Step potential (or voltage) near electric power lines
When the insulators aren't faulty, there isn't any noteworthy current flowing from the mast into ground. So the step voltage on the ground is very low.

That is much different e.g. from an earthing circuit in a TT or SWER power distribution system. Here, there is a noteable current running into the ground and countermeasures against too high step voltages near the earthing electrode have to be taken. Usually this is done by using several ring shaped earth electrodes around the building or the mast carrying the local transformer.