Circuit Interrupter Fault Timing via Second-Derivative Edge Detection
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Solution Overview
Problem
Existing circuit interrupt devices struggle to accurately determine fault durations due to challenges with using current or voltage waveform zero-crossings, especially when faults start and end at non-zero-crossings and are affected by large perturbations from trip unit contacts.
Innovation Solution
The use of a time derivative, specifically a second derivative, of the current or voltage waveform to determine fault duration in circuit interrupt devices, allowing for the identification of local maxima or minima within specific time windows to set the starting and ending times for fault duration measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If zero-crossings are used to measure fault duration, then the measurement method is simple, but the measurement precision deteriorates when faults start and end at non-zero-crossings or when large perturbations are present
Solution Approach 1:
The patent transforms the measurement approach from direct zero-crossing detection to derivative-based peak detection. By computing the first derivative and then the second derivative of the current waveform, the method identifies fault start and end times through local maxima/minima in the derivative signals, which are more reliable indicators than zero-crossings under perturbed conditions
Solution Approach 2:
The patent introduces derivative calculations as intermediary processing steps between the raw current waveform and the fault duration measurement. The first derivative and second derivative act as intermediate signals that highlight the true fault boundaries by emphasizing rate of change, thereby mediating between the noisy original signal and the accurate measurement requirement
2Measurement precision
If the second derivative is computed for the entire waveform, then the fault duration determination is accurate, but the computational complexity increases
Solution Approach 1:
The patent divides the waveform analysis into distinct segments: a starting time window to identify fault initiation and an ending time window to identify fault termination. By segmenting the computation to only these relevant portions rather than processing the entire waveform, the method maintains measurement precision while reducing computational complexity
Solution Approach 2:
The patent applies partial action by computing the second derivative only within specific time windows that are sufficient to capture the fault characteristics, rather than computing it for the entire waveform duration. This partial computation provides adequate accuracy for fault duration determination while significantly reducing the computational burden
Data Source
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AI summary
Methods/systems for monitoring fault duration in circuit interrupt devices. The method includes performing edge detection using a second time derivative of a current or voltage waveform. The second derivative reveals peaks that may be used to establish starting and ending times for the fault duration. The second derivatives are calculated only for portions of the waveform within time windows that enclose the fault duration starting and ending times, respectively. The above arrangement provides a consistent way of determining durations of transitory events, such as durations of faults, and the like, that does not rely on waveform zero-crossings. The duration determinations may be implemented locally within a device, and/or the device may acquire and transfer underlying waveform data to an external system for the duration determinations. Data from multiple devices may be collected over time for analysis and modeling to provide remote support and monitoring of local devices via digital twins. Fig. 4