Method and apparatus for the measurement of a resistance of a switching contact of an electrical circuit breaker

Abstract

An apparatus and method for the measurement of a resistance of a switching contact of an electrical circuit breaker. A first resistance value across the circuit breaker is determined while the circuit breaker is grounded at both sides and the switching contact is closed. Further, a second resistance value across the circuit breaker is determined while the circuit breaker is grounded at both sides and the switching contact is open. The resistance of the closed switching contact is then determined based on the first resistance value and the second resistance value.

Claims

1. A method for the measurement of resistances of switching contacts arranged in a series connection of an electrical circuit breaker, comprising the steps: feeding a first measurement current in a first direction through a first switching contact of the switching contacts arranged in the series connection, wherein the first measurement current is fed in a first terminal of the first switching contact and drawn at a second terminal of the first switching contact; feeding a second measurement current in a second direction through a second switching contact of the switching contacts arranged in the series connection, wherein the second measurement current is fed in a first terminal of the second switching contact and drawn at a second terminal of the second switching contact, the first direction and the second direction being opposite to one another with respect to the series connection of the switching contacts, and the first measurement current and the second measurement current being fed while the series connection is grounded at both sides resulting in a grounding loop; adjusting the first measurement current and the second measurement current such that a voltage drop across the first switching contact equals a voltage drop across the second switching contact, resulting in a voltage drop across the grounding loop being zero; and determining a resistance value of the first switching contact on the basis of the first measurement current while the first switching contact and the second switching contact are closed.

2. The method according to claim 1, further comprising the step: determining a resistance value of the second switching contact based on the second measurement current while the first switching contact and the second switching contact are closed.

3. The method according to claim 2, wherein the circuit breaker comprises more than two switching contacts arranged in a series connection with the first switching contact and the second switching contact, and wherein all the switching contacts of the circuit breaker are closed while the determining of the resistance values of the first and second switching contacts.

4. The method according to claim 2, wherein the determining of the resistance values of the first and second switching contacts comprises: measuring a first voltage across the first switching contact; and measuring a second voltage across the second switching contact.

5. The method according to claim 1, wherein the first and second measurement currents are fed while the circuit breaker is grounded at both sides.

6. The method according to claim 1, wherein in the series connection the first switching contact is arranged adjacent to the second switching contact.

7. The method according to claim 1, wherein the circuit breaker comprises a plurality of pairs of switching contacts, each of the pairs of switching contacts comprising a first switching contact and an adjacent second switching contact, and wherein the method is simultaneously carried out on several of the pairs of adjacent switching contacts of the circuit breaker.

8. The method according to claim 1, wherein the circuit breaker comprises at least one of an ultra-high voltage switch, a high voltage switch, and a medium voltage switch.

9. An apparatus for the measurement of resistances of switching contacts arranged in a series connection of an electrical circuit breaker, comprising: a first device for feeding a first measurement current in a first direction through a first switching contact of the switching contacts arranged in the series connection, wherein the first measurement current is fed in a first terminal of the first switching contact and drawn at a second terminal of the first switching contact; a second device for feeding a second measurement current in a second direction through a second switching contact of the switching contacts arranged in the series connection, wherein the second measurement current is fed in a first terminal of the second switching contact and drawn at a second terminal of the second switching contact, the first direction and the second direction being opposite to one another with respect to the series connection of the switching contacts, and the first measurement current and the second measurement current being fed while the series connection is grounded at both sides resulting in a grounding loop; and a processing unit coupled to the first device and the second device and configured to determine a resistance value of the first switching contact on the basis of the first measurement current while the first switching contact and the second switching contact are closed, the processing unit also configured to adjust the first measurement current and the second measurement current such that a voltage drop across the first switching contact equals a voltage drop across the second switching contact, resulting in a voltage drop across the grounding loop being zero.

10. The apparatus according to claim 9, wherein a first switch is connected in parallel with the first switching contact and a second switch is connected in parallel with the second switching contact.

11. The apparatus according to claim 9, wherein a first grounding device is connected with the first switching contact and a second grounding device is connected with the second switching contact.

12. The apparatus according to claim 11, wherein a third grounding device is connected with a point between the first switching contact and the second switching contact.

Description

DETAILED DESCRIPTION OF THE DRAWINGS

(1) In the following, preferred embodiments of the invention will be described in more detail with reference to the accompanying drawing.

(2) FIG. 1 shows a test environment which comprises an electrical circuit breaker being grounded at both sides and an apparatus for the measurement of a resistance of a switching contact of the circuit breaker according to an embodiment of the present invention.

