CN101506911B - High voltage bushing - Google Patents

Abstract

A high voltage direct current bushing with a grounding flange has an outer casing (13) having a plurality of flange portions (13a) extending at an angle and pointing away from the grounding flange direction of the edge.

Description

High voltage bushing

technical field

The present invention generally relates to high-voltage DC bushings, and in particular to a high-voltage bushing with an improved insulator skirt profile. The invention also relates to a high voltage transformer comprising such a high voltage bushing.

Background technique

As is well known, electrical equipment and installations such as high voltage transformers are usually equipped with bushings adapted to carry current at high potential through a grounded barrier such as a transformer tank.

A conventional bushing consists of an insulator made of ceramic or composite material, provided with a skirt or flange portion and usually hollow, with or without a capacitor body through which the electrical conductor passes, inside which is Voltage grading is possible, allowing the inside and outside of the equipment on which the bushing is mounted to be connected.

An example of a prior art bushing disclosed in European Patent Publication EP1014388A2 will now be briefly described with reference to FIG. 1 . The bushing comprises an insulating and supporting body 2 made of polymer material, which surrounds an inner high voltage conductor 1 . Insulators 3, usually made of silicone rubber, are molded on the insulating support body 2 to obtain selected creepage distances, thus ensuring high electric strength characteristics even in highly polluted environments. The insulator is provided with a number of skirt or flange parts 3 . In order to avoid accumulation of contaminating material and to enable water to flow out of the insulator, the skirt flange portion is designed to extend at a sub-horizontal angle relative to the support body. However, this results in a non-optimal DC electric field in DC applications, causing DC stress at the tip of the skirt.

Contents of the invention

The object of the present invention is to provide a high voltage DC bushing and a transformer with reduced DC stress on the bushing.

The invention is based on the realization that as the skirt or flange portion extends from the supporting body of the DC bushing at an angle above the horizontal, the flange portion will gradually follow the DC electric field so that the DC current at the tip of the flange portion stress reduction.

According to a first aspect of the present invention, there is provided a high-voltage DC bushing, comprising an insulating and supporting body; a grounding flange (14) arranged on the insulating and supporting body; an outer casing arranged on the insulating and supporting body, Wherein the outer housing is provided with a plurality of flange portions; the bushing is characterized in that the flange portions extend from the support body at an angle relative to the longitudinal axis and point away from the grounding flange.

According to a second aspect of the present invention there is provided a high voltage direct current device comprising such a bushing. With the bushing of the present invention, the DC stress on the flange portion will be less compared to conventional prior art bushings.

In a preferred embodiment, said flange portion extends at an angle within the interval 0°<α<90°, and more preferably within the interval 75°<α<85°.

In another preferred embodiment, the HVDC bushing includes a grounding flange approximately midway along the longitudinal axis of the bushing to support wall mounting. Thus, the flange portion preferably extends in different directions on different sides of the ground flange.

Further embodiments are defined in the dependent claims.

Description of drawings

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is an overall view of the prior art high voltage bushing;

Figure 2 is a detailed view of a sleeve according to the invention;

Figure 3 is an overall view of a high voltage direct current device provided with a bushing of the type shown in Figure 2; and

Figure 4 is a view of an alternative embodiment of a wall mounted bushing according to the present invention.

Detailed ways

Hereinafter, preferred embodiments of the present invention will be described in detail. In this description, reference numerals will give directions and orientations, eg horizontal. It is understood that these reference numerals are used in normal operation. Also, in this description, the term "high voltage" will be used for voltages of 50 kV or higher. Currently, the upper limit for commercial high voltage installations is 800kV, but higher voltages such as 1000kV or 1200kV are envisaged in the near future.

The arrangement of high voltage bushings in the prior art has been described with reference to FIG. 1 in the background art section, and no further description of this figure will be made here.

In Fig. 2, an enlarged view of the upper part of a bushing according to the invention is shown, wherein in this figure an example of a DC field potential is shown as an equipotential curve during DC operation.

The bushing, generally designated 10, comprises an insulating and supporting body 12 of polymeric material, which surrounds an inner high voltage conductor (not shown). On said insulating and supporting body 12 is molded an external casing in the form of an insulator 13 made of relatively low electrical resistance silicone rubber. The insulator comprises a plurality of flange portions or skirts 13a extending from the support body at an angle above horizontal.

Because of the conductive properties of the material of the insulator 13, said equipotential lines substantially follow the direction of the skirt 13a. In the air outside the insulator 13, the equipotential lines generally run more vertically. This means that in these lines, there are bends or curves.

