1. Field of the Invention
The present invention relates to a grounding switch that is incorporated in gas insulated switchgear.
2. Description of the Related Art
A grounding switch is incorporated in gas insulated switchgear (GIS). The grounding switch is used as a contact in grounding of a main circuit when testing equipment, or as an earth terminal when measuring equipment. When grounding a main circuit, typically, a moving contact, which is grounded, is moved along a center axis of the grounding switch so as to be inserted into a high-voltage electrode, which is connected to high voltage. If, by any possibility, the moving contact moves in an axial direction of the grounding switch and is inserted into a high-voltage electrode as the result of an erroneous operation when high voltage is being applied to the main circuit, there has been a need of a function which is capable of opening the grounding switch afterwards with a reliable earth connection taken and without fusing across electrodes. This is to say that if the moving contact erroneously enters into the high-voltage electrode in a state where a high voltage is applied, an arc occurs due to breakdown of insulation between the electrodes. The surrounding gas therefore reaches a high temperature and the gas pressure rises abruptly. Gas for which the pressure has abruptly risen then acts as a repulsive force on the moving contact during operation. When operation of the moving contact continues so that the high-voltage arc contact and the moving arc contact make contact, frictional resistance occurs between the electrodes and there is further repulsive force exerted on the moving contact. In Japanese Utility Model Application Publication S50-46947, one contact piece of a number of arranged contact pieces (high-voltage main contacts) extends in the direction of a center axis, with a tip of the one contact piece constituting an arc-focusing contact (high-voltage arc contact).
This means that surrounding gas is heated and expands as a result of an arc occurring across the moving arc contact and the high-voltage arc contact. However, gas that has increased in temperature does not cool instantaneously directly after the arc is extinguished and the pressure of the gas that has risen abruptly does also not return to its original state instantaneously. At this stage, the moving contact is subject to two repulsive forces at the same time, repulsive force due to hot gas caused by arcing, and repulsive force due to frictional resistance. A substantial mechanical burden is therefore placed on the operation of the drive mechanism.
In the structure shown in FIG. 1 of Japanese Utility Model Application Publication S50-46947, a fixed angle taper is provided from the tip of the arc-focusing contact to the main contact section. This means that the moving contact continues to be subject to a substantial repulsive force in the direction of insertion as a result of substantial frictional resistance between the contacts directly after the moving contact makes contact.
It is an object of the present invention to at least partially solve the problems in the conventional technology.
According to an aspect of the present invention, there is provided a grounding switch that includes a high-voltage electrode and an earth electrode located facing each other along a same center axis within tanks that encapsulate an insulating gas; a moving contact that is electrically connected to the earth electrode and that is capable of being reciprocally driven along the center axis; a moving arc contact provided at an end part of the high-voltage electrode at the moving contact; a plurality of high-voltage contacts, each having a high-voltage main contact that make contact with the moving contact in a closed state, electrically connected to the high-voltage electrode, and arranged along a circumferential direction taking the center axis as a center; a high-voltage arc contact, provided at least one of the high-voltage contacts, provided further towards the side of the moving electrode than the position of the high-voltage main contacts at the end part of the high-voltage contact; and a drive mechanism that reciprocally drives the moving contact in the direction of the center axis. A valley section is provided between the high-voltage arc contact and the high-voltage main contact at the high-voltage contact such that the moving arc contact does not make contact with the valley section.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Exemplary embodiments of a grounding switch of the present invention are explained in detail with reference to the drawings. The invention is by no means limited to the embodiments.
A rotating shaft 5 extends to the outside of the tank (in a vertical direction with respect to the page surface) in such a manner that the insulating gas within the tank 1b does not leak to the outside. The rotating shaft 5 communicates with a drive mechanism (not shown), which is located outside of the tank 1b, enabling the grounding switch to operated by using the drive mechanism. One end of a lever 2 that rotates centrally about the rotating shaft 5 is coupled to one end of a link 3 via a pin 4b. The other end of the link 3 is coupled to one end of a moving contact 9 via a pin 4a. An earth main contact 7 is provided on the earth electrode 8 between bearings 6a, 6b that support the moving contact 9 on the earth electrode 8. This earth main contact 7 is capable of sliding with respect to the moving contact 9. The moving contact 9 and the earth electrode 8 are electrically connected via the earth main contact 7. The earth electrode 8 is fixed to and electrically connected to the tank 1b and is held at ground potential together with the moving contact 9. The moving contact 9 is supported by the bearings 6a, 6b so as to maintain a sliding relationship and reciprocal movement along a central axis line is possible.
The high-voltage electrode 15 is electrically connected to the main circuit and is routinely applied with a high voltage from the main circuit. A number of high-voltage contacts 16 are arranged equidistantly along a circumferential direction (specifically, a circumferential direction within a plane perpendicular to the central axis line taking the center axis as center) of a central axis line within the high-voltage electrode 15 and are electrical shielded with respect to outside. One end of each of the high-voltage contacts 16 is electrically connected to the high-voltage electrode 15, and the other end is electrically connected to a high-voltage main contact 13 that connects to and disconnects from the moving contact 9. Further, high-voltage arc contacts 11 are provided at end parts on the side making contact with the moving contact 9 at some of the high-voltage contacts 16. The high-voltage arc contacts 11 are also provided equidistantly spaced along the circumferential direction. A moving arc contact 10 is provided at an end part on the side making contact with the high-voltage contacts 16 at the moving contact 9. The high-voltage main contact 13 and the high-voltage arc contacts 11 are formed in a twin-peak shape with a valley section 12 in between. Further, the high-voltage arc contacts 11 arranged at positions (position further distanced from the center axis) further away in a radial direction with respect to the center axis from the high-voltage main contact 13. When the moving contact 9 makes contact with the high-voltage arc contacts 11, the bottom part of the valley section 12 is positioned further to the outside with respect to the central axis than the external diameter of the moving contact 9 and a gap is present between the valley section 12 and the moving contact 9. The high-voltage contacts 16, which are arranged in the circumferential direction, maintain a contact pressure with respect to the moving contact 9 because of gutter springs 17 that are wrapped around the periphery thereby realizing stable earthing and energizing. An anti-arcing shield is also arranged so as to cover the high-voltage arc contacts 11 at the high-voltage electrode 15 in the vicinity of the high-voltage arc contacts 11. This means that even if an arc lets fly at this unit, marked damage to the high-voltage electrode 15 is suppressed and withstand voltage performance is not degraded.
