ABSTRACT
Instrument transformers are very important parts of electric power systems. They are indispensable for the proper functioning of the system, because they are elements of the measurement systems as well as the protection systems. The instrument transformers can be constructed as combined instrument transformers, as they consist of current and voltage transformers in the same case. The designer of current transformers should be aware of the magnitude of peak voltages that may be generated at the terminals of the designed current transformer as well as the consequences this would bring. High-voltage and medium voltage devices also create many problems concerning the electric strength of the insulation system of the instrument transformer, especially for the combined instrument transformer. The combined instrument transformer is composed of two parts: current and voltage transformers in a common housing. The electric strength of an insulation system during the design process is achieved using an iterative approach.
