WO2016198236A1

WO2016198236A1 - A support insulator with electric field distribution part

Info

Publication number: WO2016198236A1
Application number: PCT/EP2016/060979
Authority: WO
Inventors: Fredrik Jansson; Ulf ÅKESSON
Original assignee: Abb Schweiz Ag
Priority date: 2015-06-11
Filing date: 2016-05-17
Publication date: 2016-12-15

Abstract

The present disclosure relates to a support insulator (10) for supporting a high voltage electrical apparatus (30). The support insulator (10) comprises an inner volume (20) which is filled with an electrically insulating medium. Importantly, the support insulator (10) further comprises an electric field distribution part (40) which is arranged within said inner volume (20) and adapted to be electrically connected to the high voltage electrical apparatus (30). The present disclosure also relates to a method for improving the insulation performance of a support insulator (10').

Description

A SUPPORT INSULATOR WITH ELECTRIC FIELD DISTRIBUTION PART TECHNICAL FIELD

The present invention generally pertains to optimising the distribution of an electric field.

BACKGROUND

High voltage electrical apparatuses which are connected to high voltage electrical power lines are exposed to high potential differences. There is a risk of flashovers between the high voltage electrical apparatuses and ground. SUMMARY

The demands high voltage electrical apparatuses are continuously increasing with respect to voltage levels. Also, the application of such apparatuses in polluted environments presents challenges, as well as do high altitudes. Wet conditions such as rain or snow may also pose challenges. A general object of the present invention is to optimise the distribution of the electric field caused by the above mentioned difference in potential. The present invention aims at allowing high voltage electrical apparatuses to cope with higher voltage levels in a predictable and cost effective manner.

According to the present invention this object is solved by a support insulator for supporting a high voltage electrical apparatus, which support insulator comprises an inner volume which is filled with an insulating medium. The support insulator is furnished with an electric field distribution part which is arranged within said inner volume and adapted to be electrically connected to said high voltage electrical apparatus. In this way, the lowermost live portion is located within the insulating medium of the support insulator, and not outside the support insulator in the ambient air where it is subject to arbitrary conditions such as pollution, dirt, rain or snow. The inner volume of the support insulator provides a predictable and over time constant environment for the lowermost live portion.

Moreover, since the insulating medium may have a higher voltage withstand capability than the ambient air, the performance of the support insulator is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which figure l is a schematic side view of a high voltage electrical apparatus connected to an electrical power line and supported by a support insulator in accordance with the present invention figure 2 is a schematic side view of a high voltage electrical apparatus connected to an electrical power line and supported by a support insulator in accordance with prior art figure 3 is a cross-section view of a portion of a high voltage circuit breaker and a portion of a support insulator in accordance with an embodiment of the present invention and figure 4 is a cross-section view of a portion of a high voltage circuit breaker and a portion of a support insulator in accordance with prior art. DETAILED DESCRIPTION

Figure 2 very schematically shows a high voltage electrical apparatus 30' with is connected to a very schematically illustrated high voltage electrical power line 70. The electrical power line is arranged several metres up in the air by means of a number of line poles 80 (one shown). As can be seen, at the top of the line pole 80 there are two electrical terminals 85, each one of which are electrically connected to two corresponding terminals 35 on the high voltage electrical apparatus 30'. The purpose of figure 2 is to generally illustrate what is meant by a high voltage electrical apparatus in this disclosure. In the illustration of figure 2, the electric power that is conducted through the electrical power line 70 is led via the high voltage electrical apparatus 30' so that the apparatus can control (e.g. break or transform) the electric power. However, the high voltage electrical apparatus 30' may as an alternative only be connected to the electrical power line 70 for measuring the electric power. In reality, the high voltage electrical apparatus 30' is much more complex and may consists of several different units. The high voltage electrical apparatus 30' may be a circuit breaker, a switch gear, an instrument transformer and or a transformer, or include several of these.

