DEVICE FOR MONITORING THE VACUUM QUALITY OF A VACUUM CIRCUIT BREAKER

Abstract

A device for monitoring vacuum quality of a vacuum circuit breaker, the device including at least one rigid assembly including a first stationary conductive surface that is separated by an insulating layer from a second stationary conductive surface that is grounded. The assembly forms a first capacitor having a fixed value, the first stationary conductive surface being arranged opposite an electrically active portion of the vacuum circuit breaker to form, together with the portion, a second capacitor, and an electronic circuit for measuring a variation in voltage of the first capacitor that is representative of a change in state of the vacuum of the circuit breaker.

Claims

1-10. (canceled)

11. A device for monitoring vacuum quality of a vacuum circuit-breaker, comprising: at least one rigid assembly comprising a first stationary conductive surface that is separated by an insulating layer from a second stationary conductive surface, thus forming a first capacitor having a fixed value; and an electronic circuit for measuring a variation in the voltage on the first capacitor that is representative of a change in state of the vacuum of the circuit-breaker.

12. The device as claimed in claim 11, wherein the first stationary conductive surface forms a second fixed capacitor, in combination with an electrically active element of the vacuum circuit-breaker.

13. The device as claimed in claim 12, wherein the rigid assembly is arranged on an interior of a cylindrical electric shielding, at least one exterior surface of which forms a second fixed capacitor, in combination with ground.

14. The device as claimed in claim 11, wherein the insulating layer is formed by a honeycomb structure.

15. The device as claimed in claim 11, wherein the insulating layer is formed by a foam structure.

16. The device as claimed in claim 11, wherein the insulating layer is formed by an epoxy resin plate.

17. The device as claimed in claim 11, wherein the rigid assembly is formed on a printed circuit board, onto which the first conductive surface and the second conductive surface are etched, separated by the insulator.

18. The device as claimed in claim 11, wherein the rigid assembly is mounted on a moveable truck which is connected to ground.

19. The device as claimed in claim 11, wherein the rigid assembly is attached to the external surface of a vacuum bottle of the vacuum circuit-breaker in a form of a patch, in electrical contact with the electrically active element.

20. A device for monitoring vacuum quality of a three-phase vacuum circuit-breaker, comprising, for each phase, a rigid assembly as claimed in claim 11, and each rigid assembly further comprises an additional capacitor, arranged for recovery of a current for supply of the electronic circuit configured to detect a change in state of the vacuum.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further characteristics and advantages of the invention will be identified from the following description, which is provided by way of an example and not by way of limitation, with reference to the attached figures, in which:

[0025] FIG. 1, as described above, shows a schematic illustration of the principle of a device for monitoring the quality of a vacuum in a vacuum circuit-breaker according to the prior art,

[0026] FIG. 2 shows a schematic illustration of a first form of embodiment of a device for monitoring the quality of a vacuum in a vacuum circuit-breaker according to the invention,

[0027] FIG. 3 shows a schematic illustration of a second form of embodiment of a device for monitoring the quality of a vacuum in a vacuum circuit-breaker according to the invention,

[0028] FIG. 4 shows a schematic illustration of a third form of embodiment of a device for monitoring the quality of a vacuum in a vacuum circuit-breaker according to the invention,

[0029] FIG. 5 shows a curve illustrating the variation in the dielectric withstand voltage of an industrial vacuum circuit-breaker.

DETAILED DESCRIPTION OF SPECIFIC FORMS OF EMBODIMENT

[0030] In the interests of clarity, identical reference symbols will be used to designate elements of the device according to the prior art shown in FIG. 1, and of the devices according to the invention.

[0031] FIG. 2 shows a schematic illustration of a vacuum circuit-breaker comprising a truck 12 and at least one vacuum bottle 1, and a rigid assembly 2 forming a detector for variations in the state of the vacuum in the bottle 1. This detector comprises a first stationary conductive surface 4, separated by an insulating layer 30 from a second stationary conductive surface 10 which is connected to ground T. The rigid assembly 2 comprised of the first stationary conductive surface 4 and the second stationary conductive surface 10 form a first capacitor 32 having a fixed value (or set value). The rigid assembly thus formed is mounted on the truck 12, and is arranged such that the first stationary conductive surface 4 is arranged opposite an electrically active element 18 of the vacuum circuit-breaker. The first conductive surface 4 thus forms a second capacitor 34, in combination with this electrically active element 18. An electronic circuit, which is not represented, is connected to the rigid assembly 2 for the measurement of current variations in the first capacitor 32 and the second capacitor 34, and for the delivery of an indication of the state of vacuum in the bottle 1, as a function of the result of measurements.

[0032] The connection to ground of the second stationary conductive surface 10 is executed in the form of a bolt or a rivet 40 which secures the insulating layer 30 and forms a rigid connection to the truck 12. A spacer element 41 attached to the bolt 40 permits the maintenance of a sufficient clearance between the rigid assembly 2 and the electronic components mounted on the detection circuit which is installed on the truck 12. As a result of the rigidity of the assembly thus formed, the capacitor 32 has a fixed value. The thickness of the insulating layer 30 ranges from 0.1 to 10 mm. An excessively low value results in an excessive increase in the value of the capacitor 32, and inappropriately reduces the transient voltage measured on the first stationary conductive surface 4.

[0033] FIG. 3 illustrates a second form of embodiment of the invention, in which the rigid assembly 2 is arranged on the interior of a cylindrical electrical shielding 50 which encloses the vacuum bottle 1. Said shielding is connected to the second conductive surface 10, and the first conductive surface 4 is connected to the electrically active element 18 of the vacuum bottle. The second capacitor 34 is formed between the exterior surface of the electric shielding 50 and ground.

[0034] The assembly thus formed can be fitted to the external surface of the vacuum bottle 1, around the metal screen 18, in the form of a “patch”, as illustrated in FIG. 4. The conductive surface 4 is in direct electrical contact with the electrically active element 18.

[0035] As a result of the direct contact with the metal screen 18, the system can be self-powered.

[0036] In operation, the voltage of the first capacitor 32 V.sub.32 is used to monitor the state of the vacuum in the vacuum circuit-breaker. In the case of a vacuum circuit-breaker with a good level of vacuum, the string of capacitors 14, 32 and 34 permits the determination of the current flowing in said capacitors, and the deduction therefrom of the voltage V.sub.32, using the following formula:

[00002]$V_{32}=\frac{1/C_{32}}{\left(\frac{1}{C_{14}}+\frac{1}{C_{34}}+\frac{1}{C_{32}}\right)}*V_{\mathrm{HV}}$

[0037] In the case of a circuit-breaker with a vacuum defect, the pressure in the vacuum bottle of the circuit-breaker will increase steadily, and the dielectric withstand of the circuit-breaker observes Paschen's law, as illustrated in FIG. 5.

[0038] Where the level of vacuum in the circuit-breaker achieves a value described as the “Paschen minimum”, the dielectric withstand will be lower than the system voltage. This results in short-circuits between the electrodes 16 and the metal screen 18. The capacitor 14 is thus short-circuited, resulting in an increase in the current flowing in the remaining capacitors 32 and 34 in the string. The voltage V.sub.32 thus varies as follows:

[00003]$V_{32}=\frac{1/C_{32}}{\left(\frac{1}{C_{32}}+\frac{1}{C_{34}}\right)}*V_{\mathrm{HV}}$

[0039] As a result, the voltage V32 increases in the presence of a defect in the vacuum in the vacuum bottle 1.