Horizontal publication giving guidance for the harmonization of product and system standards within substations where the highest voltage for equipment is higher than 1 kV. Contains recommendations for common specifications for all HV substation product standards, each of which is augmented by the technical background specific to each TC, which naturally retains freedom in its technical choices. For use by TCs involved in high-voltage (HV) substation systems, such as TCs 13, 14, 17, 20, 22, 28, 32, 33, 36, 37, 38, 57, 95 and 99.