Introduction: Electrical power System and Supply System

electrical power system

The electrical energy is normally generated at the power stations far away from the urban areas where consumers are located. The problem, therefore, is to transmit the large blocks of power over long distances economically. There is a large network of conductors between the generating stations and the consumers. The network is called the transmission and distribution system.


The transmission system is to deliver bulk power from power stations to the load centers and large industrial  consumers beyond the economical service range of the regular primary distribution lines whereas distribution system is to deliver power from power stations or substations to the various consumers.


Although electrical power can be transmitted and distributed by either ac or dc but in practice 3-phase 3-wire ac system is universally adopted for transmission of large blocks of power and 3-phase 4-wire ac system is usually adopted for distribution of electrical power.

Electrical Power System

Modern ac electrical power systems usually consist of the






  1.  Generating Stations
  2. Step-up Transformer Stations
  3. Transmission Lines
  4. Switching stations
  5. Step-down transformer stations
  6. Primary (high voltage) distribution lines or networks
  7. Service Transformer banks
  8. Secondary ( Low Voltage ) distribution lines

Essentially elements 2, 3, 4 and 5 fall in the transmission system and elements 6, 7 and 8 fall in the distribution system. All systems of power transmission and distribution may or may not include all elements enumerated above; For example, some systems may have no primary transmission, some may not have secondary transmission and the others may not have transmission at all, being very small and so on.

The distribution system may further be divided into feeders (conductors connecting the stations, in some cases generating stations, to the areas to be fed by those stations), distributors (conductors from which numerous tapping for the supply to the consumers are taken and service mains ( the conductors connecting the consumers to the distributors).

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