The OLTC of a power transformer plays a vital role in maintaining a stable voltage level within the electrical grid. It’s a mechanical switching device that regulates the system voltage by adjusting the transformer turns ratio. Due to the thermal and mechanical stresses generated when the load current is switched, various OLTC components such as the contacts can suffer wear and tear over their lifetime.
In order to reliably assess the condition of the OLTC, increasingly advanced diagnostic tools have been developed. Typically, a static resistance measurement is performed to check for increased contact resistances. Moreover, a dynamic resistance measurement (DRM) records the change in current during the switching operation to analyze the OLTC's timing and check for possible current interruptions.