What is the chief purpose of neutral grounding?

Protection of equipment during deterioration of winding insulation in order the current will discharge to the ground. The neutral grounding is the current pathway going to the ground during ground faults due to deterioration of winding insulation. It will serve also as protection of employee preventing electric shock (touch voltage).

grounding or earthing is a zero ohm exit ,in case a surge or short circuit happened 

usually use a well ,with suitable calculated copper rod to be connected with electrical panels 

To protect the equipment and supply transformer from fault currents and humans from electric shock by providing an alternae path to the return current.

To protect the equipment from electrical fault and avoid electric shock by providing a circuit to ground

As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures.

In MLTP the neutral connected to earth to prevent fault current bad effect on transformer.

In neutral grounding system, the neutral of the system or rotating system or transformer is connected to the ground. 

c'est une protection contre les fuites de courant electrique qui sert un danger sur les humains et les machines 

la mise à la terre ,est une protection contre les courants de fuite ,et les courtcircuits.

Take the current back to the source

The neutral grounding is an important aspect of power system design because the performance of the system regarding short circuits, stability and provides greater safety to personnel and equipment.