AU2013219170A1 - A Vacuum Interrupter Assembly - Google Patents

Abstract

The present invention relates to a method of assembling a vacuum interrupter assembly. In one embodiment, the vacuum interrupter is received within a pre-formed shield layer; and a dielectric layer is applied to the shield layer shielding the vacuum interrupter. Preferably, the pre-formed shield layer is not adhered to the vacuum interrupter and prevents, at least in part, adhesion of the dielectric layer to the interrupter. * t:i~ _________-~ L.. Ca) _ U

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION STANDARD PATENT A VACUUM INTERRUPTER ASSEMBLY The following statement is a full description of this invention including the best method of performing it known to me: 1 A VACUUM INTERRUPTER ASSEMBLY TECHNICAL FIELD [0001] The present invention generally relates to a vacuum interrupter assembly. The present invention has particular application to electrical power switchgear such as reclosers which can include the vacuum interrupter assembly. BACKGROUND [0002] 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. [0003] Vacuum interrupters have been used for decades in the medium voltage switchgear industry. The benefit of using vacuum interrupters is largely financial, whereby they offer vastly longer life and greatly reduced maintenance costs when compared to other interrupters. Further, vacuum interrupters are environmentally friendly and provide the lowest environmental impact of all medium voltage switching technologies over the entire product life cycle. [0004] At least part of the reason that vacuum interrupters last is because of their simple, yet rugged construction. Turning to Figure 1, a known vacuum interrupter 100 includes a tubular ceramic insulating envelope 102 which holds opposing conductive end plates 104a, 104b. One end plate 104b is electrically connected to a fixed terminal 106, while an opposing end plate 104a is connected to a movable terminal 108. To cause interruption, one electrical contact 110 is pulled apart from the other electrical contact 112 by a few millimeters. The vacuum casing formed by the envelope 102 and plates 104, incorporates a bellows 114 to allow for this contact separation through movement of the movable terminal 108. [0005] The voltage that is impressed across the open contacts 110, 112 in the vacuum chamber is also impressed externally across the end plates 104a,b and the terminals 106, 108 of the vacuum interrupter 100. For most modern interrupters the insulating envelope 102 is formed from a high-alumina content porcelain. Internal plate like metallic end shields 116, a bellow shield 118 and a condensation shield 120 can 2 also shield electromagnetic fields. The ambient surrounding the interrupter 100 for a large number of applications is atmospheric air. [0006] In other applications, external insulation performance and compactness of the design is improved by surrounding the vacuum interrupter 100 with other dielectric media having higher dielectric strength such as mineral oil, SF6, or solid insulation. [0007] Mineral oil, which has a dielectric strength about 5 times that of air, has been used to surround vacuum interrupters in medium voltage switchgear. This insulating medium is extremely reliable and generally performs well. However, mineral oil has two distinct disadvantages, namely: (a) environmental, and (b) it is a potential fire hazard. The first disadvantage has now been alleviated with the development of biodegradable oils for high-voltage insulation. In recent years, vacuum interrupters have been placed in an SF6 ambient. Usually the SF6 at a pressure of just about I atm. gauge (i.e. 1 atm above the ambient atmosphere) has the breakdown voltage about five times that of air at 1 atm. This has permitted the use of relatively short-vacuum interrupters in rather compact designs especially at voltages of 24 kV, 36 kV, and higher voltages. Unfortunately the realization that SF6 is a potent greenhouse gas has led to a search for alternative methods of developing compact systems. [0008] Another way to increase the external high-voltage performance of the vacuum interrupter is to encapsulate it in a solid dielectric as shown, for example, in US 7285743. In this patent, the solid dielectric material is molded over the vacuum interrupter causing chemical bonding between the vacuum interrupter ceramic and the solid dielectric material. Undesirably, adhesion between the vacuum interrupter ceramic and the solid dielectric material prevents replacement of the vacuum interrupter for any defect to the outer dielectric. The preferred embodiment of the present invention provides for improved access to the vacuum interrupter in the event of vacuum interrupter replacement. [0009] Furthermore, the hard epoxy dielectric can also be compromised through thermal expansion and contraction of the vacuum interrupter, particularly when the solid dielectric material encapsulates not only the vacuum interrupter but also the bus that connects it. The preferred embodiment of the present invention provides for improved preservation of the integrity of the outer dielectric.

