Impact of stray capacitance on HVDC harmonics

Stray capacitances inherent to HVDC converters are shown to cause all triplen harmonics to appear on the DC side. In particular, odd-triplen harmonics are produced which in a bipolar DC system will cause ground-mode simulation of the DC transmission line. The levels predicted by simulation can be large enough to cause significant telephone interference if the DC filtering, including both pole and neutral buses, is not designed to accommodate these harmonics. Field experience provides qualitative support for this theory.<>