IEC/IEEE 62271-37-013:2015(E) is applicable to three-phase a.c. high-voltage generator circuit-breakers, hereafter called generator circuit-breaker, 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 standard. This standard is also applicable to the operating mechanisms of generator circuit-breakers and to their auxiliary equipment. This standard has been prepared by a joint working group comprised of members both from IEC 17A/WG 52 representing subcommittee 17A: High-voltage switchgear and controlgear, of IEC technical committee 17: Switchgear and controlgear, in cooperation with IEEE WG P62271-37-013 representing the Switchgear Committee of the Power and Energy Society of the IEEE, under the IEC/IEEE Dual Logo Agreement.