Majority of electrical substations will be the air insulated type. All the electrical equipment live parts will be exposed. All the electrical equipment in the substation shall be arranged in such a manner to ensure the clearance space between the live parts and other equipment of the substation (grounded or ungrounded). Adequate clearances should be provided for the safety of the operating and maintenance personnel and also prevent any conducting path between the phases. Safety clearances associated with different voltage levels are given in the table below.
Safety Clearances in Substation
|Minimum Clearances (mm)||765 kV||400 kV||220 kV||132kV||33kV|
|Phase to Phase||9400||4200||2100||1300||320|
|Phase to earth||6400||3500||2100||1300||320|
- Phase to phase clearance is the minimum clearance required to be provided between the live parts of different phases or is the minimum clearance between the same phases.
- Phase to earth clearance is the minimum clearance required to be provided between the live parts of the system and earth structures.
- Sectional clearance is the distance between the live parts of the phases and the terminals of the work section. This limits of work section or maintenance section may be a platform or ground on which operation personnel can carry out his task safely.
- Ground clearance is the vertical clearance between the live parts of the equipment and the earth surface.