During on-load switching of oil-immersed vacuum on-load tap-changers (OLTCs)

only the electrical waveforms on the odd and even sides are available. However

when these waveforms exhibit anomalies

the complex structure and switching logic of OLTCs make it difficult to identify the causes. Therefore

this paper takes the on-load switching test of a single-resistor vacuum OLTC as an example. First

a circuit simulation model of the switching test is constructed. By comparing the simulated waveforms with the waveform recordings

the accuracy of the model is confirmed. Subsequently

a simulation module that qualitatively describes the arc discharges between switch contacts is introduced. The model outputs are compared with abnormal waveform recordings to localize the anomalies and reproduce them via simulation for validation. Results indicate that two typical abnormal waveforms are attributed to “arcing between the changeover switch contacts” and “current crossing zero during the closing bounce of the main vacuum circuit breaker (VCB)”; these determinations are consistent with the core inspection. In this study

the analysis framework that combines abnormal waveform recordings with circuit simulation facilitates the localization of OLTC switching anomalies

and provides a reference for online fault diagnosis and performance improvement of vacuum OLTCs.