What Parameters / Factors to consider while selecting a CT for an Application?

i assuming you are asking about the current transformer,

Factors are:

1- load current rating to determine the rated primary current of the CT.

2- the metering or the protection sys. used (1A or5A) to determine the secoundry of the CT.

3-Rated burden of the CT this can be detemined by CT calculation

4-Accurcy class needed

5-aplication (Metering or protection)

6-withstand short circuit current

7-Rated voltage

8- Knee point voltage for saturation