On high voltage bushings, it is important to control the electrical stress in the air, because excess stress in the air can attract charges and fundamentally change the voltage distribution. By providing the insulator 13 with the skirt 13a extending outwardly from the support body 12 at an angle above the horizontal, the skirt will better follow said A roughly more vertical extension of the equipotential lines.

In FIG. 2, the angle at which the skirt 13a extends is indicated as α. In other words, the angle α is the angle in the direction in which the skirt 13a extends, and the longitudinal axis of the sleeve 10 is in the "upward" direction. Using the definition given earlier, the "upward" direction is the direction in which the potential increases.

The angle α is preferably the same as the angle of the equipotential lines in air, but for outdoor applications it is preferably slightly smaller than the installation angle of the bushing to ensure drainage. Preferably, the angle α is located within the interval 0°<α<90°, more preferably within the interval 75°<α<85°.

The aforementioned vertical bushing is preferably arranged to operate indoors, since the skirt 13a of said bushing is able to collect eg rainwater on the insulator. The bushing can be used both indoors and outdoors if it is sloped to allow eg rainwater to drain off the skirt.

Since the cannula in Figure 2 is oriented in an upright position, the definition of "horizontal" is straightforward. This definition should relate to the orientation of the bushing, not the orientation of the ground. Thus, in the case of an inclination of the casing, a "horizontal direction" is the direction of a plane extending perpendicularly to the longitudinal axis of the casing. "Up" is the direction from the grounded portion of the bushing towards the end of the bushing, ie the direction of increasing voltage potential. This will be discussed further below with reference to FIG. 4 .

Figure 3 shows a HVDC installation in the form of a transformer 20 provided with a bushing 10 of the type described above. The bushing is electrically connected to the internal components of the transformer, such as the transformer core and windings. Since the bushings in Figure 3 are arranged substantially vertically, such a transformer is preferably located indoors.

An alternative embodiment of the HVDC bushing according to the invention will now be described with reference to FIG. 4 . The bushing, generally designated 10', is mounted to extend through the wall 30 of the building. Thus, the bushing 10' presents two air sides, one indoors towards the left in the figure and one outdoors towards the right en route.

A grounding flange 14 disposed approximately centrally along the longitudinal axis of the bushing acts as a grounding means. Using the definition of angle α given above, it can be appreciated that this angle is calculated in different directions on different sides of the ground flange. On the indoor side of the cannula, the "up" direction is generally to the left, and on the outdoor side of the cannula, the "up" direction is generally to the right. This in turn means that the skirt 13a points in different directions on both sides of the wall 30 .

The angle α on different sides of the wall 30 is not necessarily the same; it may also be that circumstances require different skirt angles for indoors and outdoors.

The preferred embodiments of the HVDC bushing and the HVDC device according to the present invention have been described above. A person skilled in the art realizes that changes may be made within the scope of the appended claims. Thus, the exact shape of the skirt can vary as long as the flange extends in a direction above horizontal.

All flange portions 13a of the embodiment extend substantially in the same direction. It should be understood that different skirts 13a may extend at different angles α to better follow equipotential lines in air.

Although the high-voltage device connected with the high-voltage DC bushing of the present invention is described as a transformer, it should be understood that the device may also be other devices, such as reactors, circuit breakers, generators or other devices used in high-voltage systems. device.

Claims (10)

1. A high-voltage DC bushing, comprising: an insulating and supporting body (12) having a longitudinal axis; a grounding flange (14) provided on said insulating and supporting body; an outer casing (13) arranged on said insulating and supporting body, wherein said outer casing is provided with a plurality of flange portions (13a); It is characterized by: The flange portion extends from the insulating and supporting body at an angle α with respect to the longitudinal axis in the direction of increasing electrical potential and points in a direction away from the ground flange (14). 2. The high voltage direct current bushing according to claim 1, wherein the angle α is located in the interval 0°<α<90°. 3. The high voltage direct current bushing according to claim 2, wherein the angle α is located in the interval 75°<α<85°. 4. The high voltage direct current bushing according to any one of claims 1-3, wherein the bushing is configured to operate indoors. 5. The HVDC bushing according to any one of claims 1-3, wherein the grounding flange (14) is arranged approximately in the middle along the longitudinal axis of the bushing. 6. The HVDC bushing according to claim 5, wherein the flange portions (13a) extend in different directions on different sides of the ground flange (14). 7. The HVDC bushing according to any one of claims 1-3, wherein different flange portions (13a) extend at different angles α to better follow equipotential lines in the air. 8. The high-voltage DC bushing according to any one of claims 1-3, wherein the outer shell (13) is made of silicone rubber. 9. A high voltage direct current device comprising the bushing according to claim 1. 10. The high voltage direct current device according to claim 9, wherein the device is installed indoors.

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