Abstract:Monitoring of winding faults is the most important item used to determine the maintenance status of a transformer. Commonly used methods for winding-fault diagnosis require the transformer to exit operation before testing and an external exciting signal, whether the transformer is malfunctioning or not. However, if an overvoltage signal can be regarded as a broadband excitation source for fault diagnosis, then the interference caused by signal injection can be eliminated without the need for additional pulse or impulse signals. In this paper, a tapped transformer is designed and test platforms are built to compare winding diagnoses using the impulse wave and sweep frequency response analysis methods by recording voltage responses on both the high-and low-voltage sides and calculating the respective transfer functions. Based on comparison of statistical indicators, it is found that the sensitivities of both methods are similar for detecting conditions of winding-ground and winding-interlayer short circuits. It is concluded that it is feasible to use a transient overvoltage monitoring system for winding-fault diagnosis.

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Winding status is an important part of transformer fault diagnosis. In this paper, the diagnosis test platform includes a reduced-scale transformer with the connection group model of Ynyn0, and its voltage ratio is 10 kV/0.4 kV. The voltage response of single-phase windings of three-winding transformers with varying degrees of short-circuit faults is measured under a damped oscillation wave with an amplitude of 4 kV and an equivalent frequency of 20 kHz. The transfer function of high-voltage phase and its corresponding low-voltage phase in the normal and fault condition is calculated. Three characteristic criterion of the transfer function are analysed in order to diagnose short-circuit faults in single-phase windings of three-winding transformers.