AU2015203196B2

AU2015203196B2 - An Electrical Isolator

Info

Publication number: AU2015203196B2
Application number: AU2015203196A
Authority: AU
Inventors: Joni Sahak Tortian
Original assignee: NOJA POWER SWITCHGEAR Pty Ltd
Current assignee: NOJA POWER SWITCHGEAR Pty Ltd
Priority date: 2014-07-08
Filing date: 2015-06-15
Publication date: 2018-09-20
Anticipated expiration: 2035-06-15
Also published as: AU2015203196A1

Abstract

The present invention relates to an electrical isolator. The isolator includes two separable contacts. Two adjacent triple points are located on either side of a main electrical field between the two separated contacts. The triple points are located in a region of low electrical field intensity when compared with the main electrical field. Advantageously, the triple points in the region of low electrical field intensity are subject to lower field stresses and are therefore less prone to voltage breakdown failure. 21 2--,\ z - 20 23+ Figure 1 Figure 2 0

Description

AN ELECTRICAL ISOLATOR

TECHNICAL FIELD

[0001] The present invention generally relates to an electrical isolator. The present invention has particular application to electrical power switchgear including the electrical isolator.

BACKGROUND

[0001] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

[0002] Air insulated isolators are commonly used in electrical switchgear. Traditionally, air isolators were large in size to ameliorate the effects of the break down voltage of air, at voltages typically between 10-38kV.

[0003] WO2012/003527 discloses an air isolator incorporating electrical field screens to control the electric field distribution and advantageously reduce the size of the isolator. However, the present Applicant perceives that the reduced size of the isolator will result in higher electrical fields and increased electrical field stresses on the isolator, particularly at each “triple point” where a metal screen, dielectric and contact chamber intersect. These increased stresses can undesirably contribute to voltage breakdown failures [0004] It is an object of the present invention to provide an improved electrical isolator which is less susceptible to voltage breakdowns at a triple point than prior art air isolators, such as WO2012/003527.

SUMMARY OF THE INVENTION

[0005] According to one aspect of the present invention, there is provided an electrical isolator for electrical power switchgear, the isolator including: two separable contacts; two electrical field control screens associated with respective contacts; and two adjacent triple points located on either side of a main electrical field between the two separated contacts, and located on the control screens in a region of low electrical field intensity when compared with the main electrical field.

[0006] Advantageously, in contrast to the prior art such as WO2012/003527 where at least one triple point is in the main electrical field, the triple points in the region of low electrical field intensity are subject to lower field stresses and are less prone to voltage breakdown failure.

[0007] The field intensity in the region of low field intensity may be less than half the main electrical field. The field intensity in the region of low field intensity may be less than one quarter the main electrical field. The field intensity in the region of low field intensity may be negligible when compared with the main electrical field. Preferably, each triple point is set back or located distal from a free end of a respective contact.

[0008] The isolator may include a pair of opposed and widening electrical field control screens. Each control screen may define a narrower throat in which the triple point is located and from which a wider mouth extends. In one embodiment, at least one control screen and corresponding contact together form a channel in which the triple point is located. In another embodiment, the control screen wholly defines a channel in which the triple point is located. Each triple point may be located at a closed end of a cavity adjacent the contact.

[0009] Each triple point may be formed at the junction of an electrical field control screen, dielectric housing and contact air chamber. The control screen may be formed from dielectric material having a higher permittivity compared with the dielectric housing. The dielectric housing may have a lower permittivity region coincident with the main electrical field and a higher permittivity region outside the main electrical field. The dielectric housing may be made of transparent or translucent material to facilitate viewing of the contacts.

[00010] The control screens may contact respective contacts. Alternatively, the control screens may be capacitively coupled to respective contacts. One of the control screens may include a hub which receives a movable contact.

