budhiman (Electrical)(OP)25 Oct 23 21:30
"...#1. Can a Current Transformer with a ratio of 50/5 be effectively utilized on a 1200A bus or incoming cables? ....#2. What are the key considerations when using this CT on a higher ampacity application?...#3 any recommendations for CTs that can accurately detect 48 Amps?"
1. No. A 50/5 CT shall NOT be used on 1200 A bus/incoming cable. Not only the current rating but also the "window size" is unlikely to be able to accommodate 1200 A bar/cable.
2. The CT primary shall be = or > 1200 A. The secondary may be 1 or 5 A. Therefore, the CT shall be minimum 1200/5 or 1200/1, may use 1600/5 or 1600/1 ; which are the standard ratings.
3. Use any 1200/5 measuring CT would be able to detect 48 A, which 48A x 1200/5 = 0.2 A. Note: use "measuring" CT NOT "protection" CT.
3.1 Why you want to detect 48A accurately on a 1200A system? Do you mean 48A earth-fault current? If so, see 3.2.
3.2 To detect 48A for earth-fault protection, you may use a very big window zero-sequent CT (Z CT) with a corresponding protection relay by the OEM. In this case, detection accurately 48A zero sequency-current is possible without any difficulty.
Che Kuan Yau (Singapore)