Thermomagnetic Breaker Overload Protection with Dual Heating Bands
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Solution Overview
Problem
Existing thermal magnetic trip units with lower rated currents suffer from unreliable overload protection due to low temperature rising and minor deflection of the bimetallic strip, leading to difficulties in industrialized thermal tuning and increased manufacturing costs, as well as risk of damage from short-circuit currents.
Innovation Solution
The addition of a second heating band connected through a braided wire to the bimetallic strip forms an odd-numbered current loop, increasing the length and resistance of the circuit, enhancing temperature rising and deflection, and incorporating a thermal magnetic adjustable releaser for improved overload and short-circuit protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the bimetallic strip is directly connected to client terminals through braided wire, then heat dissipation is rapid, but temperature rising of the bimetallic strip is low and deflection is minor
Solution Approach 1:
The current loop is segmented into multiple heating sections by introducing first and second heating bands at different positions along the bimetallic strip. This segmentation allows heat to be generated at multiple locations, increasing overall temperature rising while maintaining controlled heat dissipation pathways.
Solution Approach 2:
Heating bands are introduced as intermediary elements between the client terminals and the bimetallic strip. These heating bands have higher resistance and generate heat locally, acting as thermal mediators that transfer energy to the bimetallic strip more effectively than direct wire connection.
2Power
If the bimetallic strip length is limited, then the device structure is compact, but heat output is low
Solution Approach 1:
Instead of requiring a longer bimetallic strip, heating bands are placed at specific locations along the strip to create localized high-heat-generation zones. This allows compact strip length while achieving sufficient total heat output through concentrated heating at critical positions.
Solution Approach 2:
The resistance parameter is changed by introducing heating bands made of materials with higher resistance than the bimetallic strip. This parameter change enables increased heat generation (Q=I²R) without changing the physical dimensions of the bimetallic strip, thereby maintaining compact structure while increasing power output.
3Object-affected harmful factors
If odd-numbered current loops are used between moving and static armatures, then magnetic fields counteract effectively, but the design complexity increases
Solution Approach 1:
The heating bands serve multiple functions: they act as current conduits, generate heat for bimetallic strip activation, and contribute to the odd-numbered current loop configuration for magnetic field counteraction. This multi-functionality reduces overall device complexity despite the sophisticated current loop design.
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 provides more reliable overload protection, easier thermal tuning, reduced manufacturing costs, and effective short-circuit current restriction, with improved deflection of the bimetallic strip and broader thermal tuning range, increasing the design margin for temperature rising and protecting the circuit.
Implementation Method 1
Current is flowing through the upper part of the first heating band, the lower part of the first heating band, the lower part of the bimetallic strip, the upper part of the bimetallic strip, the braided wire, the upper part of the second heating band, and the lower part of the second heating band, thus forming an odd-numbered current loop.
Implementation Method 2
the bimetallic strip in a current loop mainly depends on the heat generated by the bimetallic strip per se, however, such heat output is low due to the limited length of the bimetallic strip
Implementation Method 3
with the short-circuit current flowing through the overload protection device, a magnetic field occurs in the air gap enclosed by the static armature and the moving armature (the magnetic fields created by the currents flowing in inversed directions counteracts with each other)
Data Source
Figure 1
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AI summary
An overload protection device, comprising: a first heating band (i.e. terminal), a second heating band, a bimetallic strip, and a litzendraht wire; the lower part of the first heating band is mechanically connected to the lower part of the bimetallic strip; and the two ends of the litzendraht wire are respectively and mechanically connected to the upper part of the second heating band and the upper part of the bimetallic strip.