CA-3184350-C - MANUFACTURING PROCESS FOR SURGE ARRESTOR MODULE USING COMPACTION BLADDER SYSTEM

Abstract

The present disclosure is directed to a method of producing a surge arrestor module, comprising the acts of (i) providing a plurality of MOV blocks arranged in a stack, (ii) applying an epoxy-reinforced structural layer to an outer surface of the stack, (iii) after the applying, inserting the stack into a flexible bladder, and (iv) curing the epoxy-reinforced structural layer with elevated temperatures while the flexible bladder applies radially aligned pressure to the stack and a tool applies axially aligned pressure to the stack. The present disclosure also includes an apparatus for performing the methods described herein. The apparatus includes an outer case structure and a flexible bladder that fits within the outer case structure. A hollow inner region of the outer case structure is pressurized to force the flexible bladder against the surge arrestor module as the surge arrestor module is curing.

Inventors

• CHRISTOPHER A. JUILLET
• Jeffrey J. Madden
• Bruce Bier

Assignees

• RICHARDS MFG. CO., A NEW JERSEY LIMITED PARTNERSHIP

Dates

Publication Date

20260505

Application Date

20221216

Priority Date

20220105

Claims (20)

1. Attorney Ref.: 1057P091CA01 12 WE CLAIM: 1. A method of producing a surge arrestor module, comprising: providing a plurality of MOV blocks arranged in a stack; applying an epoxy-fiberglass layer to surround an outer surface of the stack; placing the stack with the applied epoxy-fiberglass layer into a flexible bladder, the flexible bladder being located in an outer tube structure; and while the epoxy-fiberglass layer is curing around the outer surface of the stack, applying air pressure between an outer surface of the flexible bladder and an inner surface of the outer tube structure to generate a compressive force to the epoxy-fiberglass layer and the stack.
2. 2. The method of claim 1, further including, applying heat to create a curing temperature that is greater than 200°F.
3. 3. The method of claim 2, further including, after the curing, releasing the pressure to the flexible bladder, and removing the stack with the cured epoxy -fiberglass layer from the flexible bladder.
4. 4. The method of claim 1, wherein the epoxy-fiberglass layer is comprised of an epoxyimpregnated fiberglass material that is wrapped around the stack multiple times before the act of placing the stack into the flexible bladder.
5. 5. The method of claim 1, wherein the air pressure increases the size of a gap between the outer surface of the flexible bladder and the inner surface of the outer tube structure during the curing process.
6. 6. The method of claim 5, wherein the air pressure is at least 30 psi.
7. 7. The method of claim 1, further including, while the epoxy-reinforced fiberglass layer is curing around the outer surface of the stack, applying axial pressure to the stack to force the plurality of MOV blocks into tight engagement. Attorney Ref.: 1057P091CA01 13
8. 8. The method of claim 7, wherein the axial pressure is applied by at least one screw that is coupled to a moveable press tool adjacent to an end region of the outer tube structure.
9. 9. A method of producing a surge arrestor module, comprising: providing a plurality of MOV blocks arranged in a stack; surrounding the stack with an uncured epoxy-reinforced structural layer; after the applying, inserting the stack into a flexible bladder that is located in an outer tube structure; and curing the epoxy-reinforced structural layer with elevated temperatures while the flexible bladder applies radially aligned pressure to the stack and a tool applies axially aligned pressure to the stack, the radially aligned pressure being due to air pressure between an outer surface of the flexible bladder and an inner surface of the outer tube structure.
10. 10. The method of claim 9, wherein the air pressure increases the size of a gap between the outer surface of the flexible bladder and the inner surface of the outer tube structure during the act of curing.
11. 11. The method of claim 9, wherein the axially aligned pressure is due to rotation of least one screw that is coupled to the tool, the rotation of the at least one screw axially moving the tool toward the stack.
12. 12. The method of claim 9, wherein the epoxy-reinforced structural layer is an epoxyimpregnated fiberglass material that is wrapped around the stack multiple times before the act of inserting the stack into the flexible bladder.
13. 13. The method of claim 9, further including applying an outer layer of material to the epoxy-reinforced structural layer to serve as a barrier between the flexible bladder and the epoxy-reinforced structural layer, the outer layer of material being a thin layer of PVDC material or a polyethylene-based material.
14. 14. An apparatus for producing a surge arrestor module, comprising: an outer case structure having an inner surface and an outer surface, the inner Attorney Ref.: 1057P091CA01 14 surface forming a hollow region, the outer case structure including a port that provides access to the hollow region; a flexible bladder located within the hollow region, the flexible bladder being sized and configured to receive the surge-arrestor stack, the surge arrestor stack having a plurality of MOV blocks and a layer of epoxy-reinforced structural material on exterior surfaces of the plurality of MOV blocks; and a pressure source for delivering pressurized air into the hollow region of the outer case structure via the port, the pressurized air forcing the flexible bladder to compress against the surge-arrestor stack while the epoxy-reinforced structural material cures.
15. 15. The apparatus of claim 14, wherein the pressurized air is heated air to assist with the curing process.
16. 16. The apparatus of claim 14, further including at least one moveable press tool that applies compressive force along a central axis of the surge-arrestor stack during the curing process.
17. 17. The apparatus of claim 16, wherein the moveable press tool is driven by a screw that urges the moveable press tool toward the surge-arrestor stack.
18. 18. The apparatus of claim 16, wherein the flexible bladder provides a compressive force to the surge-arrestor stack in a radial direction relative to the central axis.
19. 19. The method of claim 1, wherein the epoxy-fiberglass layer is in direct contact with the outer surface of the stack when surrounding the outer surface of the stack.
20. 20. A method of producing a surge arrestor module, comprising: providing a plurality of MOV blocks arranged in a stack; applying an epoxy-fiberglass layer to surround an outer surface of the stack; placing the stack with the applied epoxy-fiberglass layer into a flexible bladder; applying heat to create a curing temperature that is greater than 200° F.; Attorney Ref.: 1057P091CA01 while the epoxy-fiberglass layer is curing around the outer surface of the stack, applying pressure to the flexible bladder to generate a compressive force to the epoxyfiberglass layer and the stack; and after the curing, releasing the pressure to the flexible bladder, and removing the stack with the cured epoxy-fiberglass from the flexible bladder.

