Electric Leakage Detecting Device Digital Filter Noise Suppression
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Solution Overview
Problem
Existing electric leakage detecting devices are prone to erroneous detection due to harmonic noise, surges, and abnormal waveforms, and struggle with high accuracy, especially when dealing with load-rectified waveforms, as they rely on analog comparators and lack effective filtering mechanisms.
Innovation Solution
An electric leakage detecting device that employs an A/D converter, digital filter, digital comparator, trip control signal generator, and delay counter to suppress high-frequency noise and accurately detect ground-fault currents by converting zero-phase current transformer signals into digital form, filtering out high-frequency components, and using threshold comparisons for precise detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If analog comparators are used for signal level detection, then the device complexity is reduced, but the measurement precision deteriorates due to dependency on analog comparator accuracy
Solution Approach 1:
The patent replaces the analog comparator system with a digital signal processing system consisting of an A/D converter, digital filter, and digital comparator. This substitution transitions from analog to digital domain, eliminating the limitations of analog comparator accuracy while maintaining relatively simple device architecture through standardized digital components.
2Device complexity
If no filtering mechanism is applied, then the device complexity is minimized, but the reliability deteriorates due to erroneous detection from harmonic noise and surges
Solution Approach 1:
The patent introduces a digital filter as an intermediary component between the A/D converter and the digital comparator. This filter acts as a mediator that selectively removes harmful high-frequency components (harmonic noise and surges) while preserving the fundamental frequency signal, thereby improving detection reliability without significantly increasing overall device complexity.
3Speed
If high-frequency noise is not suppressed, then the processing speed is maintained, but the measurement precision deteriorates due to erroneous detection of noise as leakage current
Solution Approach 1:
The patent applies preliminary filtering action by placing the digital filter in the signal processing chain before the final comparison and decision-making stages. The filter pre-processes the digital signal by attenuating high-frequency noise components before they reach the digital comparator, ensuring that subsequent processing operates on cleaned signal data without sacrificing processing speed.
4Device complexity
If analog signal processing is used, then the device complexity is reduced, but the adaptability deteriorates when dealing with load-rectified waveforms and abnormal waveforms
Solution Approach 1:
The patent changes the operating domain from analog to digital, enabling flexible parameter manipulation through software or digital logic. The digital filter can be configured with different cutoff frequencies and characteristics to adapt to various waveform types including load-rectified waveforms, while the digital comparator can adjust thresholds dynamically. This parameter flexibility provides high adaptability without requiring complex analog circuit redesign.
Data Source
AI summary
One embodiment provides an electric leakage detecting device for shutting off an AC electric circuit. A digital comparator generates a detection signal by comparing an output signal corresponding to output signals of a zero-phase current transformer with positive and negative thresholds, a control signal generator generates a control signal based on the detection signal, and a judging device generates a judgment signal if an electric leakage state is judged. In addition, a delay counter generates a final control signal if the judgment signal has been received continuously more than a first prescribed time, a reset counter resets every time the control signal is received, and resets the judging device and the delay counter if the control signal is not received in a second prescribed time, and a switch driving circuit shuts off the AC electric circuit based on the final control signal.