Composite Movable Contact Arm for Circuit Breaker
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Solution Overview
Problem
Movable contact arms in circuit breakers are limited by material strength and thermal conductivity requirements, leading to increased weight and moment-of-inertia, which hinder angular opening velocity and short-circuit interruption performance.
Innovation Solution
A lightweight, high-strength movable contact arm design with optimized size and shape, featuring a composite structure and reduced width-to-length ratio, coupled with spacers at the pivot portion to minimize moment-of-inertia and increase angular opening velocity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper or copper alloys are used for movable contact arm to ensure good electrical and thermal conductivity, then electrical and thermal performance is improved, but weight and moment-of-inertia increase
Solution Approach 1:
The movable contact arm is constructed as a composite structure with a copper core providing electrical and thermal conductivity, and a fiberglass reinforcement providing mechanical strength. This allows the arm to achieve the required structural integrity with less copper material, thereby reducing weight and moment-of-inertia while maintaining electrical and thermal performance.
Solution Approach 2:
The movable contact arm is divided into distinct functional segments: a copper core for electrical conduction and thermal management, and a fiberglass reinforcement layer for mechanical strength. This segmentation allows each material to be optimized for its specific function, reducing the total amount of heavy copper needed while maintaining overall performance.
2Strength
If the width of movable contact arm is increased to provide sufficient strength, then mechanical strength is improved, but moment-of-inertia increases and angular opening velocity decreases
Solution Approach 1:
By using a composite structure with fiberglass reinforcement, the contact arm achieves high mechanical strength without increasing width. The fiberglass provides structural rigidity and strength-to-weight ratio, allowing the arm to maintain sufficient strength with a narrower profile, thereby reducing moment-of-inertia and increasing angular opening velocity.
Solution Approach 2:
The fiberglass reinforcement is strategically positioned in areas where mechanical strength is most needed, such as along the length of the arm and at critical stress points. This localized reinforcement provides the necessary strength without uniformly increasing the width of the entire arm, thus minimizing the increase in moment-of-inertia.
3Reliability
If the length of movable contact arm is increased to maximize contact gap, then short-circuit interruption performance is improved, but moment-of-inertia increases
Solution Approach 1:
The composite construction with fiberglass reinforcement enables the contact arm to be made longer while maintaining low moment-of-inertia. The high strength-to-weight ratio of the composite material allows the arm to extend further from the pivot point, maximizing the contact gap for improved arc interruption, without proportionally increasing the moment-of-inertia that would occur with solid copper construction.
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 design enhances the angular opening velocity, reduces let-through current, and improves short-circuit interruption performance by minimizing weight and maximizing the gap between contacts, while maintaining sufficient strength and thermal conductivity.
Implementation Method 1
the movable contact arm has a moment-of-inertia and an angular opening velocity, and wherein the second width of the moving arm portion of the movable contact arm is less than the first width of the pivot portion of the movable contact arm to minimize the moment-of-inertia of the movable contact arm, thereby increasing the angular opening velocity
Data Source
Figure 1~3
Figure 4~5
Figure 6~8B
AI summary
A contact assembly for a circuit breaker includes a fixed contact, a movable contact, and a movable contact arm. The movable contact arm includes a first end (117) carrying the movable contact (112), a second end (119), and a pivot portion (121) proximate the second end. A moving arm portion extends from the first end toward the pivot portion. The moving arm portion has a width (125), an upper edge (728), a lower edge (730), and a height (726) defined by the distance between the upper edge and the lower edge. In response to a trip condition, the movable contact separates from the fixed contact and the movable contact arm pivots open at an angular opening velocity. The height of the moving arm portion of the movable contact arm is at least four times the width of the moving arm portion, thus minimizing the moment-of-inertia of the movable contact arm, and increasing the angular opening velocity.