Magnetic Trip Device with Closed Magnetic Circuit
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Solution Overview
Problem
Existing magnetic trip devices for circuit breakers or contactors face challenges in maintaining the shunt contact open with alternating current due to high force/current ratios, requiring a large number of coil turns and complicating adjustment and manufacturing, while also being difficult to manufacture and having reduced breaking performance.
Innovation Solution
A magnetic trip device with a closed magnetic circuit formed by the first fixed and second mobile parts, featuring a central part extending inside the coil and a cavity for the third mobile part, allowing a reduction in coil turns and size, and independent springs for each movable part to optimize movement and force distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a guide and insulating tube are used to create a parasitic air gap, then the first moving core can be returned to position, but the force-to-current ratio of the Frager coil is significantly degraded
Solution Approach 1:
The patent removes the guide and insulating tube that created the parasitic air gap from the magnetic circuit. By extracting this unnecessary component, the magnetic flux path is improved and the force-to-current ratio is restored without compromising the return mechanism functionality.
2Force
If the number of coil turns is increased to compensate for degraded force-to-current ratio, then the magnetic force is sufficient, but the device size and complexity increase
Solution Approach 1:
The patent converts the harmful effect of the parasitic air gap into a benefit by removing the source of the problem (the guide and insulating tube). This eliminates the need for additional coil turns while maintaining sufficient magnetic force, thereby reducing device complexity.
3Adaptability or versatility
If the second moving core must simultaneously repel the shunt contact, compress the spring, actuate the release, and tear off the breaking contact, then all functions are achieved, but a large magnetic force is required
Solution Approach 1:
The patent employs a Frager loop mechanism that performs preliminary action by maintaining magnetic force during the entire operation sequence. The Frager loop ensures that the magnetic field remains active and sufficient to handle all required functions (repelling shunt contact, compressing spring, actuating release, and tearing off breaking contact) without requiring an excessive peak force.
4Volume of moving object
If the two moving cores are coaxial with the first moving core sliding inside the second, then the structure is compact, but the air gap areas are limited
Solution Approach 1:
The patent segments the magnetic circuit into distinct components (first moving core, second moving core, Frager loop) with separate magnetic flux paths. This segmentation allows each component to have optimized air gap areas without being constrained by a coaxial sliding configuration, thereby increasing the effective air gap area while maintaining compactness.
5Measurement precision
If the spring is adjusted to calibrate the first thermal threshold, then the thermal threshold is set correctly, but the second magnetic activation threshold is also modified
Solution Approach 1:
The patent segments the threshold adjustment mechanisms by introducing a dedicated adjustment element for the second magnetic activation threshold that is independent of the spring adjustment for the thermal threshold. This allows precise calibration of the thermal threshold via spring adjustment without affecting the magnetic threshold, enabling independent tuning of both parameters.
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 reduces the size of the electrical switching device, facilitates adjustment, and enhances breaking performance by minimizing parasitic air gaps and optimizing magnetic field channeling, ensuring reliable operation and efficient contact opening.
Implementation Method 1
the magnetic force on the first moving core must counteract the contact force of the shunt contact
Implementation Method 2
a magnetic shunt zone of the first moving core will saturate
Implementation Method 3
the second moving core will quickly close (because its activation threshold is significantly lower), a magnetic shunt zone of the first moving core will saturate, and a second moving core will close
Data Source
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AI summary
The invention relates to a magnetic trip unit for an electrical switching device such as a circuit breaker or contactor, comprising a coil (40), a yoke (60) forming the core of the coil (40), a first spring element (80), and a second spring element (82). The yoke (60) comprises a first fixed part (62), a second movable part (64), and a third movable part (66). The coil (40), the yoke (60), the first spring element (80), and the second spring element (82) are configured and arranged to cause the second movable part (64) to move from a disengaged position (PE) to an engaged position when the coil (60) carries a current of a first intensity, and configured and arranged to cause the third movable part (64) to move from a rest position (PR) to an actuated position when the coil (40) carries a current of a second intensity greater than the first intensity.