Adaptive Injection Frequency for Generator Ground-Fault Protection
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Solution Overview
Problem
Existing ground-fault protection systems in electrical machines are sensitive to system noise and frequency deviations, leading to false operations or non-operations, particularly during changes in grid frequency, which can cause spontaneous trips and reduce the reliability of fault detection.
Innovation Solution
Adapting the injection frequency in the ground-fault protection system based on system noise and grid frequency deviations to minimize interference from parasitic noise, allowing for a dynamic selection of injection frequencies that optimize noise reduction and stability, ensuring reliable fault detection across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a static injection frequency is used in ground-fault protection systems, then the system structure is simple, but the system becomes sensitive to system noise and frequency deviations causing false operations
Solution Approach 1:
The patent applies dynamics by transitioning from a static injection frequency to a dynamic adaptive injection frequency that automatically adjusts based on detected system noise levels and frequency deviations. The protection relay continuously monitors the electrical machine's operating conditions and modifies the injection frequency in real-time to maintain optimal protection performance while avoiding noise interference.
Solution Approach 2:
The patent implements parameter changes by modifying the injection frequency parameter according to detected system conditions. When noise or frequency deviations are detected, the system changes the injection frequency parameter to a different value that avoids the interfering frequencies, thereby maintaining reliable fault detection without requiring complex additional hardware.
2Reliability
If the injection frequency is adapted dynamically based on system conditions, then the reliability of fault detection is improved, but the device complexity increases
Solution Approach 1:
The patent applies self-service by enabling the protection relay to automatically detect system noise and frequency deviations, then autonomously adjust the injection frequency without external intervention. The system monitors its own operating conditions and performs self-tuning, eliminating the need for manual configuration or external control systems while maintaining high reliability.
Solution Approach 2:
The patent implements feedback by creating a closed-loop control system where the protection relay continuously monitors system noise and frequency conditions, compares them against threshold values, and adjusts the injection frequency based on the detected deviations. This feedback mechanism ensures the system adapts to changing conditions while maintaining reliable protection operation.
3Measurement precision
If digital filters with fixed frequencies are used, then the filtering is effective at nominal frequency, but noise leaks into the protection function when generator speed deviates from nominal frequency
Solution Approach 1:
The patent applies dynamics by making the filter frequencies dynamic rather than fixed. The digital filters continuously adjust their center frequencies to track the actual generator operating frequency, which varies with speed. This dynamic filtering maintains precise noise rejection across the full operating range of the generator, preventing noise leakage during frequency deviations.
Solution Approach 2:
The patent implements preliminary action by pre-adapting the filter frequencies to match the expected operating conditions before measurement occurs. The system proactively adjusts the filter parameters based on the current generator speed and frequency, ensuring the filters are optimally configured to reject noise at the actual operating frequency before any fault detection measurement is taken.
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 adaptive frequency approach enhances the robustness and reliability of ground-fault protection by reducing noise interference, enabling 100% Stator Earth Fault Protection in generators with lower rated power without additional investments, and maintaining stability during generator start-ups and frequency changes.
Implementation Method 1
an injection signal with an injection frequency fi is applied to the electrical machine in order to generate a periodic bias voltage on a conductor of the electrical machine
Data Source
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Figure 3
AI summary
The present invention is concerned with a robust ground-fault protection system having a reduced sensitivity to system noise. In a ground-fault protection system for an electrical machine such as a generator, an injection signal with an injection frequency i is applied to the electrical machine in order to generate a periodic bias voltage on a conductor of the electrical machine, and a response signal thereto is evaluated. The injection frequency is adapted, i.e. adjusted or selected depending on a system quantity or system property of the electrical machine that is indicative of system noise interfering with, or superposing, the response signal. Hence, a static, predetermined choice of the injection frequency is abandoned in favour of a flexible approach respective of a most recent value of a system quantity of the electrical machine, which ultimately results in increased stability and reliability of the ground-fault protection system.