At the moment there is a big storm going on in my area with a lot of lightning and thunder.

A few minutes ago there was a big flash and loud thundrclap, and everything went dark.

I looked outside and the street lights were still on, so there must be electric.

Went to my fuse box and all three safety cuts had tripped, no other breaker tripped.

To describe my situation. I have my own transformer single phase 30KVA.

Below the transformer is a 100A breaker, from where the cables go into the house. In the fuse box it is split up in 3 circuits that have each their safety cut and and surge protector.

I switched on the three safety cuts and all was fine again.

What has happened, and where should I look for eventual damage ??

^{My guess is that the lightning created an imbalanced surge on your lines which caused the RCD's (SafetyCut) to trip. Make sure they still work (use the TEST) but most likely all is fine.}

Do press the 'Test' buttons to verify the Safe-T-Cuts are still operational, other than that (assuming they do trip) don't worry.