There are many but, these are some of the most essentials :

1- Invironmental nature of the substation.

2- Climatic nature

3- Nature of your network

4- Transformer capacity

5- Types of protection to be provided

DANGAMBO HUSSAINI

P.H.C.N KANO NIGERIA

The main criteria are transformer size, type, usage, voltage level, special requirement etc.

Based on these criteria, the transformers have the sub-set of the following protections and/or alarms:

(1) Over current

(2) Earth Fault

(3) Differential

(4) Under/Over Voltage

(5) Sudden Tank Pressure Rise

(6) Directional protection for parallel operation

(7) Buchholz protection

(8) Oil Temperature

- MS