Coaxial-Shaft Earthing Switch for Arc-Free Closing
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Solution Overview
Problem
Existing earthing switches in medium-voltage electric switchgears face challenges in preventing electric arcs during the closing movement, especially when an operator decides to stop the closing process due to line overvoltages, which can lead to unpredictable consequences.
Innovation Solution
The design incorporates a mechanism with a first shaft and a second coaxial shaft, where the second shaft is free to rotate initially and then becomes rotationally connected after a pre-established angle, utilizing spring means to ensure the moving contacts reach the closed position independently, reducing operator dependency and preventing electric arcs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the operator controls the closing movement of the earthing switch, then the operator can stop the closing process to prevent electric arcs during line overvoltages, but the operator dependency increases the risk of arc formation when the operator changes mind or delays action
Solution Approach 1:
The spring means are pre-loaded during the opening phase to store elastic energy. When the closing movement is initiated, this pre-stored energy automatically propels the moving contacts to engage with the fixed contacts without requiring continuous operator control, thereby preventing arcs by ensuring rapid, complete closure
Solution Approach 2:
The earthing switch mechanism uses its own stored elastic energy from the spring means to complete the closing movement independently. Once triggered, the system self-accelerates the contacts to their engaged position without needing further operator intervention, making the system self-sufficient and eliminating the safety risk of operator hesitation
2Reliability
If spring means are used to complete the closing movement automatically, then operator dependency is reduced and arc prevention is improved, but the device complexity increases due to additional mechanical components
Solution Approach 1:
The spring means are integrated into the existing earthing switch mechanism, combining the energy storage function with the contact movement function. The spring is mechanically coupled to the moving contacts and shaft, creating a unified system where the spring's elastic energy directly drives the closing action without requiring separate actuation mechanisms
Solution Approach 2:
The spring means serve multiple functions: they provide the driving force for closing movement, ensure rapid contact engagement to prevent arcs, and can be pre-loaded during the opening phase. This multi-functional design reduces the need for additional dedicated components for each function
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 electric arcs during the closing movement by ensuring the moving contacts reach the closed position independently, enhancing safety and reducing the risk of arc formation, while maintaining a cost-effective and industrially feasible design.
Implementation Method 1
spring means operatively connected to the shaft that support the moving contacts, wherein the spring means are loaded during a first rotational phase of the shaft and release their elastic energy on the shaft when the first rotational phase has been completed
Data Source
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AI summary
The present invention relates to an earthing switch (1) for a medium voltage switchgear wherein said earthing switch comprises a frame (5) supporting a mechanism (4) for rotating a plurality of moving contacts (2) between a first reference position and a second reference position. Said mechanism comprises a first shaft (11) on which the moving contacts (2) are rigidly mounted, said first shaft (11) rotating around a longitudinal axis (101) in a closing direction (W1) for which said moving contacts (2) reach said second reference position and in an opening direction (W2) for which said moving contacts (2) reach said first reference position. According to the invention, the mechanism comprises also a second shaft (12) coaxial to said first shaft (11) and connectable to an operating mechanism for the control of said second shaft (12). The mechanism further comprises first coupling means (15A, 15B) of said shafts (11,12) configured so that said second shaft (12) is free to rotate with respect to said first shaft (11), for at least a first rotational phase, when said second shaft (12) rotates according to said closing direction (W1). Said mechanism also comprises spring means (13A,13B) operatively connected to said first coupling means (15A, 15B), wherein said spring means (13A, 13B) are loaded during said first rotational phase and release their elastic energy on the two shafts (11, 12) by means of said first coupling means (15A, 15B) when said first rotational phase has been completed.