Thunder, Lightning and LT ACB Trip

Your earth chamber and impedance is in good condition is another story. What about your factory roof lighting earthing chamber?

Do your factory had a lighting strike earthing chamber and where, which location do you earth your factory lighting strike earth chamber?.

Without knowing a lot more details, it sounds to me as though your circuit breakers did exactly what they were intended to do!

Check the lightning protection system installed in the factory. Adding a Voltage Surge Divertor to the incomer of the Main LT Panel will make a difference

Eventhough your earthing and impedance are good,but you need to check the bonding among those grounding chamber.

The cause of the promblem are from "Different Voltage Potential"between grounding point.

You need to make sure that all the earthing chamber are bonding together by the ground wire that are buried under ground.

On what fault the LV ACB tripped? If you have a micro-processor based protection release in the ACB, there might be a possibility of earth fault trip. Pl. confirm.