Ok, if this isn't some monkey business but proper engineering design, this has to be 230 kV. Althought I've never seen a 220 kV pylon with as many as 18 standard disc units in a suspension string in EU (I think 16 being the most), that number can vary on several things (altitude, predicted contamination/polution level etc). OTOH, I heard there are still operating 345 kV lines with single conductor per phase somewhere in the states. And these are rare. In such cases used ACSR conductors are massive (dia> 1.7"). More importantly, corona suppression rings are put on ends of insulators with no exception.