[00011] According to another aspect of the present invention, there is provided electrical power switchgear including: two separable contacts; two electrical field control screens associated with respective contacts; and two adjacent triple points located on either side of a main electrical field between the two separated contacts, and located on the control screens in a region of low electrical field intensity when compared with the main electrical field.

[00012] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[00013] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in anyway. The Detailed Description will make reference to a number of drawings as follows: [00014] Figure 1 is a sectional schematic view of an electrical isolator in accordance with a first embodiment of the present invention; [00015] Figure 2 shows the electrical fields lines in the electrical isolator of Figure 1; [00016] Figure 3 is an electrical field strength plot showing the electrical field strength between the triple points and along the dielectric bore of the electrical isolator of Figure 1; [00017] Figure 4 shows the electrical field lines in an electrical isolator in accordance with a second embodiment of the present invention; and [00018] Figure 5 is a sectional schematic view of an electrical isolator in accordance with a third embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[00019] According to a first embodiment of the present invention, there is provided an electrical isolator 1 as shown in Figure 1. The isolator 1 includes two separable contacts 10, 11 (or electrodes), with the right contact 10 being fixed and the left contact 11 being movable. Two adjacent triple points 22, 23 are located on either side of a uniform main electrical field 200 (see Fig. 2) between the two fully separated contacts 10, 11. Each triple point 22, 23 is formed at the junction of an electrically conductive or semiconductive electrical field control screen 20, 21, an electrical insulating housing 2 formed from dielectric material, and a contact air chamber 3 in a central bore 100 of the housing 2. An example of the magnitudes of typical electrical field strengths (in V/m) are shown in the plot illustrated in Figure 3 in relation to a particularly dimensioned air isolator.

[00020] As shown in Figure 1, each triple point 22, 23 is set back or located distal from a free contact end 12, 13 of a respective contact 10, 11. As can best be seen in Figures 2 and 3, the triple points 22, 23 are located in a region of low electrical field intensity, which is negligible when compared with the main electrical field 200. Advantageously, in contrast to WO2012/003527 where at least one triple point is in the main electrical field, the triple points 22, 23 in the region of low electrical field intensity are subject to lower field stresses and are less prone to voltage breakdown failure. The electron emission from the triple points 22, 23 is limited to avoid voltage flashover and tracking.

[00021] Returning to Figure 1, the isolator 1 includes a pair of opposed and widening electrical field control screens 20, 21 that create the substantially uniform main electrical field 200 which enables the contact separation to be lessened by three to four times should the screens 20, 21 not otherwise be provided. The screens 20, 21 are in electrical contact with respective ones of the contacts 10, 11. Each screen 20, 21 defines a narrower throat 102 in which the triple point 22, 23 is located and from which a wider mouth 104 extends. Each screen 20, 21 and corresponding contact 10, 11 together form a narrow cavity 106 therearound with a closed end where the triple point 22, 23 is deeply located.

[00022] According to a second embodiment of the present invention, there is provided an electrical isolator 400 as shown in Figure 4. Like reference numerals refer to like features previously described.

[00023] The lateral screens 20’, 21’ are formed from dielectric material having a higher permittivity compared with the central dielectric housing 2’. The dielectric housing 2’ has a lower permittivity region coincident with the main electrical field 200’ and higher permittivity screen regions outside the main electrical field 200’. The dielectric housing 2’ is made of transparent or translucent material to facilitate viewing of the contacts 10, 11.

[00024] The triple points 22’, 23’ are formed at the junction of the tapered screens 20’, 2T, the contacts 10, 11, and the air chamber 3’ in the housing 2’. Once again, the triple points 22’, 23’ are safely set back from the contact ends 12, 13, and in a recess end outside the main field 200’.

[00025] According to a third embodiment of the present invention, there is provided an electrical isolator 1” as shown in Figure 5. Like reference numerals refer to like features previously described. A first electric field control screen 21 wholly defines a narrow cavity 106 in which the triple point 23 is located. The first screen 21 includes a protruding annular hub 14 which receives and shields the sunken contact end 13 of the retracted movable contact 11 to reduce the impact of end surface irregularities on the electric field distribution. The second screen 22 is in physical contact or integrally formed with the fixed contact 12 in this embodiment.

