Low-Voltage Circuit Breaker With Phase-Correct Rogowski Sensing
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Solution Overview
Problem
Conventional protection systems for low-voltage AC circuits are inadequate in detecting and extinguishing arcing faults within the required time frame, leading to potential equipment damage and safety risks due to the phase inaccuracy of current measurements using Rogowski coils.
Innovation Solution
A low-voltage circuit breaker design that incorporates Rogowski coils connected to an analog integrator and an analog-digital converter, with a microprocessor to compensate for phase shifts, enabling phase-accurate current determination for arc fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Rogowski coils are used for current measurement, then electrical isolation and high current capability are improved, but phase accuracy deteriorates due to stray field inductance
Solution Approach 1:
The patent replaces traditional shunt resistors with Rogowski coils for current measurement. Shunt resistors provide accurate phase information but cause power losses and cannot provide electrical isolation. Rogowski coils provide electrical isolation and handle high currents but introduce phase shifts due to stray field inductance. The patent compensates for this phase shift through calibration and signal processing techniques, thereby maintaining measurement precision while achieving electrical isolation.
2Device complexity
If conventional protection systems are used, then device simplicity is maintained, but arc fault detection speed and reliability deteriorate
Solution Approach 1:
The patent introduces an electronic trip unit with microprocessor-based arc fault detection algorithms that analyze voltage and current waveforms. This electronic system replaces or supplements conventional thermal-magnetic trip mechanisms, enabling detection of arc faults within milliseconds by identifying characteristic waveform distortions caused by arcs, thereby significantly improving detection reliability and speed.
Solution Approach 2:
The patent implements continuous monitoring of voltage and current signals with real-time analysis by the electronic trip unit. The system continuously compares measured values against predetermined thresholds and patterns, providing immediate feedback when arc fault conditions are detected, triggering rapid circuit interruption to prevent equipment damage and safety hazards.
3Measurement precision
If shunt resistors are used for current determination, then phase accuracy is improved, but power losses increase proportionally to current level
Solution Approach 1:
The patent replaces shunt resistors with Rogowski coils for current measurement. Shunt resistors dissipate power proportional to the square of the current (P=I²R), which becomes significant in high-current applications. Rogowski coils are inductive sensors that measure current through magnetic coupling without direct electrical contact, eliminating resistive power losses while maintaining measurement capability across the full current range.
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 solution allows for reliable detection of arcing faults, preventing unnecessary interruptions and ensuring the safety of low-voltage AC circuits by providing phase-accurate current measurements, thus enhancing protection and reducing damage.
Implementation Method 1
at least one Rogowski coil for determining the magnitude of the electric current of a conductor... which outputs an analog voltage (P1) which is equivalent to the magnitude of the electric current of the conductor
Implementation Method 2
the Rogowski coil (or each Rogowski coil) is connected to an analog integrator (each), which is followed by an analog-to-digital converter (each)
Data Source
Figure 1
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Figure 4~5
AI summary
The invention relates to a Rogowski coil for determining the magnitude of the electric current in a conductor of a low-voltage AC circuit, which outputs an analog voltage equivalent to the magnitude of the conductor's electric current. The Rogowski coil is connected to an analog integrator, followed by an analog-to-digital converter, which converts the integrated analog voltage into a digital signal. This digital signal is further processed by a microprocessor in such a way that the phase shift generated by the Rogowski coil and the components downstream of the Rogowski coil is compensated, thus providing phase-correct current values for fault detection to protect the low-voltage AC circuit, in particular a low-voltage circuit breaker.