Transmission Line Distance Protection Using Short-Window Phasors
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Solution Overview
Problem
Conventional distance protection algorithms for high voltage transmission lines fail to operate within a single power cycle and are prone to transient overreach due to capacitor voltage transformer (CVT) induced transients and decaying direct current (DC) components, compromising system stability.
Innovation Solution
Implementing a sub-cycle distance protection algorithm using short-window phasor estimation that accounts for decaying DC, combined with a second distance protection element that supplements conventional algorithms, ensuring robustness and accuracy by minimizing DC offset impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If full-cycle DFT algorithms are used for distance protection, then measurement accuracy is improved, but operation time exceeds one power cycle
Solution Approach 1:
The patent uses a half-cycle DFT algorithm that processes only half of the power cycle data (32 samples out of 64) to achieve sub-cycle operation time while maintaining acceptable measurement accuracy for distance protection. This partial action approach trades some measurement precision for faster fault clearing speed.
2Loss of time
If phaselet-based algorithms are used to meet sub-cycle operation time requirements, then operation time is reduced, but robustness deteriorates due to transient overreach
Solution Approach 1:
The patent converts the harmful effect of decaying DC components and CVT transients into beneficial information by using a decaying DC model that explicitly accounts for these transients. The model uses the transient characteristics to improve phasor estimation accuracy rather than treating them as noise to be filtered out.
Solution Approach 2:
The patent changes the modeling parameters by introducing a decaying DC time constant and using a second-order differential equation model to represent the transient behavior. This parameter-based approach allows the algorithm to adapt to different transient conditions and maintain robustness across various fault scenarios.
3Device complexity
If conventional distance protection elements are used, then system simplicity is maintained, but fault clearing speed is insufficient for EHV and UHV transmission lines
Solution Approach 1:
The patent implements a dynamic protection scheme that switches between different algorithms based on system conditions. The distance protection element uses a decaying DC model during transient periods and transitions to conventional algorithms when the system stabilizes, optimizing both speed and accuracy dynamically.
Data Source
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AI summary
Systems and methods are provided herein for improving distance protection in transmission lines. Such systems and methods may involve receiving one or more current and voltage inputs, and determining, based on the one or more current and voltage inputs, one or more current and voltage phasors, wherein the one or more current and voltage phasors are determined using a short window phasor estimation. Such systems and methods may also involve determining, within a single power cycle and based on the one or more current and voltage phasors, a fault in a transmission line. Such systems and methods may also involve sending, to a distance protection element and based on the determination that the fault exists, a signal to clear the fault in the transmission line, and clearing the fault in the transmission line.