(3) FIGS. 2-4 show test arrangements with an apparatus for the measurement of resistances of switching contacts of an electrical circuit breaker according to further embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows a test environment 10 with a circuit breaker or power switch 11 which selectively connects or disconnects a first high voltage line 12 and a second high voltage line 13. The test environment 10 further comprises a first grounding device or grounding set 14 coupled with a first side of the circuit breaker 11 and a second grounding device or grounding set 15 coupled with a second side of the circuit breaker 11. The grounding of the circuit breaker 11 at both sides ensures that no dangerous high voltages occur at the circuit breaker 11. The test environment 10 further comprises a micro-ohm measurement apparatus 17 which is coupled with both sides of the circuit breaker 11 via four connections 24-27. The circuit breaker 11 comprises an electrical switching contact 16 that can be selectively opened or closed by a control drive 19 and a mechanical coupling 18 to establish a connection between the lines 12 and 13 or to interrupt the connection. The control drive 19, for example, can be controlled via a control line 28 to open or close the switching contact 16. Furthermore, it is also possible that the control drive 19 is manually controlled or actuated by an operator to selectively open or close the switching contact 16.

(5) The apparatus 17 comprises a resistance measurement device which, for example, comprises a current source 23 and a voltage meter 22. Via the connections 24 and 25, the current source 23 supplies and impresses a current I flowing through the circuit breaker 11 and both grounding devices 14, 15, and the voltage meter 22 detects via the connections 26, 27 a voltage drop V across the circuit breaker 11. The apparatus 17 further comprises a processing unit 20 which determines or calculates a resistance across the circuit breaker 11 on the basis of the current I impressed by the current source 23 and the voltage V measured by the voltage meter 22. In addition, the processing unit 20 is coupled with a control unit 21 of the apparatus 17, the control unit 21 controlling the control drive 19 of the circuit breaker 11 via the connection 28. Thus, the processing unit 20 is able to selectively open or close the switching contact 16. In the following, the functioning and operation of the apparatus 17 will be described.

(6) First, the circuit breaker 11 is grounded at both sides by means of the grounding devices 14 and 15. Then, as shown in FIG. 1, the resistance measurement device 22, 23 is connected to the circuit breaker 11 such that a resistance across the circuit breaker 11 can be measured. Thereafter, two resistance values are determined one after the other. One resistance value R.sub.1 is determined when the switching contact 16 is closed, and one resistance value R.sub.2 is determined when the switching contact 16 is open. The resistance R.sub.1 thus corresponds to a resistance of a parallel circuit of the resistance of the switching contact 16 and the resistance of the grounding loop via the grounding devices 14 and 15, while the resistance R.sub.2 only corresponds to the resistance of the grounding loop via the grounding devices 14 and 15. The resistance of the closed switching contact 16 can be calculated from these two resistance values using the equation described above. This is done by the processing unit 20. In addition, the processing unit 20 can selectively open and close the switching contact 16 via the control unit 21, so that the processing unit 20 can conduct both resistance measurements one after the other when the switching contact is open and when the switching contact is closed, respectively, and thereafter calculate the resistance of the closed switching contact 16 therefrom. The order, in which both resistance measurements are conducted, is arbitrary. Alternatively, the processing unit 20 can instruct an operator through a corresponding display to open or close the switching contact 16 manually or by means of a corresponding actuator device if no automatic control via the control unit 21 and the connection 28 is provided. As the circuit breaker 11 is grounded at both sides during the whole measurement, it can be ensured that no dangerous high voltages occur at the circuit breaker 11.

(7) FIG. 2 shows a further test environment 50 with a circuit breaker 51 having two switching contacts 56 and 57. The switching contacts 56 and 57 are arranged in a series connection. The circuit breaker 51 can comprise further switching contacts which are arranged in a series connection together with the switching contacts 56 and 57. In general, the switching contacts 56 and 57 and the further switching contacts, if any, are selectively opened or closed at the same time by an actuator (not shown). The circuit breaker 51 is coupled with high voltage lines 52 and 53 which can be selectively connected or disconnected by means of the switching contacts 56, 57. The test environment 50 further comprises two grounding devices or grounding sets 54 and 55 which connect the high voltage lines 52 and 53, respectively, with ground or earth. In addition, the test environment 50 comprises an apparatus 58 for the measurement of the resistances of the switching contacts 56 and 57. The apparatus 58 comprises a first resistance measurement device comprising a voltage meter 60 and a current source 61, and a second resistance measurement device comprising a voltage meter 66 and a current source 67. The first resistance measurement device 60, 61 is connected through connections 62-65 with the first switching contact 56 such that a current I.sub.1 of the current source 61 can be impressed via the switching contact 65 when the switching contact 56 is closed. The voltage meter 60 is connected through the connections 64 and 65 with the switching contact 56 such that a voltage drop U.sub.1 across the switching contact 56 can be measured. Similar to the first resistance measurement device 60, 61, the second resistance measurement device 66, 67 is coupled with the switching contact 57 through connections 68-71 to impress a current I.sub.2 flowing through the closed switching contact 57 and to measure a voltage drop U.sub.2 across the switching contact 57. A processing unit 59 is connected with the resistance measurement devices 60, 61 and 66, 67, respectively. The operating principle and functioning of the apparatus 58 will be described in the following.

