Bimetal Trip Device for MCCB Over-Current Protection
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Solution Overview
Problem
Current trip devices for molded case circuit breakers (MCCBs) face challenges in sensitivity during over-current interruptions for low-voltage MCCBs and lack distinct over-current interruption characteristics for high-voltage MCCBs, with existing bimetal types either being inadequate for low-voltage sensitivity or overly deformed for high-voltage applications.
Innovation Solution
A multi-purpose trip device is developed, incorporating both direct and indirect heating mechanisms using a bimetal with a direct heat unit and an indirect heat unit, partially fixed between power source and load side heaters, allowing for curvature when over-current or short-circuited currents flow, thereby enhancing sensitivity and reliability across both low and high voltage MCCBs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a direct heating type trip device is used, then sensitivity during over-current interruption is improved, but the bimetal is overly deformed and reliability during short-circuit interruption deteriorates
Solution Approach 1:
The bimetal is divided into two functional segments: a direct heat receiving unit that contacts the power source side heater for sensitive over-current detection, and an indirect heat receiving unit that faces the power source side heater for stable short-circuit response. This segmentation allows each unit to perform its specific function optimally without the drawbacks of the other approach.
2Reliability
If an indirect heating type trip device is used, then reliability during short-circuit interruption is improved, but sensitivity during over-current interruption deteriorates
Solution Approach 1:
Different portions of the bimetal structure are given different thermal coupling characteristics to the heater. The direct heat receiving unit has high thermal coupling for sensitivity, while the indirect heat receiving unit has lower thermal coupling for stability. This local differentiation of thermal properties resolves the contradiction between sensitivity and reliability.
3Measurement precision
If a trip device is designed for low-voltage MCCBs, then sensitivity during over-current interruption is improved, but adaptability to high-voltage MCCBs deteriorates
Solution Approach 1:
The trip device achieves multi-functionality by combining both direct and indirect heating mechanisms in a single bimetal structure. This dual-mode operation allows the same device to be effectively applied to both low-voltage MCCBs (where sensitivity is critical) and high-voltage MCCBs (where stability is critical), making it a universal solution across different voltage applications.
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 multi-purpose trip device improves sensitivity and reliability in interrupting over-currents and short-circuited currents, effectively addressing the limitations of existing bimetal types by combining direct and indirect heating effects, enabling its application in both low and high voltage MCCBs.
Implementation Method 1
a power source side heater connected to a power source side of a molded case circuit breaker (MCCB) to receive current; a load side heater connected to a load side of the MCCB to receive the current
Implementation Method 2
a bimetal including a direct heat unit contacting the power source side heater and an indirect heating unit facing the power source side heater, wherein the bimetal is partially fixed between the power source side heater and the load side heater and is curved when over-current or short-circuited current flows in the MCCB
Data Source
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AI summary
A trip device is disclosed, the device comprising: a power source side heater connected to a power source side of a molded case circuit breaker (MCCB) to receive current; a load side heater connected to a load side of the MCCB to receive the current; and a bimetal including a direct heat unit contacting the power source side heater and an indirect heating unit facing the power source side heater, wherein the bimetal is partially fixed between the power source side heater and the load side heater and is curved when over-current or short-circuited current flows in the MCCB.