Most utilities require grounding transformers to satisfy their effective grounding requirement. However most utilities apply the X0/X1<3 and R0/X1<1 criterium to meet this requirement which is inconsistent with the recommendations of C62.96.6. Standard C62.92.6 has some further discussion on Effective Grounding in Section 8.1. In addition there is a report published by EPRI with some additional information titled Effective Grounding for Inverter-Connected DER. Good luck!
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic ù and this we know it is, for certain ù then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". û Nikola Tesla