Combined measuring transformers are a combination of voltage and current transformer. The most commonly applicable solution consists of a combined transformer with an inverse current transformer and an inductive voltage transformer. Measuring transformers of all manufacturers should comply with the international standard for measuring transformers under the designation IEC-61869-1. Additional requirements for combined transformers are found in the IEC standard under the designation 61869-4. In the fourth chapter of the work, a comparison is made between the manufacturers of Koncar, Siemens and ABB combined transformers and, based on their characteristics, common characteristics are reached for oil combined transformers and combined transformers insulated with SF6 gas.