Winding Deformation Tester (Transformer Winding Deformation Tester) is typically based on Frequency Response Analysis (FRA) or short-circuit impedance method. It is the "CT scanner" for diagnosing whether the internal windings of a power transformer have undergone mechanical displacement, distortion, bulging, or inter-turn short circuits. After a transformer experiences short-circuit current impact, transportation collisions, or long-term operational vibration, the windings may suffer from minor deformations invisible to the naked eye. If not detected in time, these deformations can lead to catastrophic winding collapse during the next short-circuit impact. The following is an in-depth analysis combined with the technological status in 2026: 1. Core Working Principle A. Frequency Response Analysis (FRA) - Mainstream Method Principle: The transformer winding can be regarded as a complex distributed parameter network composed of resistance (R), inductance (L), and capacitance (C). The geometric shape of the winding (such as turn spacing, distance to ground) determines its capacitance and inductance values. Process: The instrument injects a swept sine wave signal (typically from 10Hz to 2MHz or higher) into one end of the winding. The response signal is measured at the other end. The amplitude-frequency characteristic curve (gain vs. frequency) is calculated and plotted. Diagnostic Logic: If the winding deforms (e.g., axial displacement, radial bulging), the internal L and C distribution parameters will change. This causes shifts in the resonant point frequency, changes in peak/valley amplitudes, or distortion of the curve shape. By comparing the current curve with the original fingerprint curve (from factory or initial commissioning) or with three-phase transverse comparison curves, the degree and location of deformation can be determined. B. Short-Circuit Impedance Method (Auxiliary Method) Principle: Measures the equivalent impedance of the transformer when the low-voltage side is short-circuited. Logic: Winding deformation leads to changes in leakage flux, causing a change in short-circuit impedance (typically a change of more than 1%-2% is considered abnormal). Features: Simple operation, but insensitive to minor deformations; usually used as a supplementary verification method for FRA. 2. Main Application Scenarios Diagnosis after Short-Circuit Impact: After a short-circuit fault occurs at or near the transformer outlet, immediate testing is required to determine if the winding is damaged and whether it is necessary to lift the cover for inspection. Inspection after Transportation/Installation: Verify the internal structural integrity of large transformers after long-distance transportation or severe jolts. Periodic Preventive Testing: Incorporate into condition-based maintenance plans, establish winding health records, and monitor deformation trends. Fault Location: Use the curve change characteristics in different frequency bands (low, medium, high) to preliminarily determine the location of deformation (e.g., middle of low-voltage winding, end of high-voltage winding, etc.). 3. New Technology Trends in 2025-2026 High-Precision Wideband Scanning: The frequency range of new-generation instruments extends to 10Hz - 5MHz or even 10MHz. High-frequency bands (>1MHz) are more sensitive to winding end insulation and lead deformation, while low-frequency bands (<1kHz) are more sensitive to the core and overall structure. Intelligent Correlation Coefficient Algorithm: No longer relies on manual visual inspection; built-in algorithms from DL/T 911 (China Electric Power Industry Standard) and IEC 60076-18. Automatically calculates correlation coefficient (R), standard deviation (SD), and root mean square error (RMSE). Directly provides diagnostic conclusions: "Normal", "Mild Deformation", "Moderate Deformation", "Severe Deformation", and marks suspicious frequency bands. Enhanced Anti-Interference Capability: In response to the complex electromagnetic environment at substation sites, digital filtering, multiple averaging, and adaptive noise cancellation techniques are used to obtain smooth curves even under strong interference or during live testing (with special wiring). 3D Visualization and Cloud Comparison: Supports superimposed display of three-phase curves and provides 3D view analysis. Data can be directly uploaded to the cloud for comparison with a "big data fingerprint library" of transformers of the same model and batch, solving the problem of missing original data for some old transformers. Integrated Design: Integrates FRA, short-circuit impedance, and no-load loss testing into one device, enabling multiple diagnostics with a single instrument.
