Zero-Sequence Impedance Measurement on Coupled AC Transmission Lines
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Solution Overview
Problem
Existing impedance measurement methods for AC transmission lines are inaccurate due to signal interference from coupled lines, requiring costly and disruptive equipment or complex frequency adjustments, and lack cost-effective, portable solutions.
Innovation Solution
A method for zero-sequence impedance measurement of coupled AC transmission lines involves disconnecting the line, grounding ends, measuring induced currents and voltages, and calculating impedance using reference signals to compensate for phase differences, enabling accurate measurements without large equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional impedance measurement methods are used on coupled transmission lines, then measurement can be performed without disconnecting lines, but measurement accuracy deteriorates due to signal interference from adjacent lines
Solution Approach 1:
The patent extracts the zero-sequence component from the composite signal containing both power frequency and interference components. By applying zero-sequence filtering to isolate the zero-sequence current and voltage, the method separates the useful measurement signal from the harmful interference, thereby maintaining measurement accuracy without requiring physical disconnection of coupled lines
Solution Approach 2:
The patent transforms the measurement approach by changing from measuring total current and voltage to measuring zero-sequence components. This parameter transformation allows the measurement system to focus on the specific component containing impedance information while automatically rejecting the interfering power frequency signals from adjacent lines
2Measurement precision
If large test signals are used to override signal interference, then measurement accuracy improves, but equipment size, weight, and cost increase
Solution Approach 1:
The patent converts the harmful signal interference from adjacent lines into a beneficial source of zero-sequence voltage. The induced voltage from coupled lines, which was previously considered noise, is now utilized as the excitation source for impedance measurement, eliminating the need for large external test signal generators and reducing equipment weight and cost
Solution Approach 2:
The measurement system uses the naturally induced voltage from coupled lines as its own excitation source. By measuring the zero-sequence current flowing through the line and the corresponding zero-sequence voltage, the system performs self-measurement without requiring external heavy equipment, thereby achieving portability and cost-effectiveness
3Adaptability or versatility
If off-frequency power supply with adjustable frequency is used, then impedance measurement becomes possible on out of service lines, but system complexity and cost increase
Solution Approach 1:
The patent extracts zero-sequence components from the naturally induced voltage on the out-of-service line, eliminating the need for complex adjustable frequency power supplies. By filtering and processing the zero-sequence current and voltage, the system achieves measurement capability on disconnected lines using simple fixed-frequency equipment
Solution Approach 2:
The patent replaces expensive, complex adjustable frequency inverters with simple, fixed-frequency measurement equipment. The zero-sequence filtering and processing system provides the necessary adaptability at minimal cost, making the measurement system economically viable for utility applications
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
This method provides robust, accurate impedance measurements with minimal disruption and cost, using portable equipment, reducing errors to less than 0.7% in simulated scenarios.
Implementation Method 1
An induced voltage may exist on a line under test due to current passing through an adjacent line
Data Source
AI summary
A method for impedance measurement of coupled AC transmission lines. The method includes measuring a zero-sequence impedance of a three-phase transmission line that are configured to transmit electric power from a first substation of a power system to a second substation of the power system. Measuring the zero-sequence impedance includes disconnecting the three-phase transmission line from the power system, connecting a receiving end of the first three-phase transmission line to a local ground, connecting each phase of the three-phase transmission line at a sending end of the three-phase transmission line to a terminal node, measuring a zero-sequence current of the first three-phase transmission line, measuring a zero-sequence voltage of the three-phase transmission line, and calculating the zero-sequence impedance based on the zero-sequence current and the zero-sequence voltage.