Next, the operation is explained with reference to
In the state shown in
As shown in
Moreover, as shown in
As shown in
As the moving contact 9 moves further, as shown in
Changes in the gas pressure inside the cavity of the high-voltage electrode 15 when the grounding switch is erroneously thrown on are explained together with a displacement-time characteristic of the moving contact 9.
The durations for abrupt rise and fall of the gas pressure are only in the order of a few milliseconds in either case. The speed of the moving contact 9 is in the order of a few m/s. The distance from the arc occurring to the moving arc contact 10 making contact with the high-voltage arc contacts 11 is from a few millimeters to tens-odd millimeters. The arcing time during this time is therefore made as short as possible. Further, after the arc is extinguished, a dimension is adopted that ensures that the moving arc contact 10 makes contact with the high-voltage main contact 13 at a time where the gas pressure has fallen sufficiently. The gap between the high-voltage arc contact 11 and the high-voltage main contact 13 is therefore similarly taken to be in the order of a few millimeters to a number of tens of millimeters.
The grounding switch is thus provided with the valley section 12 at the high-voltage contacts 16. Because of this valley section 12, the grounding switch has a reduced sum of repulsive force due to hot gas caused by the arc 21 across the moving arc contact 10 and the high-voltage arc contacts 11 when high voltage is applied to the main circuit and the moving contact 9 is erroneously thrown on and a repulsive force in a direction of insertion due to the moving contact 9 advancing so as to push out the high-voltage contacts 16. Consequently, the mechanical burden on the drive mechanism is reduced and the operation energy is also lowered.
It is preferable to arrange a plurality of the high-voltage arc contacts 11. This enables the resistance to arcing to be further improved.
It is preferable to arrange a number of the high-voltage arc contacts 11 equidistantly along the circumferential direction. In such a configuration, the moving contact 9 can reliably make contact with any of the high-voltage arc contacts even in cases of eccentricity due to variation in the dimension of parts or errors in assembly for the moving contact 9.
In the structure of this embodiment, in addition to the structure of the first embodiment, the high-voltage arc electrode 19 extending in a center axis direction is located at a central part of the high-voltage electrode 15 and an arc contact 18 is located at the tip of the high-voltage arc electrode 19. Further, a hole 20 open to the side of the high-voltage arc electrode 19 is provided at the moving contact 9 and the moving arc contact 10. This hole 20 is formed to a predetermined depth along a center axis direction from the end of the moving contact 9. By providing the hole 20 centrally between the moving arc contact 10 and the moving contact 9, the moving arc contact 10 and the moving contact 9 are given a structure where there is no contact between the arc contact 18 of the high-voltage arc electrode 19 and the high-voltage arc electrode 19 when the grounding switch is in a closed state. Further, at the end of the moving arc contact 10, a radius of curvature (for example, the radius of curvature of the portion shown in B of
Next, an explanation is given of the operation. Up to immediately before an arc occurring, the operation is the same as for the first embodiment. The arc 21 then occurs across the moving arc contact 10 and the arc contact 18 of the high-voltage arc electrode 19 and the gas pressure rises. When movement of the moving contact 9 then continues in a straight line in the direction of insertion, the moving arc contact 10 makes contact with the high-voltage arc contacts 11 and the arc 21 is extinguished. The operation from then on is the same as for the first embodiment. In a closed state, the high-voltage arc electrode 19 and the arc contact 18 are housed within the hole 20.
With the grounding switch of the second embodiment, in addition to the effects of the first embodiment, by making the electrical field across the moving arc contact 10 and the arc contact 18 of the high-voltage arc electrode 19 large so that an arc occurs across the moving arc contact 10 and the arc contact 18 of the high-voltage arc electrode 19, it is possible to more reliably prevent the flying of the arc 21 to the arc-resistant shield 14 or to the high-voltage main contact 13 positioned in the vicinity of the high-voltage arc contacts 11.
According to an aspect of the present invention, a valley section is provided across a high-voltage arc contact and a high-voltage main contact and the moving arc contact does not make contact with the valley section in the middle of operation of the moving contact. It is therefore possible to reduce frictional resistance occurring between the moving contact and the high-voltage contact while moving the moving arc contact from making contact with the high-voltage arc contact to making contact with the high-voltage main contact. This means that even if high voltage is applied to the main circuit, the moving contact is erroneously thrown on, and an arc occurs across the high-voltage arc contact and the moving arc contact, the sum of the repulsive force due to the hot gas and the repulsive force due to the frictional resistance is reduced for from when the moving arc contact makes contact with the high-voltage arc contact until contact is made with the high-voltage main contact, i.e. until the arc cools and the surrounding gas pressure falls. The mechanical load on the drive mechanism is therefore alleviated and operation energy of the drive mechanism required for successful completion of an erroneous ON operation can be reduced.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
Number | Date | Country | Kind |
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2007-341063 | Dec 2007 | JP | national |