Hi folks,
Just for your information, in our grid (Chesf, Northeast of Brazil), all 500kV, 230kV, 138kV systems are solidly grounded. But our 69kV system is supplyed from a delta winding conneted tranformer and there is a zig-zag reactor in each 69kV busbar for grounding reference.
Remember that the "guard cable" or "earth wire" which is installed at the top of the trasmission line towers for lightning protection, connects the grounding mesh of system substations and seems to work as a (almost) "neutral wire" for HV grounded systems.
Best regards,
Herivelto Bronzeado