Fault Location in Medium-Voltage Distribution Networks
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Solution Overview
Problem
Current methods for locating single-phase faults in medium-voltage distribution networks, particularly those with high earth resistance, suffer from inaccuracy due to the impact of load impedance and resistance values, leading to unreliable fault distance calculations.
Innovation Solution
The method employs measurements of current and voltage before and during the fault, using forward and reverse impedances in symmetrical components modeling to calculate the fault distance, assuming a balanced load and negligible line impedance, and iteratively solving a system of equations to improve precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional impedance calculation methods are used for fault location, then the calculation process is simple, but the measurement precision deteriorates for high resistance faults
Solution Approach 1:
The patent measures and stores the impedance of the healthy phase before the fault occurs. This preliminary measurement of the load impedance is then used during fault analysis to accurately calculate fault distance even for high resistance faults, eliminating the need for complex real-time adjustments during the fault condition.
Solution Approach 2:
The patent changes the approach by using the impedance measured in the healthy state as a parameter for fault calculation. Instead of trying to measure fault conditions directly, it utilizes the pre-fault healthy phase impedance to derive accurate fault location, transforming the problem from direct fault measurement to comparative analysis.
2Ease of operation
If measurements are taken during fault condition only, then the measurement process is simple, but the reliability deteriorates due to unknown load impedance
Solution Approach 1:
The system performs preliminary measurements of voltage and current in the healthy phase before fault occurrence to determine the load impedance. This pre-acquired information is then incorporated into the fault location calculation, ensuring reliable results even when only simple fault-condition measurements are taken.
Solution Approach 2:
The patent uses the pre-measured healthy phase impedance as feedback information to improve the accuracy of fault location calculations. The system continuously monitors and stores normal operating parameters, then uses this feedback during fault conditions to maintain calculation reliability.
3Measurement precision
If complex modeling with load impedance is used, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent simplifies the modeling complexity by pre-calculating and storing the load impedance from healthy phase measurements. This preliminary action eliminates the need for complex real-time load modeling during fault conditions, maintaining measurement precision while reducing operational complexity.
Solution Approach 2:
The patent extracts the load impedance parameter from the complex fault condition and determines it separately using healthy phase measurements. By taking out this parameter beforehand, the system avoids the complexity of simultaneously solving for both load impedance and fault location during the fault condition.
4Measurement precision
If high frequency transient signals are measured, then the measurement precision improves, but the device complexity and cost increase
Solution Approach 1:
The patent uses standard power frequency voltage and current measurements instead of expensive high-frequency transient measurement equipment. By utilizing readily available measurement data at normal power frequencies, the system achieves accurate fault location without requiring specialized expensive hardware.
Solution Approach 2:
The patent replaces the need for complex high-frequency measurement systems with a computational approach using standard measurements. Instead of relying on sophisticated hardware to capture transient signals, it uses mathematical modeling with常规 measurements to achieve the same measurement precision.
Data Source
Figure 1~2
Figure 3A~3B
AI summary
The method involves measuring current and voltage of a public distribution network at a source post (7) before occurrence of a defect (10). Impedance (Zch) of a load (8) is determined through a ratio between complex values of the measured current and voltage. Current and voltage at the post are measured during the defect. Current (Ich) circulating in the load during the defect is determined by considering unchanged load impedance. Distance of the defect with respect to the post is determined using the current and voltage values measured during the defect and the determined current value. An independent claim is also included for a system for locating a defect in a medium-voltage public distribution network, comprising current and voltage measurement units.