Analysis of three-phase transformer no-load characteristics

The traditional laboratory experiment on three-phase transformer connections consists of a qualitative observation of current and phase voltage waveforms by means of an oscilloscope, with emphasis placed on the dominant third harmonic component. Some recorded waveshapes, however, cannot be explained in simple terms without considering other harmonic components and the quality of power supply. This paper outlines an improved lecture/experiment that quantitatively analyzes the waveforms of various transformer connections under steady-state no-load conditions while taking into account the nonideal voltage supply. The experimental data obtained with the aid of a harmonic analyzer are then compared to the qualitative predictions and the discrepancies are discussed