Vacuum Switching Device with External Spring Contact for NSDD Control
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Solution Overview
Problem
Vacuum switches in medium and high-voltage switchgear face issues such as non-sustained disruptive discharges (NSDD) and welding of switching contacts due to high impact speeds or slow closing movements, which damage the contacts and reduce their effectiveness.
Innovation Solution
A vacuum switching device with a spring contact outside the vacuum chamber, connected to the drive rod via an actuator rod with a modified cross-sectional contour, provides targeted friction and resistance to control the closing movement, interrupting the current path twice to minimize NSDD and reduce bouncing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the moving contact is strongly accelerated by a strong drive spring to close the switchgear quickly, then the switching speed is improved, but the impact speed becomes too high causing welding of contacts and damage to the vacuum interrupter
Solution Approach 1:
A buffer element is introduced into the drive mechanism that absorbs excess kinetic energy before the contacts make final contact. This cushioning element is positioned and dimensioned to engage when the moving contact approaches the stationary contact, reducing the impact speed to a safe level while maintaining the overall fast switching performance.
Solution Approach 2:
The drive spring characteristics are optimized by selecting specific material properties and geometric parameters (wire diameter, coil spacing, active coils) to achieve the desired force-displacement curve. The spring is designed to provide high initial acceleration followed by a controlled force reduction, transforming the abrupt ballistic motion into a more controlled closing sequence that maintains speed while reducing impact.
2Object-affected harmful factors
If the closing movement is slowed down to prevent contact welding, then contact damage is reduced, but the switching speed becomes too slow causing arc burning on contact surfaces
Solution Approach 1:
The drive mechanism utilizes a two-phase action pattern: an initial high-force phase that rapidly accelerates the moving contact, followed by a buffer engagement phase that absorbs excess energy. This periodic variation in force application allows the contacts to close quickly enough to prevent arc burning while ensuring the final impact velocity remains below welding thresholds.
3Reliability
If a vacuum tube with parallel contact surfaces is used to achieve high breaking capacity and small contact gap, then the breaking capacity is improved, but the contacts are vulnerable to welding and vacuum interrupter damage from high impact speeds
Solution Approach 1:
The buffer element serves as an intermediary component between the drive spring and the moving contact. It mediates the energy transfer by absorbing excess kinetic energy, thereby protecting the vulnerable parallel contact surfaces of the vacuum interrupter from welding while preserving the high breaking capacity enabled by the vacuum tube design.
4Use of energy by moving object
If the contacts are mechanically closed after arc creation to dissipate kinetic energy through deformation and bouncing, then the kinetic energy is dissipated, but the contacts can fuse together due to prior melting
Solution Approach 1:
The buffer element prevents the kinetic energy from being converted into contact deformation and bouncing by absorbing it in advance. This eliminates the thermal cycle of melting and potential fusion that would otherwise occur during mechanical closing, while still allowing controlled energy dissipation through the buffer's elastic or viscoelastic properties.
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 solution effectively reduces NSDD occurrences and minimizes contact bouncing, preventing welding and damage to contact surfaces, enhancing the reliability and performance of vacuum switches.
Implementation Method 1
the spring contact resting on the actuator rod allows for targeted friction to be set between the spring contact and the actuator rod, creating appropriate resistance when the actuator rod moves
Implementation Method 2
a technical vacuum at approximately 10 -6 bar (abs). Accordingly, the switches are referred to as gas switches or vacuum switches
Implementation Method 3
the actuator rod has a modified cross-sectional contour along a switching axis... allowing for targeted friction to be set between the spring contact and the actuator rod
Data Source
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AI summary
The invention relates to a vacuum switching device (20) for medium or high voltages, comprising two contacts (22, 24), at least one contact (22) of which is mechanically movably mounted by means of a drive rod (26) and thus is in electrical contact with said drive rod (26), wherein the vacuum switching device (20) has a vacuum chamber (28) in which the contacts (22, 24) are arranged. The invention is characterised in that the vacuum switching device has a spring contact, which is outside the vacuum chamber (28), and the drive rod (26), when the contacts (22, 24) are closed, is in electrical contact with a power line via the spring contact (32), and in that the spring contact (32), when the contacts (22, 24) are open (34), is electrically insulated from the drive rod (26).