Why we do 2 types of earthing on tranformer ie:body earthing & nutral earthing , what is function?

There are two types of earthing are Familiar as Equipment earthing and System earthing.
 In Equipment earthing: body ( non conducting part)of the equipment should be earthed to safeguard the human beings.
System Earthing: The neutral of the supply source ( Transformer or Generator) should be grounded.

Figure: Transformer Earthing

• With this, in case of unbalanced loading neutral will not be shifted.so that unbalanced voltages will not arise. We can protect the equipment also. 
• With size of the equipment( transformer or alternator)and selection of relying system earthing will be further classified into:

1. directly earthed, 
2. Impedance earthing, 
3. Resistive (NGRs) earthing.

Why Transformer Body need earthing?