Thermally Responsive Switch Helium Arc Suppression
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Solution Overview
Problem
Thermally responsive switches used in compressors face challenges with cadmiumless contacts, requiring high durability and current cutoff performance while maintaining a small size, as existing solutions either compromise on size or reduce current cutoff performance when replacing silver-cadmium oxide contacts.
Innovation Solution
A thermally responsive switch with a hermetically sealed container using silver-tin oxide system contacts and filled with helium gas at specific pressures to enhance durability and current cutoff performance, preventing contact welding and arc damage, allowing for a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver-cadmium oxide contacts are replaced with cadmiumless contacts, then environmental compliance is improved, but current cutoff performance is reduced by half
Solution Approach 1:
The patent changes the material composition parameter of the contacts from silver-cadmium oxide to silver-tin oxide, and simultaneously changes the gaseous environment parameter from air to helium-filled container. These parameter changes enable the use of environmentally friendly cadmiumless contacts while maintaining high current cutoff performance through the helium atmosphere's arc-suppressing properties.
Solution Approach 2:
The patent employs an inert helium atmosphere within the container to replace the harmful cadmium-based contacts. The helium gas creates an inert environment that suppresses arc generation and contact welding, allowing cadmiumless silver-tin oxide contacts to achieve performance equivalent to or better than traditional silver-cadmium oxide contacts.
2Reliability
If contact size is increased to improve current cutoff performance, then durability is improved, but device size increases making it difficult to mount in hermetic housing
Solution Approach 1:
The patent uses the pneumatic properties of helium gas at controlled pressure (0.3 to 0.7 atmosphere) to suppress arcs and prevent contact welding. This pneumatic approach allows the use of smaller contacts while maintaining high current cutoff performance, as the helium atmosphere provides arc suppression without requiring larger contact surfaces.
Solution Approach 2:
The patent changes the gaseous environment parameter from air to helium at specific pressure ranges, which fundamentally alters the arc behavior and contact performance characteristics. This parameter change enables smaller contact dimensions to achieve the same or better current cutoff performance that would otherwise require larger contacts in atmospheric conditions.
3Reliability
If thermally responsive plate size is increased to increase separating force, then contact welding is reduced, but device size increases
Solution Approach 1:
The patent employs the pneumatic pressure of helium gas (0.3 to 0.7 atmosphere) to assist in arc suppression and contact separation. The pressurized helium atmosphere provides additional force to help separate contacts during arcing events, reducing the need for a larger thermally responsive plate while maintaining effective contact separation capability.
Solution Approach 2:
The inert helium atmosphere reduces the severity of arc damage and contact welding, which means that a smaller thermally responsive plate is sufficient to provide the necessary separating force. The helium environment protects the contacts from severe welding effects, allowing reduced plate dimensions while maintaining reliability.
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 solution provides high durability and effective current cutoff performance without increasing the switch's size, with the helium-filled environment allowing arcs to move on contact surfaces, reducing damage and maintaining equivalent performance to cadmium-based systems.
Implementation Method 1
The thermally responsive plate reverses a direction of curvature at a predetermined temperature
Implementation Method 2
When current having such a large inductively is cut off by the opening of contacts, arc is generated between the contacts
Implementation Method 3
the container is filled with a gas containing helium ranging from 50% to 95% so that an internal pressure of the container ranges from 0.35 atmosphere to 0.7 atmosphere
Data Source
AI summary
A thermally responsive switch includes an airtight container including a metal housing and a header plate, conductive terminal pins airtightly fixed to the header plate, a fixed contact fixed to the conductive terminal pin, a thermally responsive plate one end of which is conductively connected to and fixed to the inner surface of the airtight container and the bending direction of which is reversed at a predetermined temperature, and a movable contact fixed to the other end of the thermally responsive plate. In the thermally responsive switch, the movable contact and the fixed contact are composed of a silver tin oxide based contact and gas containing 50% or more and 95% or less of helium is encapsulated in the airtight container in such a manner that gas pressure is equal to or more than 0.35 and equal to or less than 0.7 at ordinary temperature.