Pilot Protection Using Wavelet Structural Similarity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional differential protections in power systems with renewable energy sources face reduced sensitivity and reliability due to changes in fault characteristics, such as limited amplitude and frequency offset, leading to potential malfunctions and unsafe operation.
Innovation Solution
A structural similarity based pilot protection system that uses wavelet transforms to analyze current signals from both ends of a transmission line, determining structural similarity and residual sum of squares to differentiate between internal and external faults, and generate trip signals accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional differential protections are used in power systems with renewable energy sources, then the protection system can operate with traditional settings, but the sensitivity and reliability are reduced due to changed fault characteristics
Solution Approach 1:
The patent changes the fundamental parameters of the protection method by transitioning from conventional amplitude-based differential protection to wavelet transform-based structural similarity analysis. This parameter change enables the protection system to adapt to the altered fault characteristics of renewable energy sources, including limited amplitude and frequency offset, while maintaining high reliability through structural pattern recognition rather than magnitude comparison
Solution Approach 2:
The patent substitutes the conventional mechanical/amplitude-based protection mechanism with a signal processing approach using wavelet transforms. Instead of comparing current magnitudes directly, the system transforms current signals into wavelet coefficient matrices and compares their structural similarity, replacing the traditional protection mechanism with a more adaptable signal analysis method
2Ease of operation
If conventional phasor measurement and amplitude comparison based protections are used, then the protection system can function with traditional methods, but the likelihood of malfunction increases due to reduced fault currents
Solution Approach 1:
The patent replaces conventional phasor measurement and amplitude comparison methods with wavelet transform-based structural similarity analysis. This substitution enables reliable fault detection even with reduced fault currents by analyzing the structural characteristics of wavelet coefficients rather than relying on current magnitude comparisons, thereby maintaining ease of operation while significantly improving reliability
Solution Approach 2:
The patent changes the measurement parameters from time-domain amplitude values to frequency-time domain wavelet coefficient structures. This parameter transformation allows the protection system to detect faults based on structural patterns in the wavelet coefficients, which remain distinctive even when fault current amplitudes are reduced, thus improving reliability without complicating operation
3Measurement precision
If traditional protection configurations are used, then the protection system can be implemented with conventional settings, but it is difficult to satisfy both sensitivity and reliability requirements simultaneously
Solution Approach 1:
The patent transforms the protection parameters from conventional current amplitude measurements to wavelet coefficient structural similarities. This parameter change enables simultaneous achievement of high sensitivity and reliability because the structural similarity metric is highly sensitive to fault patterns while being reliable against false positives from normal variations in renewable energy output
Solution Approach 2:
The patent introduces wavelet transform as an intermediary processing step between current measurement and fault determination. This intermediary transforms raw current signals into wavelet coefficient matrices, allowing the system to achieve both sensitivity (through detailed structural analysis) and reliability (through normalized similarity comparison) that cannot be achieved with direct amplitude comparison
Data Source
AI summary
The wide application of power electronic components in power systems with renewable energy sources has changed the fault characteristics of conventional power systems, resulting in the performance degradation of conventional protections. To solve these problems, a novel principle of pilot protection based on structural similarity and square error criteria is provided. The structural similarity criterion utilizes the difference of fault characteristics between renewable sources and synchronous generators to identify internal faults, and the square error criterion is used to solve abnormal calculation of the conventional similarity based protection. Compared with conventional differential protections, the disclosed protection shows excellent performance in speed and reliability during various faults.