Isolated Neutral Working Voltage from Phase Unbalance Sampling
Solution Overview
Problem
In isolated neutral systems, capacitance value inconsistencies and measurement difficulties lead to inaccurate working voltage determination, potentially causing false relay protection actions.
Innovation Solution
A method and apparatus for determining the working voltage by periodically sampling phase voltages, calculating unbalance rates between capacitor banks, and using these rates to accurately determine the working voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If capacitance values of capacitor banks are assumed equal for simplified calculation, then calculation complexity is reduced, but working voltage determination accuracy deteriorates due to capacitance inconsistencies causing neutral point voltage shift
Solution Approach 1:
The patent changes the calculation parameters from assuming equal capacitance values to using measured phase voltages to determine unbalance rates. By periodically sampling phase voltages and calculating unbalance rates between phases, the system dynamically adjusts for capacitance variations without requiring direct capacitance measurement, thus maintaining accuracy while managing complexity.
Solution Approach 2:
The patent replaces direct capacitance measurement (which would require complex measurement equipment and system disassembly) with voltage-based indirect measurement. By using standard voltage sensors to measure phase voltages and deriving capacitance unbalance information from voltage unbalance rates, the system substitutes a simple electrical measurement approach for a complex direct capacitance measurement system.
2Measurement precision
If direct capacitance measurement is performed to ensure accurate working voltage determination, then working voltage determination accuracy is improved, but measurement difficulty and device complexity increase
Solution Approach 1:
The patent introduces phase voltage as an intermediary parameter to indirectly determine capacitance unbalance. Instead of directly measuring capacitance values (which is difficult), the system measures phase voltages across the capacitor banks and uses the voltage unbalance rates to infer capacitance variations. This intermediary measurement approach simplifies the measurement process while maintaining accuracy.
Solution Approach 2:
The patent substitutes direct capacitance measurement with voltage-based indirect measurement. By using standard voltage sensors to measure phase voltages and deriving capacitance unbalance information from voltage unbalance rates, the system replaces a complex direct capacitance measurement system with a simpler electrical measurement approach.
3Ease of operation
If capacitance inconsistencies are not accounted for, then system operation simplicity is maintained, but false relay protection actions occur due to inaccurate working voltage determination
Solution Approach 1:
The patent implements a feedback mechanism where phase voltages are continuously monitored and unbalance rates are calculated in real-time. This feedback information is used to adjust the working voltage determination, ensuring that relay protection decisions are based on accurate, up-to-date information about actual capacitance variations, thereby preventing false actions while maintaining operational simplicity.
Solution Approach 2:
The patent performs preliminary calculation of unbalance rates between phases before determining working voltage for relay protection decisions. By pre-calculating the unbalance rates from phase voltage measurements and storing this information for use in working voltage determination, the system ensures accurate protection reliability while keeping the actual protection operation simple and straightforward.
Data Source
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AI summary
The present invention provides a determining method and apparatus for a work-ing voltage of an isolated neutral system. A power system includes three phase wires and three capacitor banks. One terminal of each capacitor bank is connected to one phase wire, and the respective other terminals of the capacitor banks areconnected to one another to form a neutral point. Each capacitor bank includes a plurality of capacitors. The method includes: periodically sampling a phase volt-age of each phase wire, to obtain a plurality of groups of sampling values of re-al-time phase voltages, where each group of sampling values of real-time phase voltages includes a sampling value of a phase voltage of each phase wire that is obtained by simultaneously measuring each phase wire; determining unbalance rates between the capacitor banks based on the plurality of groups of sampling values of real-time phase voltages, where the unbalance rate is a ratio between capacitance values of every two phase wires; and determining a working voltage of the isolated neutral system based on the unbalance rates. The unbalance rates between the capacitor banks are obtained based on the sampling values of the phase voltages measured in real time, and the working voltage is accurately de-termined based on the unbalance rates, so that subsequent operations can be ac-curately performed.