Vacuum Valve Electrostatic Shield for Switchgear
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Solution Overview
Problem
Existing switchgear with vacuum valves experiences partial discharges and reliability issues due to thermal stress and electric field concentrations, particularly at the interface between RTV rubber and epoxy resin molds, which are exacerbated by temperature changes.
Innovation Solution
The implementation of annular electrostatic shield members made of coiled metal or conductive materials that contract radially, applied to the outer peripheral surface of the vacuum vessel to relax electric fields and thermal stresses, thereby preventing partial discharges and enhancing reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If RTV rubber is applied as coating to thermal stress concentration parts, then thermal stress relaxation is achieved, but air bubbles may be trapped causing partial discharges and the coating operation requires much labor and time
Solution Approach 1:
The patent applies preliminary action by embedding the electrostatic shield member into the RTV rubber coating before the coating is applied. This ensures that the shield is already in position when the coating is applied, eliminating the risk of air bubbles being trapped around the shield and preventing partial discharges. The shield member is placed in advance, and then the RTV rubber coating is applied over it in a continuous operation.
2Strength
If RTV rubber coating is applied to the vacuum vessel, then thermal stress relaxation is achieved, but gaps will appear between the RTV rubber and epoxy resin when temperature changes, forming causes for partial discharges
Solution Approach 1:
The electrostatic shield member acts as an intermediary between the RTV rubber coating and the epoxy resin mold. It is embedded in the RTV rubber and extends to the surface, providing continuous electric field relaxation at the interface. This intermediary structure ensures that even when gaps form between the RTV rubber and epoxy resin due to thermal expansion differences, the electric field is properly controlled and partial discharges are prevented.
3Reliability
If electrostatic shield member is added to the vacuum valve structure, then electric field relaxation is achieved, but device complexity increases
Solution Approach 1:
The electrostatic shield member is merged with the RTV rubber coating by embedding it within the coating material. This integration means the shield is not a separate, additional component but rather an embedded element within the existing coating structure. The shield member combines the functions of the RTV rubber (thermal stress relaxation) and the electrostatic shield (electric field relaxation) into a single integrated structure, reducing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively prevents partial discharges and improves the reliability of switchgear by relaxing electric fields and thermal stresses, even when gaps form between the RTV rubber and resin molds, ensuring consistent performance across temperature changes.
Implementation Method 1
an annular electrostatic shield member which contracts in its radial direction is retained on an outer peripheral surface of the vacuum vessel, thereby to relax an electric field of an electric field relaxation-requiring part of the vacuum vessel
Implementation Method 2
it is practiced to apply thermal stress relaxation members to only required parts... Signs 3B in FIG. 8 of Patent Document 1 denote room-temperature vulcanizing type silicone rubber being the stress relaxation members
Data Source
AI summary
A switchgear including a vacuum valve which prevents partial discharges infallibly and whose reliability is high, and a method of fabricating the same are obtained.In a vacuum valve 1 wherein a stationary electrode 1a and a movable electrode 1b are disposed within a vacuum vessel 2 which is constituted by a metal flange 2a as well as a metal tube 2e and an insulating tube 2b, and wherein a resin mold 3 is applied onto the outer peripheral surface of the vacuum vessel 2; coiled metal-made shields 4a and 4b, in each of which a coiled metal wire is brought into an annular shape, are retained on the outer peripheral surface of the vacuum vessel 2 so as to relax the electric fields of the electric field relaxation-requiring parts 21d of the vacuum vessel 2.