Impedance-Angle Fault Detection During Power Transmission Swings
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Solution Overview
Problem
Existing fault detection methods in power transmission systems during power swings are unreliable, particularly when delta currents are not available, leading to undetected faults and potential system failures or blackouts, due to dependence on threshold-based incremental current measurements which are influenced by source impedance ratios, fault inception angles, and fault locations.
Innovation Solution
A method utilizing the change in impedance angle, calculated from sampled voltage and current measurements, to detect and classify faults in power transmission systems, independent of current thresholds, allowing for accurate single-ended fault detection and classification during power swings, especially at swing center voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If threshold-based incremental current measurements are used for fault detection during power swings, then fault detection can be performed, but the detection reliability deteriorates when delta currents are minimal or absent
Solution Approach 1:
The patent changes the measurement parameter from incremental current (delta current) to impedance angle. By calculating the impedance angle from voltage and current measurements and monitoring its rate of change, the system achieves reliable fault detection during power swings even when delta currents are minimal or absent. This parameter transformation resolves the contradiction by making the measurement independent of current magnitude while maintaining fault detection capability.
2Stability of the object's composition
If relays are blocked during power swings to prevent false tripping, then relay operation stability is improved, but fault detection capability deteriorates
Solution Approach 1:
The patent introduces an intermediary fault detection mechanism that operates independently of the blocked relay system. The impedance angle monitoring system acts as a mediator that can detect faults during power swings and trigger relay unblocking only when necessary, thus maintaining relay stability during normal power swings while enabling fault detection when needed.
Solution Approach 2:
The system performs preliminary fault detection using impedance angle monitoring before relay tripping decisions are made. By continuously monitoring the rate of change of impedance angle during power swings, the system can identify faults in advance and prepare for appropriate relay action, ensuring both stability and fault detection capability.
3Reliability
If delta current based fault detection is used, then fault detection can be achieved, but the system becomes sensitive to source impedance ratios, fault inception angles, and fault locations
Solution Approach 1:
The patent transforms the fault detection parameter from delta current to impedance angle and its rate of change. This parameter change makes the detection method independent of source impedance ratios, fault inception angles, and fault locations, as the impedance angle characteristics during faults are more consistent and less influenced by these varying system parameters.
Data Source
AI summary
Fault detection during a power swing in a power transmission system is described. Voltage and current measurements are obtained for each phase at a terminal of the power transmission system. Based on measurements obtained, a value of change in an impedance angle for each phase-to-ground loop and each phase-to-phase loop for each sample of the voltage and current values is calculated, where the value of change in the impedance angle is a difference between impedance angles of two samples separated by a predetermined interval. The average values for change in impedance angle based on a predetermined number of values of change in the impedance angle for each phase-to-ground loop and each phase-to-phase loop is calculated. The average values are compared with a threshold range of change in impedance angle. Based on the comparison, a fault in one or more of the phase-to-ground loops or phase-to-phase loops is detected and classified.