This part of IEC 62271 is applicable to three-phase AC high-voltage generator circuit-breakers, hereafter called generator circuit-breakers, designed for indoor or outdoor installation and for operation at frequencies of 50 Hz and 60 Hz on systems having voltages above 1 kV and up to 38 kV. It is applicable to generator circuit-breakers that are installed between the generator and the transformer terminals. Requirements relative to generator circuit-breakers intended for use with generators and transformers rated 10 MVA or more are covered specifically. Generator circuits rated less than 10 MVA and pumped-storage installations are considered special applications, and their requirements are not completely covered by this document. This document is also applicable to the operating mechanisms of generator circuit-breakers and to their auxiliary equipment.