Protected Line Fault Detection Using Sequence Components
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Solution Overview
Problem
Existing methods for detecting faults in AC power transmission systems, such as high-voltage or medium-voltage systems, face challenges in accurately identifying fault locations and distinguishing between healthy and faulty phases, especially with high-impedance faults and remote end infeed, which can lead to incorrect impedance measurements.
Innovation Solution
A method that uses intelligent electric devices (IEDs) to determine sequence components of phase voltages or currents, calculates operating and restraining quantities based on these components, and compares their properties to detect faults, thereby avoiding uncertain impedance calculations and providing reliable fault detection and phase identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance measurements are used to detect faults, then fault detection capability is provided, but measurement accuracy deteriorates due to high-impedance faults and remote end infeed effects
Solution Approach 1:
The patent changes the measurement parameters from traditional impedance-based measurements to sequence component-based measurements (positive, negative, and zero sequence voltages and currents). This parameter transformation allows the system to maintain fault detection capability while avoiding the measurement inaccuracies that occur with high-impedance faults and remote end infeed conditions, as sequence components provide a different perspective on the electrical state that is less susceptible to these specific error sources.
2Loss of information
If measurement values are sent between devices at different ends of the transmission line to identify fault position, then fault location capability is achieved, but system complexity and communication requirements increase
Solution Approach 1:
The patent enables each end of the transmission line to independently determine sequence components and evaluate fault conditions using local measurements only. The sequence component calculation and fault detection logic are performed locally at each intelligent electronic device without requiring exchange of measurement data between ends. This self-service approach eliminates the need for complex communication protocols and data synchronization while maintaining full fault location capability.
3Reliability
If impedance measurements are performed for healthy phases, then complete system monitoring is achieved, but measurement uncertainty increases due to semaphore effect and other interference
Solution Approach 1:
The patent segments the three-phase system into independent sequence component systems (positive sequence, negative sequence, and zero sequence). By analyzing each sequence component separately, the method can identify faults in specific phases without the measurements being affected by phenomena like the semaphore effect that interfere with traditional impedance measurements of healthy phases. Each sequence component provides independent information about the system state.
Data Source
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AI summary
The present disclosure relates to a method of detecting a fault in a protected line (114) constituting at least a portion of a transmission line (101) in an alternating current, AC, power transmission system (100). The transmission line has at least one phase, and the AC power transmission system has at least one intelligent electric device, IED, (111, 112) connected with the transmission line. The method comprises: - determining, for each phase, based on measurements at the at least one lED of at least one of a phase voltage and a phase current, at least one electric parameter; - determining sequence components at a chosen point of the transmission line, on basis of the electric parameters; - determining, for each phase, an operating quantity, OP, on basis of at least one of a first and a second sequence component of the sequence components; - determining, for each phase, a restraining quantity, RST, on basis of a third sequence component of the sequence components; and - comparing, for at least one phase, a property of the OP with a corresponding property of an associated RST, which is the RST for the same phase as the OP.