Adaptive Control Circuit for Rapid Fault Current Detection
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Solution Overview
Problem
Existing digital protective relays require a detection time equal to or more than one period to determine fault currents in electric power systems, leading to prolonged exposure of the system to fault currents and potential damage during large fault events.
Innovation Solution
A control circuit for an electric power circuit switch that combines a sampling/hold circuit, discrete Fourier transforming circuit, differentiator, and controller to quickly determine fault currents by analyzing the rate of change of the current, allowing for rapid trip control based on both the magnitude and phase of the frequency component, and the rate of change of the current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete Fourier transforming is used to determine fault currents, then the method is simply implemented and resistant to noise, but a detection time equal to or more than one period is required
Solution Approach 1:
The patent applies dynamics by making the detection method adaptive based on current magnitude. The system dynamically switches between DFT (for small currents where noise resistance is needed) and rate of change detection (for large currents where speed is critical). This dynamic adaptation resolves the contradiction by optimizing the detection approach according to real-time conditions.
Solution Approach 2:
The patent changes the detection parameter based on current magnitude. When current exceeds a threshold, the system transitions from frequency-based detection (DFT) to rate-of-change-based detection. This parameter change allows the system to achieve fast detection for large fault currents while maintaining noise resistance for smaller currents through DFT.
2Ease of manufacture
If discrete Fourier transforming is used to determine fault currents, then the method is simply implemented, but a detection time equal to or more than one period is required
Solution Approach 1:
The patent segments the detection process into two distinct pathways: DFT-based detection for small currents and rate-of-change-based detection for large currents. This segmentation allows each method to be optimized for its specific use case, maintaining implementation simplicity while achieving fast detection when needed.
Solution Approach 2:
The system dynamically selects the detection method based on current magnitude, switching between DFT and rate of change detection. This dynamic approach maintains the simplicity of DFT implementation while adding a fast detection capability for large fault currents through the alternative rate-of-change method.
3Measurement precision
If a detection time equal to or more than one period is required, then the fault current can be accurately determined, but the load device and electric power system are exposed to the fault current for an unnecessarily long period of time
Solution Approach 1:
The patent changes the detection parameter based on current magnitude. For large fault currents exceeding a threshold, the system uses rate of change detection which provides sufficient accuracy for rapid trip decisions without requiring a full period measurement. This parameter change reduces harmful exposure time while maintaining adequate detection accuracy for critical large faults.
Solution Approach 2:
The system dynamically adapts the detection method based on current magnitude, using DFT for small currents where full-period measurement ensures accuracy, and rate-of-change detection for large currents where speed is critical. This dynamic adaptation reduces damage from fault current exposure while maintaining measurement precision when needed.
Data Source
AI summary
A control circuit for an electric power circuit switch includes: a sampling/hold circuit section configured to sample a period of a detection signal of a current of an electric power system and provide a sampled signal; a discrete Fourier transforming (abbreviated as DFT) circuit section perform DFT on the one-period sampled signal to provide a magnitude and a phase of a frequency component of the current of the electric power system; a differentiator configured to differentiate the detection signal to provide a rate of change of the current over time; and a controller to determine whether to perform trip controlling according to the magnitude of the frequency component of the current from the DFT circuit section or the rate of change from the differentiator on the basis of the rate of change of the current and the reference rate of change.