EP0040781B1 - Disconnecting switch for high-voltage metal-enclosed switchgear - Google Patents

Description

The invention relates to a high voltage shielded substation disconnector in a coaxial metal casing filled with compressed dielectric gas, said disconnector comprising a movable contact, cooperating with a fixed contact, said contacts being each carried by a fixed tubular contact holder coaxial with the 'envelope, the opposite ends of the contact carriers being each provided with a substantially hemispherical corona hood having a re-entrant cylindrical neck intended for the passage of the associated contact, said movable contact having a hemispherical tip.

Patent CH-A-399,569 illustrates a known embodiment of contacts with hemispherical tips.

A disconnector only cuts and establishes very low currents, generally capacitive currents corresponding to the capacitance of a busbar under voltage.

In the case of a disconnector placed in the open air, inside a building or outside, the interruption of such a current and its establishment only cause negligible effects, the distances between rooms under tension and the earthed frames or walls being large. However, for shielded substations in a metal envelope filled with insulating gas, as they are used for voltages up to 800 kV, the distances are short and the voltage gradients are high.

To have the minimum distances, the distribution of the electric field must be homogeneous; we also use energized hoods which raise the voltage threshold for the appearance of aromas. Such covers often have a flat part between the input and output of the disconnector perpendicular to the axis of the disconnector, associated by rounding with a very smooth cylindrical part, the axis of which merges with the axis of the disconnector.

During the opening and closing operations of a disconnector, at a slow operating speed, a pre-ignition cut-off arc arises. This arc will tend to move under the action of the electric field at the periphery of the corona hoods, then the root of the arc may jump on the metal casing located at a short distance. The hailing arc due to the capacitive current then degenerates into a power arc, an earth fault arc, inside the envelope.

It is known from document DE-A 27 04 385 to place a metallic screen under tension around the fixed contact and at a radial distance greater than the pre-priming distance. The pre-strike or cut-off arc is then trapped by the screen, it cannot extend to the enclosure, but this increases the stroke of the disconnector.

It is also known to use an abrupt opening and closing mechanism which, considerably reducing the duration of the arc, prevents the arc from developing erratically. Such a device, generally adopted for switches, is very expensive for the disconnector.

The object of the invention is to provide a slow-action disconnector, in which the fixed and movable contacts and the corona shields have a shape such that the length of the arc is small, the electric field in the vicinity of the axis of the contacts. is also weak and that the arc from its birth and during its development remains in the zone with weak field in the vicinity of the axis.

The subject of the invention is a disconnector for a shielded substation in a coaxial metal casing filled with compressed dielectric gas, said disconnector comprising a movable contact, cooperating with a fixed contact, said contacts being each carried by a fixed tubular contact carrier coaxial with the casing , the opposite ends of the contact carriers being provided with a substantially hemispherical corona hood having a re-entrant cylindrical neck intended for the passage of the movable contact, said movable contact having a hemispherical tip, the fixed contact comprising a moving contact piece limited to hemispherical tip of the same diameter as that of the tip of the movable contact, characterized in that in the open position, the end of the tip of the contact piece is preferably of limited movement disposed between the threshold inlet of the fume hood and the end of the inscription circle of its hemispherical part.

According to a preferred implementation of the invention, the tip of the movable contact being disposed set back from the entry threshold of the cylindrical neck of the corona hood, the distance separating the thresholds of the corona hoods is between 50% and 100% of the diameter of the hemispherical parts. The diameter of the cylindrical necks is preferably between 20% and 35% of the diameter of the hemispherical parts.

• La figure 1 représente une vue schématique partielle et en coupe axiale d'un sectionneur de poste blindé selon l'invention.
• La figure 2 représente une vue schématique en coupe axiale d'une variante de capot pare-effluves d'un sectionneur selon l'invention.
• La figure 3 représente une vue en coupe agrandie d'une variante d'un embout de contact.

The invention will be described below in more detail with the aid of the appended figures.

• FIG. 1 represents a partial schematic view in axial section of an armored substation disconnector according to the invention.
• FIG. 2 represents a schematic view in axial section of a variant of the corona hood of a disconnector according to the invention.
• Figure 3 shows an enlarged sectional view of a variant of a contact tip.

In Figure 1 there is shown a portion of an armored substation, made up of tubular metallic envelopes 1, the ends of which have connection flanges 2, between which are insulated isolators 3 which support active parts of the installation arranged coaxially. The tubular casings 1 are filled with a dielectric gas such as sulfur hexafluoride under a pressure of three to five bars.

The envelopes 1 contain the constituent elements of a disconnector, the movable part of which is arranged on the right and the fixed part is arranged on the left.

The movable part of the disconnector comprises a tubular movable contact 8, coaxial with the casing 1, the visible end of which comprises a hemispherical end piece 9. The axial movement of the movable contact 8 is controlled by means of a mechanism not shown under operator dependence. The movable contact 8 is placed inside a tubular contact carrier 4 supported by the insulator 3. The movable contact 8 is connected to the contact carrier 4 by means of sliding contacts 46 arranged in circular grooves 45 formed inside the contact holder 4. A corona hood 7 is disposed between the insulator 3 and the end of the contact holder 4 surrounding the nozzle 9. The cover 7 comprises a hemispherical part 70 connecting an envelope cylindrical 71 to a cylindrical neck 72 returning inwards, the cylindrical parts comprise a generator parallel to the axis of the disconnector.