[00026] The electrical isolators described in the above embodiment provide a compact and lightweight design with high reliability. These air type isolators are simple in design and therefore cost effective to manufacture.

[00027] A person skilled in the art will appreciate that many embodiments and variations can be made without departing from the ambit of the present invention.

[00028] In the first embodiment above, the screens 20, 21 were in electrical contact with respective contacts 10, 11. Alternatively, the screens 20, 21 can be associated with the contacts by being capacitively coupled to respective contacts 10, 11.

[00029] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect.

[00030] Reference throughout this specification to ‘one embodiment’ or ‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases ‘in one embodiment’ or ‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

Claims

The claims defining the invention are as follows:

1. An electrical isolator for electrical power switchgear, the isolator including: two separable contacts; two electrical field control screens associated with respective contacts; and two adjacent triple points located on either side of a main electrical field between the two separated contacts, and located on the control screens in a region of low electrical field intensity when compared with the main electrical field.
2. An electrical isolator as claimed in claim 1, wherein the field intensity in the region of low field intensity is less than half the main electrical field.
3. An electrical isolator as claimed in claim 2, wherein the field intensity in the region of low field intensity is less than one quarter the main electrical field.
4. An electrical isolator as claimed in claim 3, wherein the field intensity in the region of low field intensity is negligible when compared with the main electrical field.
5. An electrical isolator as claimed in any one of the preceding claims, wherein each triple point is set back or located distal from a free end of a respective contact.
6. An electrical isolator as claimed in any one of the preceding claims, wherein the electrical field control screens comprise a pair of opposed and widening control screens.
7. An electrical isolator as claimed in any one of claims 1 to 6, wherein each control screen defines a narrower throat in which the triple point is located and from which a wider mouth extends.
8. An electrical isolator as claimed in any one of claims 1 to 7, wherein at least one control screen and corresponding contact together form a channel in which the triple point is located.
9. An electrical isolator as claimed in claim 6 or claim 7, wherein at least one control screen wholly defines a channel in which the triple point is located.
10. An electrical isolator as claimed in any one of the preceding claims, wherein each triple point is located at a closed end of a cavity adjacent a respective contact.
11. An electrical isolator as claimed in any one of the preceding claims, wherein each triple point is formed at the junction of an electrical field control screen, a dielectric housing and a contact air chamber.
12. An electrical isolator as claimed in claim 11, wherein the control screen is formed from dielectric material having a higher permittivity compared with the dielectric housing.
13. An electrical isolator as claimed in claim 11 or claim 12, wherein the dielectric housing has a lower permittivity region coincident with the main electrical field and a higher permittivity region outside the main electrical field.
14. An electrical isolator as claimed in any one of claims 11 to 13, wherein the dielectric housing is made of transparent or translucent material to facilitate viewing of the contacts.
15. An electrical isolator as claimed in any one of the preceding claims, wherein the control screens contact respective contacts.
16. An electrical isolator as claimed in any one of claims 1 to 14, wherein the control screens are capacitively coupled to respective contacts.
17. An electrical isolator as claimed in any one of the preceding claims, wherein a control screen includes a hub which receives a movable contact.
18. Electrical power switchgear including: two separable contacts; two electrical field control screens associated with respective contacts; and two adjacent triple points located on either side of a main electrical field between the two separated contacts, and located on the control screens in a region of low electrical field intensity when compared with the main electrical field.
19. Electrical power switchgear as claimed in claim 18, wherein the control screens are coupled to respective contacts.
20. Electrical power switchgear as claimed in either claim 18 or claim 19, further including a dielectric housing and a contact air chamber that together with a control screen form one of the triple points.