Transformer Winding Fault Detection Using Negative Sequence Power
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Solution Overview
Problem
Conventional methods for detecting winding faults in transformers, such as differential protection, struggle to sensitively detect internal faults like turn-to-turn shorts due to high currents being difficult to measure externally, leading to delayed detection and potential transformer damage.
Innovation Solution
The method involves determining negative sequence system currents and voltages on both high-voltage and low-voltage sides of the transformer, using the negative sequence power calculated from these values to detect winding faults by examining power direction and position in a tripping diagram, enhancing sensitivity and ease of detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional differential protection methods are used to detect winding faults, then the protection mechanism can identify external faults, but internal faults like turn-to-turn shorts remain difficult to detect due to insufficient sensitivity
Solution Approach 1:
The invention changes the detection parameter from conventional differential current to negative sequence power (combining negative sequence current and voltage). This parameter transformation enables sensitive detection of internal winding faults by capturing the asymmetric characteristics of fault currents, resolving the contradiction between measurement precision and reliability for internal fault detection.
Solution Approach 2:
The invention introduces negative sequence power as an intermediary parameter that mediates between the difficult-to-measure internal fault currents and the external measurement system. By converting internal fault characteristics into negative sequence power calculations from external current and voltage measurements, it enables reliable internal fault detection without directly measuring internal currents.
2Productivity
If high inrush currents occur during transformer switching, then the transformer can be energized, but strong vibrations cause mechanical loads that may lead to turn-to-turn shorts
Solution Approach 1:
The invention enables preliminary detection of winding faults that may result from inrush current vibrations. By continuously monitoring negative sequence power during and after switching operations, the system can detect early signs of turn-to-turn shorts caused by mechanical damage, allowing preventive action before catastrophic failure occurs.
3Reliability
If a very high current flows within a short-circuited turn, then the fault is severe and dangerous, but this current can hardly be measured from the outside
Solution Approach 1:
The invention uses negative sequence power as an intermediary that translates internal fault current information into measurable external quantities. By calculating negative sequence power from external current and voltage measurements, the system can reliably assess the severity of internal faults without directly measuring the inaccessible internal short-circuit currents.
Solution Approach 2:
The invention replaces direct electrical measurement of internal currents with a computational approach using external electrical measurements. Instead of attempting to physically measure internal currents, the system substitutes a calculation-based method using negative sequence power derived from external sensors, overcoming the measurement accessibility problem.
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-related current measurements are acquired on the high-voltage side (A) and the low-voltage side (B) of the transformer (41), and a fault signal is generated when a winding fault in the transformer (41) has been detected using the current measurements. To enable the most sensitive possible detection of a winding fault in a transformer, it is proposed that phase-related voltage measurements be acquired on the high-voltage and low-voltage sides of the transformer (41), and that the fault signal be generated when a winding fault in the transformer (41) has been detected using the current and voltage measurements. The invention also relates to an arrangement (40) for carrying out the method.