ABSTRACT
High-voltage transformers play an irreplaceable role in the distribution and transmission of electricity in the electricity system. Special power transformers are transformers used in high voltage direct current power transmission systems. The basic diagnostic electrical quantities used in the non-disassembly diagnostics of MV transformers include verification of their conversion ratios, determination of phase sequence and clock angle, winding resistances, short-circuit voltage and current, leakage current and insulation resistance, capacity, loss and polarization factor, and ratio capacitances at 2 and 50 Hz. The active resistance of the winding is measured at all windings of the disconnected transformer; while measuring one of the windings, the other windings are disconnected. In order for the transformers to run in parallel, it is necessary to observe, in addition to the same nominal primary and secondary voltages of the transformers, their same sequence and phase rotation.
