Line Fault Detection Using DC Component Extraction
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Solution Overview
Problem
Current differential protection methods in electrical power supply networks are limited by slow fault detection, insensitivity to low-current faults, and issues with transformer saturation and capacitive leakage currents, which can lead to incorrect tripping and reduced sensitivity.
Innovation Solution
A method that uses voltage and current measurements at line ends to determine comparison current values, employing a mathematical model of the line to account for capacitive leakage currents and propagate traveling waves, allowing for quick and sensitive fault detection by filtering the signals with FIR or IIR filters and using a fault variable to trigger fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If current-based differential protection using fundamental wave vectors is used, then stability is improved, but tripping time increases to at least one period of the fundamental wave signal
Solution Approach 1:
The patent extracts and utilizes the direct current component from the current signal, which is normally discarded in conventional fundamental wave analysis. By measuring and evaluating the DC component directly, the method achieves fast protection without requiring full-period fundamental wave analysis, thus reducing tripping time while maintaining stability through proper DC component compensation.
Solution Approach 2:
The patent performs preliminary measurement and evaluation of the direct current component during the transient period before fault development completes. By preparing and evaluating DC component data in advance during the initial transient phase, the system can make rapid fault decisions without waiting for steady-state fundamental wave analysis.
2Reliability
If conventional current differential protection is used, then transformer saturation causes measurement errors, but blocking the protection during saturation reduces sensitivity
Solution Approach 1:
The patent introduces the direct current component as an intermediary measurement that provides independent fault detection capability. The DC component measurement serves as a mediator that can detect faults even when AC component measurements are corrupted by transformer saturation, allowing the protection to remain sensitive without being blocked during saturation events.
Solution Approach 2:
The patent changes the measurement parameter from purely AC fundamental wave components to include the DC component. This parameter change allows the protection scheme to operate reliably during transformer saturation because the DC component behavior differs from the AC component and is less affected by saturation effects.
3Stability of the object's composition
If charge differential protection with insensitive threshold values is used, then stability is improved, but detection of low-current faults becomes difficult
Solution Approach 1:
The patent changes the measurement parameter from integrated charge to instantaneous current including DC component. This parameter change enables the use of lower threshold values for fault detection because the DC component provides immediate fault indication without the need for integration over time, thereby improving detection sensitivity for low-current faults while maintaining stability through proper threshold setting.
Data Source
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AI summary
The invention relates to a method for detecting a fault on a line (11) of an electrical power supply network, in which current values are measured at the line ends (11a, 11b) of the line (11) and the presence of a fault on the line (11) is checked using these current values. To monitor the line in such a way that faults can be detected relatively quickly and sensitively, it is proposed that voltage values also be measured at the line ends, and that corresponding reference current values be determined from the respective measured current and voltage values. These reference current values indicate the current flowing at a reference point (18) on the line (11), and the presence of a fault on the line (11) is checked using these reference current values. A fault signal is then generated if a fault is detected on the line (11) during the check.The invention also relates to a protective device (15a) for carrying out the method and a protective system with at least two protective devices.