In figure 2, a distance D is illustrated. This distance D is the minimum distance between ground and the high voltage electrical apparatus 30'. More precisely the minimum distance between ground 90 and an electrically con- ducting part of the high voltage electrical apparatus 30'. The conducting part of the high voltage electrical apparatus 30' is at the same electrical potential as the electrical power line 70. This is sometimes referred to as the high voltage electrical apparatus 30' being "live". The high voltage electrical apparatus 30' is supported by a support insulator 10', which typically comprises a porce- lain tubular housing which is filled with an electrically insulating medium. Figure 2 illustrates a prior art support insulator 10'. The task of a support insulator 10' is to mechanically carry a high voltage electrical apparatus 30' while keeping it electrically insulated from ground 90.

Thus, there is a high difference in electrical potential between the high volt- age electrical apparatus 30' and ground 90. Any flashovers typically occur between ground 90 and the lowermost live portion of the high voltage electrical apparatus 30'. As will be appreciated by the skilled person, the critical flasho- ver distance in figure 2 is distance D.

Bearing the situation illustrated in figure 2 in mind, the most straight for- ward approach for avoiding flashovers would be to increase the distance D. This can be achieved by increasing the length of the support insulator 10'. An alternative solution would be to arrange a so called corona ring around the lowermost live portion of the high voltage electrical apparatus 30'. A corona ring has a smooth and rounded shape and thereby distributes the electrical field in an advantageous manner, as is known to the skilled person. A general concept of the present invention will now be explained with reference to figure 1. Figure 1 only differs from figure 2 in that there is provided an electric field distribution part 40 within the support insulator. The electric field distribution part 40 is electrically connected to the high voltage electrical apparatus 30. The result is a shorter critical flashover distance d. The electric field distribution 40 part is made of an electrically conductive material, preferably the material that constitutes the electric field distribution part 40 is of the same electrical conductivity as the lowermost live portion of the high voltage electrical apparatus 30.

In view of the above, it would not be beneficial to decrease the distance D, ra- ther, the distance D should be increased. However, since the electric field distribution part 40 is arranged within 20 the support insulator 10, where an electrically insulating medium is present, experiments have shown that the risk of flashover is decreased by means of the electric field distribution part 40. Tests until now have shown a performance increase of several percent. The electric field distribution part 40, hereinafter referred to as the internal electric field distribution part 40 since it is arranged within the electrically insulating medium of the support insulator 10, is only shown very schematically in figure 1. However, the internal electric field distribution part 40 is illustrated as having a lower end 45 of smooth and rounded shape, which fur- ther reduces the risk of flashovers. For the same purpose, the internal electric field distribution part 40 may have a lower end 45 surface that is polished or even lapped.

Preferably, the lower end 45 of the internal electric field distribution part 40 is free from sharp edges and points, which could constitute starting points for flashovers. A spherical lower end 45 of the internal electric field distribution part 40 is beneficial. The lower end 45 of the internal electric field distribution part 40 could be a semi sphere. Said semi sphere preferably has a large diameter, preferable as large as is permitted by the room available inside the support insulator 10. Preferably, said semi sphere is polished or even lapped. The internal electric field distribution part 40 is preferably formed of a material of high electrical conductivity such as metal. The internal electric field distribution part 40 can advantageously be formed of copper, steel or aluminium (aluminum in US English).

The present invention is also applicable on existing equipment. The insula- tion performance of a prior art support insulator 10' may be improved by providing an internal electric field distribution part 40 within the inner volume 20' of the prior art support insulator 10' and electrically connecting the electric field distribution part 40 to the high voltage electrical apparatus 30' which is carried by the support insulator 10'. Such a manoeuvre typically in- corporates opening the prior art support insulator 10' which means that the prior art support insulator needs be refilled with an electrically insulating medium before reclosing.

The support insulator 10, 10' is gas tight and as mentioned filled with a dielectric medium or an electrically insulating medium such as an insulating gas. SF₆ may be used, or a mixture of SF₆ and N₂. It could be preferred to use a gas that has a global warming potential of less than 2300, and preferably less than 150. The insulating medium may be pressurised air. Other opinion are CO₂ or N₂, or a combination of these. The insulation gas may alternatively be an organofluorine compound selected from the group consisting of: a fluo- rether, an oxirane, a fluoramine, a fluoroketone, a fluoroolefin, and mixtures and/or decomposition products thereof.

