This part of IEC 62271 specifies the service conditions, rated characteristics, general structural requirements and test methods of the assemblies of the main electrical functional units of a high-voltage substation, duly interconnected, for operating voltages up to and including 52 kV on the high-voltage side, service frequency 50 Hz or 60 Hz. The CEADS is cable-connected to the high-voltage network for indoor and outdoor applications of restricted access. A CEADS as defined in this document is designed and tested to be a single product with a single serial number and one set of documentation. The functions of a CEADS can be: - switching and control for the operation of the high-voltage circuit(s); - switching and control for the operation of the low-voltage circuit(s); - protection of the power transformer functional unit; - high-voltage/high-voltage or high-voltage/low-voltage transformation; To comply with CEADS requirements it is not necessary for all main functions to exist on every product. The main functions are integrated in the following functional units: - high-voltage functional unit - power transformer functional unit - low-voltage functional unit NOTE For the purpose of this document a self-protected transformer is not considered as a CEADS, but as a functional unit, designed and type tested to its own product standard IEC 60076-13:2006.