Transmission line

what you have learnt in HV chapter of text book in college?

Arcing ground is the fault when a phase R or Y of B touched to ground or say sorted to earth and as a result high quantity of arc produced, which can really damage the line or electrical equipment.

Arcing ground is when the any of the phases are close enough to earth or a point which is connected earth the voltage jumps causing arcing.Normally when insulator strings develop fault u have arcing.It is very rare for a conductor to come close to earth U must have seen arcing horn on the insulator strings if not look at tower lines when u travelling next.