Motor Protector Contact Structure for Fast Open-Phase Trip
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Solution Overview
Problem
Existing motor protectors for hermetic electric compressors fail to quickly respond to open-phase lock currents without compromising overheat protection characteristics, particularly in compressors with small rated outputs where the open-phase lock current is small, leading to delayed temperature rise and potential motor burnout.
Innovation Solution
A motor protector design featuring a hermetic container with a movable contact point mechanism, including a thermal reaction plate that deforms to open circuits when a predetermined temperature is reached, and a fixed contact point support body with a specific width dimension ratio to ensure rapid response to open-phase lock currents without sacrificing overheat protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the operating temperature of the thermal reaction plate is lowered to shorten response time, then the response time to open-phase lock current is reduced, but the overheat protection characteristics are sacrificed
Solution Approach 1:
The patent divides the thermal reaction plate into multiple independent heating regions: a first heating region for open-phase lock current detection and a second heating region for overheat protection. This segmentation allows each region to have different operating temperatures and response characteristics, resolving the contradiction between fast response and reliable overheat protection
Solution Approach 2:
Different portions of the thermal reaction plate are assigned different thermal properties and operating temperatures. The first heating region operates at a lower temperature for rapid response to open-phase conditions, while the second heating region operates at a higher temperature for stable overheat protection, allowing each local area to optimize for its specific function
2Volume of moving object
If the rated output of the compressor is small, then the device size is reduced, but the open-phase lock current becomes smaller causing delayed temperature rise
Solution Approach 1:
The heating function is segmented into two distinct regions with different design priorities. The first heating region is optimized for small compressors with low open-phase lock currents by using lower thermal mass and lower operating temperature, enabling rapid response even with minimal heating power available from small compressors
Solution Approach 2:
The patent changes the operating temperature parameter of the first heating region to be lower than traditional designs, which reduces the thermal mass required and allows faster temperature rise. This parameter change enables small compressors to achieve rapid protection response despite having smaller open-phase lock currents
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 enables rapid disconnection of power supply to the motor in response to open-phase lock currents, preventing overheating and potential motor burnout, while maintaining effective overheat protection.
Implementation Method 1
the temperature of the motor rises rapidly due to Joule heat
Implementation Method 2
the thermal reaction plate operates due to the ambient temperature inside the compressor
Data Source
AI summary
A motor protector according to an embodiment includes a hermetic container, two conducting terminal pins, two fixed contact point support bodies, two fixed contact points, two movable contact points, and a thermal reaction plate. The fixed contact point support body is configured, by bending work on a plate material, to integrally include a conducting terminal pin side region, a fixed contact point side region arranged such that a space region is sandwiched therebetween and provided with a fixed contact point, and a connection region provided across the space region and connecting the conducting terminal pin side region and the fixed contact point side region. The total width dimension of the connection region is set to be smaller than the total width dimension of the space region.