Current Differential Relay Segmentation for High-Speed Fault Detection
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Solution Overview
Problem
Conventional current differential relay apparatuses fail to operate at high speeds during internal failures in power systems, particularly when fault currents are small, due to issues with CT saturation and malfunction prevention.
Innovation Solution
The current differential relay apparatus employs multiple relays that calculate differential and suppression currents using filtered current data, performing ratio differential operations to quickly detect internal failures, with additional harmonic detection to prevent malfunctions from external failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current differential relay apparatus uses single relay operation with suppression current calculation, then malfunction prevention during external failure is achieved, but operating speed during internal failure is reduced
Solution Approach 1:
The relay apparatus is divided into multiple independent relay units (first relay, second relay, third relay) that perform different calculation operations. The first relay calculates suppression current for external failure protection, while the second and third relays calculate differential current for high-speed internal failure detection. This segmentation allows each relay to specialize in specific failure scenarios without compromising overall system reliability or speed.
Solution Approach 2:
The apparatus performs partial suppression current calculation in the first relay while simultaneously performing excessive differential current calculation in the second and third relays. This partial action approach allows the system to maintain malfunction prevention capabilities while adding high-speed detection pathways that activate only when needed for internal failures.
2Measurement precision
If filtering process extracts fundamental wave component only, then measurement precision is improved, but response time for small fault currents is increased
Solution Approach 1:
Different filtering processes with different quality characteristics are applied in different relay units. The first relay uses a filtering process that extracts only the fundamental wave component for precise measurement. The second relay uses a different filtering process that removes DC component for faster response. This local quality differentiation allows each relay to optimize for its specific function.
Solution Approach 2:
The system changes the filtering parameters based on the relay unit and detection needs. The first relay uses filtering parameters optimized for fundamental wave extraction, while the second relay uses parameters optimized for DC component removal. This parameter change strategy enables the system to achieve both high precision and fast response times for different fault conditions.
3Measurement precision
If multiple relays perform separate calculations, then detection accuracy for internal failures is improved, but device complexity increases
Solution Approach 1:
Each relay unit is designed with multi-functionality to handle different failure scenarios. The first relay handles external failure detection through suppression current calculation, while the second and third relays handle internal failure detection through differential current calculation. This universal design allows a single relay apparatus to perform multiple detection functions without requiring separate dedicated devices for each function.
Solution Approach 2:
The patent merges multiple relay functions into a single integrated current differential relay apparatus. The first, second, and third relays are combined in one device, sharing common input current signals and output control mechanisms. This merging reduces overall system complexity compared to using separate independent relay devices while maintaining the detection accuracy benefits of multiple calculation pathways.
Data Source
AI summary
A current differential relay apparatus includes a first relay and a second relay. The first relay calculates a first differential current and a first suppression current, using a first current and a second current, and performs a ratio differential relay operation based on the first differential current and the first suppression current. The second relay calculates a maximum of results of add operations of the first current and the second current as a second differential current, calculates an add operation of the maximum of the first current and a maximum of the second current as a second suppression current, and performs a ratio differential relay operation based on the second differential current and the second suppression current. The current differential relay apparatus includes an output controller that outputs an operation signal based on results of operations performed by the first and second relays.