The economics of generations of electrical energy and the huge demands for power in the modern times require creation of bigger and bigger power houses, may these be hydroelectric, steam or atomic. The power houses may be far from load centers, as in case of hydropower houses or may be in midst of population in case of steam power houses. Long and high voltage transmission lines are necessary to transmit huge blocks of power from the sources of generation to the load centers to interconnect power house for increased reliability of supply, greater system stability and lesser stand by power plant and hence cheaper electrical energy. In between the power houses and ultimate consumers a number of transformation and switching stations have to be created .These are known as Substations.
Depending upon the purpose, the substations are classified as Step up Substation, Primary Grid Substation, Secondary Substation, Distribution Substation, Bulk Supply and industrial Substation, Mining Substation, Mobile Substation and Cinematograph Substation.
The Step up Substation is associated with the generating stations. The generating voltage is limited due to the limitation of the rotating machinery and needs to be stepped up to the primary transmission voltage so that huge blocks of power can be carried over long distances to the load centers.
The Primary Grid substation is created at suitable load centers along the primary transmission line. The primary transmission voltage is stepped down to a number of suitable secondary voltages along these secondary transmission lines. At actual load points secondary Substations are created where the voltage is further stepped down to sub transmission and primary contribution voltage.
Distribution Substations are created where the supply has to be given to the consumers by stepping it down into lower voltages say 220V or 444V. The bulk supply and industrial substation is generally distribution substation with the difference that the substations are created each for one consumer and subsequent distribution of electric power is left to particular consumer who may be bulk supply consumer or industrial consumer of large or medium supply.
The mining substation as their name indicates are substations, required for very special purposes and need special design consideration because of the extra precautions for safety needed in the operation of electric supply. The mobile substation is also of special purpose and design needed primarily for temporary requirements due to construction purposes.
Depending on construction, Substations are of four types, Outdoor type, Indoor type, Basement or underground type, Pole mounting –open or Kiosk type. For reasons of cost and safety, it is common to have outdoor substation for 33 KV and above it. The modern Substation is complex structure as it requires numerous items of equipment and allied service before it can serve the purpose.
