Motor Protector Heat-Generating Pins for Lock Current Response
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Solution Overview
Problem
Existing motor protectors for inverter-driven electric compressors struggle to distinguish between normal operation at or below maximum rated current and abnormal conditions such as lock current, due to small differences in Joule heat generation, leading to unreliable protection.
Innovation Solution
A motor protector with an airtight container, conductive terminal pins, fixed and movable contacts, a heat-sensitive movable plate, and a heat generating member, designed to be exposed to refrigerant flow, which quickly responds to abnormal conditions by interrupting power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor protector relies on heat-sensitive movable plate operation based on ambient temperature or Joule heat, then it can provide protection against burnout, but it cannot reliably distinguish between normal operation at maximum rated current and abnormal lock current conditions in inverter-driven compressors
Solution Approach 1:
The invention divides the protection function into two independent parts: (1) the heat-sensitive movable plate for overheat protection based on ambient temperature, and (2) the refrigerant flow detection mechanism for detecting abnormal current conditions. This segmentation allows each component to specialize in one type of detection, improving overall reliability and measurement precision without interference between functions.
Solution Approach 2:
The invention introduces refrigerant flow as an intermediary indicator to indirectly detect abnormal current conditions. Instead of directly measuring current or temperature, the system uses the presence or absence of refrigerant flow (which changes during lock current conditions) as a mediator to trigger protection action, enabling reliable distinction between normal and abnormal operations.
2Reliability
If the motor protector is installed inside the compressor container to respond to winding temperature, then it can provide reliable overheat protection, but it responds slowly to abnormal current conditions due to thermal inertia
Solution Approach 1:
The invention separates overheat protection and abnormal current protection into two independent mechanisms: the heat-sensitive movable plate handles overheat protection with its inherent thermal response characteristics, while the refrigerant flow detection mechanism handles abnormal current detection with rapid response. This segmentation allows each mechanism to optimize its response characteristics for its specific function without compromise.
Solution Approach 2:
The refrigerant flow serves as a rapid-response intermediary that detects abnormal current conditions almost immediately when they occur, bypassing the thermal inertia limitation of the heat-sensitive movable plate. This intermediary mechanism provides fast protection action while the heat-sensitive plate continues to provide reliable overheat protection.
3Ease of operation
If the motor protector operates at maximum rated current to ensure protection, then it may cause excessive operation during normal conditions, but if it operates at higher current threshold, it may fail to detect lock current abnormalities
Solution Approach 1:
The invention divides the protection triggering mechanisms into two independent systems with different operating thresholds: the heat-sensitive movable plate responds to temperature conditions, while the refrigerant flow detection mechanism responds to flow conditions that occur during abnormal current operation. This segmentation eliminates the need to set a single current threshold, preventing both excessive operation and failure to detect abnormalities.
Solution Approach 2:
The refrigerant flow acts as an intermediary that provides an alternative triggering condition independent of current magnitude. During normal operation at maximum rated current, refrigerant flow remains sufficient and does not trigger protection. During lock current conditions, refrigerant flow decreases or stops, triggering protection. This intermediary mechanism resolves the threshold setting dilemma by using a different physical parameter altogether.
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 motor protector effectively suppresses excessive operation during normal conditions and ensures rapid intervention during abnormalities, providing reliable protection against excessive current or lock current.
Implementation Method 1
a heat-sensitive movable plate that is provided inside the airtight container and to which the two movable contacts are attached, the heat-sensitive movable plate causing the movable contacts in contact with the respective fixed contacts to close the two fixed contacts under a normal condition when the heat-sensitive movable plate is not in operation, and deforming in a direction that separates the respective movable contacts from the respective fixed contacts to open the respective fixed contacts when an ambient temperature inside the airtight container reaches a predetermined temperature
Implementation Method 2
a heat generating member that is connected and fixed to the conductive terminal pins outside the airtight container, is made of a material different from the conductive terminal pins, is located between each of the conductive terminal pins and a winding of a motor, and generates heat when a current flows
Data Source
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AI summary
A motor protector (20) includes: an airtight container (30) made of metal; two conductive terminal pins (40); two fixed contacts (21); two movable contacts (22); a heat-sensitive movable plate (25) that is provided inside the airtight container and to which the two movable contacts are attached, the heat-sensitive movable plate (25) causing the movable contacts in contact with the respective fixed contacts to close the two fixed contacts under normal conditions when the heat-sensitive movable plate is not in operation, and deforming in a direction that separates the movable contacts from the respective fixed contacts to open the respective fixed contacts when an ambient temperature inside the airtight container reaches a predetermined temperature and the heat-sensitive movable plate operates; and a heat generating member (50) that is provided outside the airtight container and in contact with the conductive terminal pins, is made of a material different from that of the conductive terminal pins, is located between the conductive terminal pin and a winding of a motor, and generates heat when a current flows.