3 SUMMARY OF THE INVENTION [00010] According to one aspect of the present invention, there is provided a method of assembling a vacuum interrupter assembly, the method including the steps of: applying a shield layer to a vacuum interrupter; and applying a dielectric layer to the shield layer shielding the vacuum interrupter. [00011] Preferably, the step of applying involves receiving the vacuum interrupter within a preformed shield layer. Preferably, the pre-formed shield layer is not adhered to the vacuum interrupter and prevents adhesion of the dielectric layer to the interrupter. Advantageously, the shield layer and dielectric layer to which it is applied may be removed to readily access the vacuum interrupter in the event of vacuum interrupter service or replacement. [00012] The shield layer may shield the vacuum interrupter when the dielectric layer is mounted onto the shield layer. The shield layer may be compliant. [00013] Prior to the step of receiving, the method may involve the step of pre-forming the shield layer. The step of pre-forming may involve molding and permitted the shield layer to set prior to applying the shield layer. The method may involve locating one or more electrical screens in the shield layer. [00014] The method may involve hermetically sealing at least in part the vacuum interrupter with the dielectric layer and shield layer. [00015] According to another aspect of the present invention, there is provided a vacuum interrupter assembly including: a vacuum interrupter; a dielectric layer; and a compliant layer located between the vacuum interrupter and dielectric layer. [00016] Advantageously, the compliant layer absorbs outward stresses from the interrupter and inward stresses from the dielectric layer so as to preserve the integrity of the dielectric layer.

4 [00017] The compliant layer may be resilient. The compliant layer may be a sleeve. The compliant layer may be pre-formed prior to receiving the vacuum interrupter. [00018] The assembly may further include one or more electrical field screens for screening electrical fields. The electrical field screens may be embedded in the compliant layer. The compliant layer may be elongate with screens located at either end. [00019] The electrical field screens may be formed of resilient conducting or semiconducting material, or coatings, such as silicone. The compliant layer may be formed of rubber like material such as insulating silicone. The dielectric layer may be over-molded hard epoxy. The vacuum interrupter may have a ceramic case which the compliant layer covers and hermetically seals. [00020] According to another aspect of the present invention, there is provided a layer for locating between a vacuum interrupter and a dielectric layer, the layer for being applied to the vacuum interrupter before the dielectric layer is applied. Preferably, the layer is pre-formed before receiving the vacuum interrupter. [00021] 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 [00022] 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 any way. The Detailed Description will make reference to a number of drawings as follows: [00023] Figure 1 is a sectional side view of a known vacuum interrupter; and [00024] Figure 2 is a sectional side view of a vacuum interrupter assembly in accordance with an embodiment of the present invention.

5 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [00025] According to an embodiment of the present invention, there is provided a vacuum interrupter assembly 200 as shown in Figure 2. The assembly includes a vacuum interrupter 202 and a protective outer dielectric layer 204. A compliant and shielding insulating intermediate layer 206 is located between the vacuum interrupter 202 and the dielectric layer 204. Advantageously, the intermediate layer 206 absorbs outward mechanical stresses from the interrupter 202 and inward mechanical stresses from the dielectric layer 204 so as to preserve the integrity of the dielectric layer 204 and impede it from deteriorating. [00026] The intermediate layer 206 is a resilient tubular sleeve which is pre-formed and pre-set prior to receiving the vacuum interrupter 202. The assembly 200 further includes at least one (and in this embodiment two) electrical field screens 208a, 208b for screening and controlling electrical fields The electrical field screens 208a, 208b are collars embedded in the elongate intermediate layer 206 at desired locations to control the electrical fields where high electrical field stress can be present. Deterioration of the dielectric layer 204 is also impeded by the screens 208. The electrical field screens 208a, 208b are formed of resilient conducting or semiconducting material, or coatings, such as conducting grade silicone. The intermediate layer 206 is a dielectric formed of rubber like such as insulating grades silicone. [00027] The outer dielectric layer 204 can be hard protective epoxy mold over the comparatively less durable intermediate layer 206. The vacuum interrupter 202 has a ceramic casing 102 which the intermediate layer 206 covers and at least in part hermetically seals. The outer dielectric layer 204 can be thin compared with the prior art and combines with the dielectric intermediate layer 206 to desirably form a compact assembly 200. [00028] A method of assembling the vacuum interrupter assembly 200 is now described. [00029] Prior to receiving the vacuum interrupter 202, the intermediate layer 206 is first pre-molded and allowed to fully set. The molding involves molding the molded electrical screens 208a,b into the intermediate layer 206.

