Fault Condition Assessment of Transformer On-load Tap-changer Contacts Based on Joint Electromechanical Diagnosis

On-load voltage regulating transformers play a crucial role in power systems, not only connecting to the grid but also regulating reactive power and stabilizing loads. The on-load tap-changer (OLTC), as the key component of the on-load regulator, is the only movable part of the transformer, and its reliability is directly related to the safe and stable operation of the power grid. Therefore, timely identification of operational defects and rapid localization of mechanical faults in OLTCs through online monitoring is crucial for the operation and maintenance of transformers in the field. In this paper, firstly, the mechanism of on-load tap-changer contact faults is analyzed in depth, and on this basis, a diagnostic method for OLTC contact faults is proposed for the joint analysis of electric-vibrational signal features. Secondly, in order to extract high-quality fault features, the Ensemble Empirical Mode Decomposition (EEMD) algorithm is used to process the vibration signals and motor current signals to extract the fault features. Meanwhile, their envelope time-domain features are extracted by the Hilbert transform. Finally, the experimentally obtained electric-vibration joint signal features are utilized to deeply analyze the contact state of OLTC and evaluate its fault state.