Description

1 Attorney Ref.: 1057P091CA01 MANUFACTURING PROCESS FOR SURGE ARRESTOR MODULE USING COMP ACTION BLADDER SYSTEM COPYRIGHT A portion of the disclosure of this patent document may contain material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever 10 TECHNICAL FIELD The present invention relates to surge arrestor modules that protect equipment from electrical disturbances. More particularly, this invention relates to a process for making a surge arrestor having a series of metal oxide varistor (MOV) blocks in contact with each other and a fiberglass-reinforced layer that surrounds the MOV blocks. BACKGROUND A surge arrester is a protective device that is commonly connected in parallel with a more expensive piece of electrical equipment to divert current surges from over-voltage conditions safely around the electrical equipment. When exposed to the over-voltage condition, the surge 2 0 arrester operates in a low impedance mode that provides a current path to electrical ground. By doing so, the surge arrestor protects the internal circuitry of the electrical equipment from damage due to the over-voltage condition. After an over-voltage condition has been experienced, the surge arrester returns to operation in the high impedance mode in which the surge arrester provides a current path to ground having a relatively high impedance. 25 Surge arrestors are often made from a stack of MOV blocks. Each MOV block is characterized by having a relatively high resistance when exposed to a normal operating voltage, and a much lower resistance when exposed to a higher voltage, such as a higher voltage associated with over-voltage conditions. The number of MOV blocks in a stack and/or the length of each MOV block is selected to support various system voltages. There are two contacts at the end of 3 0 each MOV stack. The contact on one end is typically configured with a lug-style interface for attaching to a bushing and the contact on the other end is typically a copper tube with a crimp Date Re9ue/Date Received 2022-12-16 2 Attorney Ref.: 1057P091CA01 barrel (or other connecting structure) for attaching a ground wire. Each MOV block in the stack must maintain proper electrical contact with the adjacent MOV blocks so as to reduce the contact resistance. Furthermore, the magnitude of the current in over-voltage conditions can be significant and produce high electromechanical forces on the surge 5 arrester stack. For these reasons, surge arrester stacks must be made from high strength materials and are placed under compression loads. To provide the compression loading, the individual MOV blocks are typically held together by a fiberglass reinforcing structure applied to the outside surfaces for increased physical strength. For use in shielded distribution devices, the surge arrester's fiberglass reinforcing structure must be free of voids or air pockets. Any air voids within 10 the fiberglass or between the fiberglass and outside surface of the MOV blocks could cause electrical discharge once energized and would ultimately result in a failure of the device. One known method for applying the fiberglass onto the surge arrester stack is to use fiberglass sheet that is pre-impregnated with epoxy resin and wrapped several times around the MOV blocks and end contacts to build up the desired wall thickness. The epoxy resin, when 15 heated, cures and solidifies to form a very high strength substrate encapsulating the MOV blocks and end contacts. While curing in the oven, the fiberglass and pre-impregnated epoxy resin must be compressed to eliminate air voids between the wrapped layers of the pre-impregnated fiberglass. One method for compressing the pre-impregnated fiberglass known in the industry is disclosed in U.S. Patent No. 8,117,739, which uses a shrink film radially wrapped over the outside 2 0 of the fiberglass that shrinks when exposed to heat. This shrinking of the film exerts a compaction force on the fiberglass and epoxy while is it being heated and cured. There are at least two main issues with the use of shrink film to compact the fiberglass and epoxy while curing. One issue is that the level of compaction cannot be varied. The level of compaction is dictated by the shrink ratio of the film material being used and cannot be varied or 2 5 increased, if needed. As the layers of fiberglass wrapping increase to achieve increased strength, the amount of compaction force needed to eliminate any air voids also increases. Another issue that arises when using shrink film for compaction is that after the film is removed, there are impressions left on the fiberglass/epoxy in the areas where the shrink film overlapped itself. This results in the fiberglass and epoxy needing to be sanded and smoothed out after curing