The fixed part of the disconnector comprises a contact piece with tubular limited movement 13 coaxial with the casing 1, one end of which comprises a hemispherical end piece 14 disposed opposite the end piece 9. The part 13 has a collar 15 on its other end subjected to a fixed compression spring 16 which tends to press it against a ring 17 forming a stop. A tubular contact carrier 10, disposed around the contact piece 13 and coaxial with the casing 1, is supported by an insulator similar to the insulator 3, not shown in the figure. The spring 16 is secured inside the contact carrier 10 which supports on the opposite side a ring of contact fingers 12 capable of cooperating with the contact member with limited movement 13 slidingly arranged along the ring 17. A protective cover -effluvia 6 similar to the cover 7 is disposed at the end of the contact carrier 10 and opposite the cover 7. The cover 6 thus comprises a hemispherical part 60 connecting a cylindrical envelope 61 to a cylindrical neck 62 returning inwards, the cylindrical parts comprising a generator parallel to the axis of the disconnector. The diameters of the cylindrical parts 61 to 71 on the one hand and 62 and 72 on the other hand are equal, while the radii of curvature of the hemispherical parts 60 and 70 are the same.

In the open position shown in FIG. 1, the end of the hemispherical end piece 9 of the movable contact 8 is disposed slightly below the entry threshold 73 of the cylindrical neck 72. On the other hand, the end of the hemispherical end piece 14 is arranged substantially midway between the entry threshold 63 of the cylindrical neck 62 and what would constitute the end 64 of the sphere of inscription of the hemispherical part 60.

When the disconnector is closed, the movable contact 8 and the end piece 9 are moved from right to left. The end piece 9 takes in particular the intermediate position traced in dashes and identified at 59 in this position; the distance between the cover 6 and the end piece 59 is short and a hail arc 20 erupts between these elements. The electric field deformed in the vicinity of the end pieces 59 and 14 is represented by the equipotential lines 23 drawn by dashes, in the upper part of FIG. 1. The arc 20 remaining substantially parallel to the equipotential lines does not tend to move . They go out when the ferrules 9 and 14 come into galvanic contact. When the disconnector has finished its travel, contact is established between the contact fingers 12 and the movable contact 8, which has the same diameter as the contact with limited movement 13 and which is pushed back against the action of the spring 16; its tip 14 takes the position marked at 54 and the tip is then at 69.

Under these conditions, an electric field is obtained in the interval between the covers 7 and 6, the substantially symmetrical equipotential lines 22 of which are shown by dashes at the bottom of FIG. 1.

When opening the section, the movement of the movable contact 8 from left to right causes the same movement from left to right of the contact piece with limited movement 13 under the action of the spring 16 until the collar 15 comes to abut against the ring 17. After galvanic separation of the end pieces 9 and 14 an arc arises between these end pieces, the arc being in a zone with a low gradient remains rectilinear and moves as much as possible on the right end of the cover 6. The spherical shape of the cover 6 prevents the arc from moving towards the cylindrical part 60 and towards the envelope 1. The current has a very low value, less than one ampere, and the arc goes out by itself in the dielectric gas of sulfur hexafluoride when the distance between the ends 9 and 14 is sufficient. Good results are obtained when the opening distance separating the covers 7 and the nozzle 9 is between 50% and 100% of the diameter of the cylindrical envelopes 71 and 61, the optimum value being close to 75%.

The diameter of the hemispherical ends 9 and 14 and of the tubular contacts 8 and 13 is between 20 and 35% of the diameter of the cylindrical parts 71 and 61 of the covers 7 and 6.

In Figure 2 there is shown an alternative embodiment of the covers which still gives good results. The entry threshold 63 of the cylindrical neck 62 has a flat transverse range, the right end of the cover 6 representing a flat part with a diameter, the outside diameter does not exceed half the diameter of the cylindrical part 61.

In another variant, the contact end piece may have a blind hole. This arrangement can interest both the end piece 9 and the end piece 14. FIG. 3 represents such a end piece 80 comprising a blind hole 81; the edges of the hole are rounded, this allows the arc to be centered, forcing it to hang on the end of the end piece (rounded end of the hole). The dimensions of the hole are as follows for the best result: diameter of the hole d between 10 and 30% of the maximum diameter D of the nozzle 80, radius r of the rounding at the end of the hole between 20 and 50% of the hole diameter.

Claims (3)

1. A disconnecting switch for an armoured high voltage station under a coaxial metal sheath (1) which is filled with a pressurized dielectric gas, said disconnecting switch comprising a mobile contact (8) cooperating with a fixed contact (13, 14, 16), said contacts being carried each by a tubular fixed contact support (4, 10) which is coaxial with the sheath, the facing ends of the contact supports being furnhished each with an essentially hemispheric discharge protection cap (6, 7) presenting a cylindrical neck (62, 72) turned inwards and destined for the passage of the associated contact, said mobile contact presenting a hemispheric tip (9), the fixed contact comprising a contact piece (13) providing limited movement and having a hemispheric tip (14) of the same diameter as the tip (9) of the mobile contact (8), characterized in that in the opening position, the end of the tip (14) of the contact piece (13) with limited movement is disposed between the border of the discharge protection cap (6) and the end (64) of the inscription circle of its hemispheric part (60).

2. A disconnecting switch according to claim 1, characterized in that, the tip (9) of the mobile contact (8) being disposed in a recessed position with regard to the border (73) of the entry of the cylindrical neck (72) of the discharge protection cap (7), the distance separating the borders (72, 62) of the discharge protection caps (7, 6) is comprised between 50 and 100% of the diameter of the hemispherical parts (70, 60) of these caps.

3. A disconnecting switch according to one of the claims 1 and 2, characterized in that the tip (9, 14) of at least one of the contacts has a blind hole along its axis, the diameter of this hole being comprised between 10 and 30% of the maximum diameter of the tip, the outer end of the hole being rounded up, the radius of this rounding up is comprised between 20 and 50% of the diameter of the hole.

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