Switching Assembly With Shielded Bushing for SF6-Free Dielectric Strength
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Solution Overview
Problem
The transition from SF6 gas-insulated switchgear to clean air solutions, such as carbon dioxide and nitrogen gas mixtures, poses a challenge due to reduced dielectric strength, increasing the risk of dielectric failure in switching devices used for electric power distribution.
Innovation Solution
A switching device design that incorporates a bushing with a flange extending into the circuit-breaker tank, a stationary contact with a collar and holes for uniform electric field distribution, and a fixing arrangement with an insert and O-ring to prevent gas leakage and dielectric failures, while maintaining the same footprint as SF6 designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If clean air solutions (carbon dioxide and nitrogen gas mixtures) are used instead of SF6 gas, then environmental compatibility is improved, but dielectric strength is reduced
Solution Approach 1:
The patent applies local quality by creating regions with different gas compositions within the switching device. Specifically, the insulating gas is introduced into specific regions such as between the stationary contact and circuit-breaker tank, and between the moving contact and bus-bar tank, rather than uniformly throughout the entire device. This localized approach allows optimization of dielectric strength in critical areas while maintaining environmental compatibility with clean air solutions.
Solution Approach 2:
The patent uses composite materials by combining different insulating gases (carbon dioxide and nitrogen in specific ratios) to create a gas mixture with optimized dielectric properties. The insulating gas is composed of carbon dioxide (30-70% by volume) and nitrogen (20-50% by volume), forming a composite gas medium that provides enhanced dielectric strength compared to pure clean air, while still maintaining environmental compatibility.
2Object-affected harmful factors
If the switching device is designed for SF6-free gases, then environmental compatibility is improved, but the risk of dielectric failure increases
Solution Approach 1:
The patent applies preliminary action by pre-introducing the insulating gas into critical regions before the switching operation occurs. The insulating gas is introduced into the regions between contacts and tanks in advance, ensuring that dielectric protection is already in place before any potential arc or dielectric stress occurs. This proactive approach reduces the risk of dielectric failure during switching operations.
Solution Approach 2:
The patent uses the insulating gas mixture as an intermediary medium between electrical components to prevent dielectric failure. The gas mixture acts as a mediator that provides dielectric protection in critical regions, reducing the risk of flashover and dielectric breakdown while maintaining environmental compatibility. The gas serves as an intermediate protective layer between high-voltage components.
3Ease of manufacture
If the stationary contact is fixed onto the bushing using conventional fixing means, then ease of manufacture is improved, but dielectric clearance is reduced
Solution Approach 1:
The patent applies the taking out principle by removing the conventional nut and fixing plate assembly from the design. Instead of using external fixing means that protrude into the dielectric space, the stationary contact is directly fixed onto the bushing body. This extraction of the fixing mechanism eliminates the need for additional components that would reduce dielectric clearance, while maintaining ease of manufacture through direct fixation.
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
The design enhances dielectric strength and reduces the risk of flashovers and gas leakage, achieving dielectric test values comparable to SF6 products, even with SF6-free gases, and simplifies assembly by eliminating clamping plates and reducing dielectric stress points.
Implementation Method 1
Gas insulation offers significantly improved dielectric strength compared to atmospheric air. In the switching device, the electrical contacts are sealed inside a tank with pressurized insulating gas.
Implementation Method 2
The circuit-breaker tank consists of a vacuum interrupter which is used to connect and disconnect the circuit. The publication US 2005/056617 A1 describes a switching device comprising a bus-bar tank having the first electric terminal disposed therein, a circuit-breaker tank having the second electric terminal disposed therein.
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
A switching device (100) for opening and closing a circuit is provided. The switching device comprises a bus-bar tank (110) and a circuit-breaker tank (112). The switching device also comprises a bushing (122) arranged between and coupling the bus-bar tank and the circuit-breaker tank. The switching device further comprises a stationary contact (126, 800) mounted to the bushing by a fixing arrangement (128). The stationary contact has a first end (126a) and a second end (126b), with the first end disposed in the bus-bar tank. The switching device further comprises a circuit-breaker arrangement (130) arranged inside the circuit-breaker tank. The circuit-breaker arrangement is adapted to be disposed in contact with the second end of the stationary contact. Herein, the stationary contact is at least partially accommodated inside the bushing, and the fixing arrangement is dielectrically shielded inside the bushing.