Circuit Breaker Bimetal Current Sensing Thermal Compensation
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Solution Overview
Problem
Circuit breakers with bimetal elements face inaccuracies in current sensing due to variations in bimetal impedance with temperature, leading to potential incorrect tripping and performance issues in control algorithms.
Innovation Solution
A circuit breaker design that includes a temperature sensor distal from the bimetal, using a real-time thermal model and processor to calculate corrected temperature-dependent resistance, allowing for accurate current sensing without requiring direct contact with the bimetal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the bimetal element's impedance variation with temperature is not compensated, then the current sensing is simpler, but the measurement precision deteriorates due to up to 70% impedance variation
Solution Approach 1:
The patent introduces a temperature sensor as an intermediary element that indirectly measures the bimetal temperature. Instead of directly measuring the bimetal's temperature (which would require contact), the system uses a temperature sensor positioned near the bimetal to sense temperature changes and uses this information to compensate for impedance variations in current sensing.
Solution Approach 2:
The patent replaces direct physical contact measurement with an indirect sensing approach. Instead of requiring the temperature sensor to be in contact with the bimetal element, the system uses the temperature sensor's proximity-based measurement combined with computational compensation algorithms to achieve accurate temperature-dependent impedance correction.
2Measurement precision
If a temperature sensor is placed in close proximity to the bimetal element, then the temperature sensing is more accurate, but the sensor is subjected to extreme temperatures that may affect its performance
Solution Approach 1:
The temperature sensor acts as an intermediary that indirectly measures the bimetal temperature without being in direct contact. By positioning the sensor near the bimetal element rather than in direct contact, the system achieves sufficient temperature sensing accuracy while protecting the sensor from extreme temperature conditions that would compromise its reliability.
3Reliability
If the bimetal resistance variation with temperature is not accounted for, then the device operation is simpler, but errant tripping may occur due to incorrect current measurement
Solution Approach 1:
The patent implements a feedback mechanism where the temperature sensor continuously monitors temperature changes near the bimetal element, and this temperature information is fed back to the control system. The control system uses this feedback to dynamically compensate for resistance variations, ensuring accurate current measurement and preventing erroneous tripping decisions.
Solution Approach 2:
The patent replaces complex mechanical temperature compensation mechanisms with an electronic sensing and computational compensation system. Instead of using mechanical means to compensate for resistance variations, the system uses a temperature sensor combined with electronic processing to calculate and apply the necessary compensation, simplifying the overall device architecture while improving 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
This approach provides accurate current measurement and reduces the risk of errant tripping by compensating for bimetal resistance variations with temperature, enhancing the performance of control algorithms and reliability of circuit breakers.
Implementation Method 1
a bimetal, which heats and bends in response to a persistent overcurrent condition
Implementation Method 2
the bimetal impedance has a positive temperature coefficient (PTC). In other words, resistance increases with temperature
Implementation Method 3
a temperature sensor distal from the bimetal, the temperature sensor including an output having a signal representative of ambient temperature
Data Source
AI summary
A circuit breaker includes a bimetal electrically connected in series with separable contacts, and an operating mechanism structured to open and close the contacts. A temperature sensor distal from the bimetal includes an output having an ambient temperature signal. A trip circuit includes a first circuit having a first input electrically interconnected with a bimetal output to input a voltage representative of current, a second input electrically interconnected with the temperature sensor output to input the ambient temperature signal, a real-time thermal model structured to provide a corrected temperature dependent bimetal resistance as a function of the voltage and the ambient temperature signal, and an output including a current value which is a function of the ambient temperature signal and the corrected bimetal resistance. A second circuit includes an input having the current value and an output structured to actuate the operating mechanism in response to predetermined current conditions.