Earth Leakage Detection Device Using Fourier Analysis
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Solution Overview
Problem
In multi-common grounding environments, existing methods for detecting earth leakage faults face challenges in accurately distinguishing between actual leaks and parasitic voltage sources, leading to potential misidentification of leak locations and increased risk of electric shocks due to the formation of closed circuits and mixed circulating currents.
Innovation Solution
A device and method that utilize earth voltage measurement, Fourier transform analysis, and harmonic distortion calculations to determine the presence of actual leaks by assessing the content rate, total harmonic distortion, and zero-crossing counts, allowing for precise identification of suspicious earth leaking areas and leak points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple earth grounding points are implemented to reduce earth resistance influence, then the detection coverage and safety are improved, but closed circuits and mixed circulating currents are formed causing false detection
Solution Approach 1:
The patent segments the detection process into two independent parts: (1) measuring earth potential at multiple grounding points to identify suspicious areas, and (2) injecting exploration signals to locate precise leak points. This segmentation allows the system to operate effectively in multi-common grounding environments by separating the area identification function from the precise location function, thereby resolving the contradiction between detection coverage and accuracy.
Solution Approach 2:
The patent introduces exploration signals as an intermediary mechanism to resolve the contradiction. By injecting known exploration signals into the power line and detecting their response at multiple grounding points, the system can accurately identify leak locations even in the presence of mixed circulating currents from multiple grounding points. The exploration signals act as a mediator that enables precise measurement despite the complex electrical environment.
2Area of stationary object
If earth potential measurement is used to identify suspicious areas, then the detection range is expanded, but false alarms increase due to parasitic voltage sources
Solution Approach 1:
The patent applies preliminary action by first measuring earth potential at multiple grounding points to identify suspicious areas before conducting precise leak location. This preliminary screening step expands the detection range while the subsequent exploration signal injection step eliminates false alarms by providing definitive verification. The two-step process ensures that only areas with actual leaks proceed to detailed investigation.
Solution Approach 2:
The patent replaces direct current measurement (which is affected by mixed circulating currents) with exploration signal-based detection. By injecting AC exploration signals and measuring their response, the system substitutes the problematic DC measurement mechanism with a more reliable AC signal-based mechanism that can distinguish actual leaks from parasitic voltage sources, thereby reducing false alarms while maintaining expanded detection 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 approach effectively distinguishes between actual leaks and parasitic voltage sources, enhancing the accuracy of earth leakage detection and preventing electric shocks by identifying the true cause of earth potential rises, thereby improving safety and reducing false alarms.
Implementation Method 1
when the earth leakage fault is located at a distance far from the power source (transformer), earth resistance increases to block the fault (leak) current from reaching the grounded neutral point of the power source
Implementation Method 2
Fourier transform analysis, and harmonic distortion calculations to determine the presence of actual leaks
Implementation Method 3
harmonic distortion calculations to determine the presence of actual leaks by assessing the content rate, total harmonic distortion, and zero-crossing counts
Data Source
AI summary
The device for detecting a leak may include: an earth voltage measuring unit measuring earth voltage; an ADC unit sampling the measured earth voltage and converting the sampled earth voltage into a digital value; an effective value calculating unit calculating an effective value of the earth voltage converted into the digital value; a Fourier transforming unit performing Fourier transform of the measured earth voltage to calculate voltage for each harmonic component; a content rate calculating unit calculating a voltage content rate of the fundamental frequency to voltage; a harmonic distortion rate calculating unit calculating a total harmonic distortion and a harmonic distortion factor based on the voltage for each harmonic component; a zero-crossing estimating unit estimating a zero-crossing count; and a suspicious earth leaking area determining unit determining that the earth voltage is generated by the leak of the AC commercial power.