Power Distribution System

You are familiar along with the power supply system. You have knowledge that electricity is provided at 11 kV through electrical generators that utilize the energy from thermal, nuclear, hydro, and renewable energy resources. To transmit electricity over long distances, the supply voltage is stepped up to 132/220/400/800 kV, as required. Electricity is carried by a transmission network of high voltage lines. Commonly, these lines run into hundreds of kilometres and deliver the power within a general power pool known as the grid. The grid is linked to load centres (cities) by a sub-transmission network of usually 33 kV (or sometimes 66 kV) lines. These lines terminate into a 33 kV (or 66 kV) substation, whereas the voltage is stepped-down to 11 kV for power distribution to load points by a distribution network of lines at 11 kV and lower.

The power network of concern to the end-user is the distribution network of 11 kV lines or feeders downstream of the 33 kV substations. Every 11 kV feeder that emanates from the 33 kV substation branches additional into various subsidiary 11 kV feeders to carry power close to the load points (localities, industrial areas, villages, etc.). At these load points, a transformer further decrease the voltage from 11 kV to 415 V to gives the last-mile connection through 415 V feeders (also known as Low Tension (LT) feeders) to individual customers, either at 240 V (as single-phase supply) or at 415 V (as three-phase supply). The utility voltage of 415 V, 3-phase is used for running the motors for industry and agricultural pump sets and 240 V, schools, single phase is used for lighting in houses, hospitals and for running industries, commercial establishments and etc.