The specifications of this part refer to general respectively core communication requirements of the application functions in all domains of power utility automation systems. Dedicated communication requirements and most examples of application functions in this part are from the domain substation automation but may be reused in or extended to other domains within power utility automation systems. Note that sometimes instead of the term substation automation domain the term substation domain is used, especially if both the switchyard devices (primary system) and the automation system (secondary system) are regarded. The description of the application functions is not used to standardize these functions, but to identify communication requirements between Intelligent Electronic Devices (IEDs) hosting these functions within plants and substations in the power system, between such stations s (e.g. between substation for line protection) and between the plant or substation and higher level remote operating places (e.g. network control centres) and maintenance places. Also interfaces to remote technical services (e.g. maintenance centres) are considered. The general scope is the communication requirements for power utility automation systems. The basic goal is interoperability for all interactions providing a seamless communication system for the overall power system management. Another prerequisite for interoperability is a commonly defined method for time synchronization. Standardizing application functions and their implementation is completely outside the scope of this standard. Therefore, it cannot be assumed a single philosophy of allocating application functions to devices. To support the resulting request for free allocation of these functions, a proper breakdown of these functions into parts relevant for communication is defined. The exchanged data and their required performance are defined. The same or similar IEDs from substations like protective and control devices are found in other domains like power plants also. Using this standard for such devices in these plants facilitates the system integration e.g. between the power plant control and the related substation automation system. For some of such other application domains like wind power plants, hydro power plants and distributed energy resources specific standard parts according to IEC 61850 series have been already defined and published.