Zero-Flux Current Transformer Circuit for Full-Range Current Sensing
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Solution Overview
Problem
Conventional metering and detection apparatuses in substations suffer from a small current measurement range and low accuracy, failing to meet the high-precision and full-range requirements of new-generation substations.
Innovation Solution
An analog quantity acquisition method using a zero flux current transformer, multi-segment amplification circuit, and analog-to-digital converter to segment and amplify current signals, eliminating ratio and phase angle errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional metering and detection apparatus is used, then the device complexity is low, but the measurement precision is insufficient for small current ranges
Solution Approach 1:
The measurement range is divided into multiple segments using a multi-segment amplification circuit with different amplification factors. Each segment handles a specific current range, enabling high-precision measurement across the full range from small to large currents by selecting the appropriate amplification segment based on the input current magnitude.
Solution Approach 2:
The apparatus dynamically changes the amplification factor parameter based on the input current range. By switching between different amplification factors (e.g., 50 times, 100 times, 200 times), the system adapts to different current magnitudes, maintaining high measurement precision whether measuring small currents or large currents.
2Adaptability or versatility
If a single-range amplification circuit is used, then the device complexity is low, but the adaptability to different current ranges is poor
Solution Approach 1:
The amplification circuit is segmented into multiple independent amplification paths, each with a different amplification factor. This segmentation allows the circuit to handle different current ranges effectively, expanding the overall measurement range from 0.03A to 6A while maintaining circuit modularity and manageable complexity.
Solution Approach 2:
The multi-segment amplification circuit serves multiple functions: it amplifies small currents when needed, handles large currents when present, and provides automatic range selection. This multi-functionality allows a single apparatus to cover the full current range without requiring separate dedicated circuits for each range.
3Reliability
If excitation current is present in the current transformer, then the transformer can operate, but ratio errors and phase angle errors occur
Solution Approach 1:
The system employs feedback mechanisms where the measurement results from different amplification segments are processed and compared. The control unit selects the appropriate measurement segment based on feedback about the input current magnitude, and the final measurement result is calculated by combining feedback from the selected segment, thereby compensating for errors introduced by excitation current.
Solution Approach 2:
The system changes the measurement parameters (amplification factor and measurement segment) based on the input current characteristics. By adapting the measurement parameters to match the current range, the system minimizes the impact of excitation current effects, maintaining high accuracy across different operating conditions.
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
Achieves high-precision, full-range current acquisition by counteracting excitation current impacts and ensuring accurate measurement across varying current ranges.
Implementation Method 1
generating a reverse excitation potential by using the compensating winding; and the dynamic detection unit is configured to detect a potential difference between two ends of the compensating winding, and generate a secondary current, where the secondary current generates a demagnetized magnetic potential to counteract an excitation current
Data Source
AI summary
Disclosed are an analog quantity acquisition method and apparatus. An acquisition circuit with a zero flux current transformer is first used to acquire a current signal, where the acquisition circuit with the zero flux current transformer includes the zero flux current transformer, a compensating winding, and a dynamic detection unit, and the compensating winding generates a reverse excitation potential to counteract an excitation current and eliminate impacts of a ratio error and a phase angle error on accuracy. A multi-segment amplification circuit is used to perform segmented amplification on different ranges of the current signal, and full-range current acquisition is achieved by using different amplification circuits. An analog-to-digital converter chip is used to convert an amplified current signal into a digital signal. The acquisition circuit with the zero flux current transformer is used to eliminate the impacts of the ratio error and the phase angle error on the measurement accuracy.