The objective of this investigation is the modelling of protective current transformers. Based on a model for CTs of class P, models were developed for CTs of class TPX (closed-core), TPY and TPZ (nonclosed-core). All models are based on known rated values of the CTs. This is an advantage of the presented method, because no additional measurements of the parameters of the CTs are needed. Application examples are pointed out and a simulation example is presented.