LC Parallel Circuit Detuning Fault Protection via Current Ratio Analysis
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Solution Overview
Problem
Existing methods for protecting LC parallel circuits against detuning faults in high voltage direct current (DC) power transmission systems lack sensitivity and rapidity, often resulting in delayed protection actions due to expanded current ratio limits and prolonged protection delay constants, which compromise system stability and reliability.
Innovation Solution
A relay protection method that converts the current of a reactor into an equivalent capacitor current using differential calculus, calculates the amplitude ratios of these currents, and triggers an alarm or trip signal when the current ratio exceeds preset limits, improving the stability and speed of protection while maintaining simple wiring and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the upper and lower limit range of current ratio is expanded and protection delay constant value is prolonged to avoid system disturbance or protection maloperation during oscillation, then system stability is improved, but protection sensitivity and rapidity are reduced
Solution Approach 1:
The patent applies dynamics by making the protection system adaptive to different operating conditions. It distinguishes between oscillation states and detuning fault states, applying different protection strategies dynamically. During oscillation, the system tolerates current ratio deviations without tripping, while during detuning faults, it provides sensitive detection and rapid protection, thus achieving both stability and sensitivity through dynamic response.
Solution Approach 2:
The patent changes the parameter being monitored from the absolute current ratio to the rate of change of current ratio (dI/dt). This parameter transformation allows the system to detect detuning faults through the characteristic rapid change in current ratio, while being less sensitive to the absolute magnitude variations that occur during oscillation, thereby maintaining both stability and sensitivity.
2Stability of the object's composition
If the upper and lower limit range of current ratio is expanded and protection delay constant value is prolonged to avoid system disturbance or protection maloperation during oscillation, then system stability is improved, but protection rapidity is reduced
Solution Approach 1:
The protection system dynamically adjusts its response based on the operating state. By monitoring the rate of change of current ratio rather than relying on fixed threshold comparisons, the system can rapidly detect detuning faults (which cause rapid dI/dt changes) while maintaining stability during oscillations (where dI/dt remains relatively moderate). This dynamic approach eliminates the need to prolong protection delay constants.
Solution Approach 2:
The patent replaces the traditional mechanical threshold-based protection mechanism with a derivative-based detection mechanism. Instead of comparing current ratio against fixed upper and lower limits (mechanical approach), the system calculates the rate of change of current ratio and compares this derivative against thresholds, enabling faster and more accurate fault detection without compromising stability.
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 approach enhances the stability of current ratio calculations and increases the sensitivity and rapidity of protection, allowing for timely and accurate detection of LC parallel circuit detuning faults, reducing the risk of system disturbances and shaft damage in power transmission systems.
Implementation Method 1
converting the current of the reactor into a current of an equivalent capacitor by differentiation (or differential calculus)
Data Source
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AI summary
A relay protection method against LC parallel circuit detuning faults comprises the steps of: a relay protection device samples a current of a parallel LC, that is, a reactor and a capacitor, and samples a total current flowing through the whole LC; convert the current of the reactor into a current of an equivalent capacitor; calculate amplitudes of the current of the equivalent capacitor and a current of a realistic capacitor and calculate an amplitude of the total current flowing through the LC; calculate a current amplitude ratio of the equivalent capacitor to the realistic capacitor; and when the amplitude of the total current flowing through the LC is large enough, send an alarm signal or a trip after a setting time delay if the current ratio exceeds a preset upper and lower limit range. Also provided is a corresponding relay protection device. The relay protection method and device against LC parallel circuit detuning faults can improve stability of calculation results of a current ratio and raise sensitivity and rapidity of protection.