6 [00030] The assembly method then involves receiving the vacuum interrupter 202 within the pre-formed intermediate layer 206. The resilient intermediate layer 206 is stretched over and clings to the interrupter 202. [00031] The assembly method then involves fitting the outer dielectric layer 204 to the intermediate layer 206. In particular, the intermediate layer 206 mechanically shields the vacuum interrupter 202 when the epoxy dielectric layer 204 is mounted onto the intermediate layer 206. The pre-formed intermediate layer 206 does not adhere to the vacuum interrupter 202, and prevents adhesion of the applied dielectric layer 204 to the interrupter 202. [00032] Furthermore, the intermediate layer 206 defines spaced apart and endless external transverse grooves. The grooves contain the formation of any air pockets to between adjacent grooves when the layer 206 is force-fitted within the tubular dielectric layer 204. It is desirable to minimize these air pockets which otherwise contribute to field stress breakdown of the assembly 200, particularly if air pockets extend length of the intermediate layer 206. [00033] The outer dielectric layer 204 and intermediate layer 206 together hermetically seal the vacuum interrupter 202 and provide the required insulating properties over the external surface of the vacuum interrupter ceramic. Advantageously, the intermediate layer 206 and dielectric layer 204 to which it is applied can be removed to readily access the vacuum interrupter 202 in the event of vacuum interrupter service or replacement. [00034] 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. [00035] 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. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

7 [00036] 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 (25)

1. A method of assembling a vacuum interrupter assembly, the method including the steps of: applying a shield layer to a vacuum interrupter; and applying a dielectric layer to the shield layer shielding the vacuum interrupter.

2. A method as claimed in claim 1, wherein the shield layer is pre-formed prior to receiving the vacuum interrupter and does not adhere to the vacuum interrupter.

3. A method as claimed in claim 1 or claim 2, wherein the shield layer and dielectric layer to which it is applied can be removed to readily access the vacuum interrupter in the event of vacuum interrupter service or replacement.

4. A method as claimed in any one of claim the preceding claims, wherein the shield layer shields the vacuum interrupter when the dielectric layer is mounted onto the shield layer.

5. A method as claimed in any one of claim the preceding claims, wherein the shield layer is compliant or resilient.

6. A method as claimed in any one of claim the preceding claims wherein, prior to the step of applying the shield layer, further includes the step of pre-forming the shield layer.

7. A method as claimed in claim 6, wherein the step of pre-forming involves molding and permitted the shield layer to set prior to said step of applying the shield layer.

8. A method as claimed in any one of claim the preceding claims, further including the step of locating one or more electrical screens in the shield layer.

9. A method as claimed in any one of claim the preceding claims, further including the step of hermetically sealing at least in part the vacuum interrupter with the dielectric layer and shield layer. 9

10. A vacuum interrupter assembly formed in accordance with any one of the preceding claims.

11. A vacuum interrupter assembly including: a vacuum interrupter; a dielectric layer; and a compliant layer located between the vacuum interrupter and dielectric layer.

12. A vacuum interrupter assembly as claimed in claim 11, wherein the compliant layer is resilient.

13. A vacuum interrupter assembly as claimed in claim 11 or claim 12, wherein the compliant layer includes a sleeve.

14. A vacuum interrupter assembly as claimed in any one of claims 11 to 13, wherein the compliant layer is pre-formed prior to receiving the vacuum interrupter.

15. A vacuum interrupter assembly as claimed in any one of claims 11 to 14, further including one or more electrical field screens for screening electrical fields.

16. A vacuum interrupter assembly as claimed in claim 15, wherein the electrical field screens are embedded in the compliant layer.

17. A vacuum interrupter assembly as claimed in claim 16, wherein the compliant layer is elongate with screens located at either end, and/or defines one or more endless external grooves.

18. A vacuum interrupter assembly as claimed in any one of claims 15 to 17, wherein the electrical field screens are formed of conducting material or coatings.

19. A vacuum interrupter assembly as claimed in any one of claims 11 to 18, wherein the compliant layer is formed of rubber or insulating silicone.

20. A vacuum interrupter assembly as claimed in any one of claims 11 to 19, wherein the dielectric layer includes epoxy. 10

21. A vacuum interrupter assembly as claimed in any one of claims 11 to 20, wherein the vacuum interrupter has a ceramic case which the compliant layer covers and at least in part hermetically seals.

22. A layer for locating between a vacuum interrupter and a dielectric layer, the layer for being applied to the vacuum interrupter before the dielectric layer is applied.

23. A layer as claimed in claim 22, wherein the layer is one or more of: compliant, resilient, dielectric, a mechanical shield for over-molding, a sleeve, and pre-set.

24. A layer as claimed in claim 22 or claim 23, further including one or more conductive electrical field screens for screening electrical fields.

25. A layer as claimed in any one of claims 22 to 24, wherein the layer is pre-formed before receiving the vacuum interrupter. Dated this 2 1 st day of August 2013 NOJA POWER SWITCHGEAR PTY LTD by my attorneys Cullens Patent and Trade Mark Attorneys