DC Circuit Breaker Magnet Assembly for Bidirectional Arc Quenching
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Solution Overview
Problem
Conventional miniature circuit breakers are not designed for direct current (DC) applications and face challenges in driving arcs into arc chambers, particularly at low DC currents, due to unidirectional current flow issues with permanent magnets, leading to increased size and cost in implementing effective DC circuit breakers.
Innovation Solution
An electrical switching apparatus with a movable contact and dual arc chambers, utilizing a single permanent magnet to create a generally unidirectional magnetic field that directs arcs into specific arc chambers based on current flow direction, enabling bidirectional current operation without significant size or cost increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional AC MCBs are applied in DC applications with multiple poles connected in series, then the required interruption performance is achieved, but the device complexity and size increase significantly
Solution Approach 1:
The patent designs a single-pole DC MCB that can handle bidirectional current flow (both positive and negative polarity) using a universal magnetic field generation approach. The permanent magnet assembly creates a magnetic field that effectively drives arcs into arc chambers regardless of current direction, eliminating the need for multiple poles or separate breakers for different current directions. This universal design achieves DC interruption performance comparable to multi-pole AC MCB configurations while maintaining single-pole simplicity.
2Reliability
If permanent magnets are used to drive arcs into arc chambers in DC electrical switching apparatus, then arc extinction is improved, but the device size and cost increase significantly for bidirectional current operation
Solution Approach 1:
The patent merges the functions of multiple permanent magnets into a single integrated magnet assembly that serves both positive and negative current directions. Instead of using separate magnets for each current direction (which would double the magnet count and complexity), the invention employs one permanent magnet assembly positioned to generate an effective magnetic field for bidirectional arc driving. This consolidation maintains reliable arc extinction while significantly reducing device complexity and cost.
3Device complexity
If a single permanent magnet is used to create a unidirectional magnetic field, then device size and cost are reduced, but the ability to handle bidirectional current flow is limited
Solution Approach 1:
The patent employs an asymmetric magnetic circuit design where the permanent magnet assembly is positioned and configured to create a magnetic field that is asymmetric with respect to the arc chamber geometry. This asymmetric configuration allows the magnetic field to effectively drive arcs into the arc chamber regardless of whether the current flows in the positive or negative direction. The asymmetry in magnetic path design enables bidirectional current handling while maintaining a single permanent magnet assembly.
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 solution allows for efficient DC current switching and arc quenching across a wide current range, including low currents, with reduced costs and size, achieving bidirectional switching and minimal arc flash, suitable for applications up to 750 VDC.
Implementation Method 1
a magnet assembly comprising a permanent magnet disposed between the first and second arc chambers, said permanent magnet cooperating with the first and second arc chambers to establish a generally unidirectional magnetic field normal to the longitudinal axes of the first and second arc chambers
Implementation Method 2
the generally unidirectional magnetic field causes one of the first arc and the second arc to enter one of the first and second arc chambers, respectively, depending upon a direction of current flow
Implementation Method 3
The arc transfers to the arc plates where it is stretched, split and cooled until extinguished
Data Source
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AI summary
An electrical switching apparatus (2) includes two arc runners (4,6), two contacts (8,10) in electrical communication with the respective runners, a movable contact (12) having two portions (14,16) respectively cooperating with the contacts to provide closed and open contact positions, and two arc chambers (18,20) each including two ends (22;30,24;32), a longitudinal axis (26;34) therebetween, and arc plates (28;36) between the ends. A magnet assembly (40) cooperates with the arc chambers (18,20) to establish a generally unidirectional magnetic field (42) normal to the axes, normal to a first direction (44) of a first arc (46) between one contact (8) and the first portion (14) as it moves away from the closed toward the open contact position, and normal to an opposite second direction (48) of a second arc (50) between the other contact (10) and the second portion (16) as it moves away from the closed toward the open contact position. The magnetic field causes one arc to enter one arc chamber depending upon current flow direction between the contacts.