Stacked Bimetal Trip Unit for Miniature Circuit Breaker Width Reduction
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Solution Overview
Problem
Miniature circuit breakers face challenges in reducing width without compromising trip ratings or bimetal flexibility, as decreasing bimetal width reduces cross-sectional area and increasing thickness reduces flexibility, making thermal tripping and calibration difficult.
Innovation Solution
A trip unit design utilizing two stacked bimetals with identical cross-sectional areas and composition, attached in a front-to-back arrangement, with a pigtail conductor connected to both bimetals to maintain flexibility and consistency in tripping, allowing for a reduced overall width without sacrificing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the width of the bimetal is decreased to reduce the overall width of the circuit breaker, then the device width is reduced, but the cross-sectional area is reduced which compromises trip ratings and bimetal flexibility
Solution Approach 1:
The patent transitions from a single wide bimetal element to multiple narrower bimetal elements stacked in the depth dimension (front-to-back arrangement). This dimensional change allows the overall width to be reduced while maintaining the required cross-sectional area through the stacked configuration, thereby preserving trip ratings and flexibility despite the narrower profile.
Solution Approach 2:
The patent divides a single wide bimetal element into multiple narrower bimetal elements (first bimetal and second bimetal) that are stacked and attached together. This segmentation allows each individual bimetal to have reduced width while the combined stacked structure maintains the necessary cross-sectional area for proper tripping performance.
2Area of moving object
If the thickness of the bimetal is increased to maintain cross-sectional area, then the cross-sectional area is maintained, but the bimetal flexibility is substantially reduced rendering thermal tripping and calibration very difficult
Solution Approach 1:
Instead of using a single thick bimetal element, the patent segments the cross-sectional area into multiple thinner bimetal elements stacked together. This segmentation maintains the required cross-sectional area for trip ratings while preserving the flexibility needed for thermal tripping and calibration, as each individual element remains thin and flexible.
Solution Approach 2:
The patent creates a composite bimetal structure by stacking multiple bimetal elements together and attaching them front-to-back. This composite construction achieves the desired cross-sectional area through the combination of multiple elements rather than relying on a single thick element, thereby maintaining both area and flexibility.
3Length of stationary object
If the width of the bimetal is decreased in half-size or tandem circuit breakers, then the overall width is reduced, but the trip ratings are compromised
Solution Approach 1:
The patent uses the depth dimension (front-to-back stacking) to compensate for the reduced width. By stacking multiple narrower bimetal elements in the depth direction, the overall cross-sectional area is maintained, thereby preserving trip ratings even though the width is reduced for half-size or tandem applications.
Solution Approach 2:
The patent segments the required cross-sectional area into multiple narrower bimetal elements that are stacked together. This segmentation allows the width to be reduced while the stacked configuration maintains the total cross-sectional area necessary for the desired trip ratings.
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 stacked bimetal design enables a miniature circuit breaker to maintain the same trip ratings as a single bimetal with twice the width, while reducing the overall width to less than one inch, ensuring consistent and reliable thermal tripping.
Implementation Method 1
an overcurrent is detected when the fault current generates sufficient heat in a strip composed of a resistive element or bimetal
Implementation Method 2
The bimetal deflects in a predictable and repeatable manner across a thermal profile over a period of time
Implementation Method 3
For magnetic tripping in response to sudden overloads, a magnetic field induced relative to the magnetic yoke causes the armature to be moved relative to the yoke
Implementation Method 4
a magnetic field induced relative to the magnetic yoke causes the armature to be moved
Data Source
AI summary
A trip unit in a miniature circuit breaker having a plurality of stacked bimetal elements welded front-to-back at one end and attached to a load terminal. The bimetal elements are made of similar compositions and have the same thickness. The free ends are connected to a yoke and to a pigtail that is optionally wound around the yoke in which the bimetals are received. The pigtail is connected to the conductive blade of the trip unit. To attach the pigtail from one direction, a notch is formed in the free end of one of the bimetals, exposing part of the other bimetal behind it. Or, two notches are formed in a staggered relationship such that the pigtail connections can be made from either direction. The stacked relationship of the bimetal elements allows the overall width of the circuit breaker to be reduced without sacrificing its rating requirements with one bimetal.