1. Technology

1.1 General

The variety of instrument transformer designs depends on the voltage level to which they are subjected and, in the case of high voltage, on the substation technology into which they are integrated:

• open substations (also known as conventional), in which external isolation of the equipment is ensured by long distances in the ambient air;

• shielded substations, in which the switchgear is placed in a metal enclosure and insulation is provided by pressurized sulfur hexafluoride (SF ₆ ).

Regardless of the voltage level, three essential parts can be distinguished in instrument transformers:

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