Vector Shift Detection in AC Power Systems
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Solution Overview
Problem
Existing methods for detecting vector shifts in AC power systems lack sufficient sensitivity, often failing to detect smaller shifts and can lead to erroneous frequency measurements and unnecessary protection trips.
Innovation Solution
A method that identifies characteristic patterns in voltage waveforms by determining frequency through phase angle comparison using discrete Fourier transform and filters time derivatives to enhance sensitivity and stability, allowing for rapid detection of vector shifts within 0.5 to 1 fundamental period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing detection methods are used, then the system can detect relatively large vector shifts, but the sensitivity is insufficient and small vector shifts cannot be detected
Solution Approach 1:
The detection method segments the frequency measurement process into multiple components: nominal frequency determination, phase angle comparison, and time derivative analysis. By dividing the detection into these separate analytical stages, the system can identify vector shifts of any magnitude while filtering out noise, thus improving sensitivity without increasing false trips.
Solution Approach 2:
The patent introduces an intermediary analysis layer that compares phase angles at different time points and analyzes time derivatives of frequency measurements. This intermediary stage acts as a mediator between raw frequency data and final detection decisions, enabling the system to detect small vector shifts while maintaining reliability through multiple verification steps.
2Reliability
If frequency measurement is performed during vector shift, then frequency protection can operate, but erroneous frequency measurements occur leading to unnecessary trips
Solution Approach 1:
The system performs preliminary detection of vector shifts by analyzing phase angle comparisons and time derivatives before frequency protection decisions are made. By identifying vector shift conditions in advance, the system can prevent erroneous frequency measurements from triggering unnecessary protection trips, thus protecting against false operations.
Solution Approach 2:
The patent implements feedback mechanisms where detection results from phase angle comparison and time derivative analysis are fed back into the frequency measurement process. This feedback loop allows the system to adjust frequency measurements based on detected vector shift conditions, ensuring accurate frequency protection operation only when appropriate.
3Speed
If conventional detection methods are used, then the system operates simply, but detection speed is insufficient and cannot detect vector shifts within 0.5 to 1 fundamental period
Solution Approach 1:
The system performs preliminary calculations of phase angles and time derivatives continuously, preparing detection data in advance. This preliminary action allows the system to detect vector shifts within 0.5 to 1 fundamental period by having pre-computed phase angle comparisons and derivative values ready for immediate analysis when a shift occurs.
Solution Approach 2:
The patent employs dynamic detection thresholds and adaptive analysis windows that adjust based on system conditions. By making the detection algorithm dynamic rather than static, the system achieves fast detection of small vector shifts while maintaining operational simplicity through automated adaptation to changing power system conditions.
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
Enables the detection of even small vector shifts with high sensitivity and speed, preventing false frequency protection trips and improving measurement accuracy during vector shift phenomena.
Implementation Method 1
determining a frequency of an AC power system by comparing a first phase angle of a voltage of the AC power system and a second phase angle of the voltage of the AC power system, such that the first and second phase angles correspond to time points spaced by a fundamental period of the AC power system
Data Source
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AI summary
A method and an apparatus for detecting a vector shift in an AC power system, the apparatus comprising frequency determination means (10) adapted to determine a frequency of the AC power system, derivation means (20) adapted to determine a time derivative of the frequency, filtering means (30) adapted to filter the time derivative of the frequency, and detection means (40, 50, 60, 70) adapted to calculate time derivatives for the filtered time derivatives of the frequency over a time period having the length of the fundamental period of the AC power system, to determine a number of positive and negative time derivatives among the calculated time derivatives, and to detect a vector shift in the AC power system in response to an absolute value of a difference between the determined number of positive time derivatives and negative time derivatives exceeding a predetermined threshold value.