Electric supply system| AC power supply scheme

 The conveyance of electric power from a power station to consumers premises is known as electric supply system . 

An electric supply system consists of three  principal  components  viz. , the  power station ,.  the    transmission lines  and the distribution   system . Electric power  is produced at the power stations which are located at favourable places , generally quite away from the consumers. It is then transmitted over large distances to load centers with the help of conductors known as transmission lines.  Finally , power  is distributed  to large number of small and big  consumers  through   a   distribution network . 

The electrical supply system can be broadly classified into(I) ac or dc system (II) overhead or underground system. 

AC power supply scheme: 

          In these supply system AC power is transmitted and distributed.

(1) Generating station:

 In Fig , G.S. represents the generating station where electric power is produced  by 3-phase alternators operating in parallel. The usual generation voltage is 11 kV. For economyin the transmission of electric power, the generation voltage (i.e., 11 kV) is stepped upto132 kV (or more) at the generating station with the help of 3-phase transformers.

Generally the primary transmission is carried at 66 kV, 132 kV, 220 kV or 400 kV.

(2) primary transmission:

 electric power at 132 kV is transmitted by  3-phase, 3-wire  overhead system  to  the  outskirts of    the  city . This forms the  primary transmission.

(3) secondary transmission:

  The primary transmission     line   terminates at   the receiving station (RS) which usually lies at the outskirts of the city. At the receiving station, the voltage is reduced to 33kV by step-down transformers. From this station, electric power is transmitted at 33kV by 3-phase, 3-wire overhead system to various sub-stations (SS) located at the strategic points in the city. This forms the secondary transmission.

(4) primary distribution:

 secondary transmission line terminates at the sub-station (SS) where voltage is reduced from 33 kV to 11kV, 3-phase, 3-wire. The 11 kV   lines   run  alog  the  important  road sides of  the  city.  This forms the primary distribution. It may be noted that big consumers (having demand more than 50 kW) are generally supplied power at 11 kV for further handling with their own sub-stations.

(5) secondary distribution: 

The electric power from primary distribution line (11 kV) is delivered to distribution sub-stations (DS). These sub-stations are located near the consumers’ localities and step down the voltage to 400 V, 3-phase, 4-wire for secondary distribution. The voltage between any two phases is 400 V and between any phase and neutral is 230 V. The single-phase residential lighting load is connected between any one phase and neutral, whereas 3-phase, 400 V motor load is connected across 3-phase lines directly. It may be worthwhile to mention here that secondary distribution system consists of feeders, distributors and service mains.

Feeder:

is a conductor which connects the substation to the area where power is to be distributed .   No tapping is taken to the consumers from feeders, so the current in it remains the same throughout .

Distributors:

Are Conductor from which numerous tapping from the pole mounted transformer is taken for the supply to the consumers The current through it is not constant because tapings are taken at various places along its length Voltage drop is main consideration

Service mains :

is a small cable which connects the distributor to the consumer's meter 

I hope this helps you. Thank you ❤️.

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