Detecting transformer winding faults requires specialized techniques that can identify insulation degradation, short circuits, or mechanical damage without disassembling the transformer. One of the most effective methods is Frequency Response Analysis (FRA), which evaluates the winding’s electrical impedance across a wide frequency range (typically 10 Hz to 1 MHz). The winding acts as a complex network of inductors, capacitors, and resistors, and any physical change (such as turn-to-turn short circuits, winding displacement, or insulation breakdown) alters its frequency response. By comparing the FRA signature of a healthy transformer with that of a suspect one, technicians can detect even minor faults. For example, a turn-to-turn short circuit reduces the winding’s inductance, leading to a shift in the resonance peaks of the FRA curve.

　　Low-Voltage Impedance Testing is another commonly used method for detecting winding short circuits. This test involves applying a low AC voltage to one winding (with other windings open or shorted) and measuring the resulting current to calculate impedance. A significant decrease in impedance compared to the manufacturer’s specifications indicates a short circuit—since shorted turns reduce the effective number of turns, lowering inductance and impedance. This method is simple, cost-effective, and suitable for both on-site and factory testing.

　　Polarization Index (PI) and Insulation Resistance (IR) Testing focus on evaluating the insulation quality of the windings. IR testing measures the resistance of the winding insulation to ground (or between windings) using a high-voltage DC source, with low resistance values indicating moisture, contamination, or insulation degradation. PI testing is an extended version of IR testing, measuring insulation resistance at 1 minute and 10 minutes after voltage application. The ratio of these two values (PI = R10/R1) provides insights into the insulation’s moisture content and aging condition—a PI value below 2 typically indicates poor insulation quality, which may precede winding faults.

　　For more advanced detection, Online Winding Temperature Monitoring uses fiber-optic sensors embedded directly in the windings to measure temperature in real time. Abnormal temperature rises in specific winding sections can signal short circuits or overloading, allowing for immediate intervention. Combined, these methods provide a multi-layered approach to winding fault detection, ensuring early identification and minimizing damage to the transformer.

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