Carrier Frequency Harmonics Generated By HVDC Conversion

The operation of the Sylmar HVDC Converter Station has generated interference voltages in the carrier frequency range. Especially a 24 kHz oscillation has caused interference with carrier-type line protection in the ac system as well as with equipment in the station itself. It was shown that the 24 kHz oscillation was caused by a resonance between a RI-filter reactor and stray capacitances in the converter transformers. The comparison between digital simulations and measurements in the station gives a general indication of how complex a digitdl model of a converter station shall be for calculating interference voltages. Such calculationis are expected to be of increasing importance in the future.