Wiring Device Leakage Detection Using Human Body Frequency Filtering
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Solution Overview
Problem
Conventional wiring devices with leakage detection functions struggle to accurately detect and interrupt electrical leakage currents with distorted waveforms, leading to reduced detection accuracy and unreliable protection against electrical shock.
Innovation Solution
A wiring device equipped with a leakage determination unit that filters the leakage current using a frequency characteristic similar to human body response to electrical shock, performs a square operation on the filtered signal, and compares the result to a preset threshold value to determine electrical leakage, ensuring reliable interruption even with distorted waveforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional leakage detection methods are used, then the device structure is simple, but the leakage detection accuracy is reduced when the leakage current has large waveform distortion
Solution Approach 1:
The patent introduces an intermediary processing system between the leakage current detection and the final determination. This includes a rectification circuit that converts the leakage current to a unidirectional signal, an integration circuit that accumulates the rectified signal over time, and a frequency characteristic circuit that simulates human body response. This intermediary processing chain transforms the distorted leakage current into a reliable determination signal, resolving the contradiction between maintaining simple device structure and achieving accurate leakage detection under waveform distortion.
2Reliability
If the leakage detection sensitivity is increased, then the electrical shock protection is improved, but the device may malfunction due to noise signals
Solution Approach 1:
The patent applies preliminary action by processing the leakage current signal before final determination. The rectification circuit preliminarily converts the alternating leakage current into a unidirectional signal, and the integration circuit preliminarily accumulates the signal energy. This preliminary processing ensures that when the signal reaches the determination stage, the genuine leakage current has been sufficiently amplified while noise signals remain relatively weak, thus improving electrical shock protection without causing false malfunctions from noise.
Solution Approach 2:
The patent implements feedback through the frequency characteristic circuit that simulates human body impedance characteristics. This circuit provides frequency-selective feedback that enhances the response to genuine leakage currents (which occur at power frequency) while attenuating noise signals at other frequencies. The feedback mechanism ensures that the determination unit receives a signal that has been selectively reinforced for genuine leakage while suppressing noise, thereby improving reliability without susceptibility to noise interference.
3Object-affected harmful factors
If a low-pass filter is used to reduce noise, then the noise interference is reduced, but the detection sensitivity to distorted leakage current is reduced
Solution Approach 1:
The patent applies parameter changes by transforming the leakage current signal through rectification and integration processes before frequency filtering. Instead of directly filtering the raw leakage current, the system first changes the signal parameters through rectification (converting AC to pulsating DC) and integration (accumulating energy over time). This parameter transformation allows subsequent frequency filtering to effectively reduce noise while preserving the genuine leakage current signal, as the integrated signal has enhanced energy at the fundamental frequency and suppressed harmonic distortion components.
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 configuration enhances leakage detection accuracy and reliability, preventing electrical shock by maintaining detection sensitivity despite waveform distortion, and eliminates the need for DC offset adjustment circuits, reducing manufacturing costs.
Implementation Method 1
a filter for filtering a detected leakage current and having a frequency characteristic which a human body has with respect to an electrical shock
Implementation Method 2
an operation unit for calculating a square operation value of a signal passing through the filter
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
In a wiring device which detects a leakage current in an electrical path connecting a commercial power supply and a load to interrupt the electrical path, the electrical leakage can reliably be interrupted even when the leakage current has a distorted waveform. A wiring device (1) includes a leakage control unit (4) for detecting a leakage current flowing through an electrical path connecting a commercial power supply and a load (30) to perform a leakage determination and a switching unit (2) for interrupting the electrical path in accordance with the leakage determination of the leakage control unit (4). The leakage control unit (4) has a filter (42) for filtering the detected leakage current and having a frequency characteristic which the human body has with respect to an electrical shock, a square operation unit (43) for calculating the square operation value of a signal which relates to the leakage current passing through the filter (42), and a threshold determination unit (46) for performing the leakage determination in accordance with the square operation value obtained by the square operation unit (43). Consequently, the leakage determination is performed in accordance with the square operation value, so that the leakage can be detected with high accuracy even when the leakage current has a distorted waveform, and the electrical leakage can be reliably interrupted.