Yes, you are right to ask questions in this matter.

Even your alternators (60 or 50 Hz, does not matter) will be connected to the 220 kV grid it is very likely that any stronger lightning around the overhead lines (220 kV side) could induct a very high voltage on the 10.5 kV side and damage alternator(s) windings. All three phases of generator terminals must have surge single-phase protections. They could be in a separate cell in the switching board/panel. Their common point must be, of course, grounded.

Overcurrent protection in "traditional configuration" should have CT (Current transformers) on the back.rear side of three phase windings of the generators and if differential protection is installed with zero second time delay it should protect against overcurrent spikes too. There are very good protection schematics referred by generator manufacturers. I understand that monitoring of faults-to-ground are installed too so no significant unpredictable damages can happen.

I do not make any suggestion to step-up transformers protection. It is most of the time in the grid technical management responsibility. You may just get approval from them according to the coordination of electrical protection systems installed on your side (alternators) vs. their protections.