Leak Current Detection Using Zero-Phase Differential
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Solution Overview
Problem
Conventional electric leak detecting devices are slow in detecting ground fault current due to reliance on peak values of zero-phase current, failing to meet high-speed detection requirements, particularly in earth leakage circuit breakers where the maximum operation time is limited to 40ms.
Innovation Solution
An electric leak detecting device that includes current detection, voltage detection, and a differentiation means to calculate differential values based on phase information, allowing for faster derivation of leak current using zero-phase current and its differential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If peak value of zero-phase current is used for calculation of ground fault current, then calculation can be performed with simple measurement, but detection speed is limited by peak cycle and operation delay occurs
Solution Approach 1:
The patent calculates the differential value of zero-phase current in advance using differentiation means, so that when peak detection is needed, the calculation is already prepared. This preliminary calculation of the differential value allows the system to quickly determine ground fault current without waiting for the peak cycle, thereby reducing operation delay while maintaining simple measurement requirements.
2Measurement precision
If average value of peak values for four times is used for calculation, then measurement accuracy is improved, but detection time increases to at least 40ms
Solution Approach 1:
The patent performs preliminary calculation of the differential value of zero-phase current using differentiation means before peak detection is required. This advance preparation allows the system to quickly compute ground fault current with sufficient accuracy without needing to wait for multiple peak cycles, thus achieving both measurement precision and fast detection within the 40ms requirement.
3Productivity
If conventional peak-based calculation method is used, then device complexity is low, but productivity and detection speed are insufficient for high-speed requirements
Solution Approach 1:
The patent replaces the mechanical waiting-for-peak approach with a mathematical differentiation operation. By using differentiation means to calculate the differential value of zero-phase current, the system achieves continuous calculation capability rather than being limited by peak occurrence frequency. This substitution of calculation methodology significantly improves detection throughput while adding only moderate computational complexity.
Data Source
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AI summary
The leak current detecting device of the present invention includes: a zero-phase current detection means (1) for detecting zero-phase current on an electric path; a voltage detection means (5) for detecting voltage on the electric path; a differentiation means (12) for calculating a differential value of the zero-phase current; and a leak current deriving means (13) for deriving leak current on the basis of a value of the zero-phase current and the differential value.