) the measurement current source provides a constant direct current on an order of a few amperes and is an accumulator having a series resistor.

16. The measurement system as claimed in claim 11, wherein during a measurement phase prior to separation of the consumable contacts:

a) a switch resistance is present across the switching device, and a parallel conductor resistance is present across the parallel conductor being connected in parallel to the switching device; and

b) a ratio between the parallel conductor resistance and the switch resistance is less than 100; and

c) the parallel conductor resistance is less than 10 mΩ

.

17. The measurement system as claimed in claim 16, wherein the ratio between the parallel conductor resistance and the switch resistance is less than 5.

18. The measurement system as claimed in claim 16, wherein the parallel conductor resistance is equal to a maximum of the switch resistance.

19. The measurement system as claimed in claim 16, wherein the parallel conductor resistance is less than 1 mΩ

.

20. The measurement system as claimed in claim 11, wherein:

a) the measurement system comprises means for detecting the contact movement; and

/or

b) the measurement system is a portable device; and

/or

c) the switching device is a circuit breaker, a high current breaker, or a switch disconnector.