what is the maximum distant coverd by one lightning arrester?

Answer 1

I think you've mis-stated your question.

LIGHTNING ARRESTOR - A protective device that provides a very low resistance path to any voltage above its rated value.

In effect, a lightning arrestor will protect the phase of the device wiring *and, subsequently the device itself) immediately downstream (away from the strike). A 3-phase machine will require 3 arrestors, one per phase.

Answer 2

An area with a radius equal to the height of the lightning arrestor from the ground (approximately)