Winding Deformation Tester, typically based on Frequency Response Analysis (FRA) or low-voltage short-circuit impedance method, is a precision diagnostic instrument specifically designed to detect the mechanical condition of power transformer windings (such as displacement, distortion, bulging, inter-turn short circuits, etc.). It serves as the "CT scanner" for determining whether internal windings have deformed after short-circuit current surges, transportation impacts, or long-term operation, and is crucial for preventing catastrophic failures caused by transformers operating with defects. 1. Core Working Principle Currently, mainstream instruments adopt the Frequency Response Analysis (FRA) method, with the following principle: Sweep Excitation: The instrument injects a series of sinusoidal voltage signals at different frequencies (typically 10 Hz to 10 MHz or higher) into one end of the transformer winding. Response Acquisition: The response voltage signal is measured at the other end of the winding. Spectrum Analysis: The amplitude ratio (gain/attenuation) and phase difference between the input and output signals are calculated, and a frequency response curve (Bode plot) is plotted. Fingerprint Comparison: The winding structure of the transformer (distribution of inductance, capacitance, and resistance) determines its unique frequency response "fingerprint." If the winding deforms (e.g., inter-turn short circuit, overall displacement, local bulging), the internal distributed capacitance and inductance parameters change. This causes shifts in resonant frequencies, changes in peak/valley amplitudes, or distortion of the curve shape. By performing correlation analysis between the current test curve and the factory original curve (or cross-comparison among three phases, or longitudinal comparison with similar transformers), the degree and location of deformation can be precisely identified. Note: Some instruments also incorporate the low-voltage short-circuit impedance method as auxiliary verification, measuring the change rate of short-circuit impedance to assess overall deformation. 2. Main Types of Faults Detected Axial Displacement: The winding moves up or down along the core leg. Radial Deformation: The winding collapses inward or bulges outward (common in low-voltage windings). Inter-turn/Inter-disc Short Circuit: Local short circuit caused by insulation damage. Lead Displacement: Internal leads become loose or shift. Poor Contact of Tap Changer Contacts. Abnormal Grounding or Multiple Grounding of the Core.
