Transformer Winding Fault Detection Using Negative Sequence Current
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Solution Overview
Problem
Conventional protection methods for transformers are insufficiently sensitive in detecting winding faults, particularly internal short circuits, due to the low measurable current at the transformer terminals, making it difficult to detect faults early enough to prevent damage.
Innovation Solution
The method involves forming an auxiliary variable as an integral of the product of negative sequence current values on both the high and low voltage sides, allowing for more sensitive detection of winding faults by distinguishing between internal and external errors through the sign of the auxiliary variable and considering asymmetry in phase conductor-related differential currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional protection methods (differential protection, overcurrent protection) are used to monitor transformer currents, then the protection mechanism is simple and reliable, but the sensitivity to detect internal winding faults is insufficient because the current increase at transformer terminals is very small
Solution Approach 1:
The invention transforms the protection approach by changing the parameter being monitored from simple current magnitude to negative sequence current components. By decomposing the current into symmetrical components (positive, negative, and zero sequence), the method extracts the asymmetric part of the current that characterizes internal winding faults. This parameter transformation enables detection of small internal faults that are invisible to conventional magnitude-based protection methods.
Solution Approach 2:
The invention introduces negative sequence current as an intermediary parameter that mediates between the actual fault condition (internal winding short) and the measurable quantity at the transformer terminals. The negative sequence current component acts as a sensitive indicator that amplifies the effect of internal faults, making them detectable despite the small current increase at the terminals. This intermediary parameter bridges the gap between the fault location and the measurement point.
2Reliability
If the sensitivity of fault detection is increased to detect small internal error currents, then early fault detection is enabled, but false positives may increase due to external errors or switch-on processes
Solution Approach 1:
The invention exploits the asymmetry principle by focusing specifically on the negative sequence current component, which represents the asymmetric part of the three-phase current system. Internal winding faults create current asymmetry that manifests as negative sequence components, while external faults and normal operation typically maintain symmetry. By selectively monitoring only the asymmetric component, the method achieves high sensitivity to internal faults while inherently filtering out symmetric disturbances that cause false positives.
Solution Approach 2:
Instead of monitoring the symmetric positive sequence current that dominates normal operation and external faults, the invention inverts the approach by monitoring the small asymmetric negative sequence current component. This inversion allows the detection method to focus on the distinctive signature of internal faults rather than being overwhelmed by the larger symmetric current components present during normal operation and external faults.
Data Source
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AI summary
The invention relates to a method for detecting a winding fault in a transformer (41) of an electrical power supply network, in which phase conductor-related current measurements are recorded on the high-voltage side (A) and the low-voltage side (B) of the transformer (41), counter-system current values are determined from the phase conductor-related current measurements for the high-voltage side (A) and the low-voltage side (B) respectively, and a fault signal is generated when a winding fault in the transformer (41) has been detected using the counter-system current values.To enable even more sensitive detection of a winding fault in a transformer, it is proposed that an auxiliary quantity be formed using a sequence of counter-system current values of the high-voltage side (A) and a sequence of temporally related counter-system current values of the low-voltage side (B), a decision be made on the basis of the auxiliary quantity as to whether a winding fault is present in the transformer (41), and the fault signal be generated if a winding fault is present.