Surge Protector Thermal Disconnector Blade Design
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Solution Overview
Problem
Overvoltage protection devices, particularly those with thermal disconnectors, face challenges in effectively disconnecting varistors during thermal runaway and withstanding high short-circuit currents without causing fires, especially in direct current installations and under transient overvoltage conditions.
Innovation Solution
A protection device with a conductive blade forming a one-piece part with a connection terminal, designed to maintain current passage without contact resistance, and enhanced thermal disconnection mechanisms, including a hot-melt solder and a torsion spring, to rapidly disconnect the varistor when it reaches a threshold temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermal disconnector with a low-temperature solder joint is used to disconnect the varistor during thermal runaway, then the varistor can be isolated from the electrical installation, but the solder joint may tear off during electrical surges before thermal runaway occurs
Solution Approach 1:
The patent merges the fixed contact and the blade into a single integral piece made of highly conductive material. This eliminates the solder joint between these two components, removing the weak link that could fail during electrical surges while maintaining the thermal disconnection function through the remaining solder joint connecting the blade to the varistor.
Solution Approach 2:
The patent changes the material parameter of the fixed contact and blade assembly to have very high electrical conductivity (greater than 70% IACS). This parameter change reduces resistive heating and improves the ability to withstand electrical surges without causing the solder joint to fail, while still allowing thermal runaway detection to function.
2Reliability
If the conductive parts are made of materials with contact resistance to enable thermal protection, then the thermal disconnector can detect overheating, but the heating during electrical surges may cause the solder to tear off
Solution Approach 1:
The patent applies local quality by concentrating the thermal sensing function at the solder joint between the blade and the varistor, while the fixed contact and blade assembly use highly conductive material to minimize unwanted heating. The integral design ensures uniform heat distribution to the sensing joint without creating hot spots that could cause premature solder failure.
3Reliability
If the blade is designed to move freely for thermal disconnection, then the varistor can be disconnected during thermal runaway, but the blade may open during electrical surges due to mechanical stress
Solution Approach 1:
By merging the fixed contact and blade into one integral piece, the patent eliminates the interface between these components where mechanical stress could cause premature opening. The single-piece construction provides inherent mechanical strength and stability while preserving the blade's ability to move for thermal disconnection through its connection to the varistor via the solder joint.
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 improves the resistance to short-circuit currents and ensures reliable operation by limiting heating and preventing uncontrolled electric arcs, thus enhancing the safety and efficiency of overvoltage protection in electrical installations.
Implementation Method 1
The melting of the solder joint causes the movable contact to move under the effect of the elastic stress, thus disconnecting the varistor
Implementation Method 2
The conductive blade and one of the two connection terminals are part of a single unit, which makes it possible to ensure passage of the current without any contact resistance
Implementation Method 3
the conductive element is elastically forced towards the opening
Data Source
Figure 1~13B
Figure 4~6
Figure 9~10
AI summary
The device has two connection terminals (38, 48) connecting the device to an electrical installation. An overvoltage protection component i.e. varistor (30), is electrically connected to the terminals. A thermal disconnector includes a conductor blade maintained in a position in which the blade assures electric connection between the component and one of the terminals. The disconnector moves the blade in another position when temperature of the component exceeds a present threshold value in which the electric connection is open in the latter position. The blade and the terminal are formed as a single part.