Turning now to figure 4, a portion of a prior art high voltage electrical apparatus 30' in the form of a live high voltage circuit breaker 50' together with a portion of a prior art support insulator 10' are shown. More precisely, figure 4 illustrates the lower portion of a prior art live high voltage circuit breaker 50' and the upper part of a prior art support insulator 10'. The support insulator ιο', typically made of porcelain, comprises a number of outer sheds 15' which are provided in order to increase the creepage distance. The sheds 15' are formed on a cylindrical tube 17'. The tube is filled with the insulating medium, which medium has been described above. Inside the tube 17', there is also an actuator rod 19' witch can be controlled in the longitudinal direction of the support insulator 10' for actuating the high voltage circuit breaker 50' which is carried by the support insulator 10'.

The high voltage circuit breaker 50' is fastened on the support insulator 10' by means of a cement. The high voltage circuit breaker 50' comprises a sup- port insulator flange 52' which receives the upper end of the support insulator 10'. The aforementioned cement is arranged in-between the support insulator 10' and the support insulator flange 52'. Thereby, a gas-tight connection is formed between the support insulator 10' and the high voltage circuit breaker 50'. The high voltage circuit breaker 50' further comprises a terminal flange 56', which is connected to the electrical power line 70. Thereby, the high voltage circuit breaker 50' is at the same potential as the electrical power line 70. The terminal flange 56' is formed in one piece with the support insulator flange 52', which means that also the support insulator flange 52' is at the same po- tential as the electrical power line 70. The lowermost portion of the high voltage circuit breaker 50' is the lower edge 54' of the support insulator flange 52'. Thus, the lower edge 54' of the support insulator flange 52' comprises the point where a flashover is most likely to initiate.

An embodiment of the present invention is shown in figure 3, which only dif- fers from figure 4 in that there is provided an internal electric field distribution part 40 within the support insulator 10. The description of the internal electric field distribution part 40 illustrated in figure 1 is valid also for the internal electric field distribution part 40 of figure 3. The internal electric field distribution part 40 of figure 3 is at the same potential as the terminal flange 56 and the support insulator flange 52. As has been mentioned, and as can be seen in figures 1 and 3, the electric field distribution part 40 is arranged within the inner volume 20 of the support insulator 10 where an electrically insulating medium, preferably gas, is present. The electric field distribution part 40 is thus arranged within the electrically insulating medium which preferably is a gas. More precisely, the electric field distribution part 40 is arranged directly within the gas. As is particularly clear from figures 1 and 3, the electric field distribution part 40 is surrounded by the gas.

The internal electric field distribution part 40 of the support insulator 20 for the live high voltage circuit breaker 50 is tubular. The tubular internal electric field distribution part 40 is arranged between the actuator rod 19 and the inner surface of the cylindrical tube 17. The tubular internal electric field distribution part 40 contains the actuator rod 19. Even though not disclosed here, the tubular internal electric field distribution part 40 comprises a number of openings in the side wall thereof to allow mounting of the actuator rod 19 and especially connecting the actuator rod 19 to the high voltage circuit breaker 50.

As is shown in figure 3, the addition of the tubular internal electric field distribution part 40 has resulted in a shorter critical flashover distance, the dis- tance has been shortened from D to d. The tubular internal electric field distribution part 40 is at all points of its circumference located vertically lower than the lower edge 54 of the support insulator flange 52. Without the tubular internal electric field distribution part 40 the critical flashover distance D runs from ground to the lower edge 54 of the support insulator flange. In ac- cordance with the present embodiment of the invention, the critical flashover distance d instead runs from ground to the lower edge 45 of the tubular internal electric field distribution part 40. Preferably the material that constitutes the tubular internal electric field distribution part 40 is of the same electrical conductivity as the lower edge 54 of the support insulator flange 52. As can be seen in figure 3, the inner radius 47 of the tubular internal electric field distribution part 40 is smaller than the outer radius 49 of the tubular internal electric field distribution part 40. By inner radius 47 is meant the radius of the inner circumferential edge of the tubular internal electric field dis- tribution part 40, and by outer radius 49 is meant the radius of the outer circumferential edge of the tubular internal electric field distribution part 40.

