Self-adaptive Current Differential Protection for Half-wavelength Lines
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Solution Overview
Problem
Conventional current differential protection methods are ineffective for half-wavelength AC transmission lines due to the long electrical distance and voltage differences along the line, which render traditional capacitive current compensation methods inapplicable.
Innovation Solution
A self-adaptive current differential protection method based on a time difference method, where the fault point is determined using the time difference between protection starting elements on both sides of the line, and the braking coefficient and threshold values are adaptively changed according to the location of the fault point to ensure sensitive current differential protection across the entire line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional current differential protection method is used, then protection can be applied to medium-length AC transmission lines, but it becomes inapplicable to half-wavelength lines due to voltage differences along the line
Solution Approach 1:
The patent applies local quality by using different compensation methods for different sections of the line. For medium-length lines, traditional capacitive current compensation is used, while for half-wavelength lines, a new compensation method based on voltage difference calculation is applied. The line is divided into sections with different protection strategies tailored to their specific electrical characteristics
Solution Approach 2:
The patent changes the compensation parameters adaptively based on line length and voltage characteristics. For half-wavelength lines, the compensation current is calculated using the voltage difference between sending and receiving ends, and the capacitive current compensation factor is adjusted according to the electrical distance, transforming the protection method to suit ultralong-distance transmission
2Measurement precision
If traditional capacitive current compensation method is used, then protection works for medium-length lines, but sensitivity is insufficient for half-wavelength lines
Solution Approach 1:
The patent introduces dynamic adaptation by calculating compensation currents in real-time based on actual voltage measurements at both ends of the line. The compensation factor is not fixed but dynamically adjusted according to the instantaneous voltage difference, allowing the protection sensitivity to adapt to varying operating conditions and line lengths
Solution Approach 2:
The patent introduces an intermediary calculation step that computes the voltage difference between sending and receiving ends as a mediating parameter. This voltage difference is then used to calculate the capacitive current compensation, serving as an intermediate variable that bridges the gap between measured voltages and the required compensation current for accurate fault detection
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
This method effectively locates the fault point and calculates currents at the differential point, ensuring sensitive current differential protection and reducing losses and inconvenience caused by faults on the half-wavelength line by adapting to different fault locations.
Implementation Method 1
a fault point in the half wavelength line is determined according to the time difference method; the operation that the fault point is determined according to the time difference method includes that: action time TM and TN of protection starting elements on both sides of the half wavelength line is determined according to the time difference method
Data Source
AI summary
A current differential protection method for a self-adaptive half-wavelength line based on a time-difference method. Since an electrical distance of half-wavelength power transmission is long, after a fault occurs, there is an obvious time difference between the actuation times for protecting starting elements at two sides of a line. According to the principles of wave propagation, the position of a fault point can be determined by means of a difference between the actuation times for protecting the starting elements at the two sides of the line. By means of taking the fault point as a differential point, a current value at the differential point can be obtained according to a long line equation by means of the voltage and current at protection-mounted positions at the two sides of the line, and a differential current is then calculated.