Circuit Interrupter Thermal Overload Prediction Using Shunt Wire Sensor
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Solution Overview
Problem
Existing circuit breakers, particularly miniature ones, face challenges in accurately tripping due to ambient temperature calibration issues and inaccuracies at higher current levels, leading to potential nuisance tripping or failure to protect against overloads in varying temperature environments.
Innovation Solution
A circuit interrupter equipped with a processor having a thermal overload predictive function and a shunt wire to measure current, along with a diode temperature sensor and nonvolatile memory for ambient calibration, enabling non-linear ambient temperature compensation and accurate tripping mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bimetals or analog circuits are used to provide thermal overload protection, then the circuit breaker can simulate thermal cooling of power conductors, but ambient temperature calibration issues and inaccuracies occur at higher current levels
Solution Approach 1:
The patent replaces the mechanical bimetal system with an electronic processor that calculates thermal overload conditions using measured current and temperature data. The processor computes instantaneous power (I²R), accumulates thermal energy over time, and compares it against calibrated thresholds to determine tripping, eliminating the physical bimetal's temperature simulation limitations and improving accuracy across varying ambient conditions.
Solution Approach 2:
The patent changes the operating parameters from fixed mechanical trip points to dynamically calculated thresholds based on real-time measurements. The system continuously monitors current, ambient temperature, and cumulative thermal energy, adjusting the trip decision based on these varying parameters rather than relying on a static bimetal response curve.
2Device complexity
If most circuit breakers are not ambient temperature compensated, then the device complexity is reduced, but tripping accuracy deteriorates in varying temperature environments
Solution Approach 1:
The patent replaces complex mechanical ambient temperature compensation mechanisms with an electronic sensor and processor system. The ambient temperature sensor provides input to the processor, which automatically adjusts the thermal overload calculation thresholds based on measured ambient conditions, achieving compensation through software algorithms rather than mechanical means.
Solution Approach 2:
The system implements feedback by continuously measuring ambient temperature and using this information to adjust the trip thresholds. The processor monitors the relationship between ambient temperature and conductor temperature, dynamically modifying the accumulation threshold to maintain accurate protection across different environmental conditions.
3Measurement precision
If shunt wire is used to measure current for thermal overload function, then measurement accuracy is improved, but power dissipation increases
Solution Approach 1:
The patent optimizes the shunt wire's electrical parameters, specifically selecting low-resistance materials and geometries to minimize power dissipation while maintaining sufficient signal level for accurate measurement. The system changes the measurement parameters by using differential voltage measurement across the shunt with high-input-impedance analog-to-digital converters, allowing accurate current measurement with minimal power loss.
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 improved accuracy and reliability in tripping at different current levels, reducing nuisance tripping and ensuring protection across varying ambient temperatures, while eliminating the need for mechanical moving parts and reducing power dissipation.
Implementation Method 1
a shunt wire in series with the separable contacts and being structured to measure current flowing through the separable contacts
Implementation Method 2
a shunt wire in series with the separable contacts and being structured to measure current flowing through the separable contacts
Implementation Method 3
The thermal overload predictive function may include a diode temperature sensor cooperating with the shunt wire
Data Source
AI summary
A miniature circuit breaker includes separable contacts, an operating mechanism structured to open and close the separable contacts, a microprocessor including a thermal overload predictive function, and a shunt wire in series with the separable contacts. The shunt wire is structured to measure current flowing through the separable contacts for the thermal overload predictive function and an arc fault protective function.