Generator Ground Fault Detection Using Frequency Deviation Blocking
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Solution Overview
Problem
Existing ground fault detection methods in rotating electrical machines are unreliable during machine acceleration and retardation due to harmonic interference, leading to false protective operations.
Innovation Solution
A method that injects a test signal at a predefined frequency and continuously determines the frequency of the response signal, discarding measurements when the frequency deviates by a threshold value to prevent harmonic interference, allowing for accurate ground fault detection without false protective actions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If signal injection method is used for ground fault detection, then ground fault can be detected based on impedance estimation, but false protective operations occur during machine acceleration and retardation due to harmonic interference
Solution Approach 1:
The patent converts the harmful harmonic interference into a useful indicator by detecting frequency deviation. When harmonics coincide with the injection signal frequency during acceleration and retardation, the response signal frequency deviates from the predefined injection frequency. This frequency deviation is detected and used to block measurements, transforming the harmful interference into a detectable signal that triggers protective blocking of faulty measurements.
Solution Approach 2:
The patent introduces frequency determination as an intermediary step between signal injection and impedance estimation. By continuously determining the frequency of the response signal and comparing it with the predefined injection frequency, the system identifies when harmonic interference is present. This intermediary frequency check acts as a gatekeeper that prevents corrupted measurements from affecting the ground fault detection result.
2Reliability
If dual frequency injection is used to eliminate harmonic interference, then signal reliability improves, but device complexity and commissioning requirements increase
Solution Approach 1:
Instead of changing the injection signal frequency to avoid harmonics, the patent changes the approach by continuously monitoring the response signal frequency and adapting the measurement validity based on frequency deviation. The injection frequency remains fixed and simple, but the system dynamically adjusts which measurements are valid based on the detected frequency of the response signal, eliminating the need for complex dual-frequency injection hardware.
Data Source
AI summary
A method for enhancing the reliability of generator ground fault detection based on a signal injection scheme, wherein the generator includes a winding. The method includes injecting a test signal at a predefined frequency to the winding, measuring an electrical quantity of a response signal in the winding resulted from the injected test signal, and detecting a ground fault based on the measured value of the electrical quantity. The method further includes continuously determining the frequency of the response signal, and discarding the present measured value corresponding to the determined frequency when the determined frequency deviates from the predefined frequency with a first threshold value.