Surge Arrester Cut-Off Switch Bimetal Dynamics
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Solution Overview
Problem
Existing surge arrester disconnect devices face challenges in maintaining sufficient switching speed and preventing mechanical triggering due to the rapid decrease of prestressing force with increasing switching travel, especially with the introduction of lead-free solders, which requires a stable manufacturing process and reduced preload force.
Innovation Solution
The solution involves a configuration of prestressing forces F1, F2, and F3 acting on the solder joint, where F1 is a low or zero force in the normal state, F2 is thermally induced to support desoldering, and F3 compensates for decreasing forces during the switching process, using materials like bimetals or memory metals to enhance switching performance and prevent mechanical triggering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a prestressing force acts permanently on the solder joint to achieve sufficient switching movement, then switching speed and separation distance are improved, but mechanical triggering risk increases
Solution Approach 1:
The prestressing force is made dynamic rather than static by using a bimetallic strip that adjusts the force based on temperature. At normal temperatures, the bimetallic strip maintains a low prestressing force to prevent mechanical triggering. When overheating occurs, the bimetallic strip deforms thermally to increase the prestressing force, enabling sufficient switching speed and separation distance during the critical desoldering and switching phases.
Solution Approach 2:
The prestressing force parameter is changed dynamically through thermal influence. The bimetallic strip changes its physical state and dimensions with temperature, thereby adjusting the prestressing force applied to the switching tongue. This parameter change allows the system to have low prestressing force during normal operation (preventing mechanical triggering) and high prestressing force during thermal events (ensuring effective switching).
2Reliability
If the prestressing force is reduced to prevent mechanical triggering, then false activation is prevented, but switching performance and speed deteriorate
Solution Approach 1:
The bimetallic strip is pre-configured to provide minimal prestressing force in the normal state, which is sufficient to maintain electrical connection stability and prevent mechanical triggering. When thermal influence occurs, the bimetallic strip automatically activates additional prestressing force through thermal deformation, providing the necessary force enhancement exactly when needed for effective switching without compromising normal operation reliability.
3Length of moving object
If a high prestressing force is used to ensure sufficient switching travel and speed, then switching capability is improved, but the preload force on the solder joint increases causing mechanical triggering
Solution Approach 1:
The bimetallic strip utilizes thermal expansion and differential thermal deformation to adjust the prestressing force. When the system overheats, the bimetallic strip deforms thermally, increasing the prestressing force applied to the switching tongue. This thermal-based force adjustment enables sufficient switching travel and speed during thermal events without applying high preload force during normal operation, thereby preventing mechanical triggering while ensuring adequate switching capability when needed.
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 configuration ensures improved switching performance and speed with increased separation distance, reducing the risk of mechanical triggering and providing reliable electrical isolation, especially at higher system voltages, while maintaining a compact design and avoiding cyclic reactivation.
Implementation Method 1
a second prestressing force F2, which is induced thermally and supports the desoldering process and/or the switching process
Implementation Method 2
a second prestressing force F2, which is induced thermally and supports the desoldering process and/or the switching process; this is the case, for example, when a switching tongue used as a separating element itself supports the thermal force effect or this force is even generated by itself, for example by being made of a material that has the necessary mechanical/thermal properties
Implementation Method 3
the solder is liquefied and an electrical connection is severed as a result of a switching movement of a part of the disconnection device specially provided for this purpose that is triggered
Data Source
Figure 1a
Figure 1b
Figure 2a
AI summary
The invention relates to a process for dimensioning an cut-off switch of arresting element for a surge absorber arrester whose switching motion movement is performed by a control tab that is adjusted by a permanently active spring force in the direction opposite to the holding force established by a protective solder. As per the invention, the force of the initial stress affecting the control tab and/or its solder location that generates an unsoldering force and/or a switching force, in addition to a permanently active initial stress, by at least one additional initial prestress force not dependent upon it, as well as supporting a supplementary switching force with an identical direction of flow, whereby its distribution of force is set in such a way at rest that when in rest moderate force affects the soldering location and a resulting force that is as great as possible conducts the switching motion during the unsoldering action.