Zero sequence currents in AC lines caused by transients in adjacent DC line

The cause of large zero-sequence transients in AC lines caused by transients in a neighbouring earth-return DC circuit is discussed. Both a qualitative reasoning and a quantitative parametric study are provided. The results show that very large transients can occur even for lines relatively far apart. The transients show up only when nonzero earth resistivity is included in the model. The effect of different ground resistivities, earthing resistances, and the presence or absence of ground wires is also discussed