A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. Substations generally have switching, protection and control equipment and one or more transformers. In a large substation, circuit breakers are used to interrupt any short-circuits or overload currents that may occur on the network. Smaller distribution stations may use re closer circuit breakers or fuses for protection of distribution circuits. Substations do not usually have generators, although a power plant may have a substation nearby.

In Nepal, while the problem of lack of generating capacity had been solved by construction of hydropower stations, weaknesses in power transmission and distribution system were being disclosed.

Layout of Substation

The layout of the substation is very important since there should be a Security of Supply. In an ideal substation all circuits and equipment would be duplicated such that following a fault, or during maintenance, a connection remains available. Practically this is not feasible since the cost of implementing such a design is very high. Methods have been adopted to achieve a compromise between complete security of supply and capital investment. There are four categories of substation that give varying securities of supply:

  1. No outage is necessary within the substation for either maintenance or fault conditions.
  2. Short outage is necessary to transfer the load to an alternative circuit for maintenance or fault conditions.
  3. Loss of a circuit or section of the substation due to fault or maintenance.
  4. Loss of the entire substation due to fault or maintenance