Even though the electric field distribution part 40 has above been described as a component of a support insulator 10, the electric field distribution part 40 could also be described as a member of a high voltage electrical apparatus 30 or a member of a high voltage circuit breaker 50. A high voltage circuit breaker 50 may be delivered with a support insulator 10 already mounted thereto, therefore the electric field distribution part 40 could be described as a member of a high voltage circuit breaker 50. The electric field distribution part 40 may, as is illustrated in figure 3, be formed in one piece with a sup- port insulator flange 52. The electric field distribution part 40 may alternatively be attached to the support insulator flange 52, e.g. by screws or by welding. The electric field distribution part 40 may be formed in one piece with or attached to a terminal flange 56 of the high voltage circuit breaker 50.

When the electric field distribution part 40 is a member of a high voltage cir- cuit breaker 50, said high voltage circuit breaker 50 comprises a support insulator flange 52 for mounting a support insulator 10 to the high voltage circuit breaker 50, and further comprises an electric field distribution part 40 which, when the high voltage circuit breaker 50 is mounted, extends to a vertically lower position than the support insulator flange 52. The high voltage circuit breaker 50 of figures 3 and 4 also comprises electrical contacts (not shown) which can be brought from engagement to disengagement in the event of a fault. Such faults may for instance be a short circuit or an overload situation. The task of high voltage circuit breakers 50, and their operation, are considered known to the skilled person and therefore not de- scribed in detail herein. Information on circuit breakers can be gained from e.g. EP2317528 Bi (see figure 10), EP2097914 Bi, EP2097915 Bi and EP2246867 Bi.

Claims

1. A support insulator (10) for supporting a high voltage electrical apparatus (30; 50), comprising an inner volume (20) which is filled with an insu- lating medium,

characterised in that the support insulator (10) further comprises an electric field distribution part (40) which is arranged within said inner volume (20) and adapted to be electrically connected to said high voltage electrical apparatus (30; 50).

2. The support insulator (10) of claim 1 wherein the electric field distribution part (40) is arranged at a horizontal distance d from ground that is shorter than the minimum horizontal distance D from the high voltage electrical apparatus (30; 50) to ground.

3. The support insulator (10) of any preceding claim wherein the electrically insulating medium is any medium that has a higher voltage withstand capability than the air surrounding the support insulator (10) and the high voltage electrical apparatus (30; 50).

4. The support insulator (10) of any preceding claim wherein the lower end (45) of electric field distribution part (40) has a smooth and rounded shape.

5. The support insulator (10) of claim 4 wherein the lower surface of the lower end of electric field distribution part (40) is polished.

6. The support insulator (10) of any preceding claim wherein the electrically insulating medium is a gas. . The support insulator (10) of claim 6 wherein the electric field distribu- tion part (40) is arranged within the gas.

8. The support insulator (10) of claim 6 wherein the electric field distribution part (40) is arranged directly within the gas.

9. A high voltage electrical apparatus (30; 50) comprising a support insulator (10) of any preceding claim.

10. A high voltage circuit breaker (50) comprising a support insulator (10) of any one of claims 1-8.

11. The high voltage circuit breaker (50) of claim 10 wherein the electric field distribution part (40) is tube shaped.

12. The high voltage circuit breaker (50) of claim 11 wherein the tube shaped electric field distribution part (40) has a cylindrical lower edge (45), the inner radius (47) of said edge being smaller than the outer radius (49) of said edge.

13. A method for improving the insulation performance of a support insulator (10') for supporting a high voltage electrical apparatus (30'; 50'), wherein said support insulator (10') comprises an inner volume (20') which is filled with an electrically insulating medium, comprising the steps of arranging an electric field distribution part (40) within said inner volume (20') and electrically connecting the electric field distribution part (40) to said high voltage electrical apparatus (30'; 50').

14. The method of claim 13 wherein the electrically insulating medium is a gas.

15. The method of claim 14 comprising the step of arranging the electric field distribution part (40) directly within the gas so that the electric field distribution part (40) is surrounded by the gas.