Covering three-phase ac systems from 1kV to 800 kV, provides recommended electrical operating and safety clearances and insulation levels in air-insulated electric supply substation; addresses insulation coordination procedures; provides design procedures for the selection and coordination of the insulation levels within the station as they relate to substation clearances; and addresses how reduced clearances in high-voltage ac substations will allow for compact bus arrangements and substation voltage uprating applications.