PC 127 - Low-voltage auxiliary power systems for electric power stations and substations

IEC TS 63346-2-3:2025 specifies common rules and requirements for the design of low voltage (LV) AC auxiliary power systems (APSs) intended to be installed in substations, mainly covering the configuration of AC power sources, system wiring, protection, electric equipment selection and physical layout.
For the purpose of interpreting this document, an AC APS in this document is considered as follows:
- with a nominal voltage up to and including 1 kV AC;
- providing LV AC power to substation AC loads.
Though it is discussed where necessary, AC loads as well as high voltage (HV) part is beyond the scope of this document.
Substations in this document refer to those which are part of an electrical system and contain equipment that either receives and distributes electrical energy or transforms voltages to the levels required by the loads they supply, or both.

IEC TS 63346-1-1:2024 contains the terms used by low-voltage auxiliary power systems in power stations, substations, converter substations and associated telecommunications equipment. Terms relating to low-voltage auxiliary power systems in nuclear power stations and railways substations are beyond the scope of this document.