It is developed from the principle of electromagnetic induction and is composed of a closed core and windings.
When the equipment is running close to a short circuit, the primary large current can be converted into a small current according to the set value, and then to the secondary meter, The relay protection provides energy for measurement. "
I(P) = Primary current in Amps
I(s) = Secondary current in Amps
CT ratio formula:
CT ratio = I(P) / I(s) ————-1
Example: 1000:1. Here 1000 means it is a primary current and 1 means secondary current. Also, we can have rewritten as 1000/1.
CT secondary current will be always 1 or 5 to get easy calculation as well as we can create small rating secondary circuits to withstand up to 5 Amps.