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Operating deflection shapes (ODSs) are used for visualizing the vibration patterns of a structure. In this study, ODSs are applied to diagnose the mechanical condition of power transformer windings. First, a synchronous calibration measuring system is developed to simultaneously acquire tank vibration signals and excitation voltage signals. To perform the synchronous calibration, the phase of the excitation voltage signals is set as the reference. Next, the no-load test, load test, and variable load test are conducted on a 50-kVA transformer. The histogram of oriented gradient (HOG) and Pearson correlation coefficient (CC) are proposed to describe the differences between the different ODSs. Experimental results show that the ODSs are insensitive to the operating voltage and current, but sensitive to the clamping pressure of the windings. Field results further verify the significant change in the ODS after winding deformation. Finally, the partial ODS, which is suitable for practical transformers, is proposed to locate winding mechanical defects in power transformers. The proposed method can improve the efficiency and accuracy of the vibration-based mechanical condition monitoring of power transformers.

The vibration of the oil-tank can reflect the mechanical condition of transformer internal windings and cores. Although there were several studies about the vibration of the transformer, most of them do not take into account the inherent connection between different measuring points, which results in insufficient utilization of vibration information. To conquer this shortcoming, a fault diagnosis method for transformer winding looseness based on vibration sensor array is proposed. An array measurement system was set up, and a suitable measurement method was put forward. Because the voltage fluctuation of the transformer in actual operation is very small while the load current fluctuates greatly and the winding vibration is mainly influenced by the current. Load tests were conducted on a single-phase transformer. The influence of the current on the vibration characteristics was studied. Different levels of winding looseness were set up and their vibration characteristics were studied. The matrix distance was used to judge the deviation of the array signal. The results show that the array signal does not change with the current change. When the windings are loosened, the array distance of the array signal increases significantly. It provides a new idea for the diagnosis of the mechanical fault of transformer windings based on vibration signals.