(8) First, the high voltage lines 52, 53, which are connected to both ends of the circuit breaker 51, are connected with ground or earth via the grounding devices 54, 55. Then, the apparatus is connected to the switching contacts 56 and 57 as described above. Thereafter, the switching contacts are closed. A current I.sub.1 is impressed onto the high voltage line 52 by the current source 61. Therefore, the current I.sub.1 partly flows as a current I.sub.S1 from the left to the right through the closed switching contact 56 and partly as a current I.sub.E1 to ground or earth through the grounding device 54. The current source 67 impresses a current I.sub.2 onto the high voltage line 53. The current I.sub.2 partly flows as a current I.sub.S2 from the right to the left through the closed switching contact 57 and partly as a current I.sub.E2 to ground or earth through the grounding device 55. Due to the transition resistance of the switching contact 56 a voltage drop U.sub.1 occurs across the switching contact 56. Likewise, a voltage drop U.sub.2 occurs across the switching contact 57 due to the transition resistance of the switching contact 57. As the currents I.sub.S1 and I.sub.S2 are supplied in opposite directions, the voltage drops U.sub.1 and U.sub.2 likewise have opposite directions. If the transition resistances of the switching contacts 56 and 57 are substantially the same and, in addition, the currents I.sub.1 and I.sub.2 have substantially the same amount, the voltage drops U.sub.1 and U.sub.2 have the same amount as well. Thereby, the voltage drop U.sub.E across the grounding loop is zero, so that the currents I.sub.E1 and I.sub.E2 are both zero as well. In this case, the current I.sub.S1 through the switching contact 56 corresponds to the current I.sub.1, so that the transition resistance of the switching contact 56 can be determined solely in dependence upon the current I.sub.1 and the voltage U.sub.1 measured by the voltage meter 60. Likewise, the transition resistance of the closed switching contact 57 can be determined solely based on the current I.sub.2, which in this case corresponds to the current I.sub.S2, and the voltage U.sub.2 measured by the voltage meter 66. As the switching contacts 56 and 57 in general are identical in configuration and are subject to a similar stress and wear, they generally have the same transition resistance in the closed condition, so that the above described requirements can be fulfilled and for this so-called symmetrical case a simple and precise determination of the transition resistances is possible. The processing unit 59 can determine and output the respective resistance values on the basis of information provided by the resistance measurement devices 60, 61 and 66, 67. In the event that the transition resistances of the switching contacts 56 and 57 are not the same, the processing device 59 can adjust the currents I.sub.1 and I.sub.2 such that the voltage drops U.sub.1 and U.sub.2 substantially have the same amount. Thereby, it is achieved that, even in this non-symmetrical case, the voltage U.sub.E across the grounding loop is substantially zero, so that the transition resistance of the individual switching contacts 56 and 57 can be determined on the basis of the current I.sub.1 and I.sub.2, respectively, and the voltage drop U.sub.1 and U.sub.2, respectively.

(9) FIG. 3 shows a further test environment 50 which substantially corresponds to the test environment 50 of FIG. 2 and, in addition, comprises two additional switches 72 and 73 arranged in parallel to the switching contacts 56 and 57, respectively. This allows that, even if the switching contacts 56 and 57 are open, a current can be driven through the grounding loop realized by the grounding devices 54 and 55 to be able to determine the resistance of the grounding loop. The resistance of the grounding loop can be used for the correction of resistance values that are determined when the switching contacts 56, 57 are closed. In other words, by means of the switches 72, 73 the method described above in connection with FIG. 1 can be conducted also with the arrangement shown in FIG. 3. For example, the switch 73 can be closed, while the switch 72 can be opened. Then, a micro-ohm measurement of the switching contact 56 can be carried out with the resistance measurement device 60, 61 as described above in connection with FIG. 1. If the switch 72 is closed and the switch 73 is open, a micro-ohm measurement can be carried out at the switching contact 57 with the resistance measurement device 66, 67 as was described above in connection with FIG. 1.

(10) FIG. 4 shows a test environment 50 which substantially corresponds to the test environment 50 of FIG. 2. In addition, the test environment 50 of FIG. 4 comprises a third grounding device 74 which couples a point between the switching contact 56 and the switching contact 57 with ground or earth. In this arrangement, a micro-ohm measurement of the switching contact 56 can be conducted with the aid of the resistance measurement device 60, 61 as was described above in connection with FIG. 1. Furthermore, a micro-ohm measurement of the switching contact 57 can be conducted with the aid of the resistance measurement device 66, 67 as described above in connection with FIG. 1. Both micro-ohm measurements at the switching contacts 56 and 57 can be conducted at the same time. It can be ensured by means of this additional grounding 74 that a high voltage does also not occur between the switching contacts 56 and 57.