The purpose of this guide is to find a way to overcome the lack of consistency and unnecessary discrepancies between standards within one system. Furthermore, the cost of over-standardization of one component when the nearest linked component is under-standardized must be considered. The supplementary cost does not in any way increase the reliability of the system as a whole. Since the same external stresses (climatic, electrical, mechanical) apply to all the components of the substations, the consistency of their technical features is vital. Hence, standards will deal more and more with the same essential requirements for safety, environmental impact, end of life, availability and integration of systems. All product standards for a single system have to fulfil these requirements with the same degree of responsibility. The aim of this guide is to provide common rules for HV substation equipment.