Frequency Converter Earth Fault Detection via Common-Mode Voltage
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Solution Overview
Problem
Existing methods for detecting earth faults at frequency converters require multiple voltage sensors, increasing costs and complexity, and fail to accurately determine the side of the fault, leading to potential severe damage.
Innovation Solution
A method utilizing a single voltage sensor on one side of the converter to measure common mode voltage, employing filtering procedures to extract frequency components, and calculating RMS values to detect earth faults, allowing precise identification of the fault side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple voltage sensors are used to detect earth faults at both sides of the converter, then detection coverage is improved, but device complexity and cost increase
Solution Approach 1:
The voltage sensor installed on the second grid side performs multiple functions: it detects earth faults on the second grid side directly, and simultaneously detects earth faults on the first grid side by analyzing common mode voltage frequency components. This multi-functional approach eliminates the need for separate sensors on both sides of the converter.
Solution Approach 2:
The method utilizes frequency domain analysis by transforming the common mode voltage signal into frequency components. By analyzing the presence and magnitude of first frequency and second frequency components in the common mode voltage, the system can distinguish between faults on different grid sides, enabling a single sensor to provide comprehensive fault detection coverage.
2Measurement precision
If voltage sensors are installed on both sides of the converter, then fault location accuracy is improved, but installation space and cost increase
Solution Approach 1:
The single voltage sensor on the second grid side is designed to perform universal detection for both grid sides. Through frequency component analysis of the common mode voltage, it achieves accurate fault location identification without requiring physical sensors on both sides of the converter.
Solution Approach 2:
Instead of physically installing sensors on both grid sides, the system creates a virtual measurement copy by analyzing the common mode voltage signal. The frequency domain representation of this single sensor's measurement contains sufficient information to infer fault conditions on both grid sides, eliminating the need for physical duplication of sensors.
3Reliability
If more voltage sensors are deployed, then detection reliability is improved, but the number of potential failure points increases
Solution Approach 1:
The detection system uses a single voltage sensor that performs multiple detection functions. By processing the common mode voltage signal through frequency domain analysis, one sensor provides the same reliability coverage that would traditionally require multiple sensors, thereby reducing the total number of components that could potentially fail.
Data Source
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Figure 3A~3F
Figure 4A~5D
AI summary
A method of detecting earth faults at a frequency converter (3) connected between a first grid (1) operating at a first frequency (f1) and a second grid (2) operating at a different, second frequency (f2) comprises determining a common mode voltage (U2cm ) at the side of the converter (3) connected to the second grid (2), determining levels of components of the first frequency (f1) and the second frequency (f2) in the common mode voltage (U2cm) and determining if the levels are above pre-set threshold levels (L1, L2), indicating that an earth fault is present at the side of the converter (3) connected to the grid (1, 2) operating at the respective frequency (f1, f2).