Thermal Actuator with Segmented Direct and Indirect Heating
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Solution Overview
Problem
Existing electrical installation switching devices, such as main circuit breakers, are not suitable for very high rated currents (100A and more) due to mechanical complexity and increased metal usage with indirect heating, and mechanical simplicity is compromised with direct heating at high currents.
Innovation Solution
A thermal release mechanism that combines partial direct and indirect heating by arranging a conductor plate along the thermal bimetallic strip, allowing direct heating in one-third of its length and indirect heating in the rest, maintaining the same strip dimensions and simplifying the mechanical structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct heating is used for high rated currents, then mechanical structure is simple, but heating effectiveness and switching function deteriorate due to increased tolerance influences and reduced heating length
Solution Approach 1:
The thermal bimetallic strip is divided into multiple heating zones with different heating methods: direct heating in the first region (near clamping point) and indirect heating in the second region (toward free end). This segmentation allows each region to be optimized for its specific function, maintaining mechanical simplicity where direct contact is needed while ensuring reliable heating where thermal coupling is required.
Solution Approach 2:
Different heating methods are applied to different regions of the bimetallic strip based on local requirements. The first region uses direct heating for mechanical simplicity and robust current carrying, while the second region uses indirect heating for controlled thermal coupling and reliable switching function. This local differentiation resolves the contradiction between structural simplicity and functional reliability.
2Reliability
If indirect heating is used for high rated currents, then heating effectiveness is maintained, but mechanical complexity increases and metal usage increases unnecessarily
Solution Approach 1:
Instead of applying indirect heating to the entire bimetallic strip, the patent segments the heating approach so that only the second region (portion) receives indirect heating through the conductor plate. The first region maintains direct heating with simple mechanical connection, reducing overall mechanical complexity while preserving switching function where it matters most.
Solution Approach 2:
Indirect heating via conductor plate is applied locally only to the second region of the bimetallic strip where thermal coupling is most effective for actuation, rather than throughout the entire strip. This localized approach maintains switching reliability while minimizing mechanical complexity and metal usage in other regions.
3Manufacturing precision
If cross-sectional area of bimetal is increased for high rated currents, then heating and deflection tolerance is improved, but volume of bimetal and metal usage increase unnecessarily
Solution Approach 1:
The bimetallic strip is segmented into regions with different heating methods, allowing the cross-sectional area to be optimized for each region's function. The first region can have smaller cross-section for current carrying with direct heating, while the second region has sufficient cross-section for effective thermal coupling and switching actuation, reducing overall metal usage while maintaining manufacturing precision.
Solution Approach 2:
The heating method parameter is changed from uniform direct heating to a combination of direct and indirect heating in different regions. This parameter change allows the cross-sectional area parameter to be optimized differently in each region, reducing overall metal volume while maintaining the heating and deflection tolerance required for high rated currents.
4Reliability
If indirect heating is used, then heat input can be adapted to bimetallic strip, but mechanical complexity increases due to ensuring stable heat transfer
Solution Approach 1:
The thermal coupling is segmented so that indirect heating via conductor plate is applied only to the second region of the bimetallic strip, not the entire strip. This reduces the complexity of ensuring stable heat transfer across the whole structure, as the conductor plate only needs to maintain reliable thermal coupling in the critical actuation region rather than throughout the entire bimetallic strip.
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
Enables the use of the same thermal bimetallic strip for both low and high currents, reducing mechanical complexity and metal usage, while ensuring effective heat transfer and arc quenching, thus supporting high current applications with improved mechanical simplicity and efficiency.
Implementation Method 1
The resulting Joule heat in the thermobimetal strip ensures that the thermobimetal strip bends out
Implementation Method 2
Its heat is transferred to the thermal bimetallic strip by radiation, thermal conduction or convection and thereby heats it up indirectly
Implementation Method 3
Thermal bimetallic strip, which bends due to heating at a current above the nominal current
Data Source
Figure 1
Figure 2
AI summary
The breaker has a conductor plate connected at a current lead-out part (27). The conductor plate is extended toward direction of a free end of a double metal band sheet (5) from the current lead-out part and isolated from the double metal band sheet. Another current lead-out part (28) is arranged at an end part of the conductor plate opposite to the former current lead-out part. Movable conductors (25, 25') are connected at the latter current lead-out part for connecting the latter current lead-out part with a movable or fixed contact (7). An independent claim is also included for an electrical mounting switch equipment.