Can I connect a Sepam 2000 on 2 CTs instead of 3?

Yes, but using 2 CTs instead of 3 means that certain protection functions will not be available (current maximum, total resistance, for example). The number of CTs must be selected when the Sepam 2000 parameters are set. The way in which the negative sequence current is calculated depends on whether 2 or 3 CTs are connected.