Double-Circuit Line Protection With Zero-Sequence Coupling Compensation
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Solution Overview
Problem
Existing methods for protecting double-circuit transmission systems fail to accurately account for zero-sequence mutual coupling, leading to inaccurate apparent impedance calculations and potential overreach or underreach in distance protection.
Innovation Solution
A device and method that estimate the zero-sequence current in a parallel line without measuring the current from the healthy line, using local measurements and system impedance parameters to compute a more accurate apparent impedance for distance protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional apparent impedance calculation is used without mutual coupling compensation, then the calculation is simple, but the accuracy of distance protection is reduced due to zero-sequence mutual coupling effects
Solution Approach 1:
The protection device uses its own local measurements (voltage and current from the protected line) to estimate the zero-sequence current in the parallel line through computational algorithms. This self-service approach eliminates the need for external current measurements from the healthy line while achieving mutual coupling compensation, thereby improving accuracy without significantly increasing device complexity
Solution Approach 2:
The patent replaces the traditional approach of physically measuring current in the parallel line with computational estimation using mathematical models and algorithms. This substitution of physical measurement with computational processing achieves the same compensation effect while avoiding the complexity of additional measurement devices and inter-line connections
2Measurement precision
If current measurement from the healthy line is used for mutual coupling compensation, then the accuracy of apparent impedance calculation is improved, but the device complexity and measurement requirements increase
Solution Approach 1:
The protection device independently estimates the zero-sequence current in the parallel line using only local measurements from the protected line and computational algorithms. This self-service capability eliminates the need for current transformers, measurement devices, or data collection from the healthy line, thereby improving measurement accuracy without increasing the difficulty of detection and measurement
Solution Approach 2:
The patent introduces computational algorithms and mathematical models as intermediaries that transform local voltage and current measurements into an estimated zero-sequence current for the parallel line. This intermediary computational process bridges the gap between available local measurements and the needed mutual coupling compensation without requiring direct measurement from the healthy line
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
The solution provides adaptive mutual coupling compensation for distance protection of double-circuit lines, eliminating the need for current measurement from the healthy line and improving the accuracy of apparent impedance calculations.
Implementation Method 1
magnetic flux of one line links to the other line. Magnetic flux linkage is directly proportional to the total current flowing through the lines
Data Source
AI summary
A device is provided that is suitable for use with a double-circuit power transmission system having a first line and a second line. The device comprises an interface to receive a current measurement for the second line. The device comprises at least one processing module operative to estimate a first zero-sequence current in the first line based on a second zero-sequence current, and determine an apparent impedance based on the estimated first zero-sequence current.