AC Side Current Harmonics Measurement and Analysis of UHVDC Converter Transformer

Current harmonics is crucial for converter transformer design considering temperature/loss and vibration/noise. For line commuted current high voltage direct voltage (LCC HVDC) system, harmonics has been analyzed thoroughly with assumptions for simplification (e.g. that transformer is ideal). However, the waveforms in practice, especially for UHVDC system, can be different due to nonideal conditions and they are rarely reported in literature. This paper designed a harmonics measurement system to extract the AC side winding current for a converter transformer in a +/- 800kV UHVDC system. Harmonics characteristics is analyzed and simulation is performed for comparison. It is observed that with the increase of transmitted power, both the total harmonic distortion and single harmonic distortion decrease. The measured waveform are asymmetric with inrush spikes which is different from traditional theoretical analysis and the possible cause is given.