Basic Electrical Engineering

Power distribution system, Feeder line, Distributor, Classification of distribution system, Service lines

Power distribution system

The medium voltage transformer using transmission lines are reduced by step down transformer (415V, or 240V) are used to the consumer. This system includes the feeder lines, distributors and service mains.

Feeder line

The feeder line is nothing but similar as power transmission conductors. It connects the power from sub-station and power supply to the consumers. The voltage is uniform throughout the conductor.


Electric power is distributed to the consumer by tapings. Since electric power is taken from many tappings and the current is not uniform in all. Therefore, when designing the distribution system, care must be taken to the voltage drop.

Classification of distribution system

According to scheme of connections the distribution system is classified as,

a. Radial distribution system

b. Ring main distribution system

c. Grid or interconnected distribution system

a. Radial distribution system

In this system, each load junctions are connected through separate feeders and they are controlled by the sub-stations. This method is used when the low voltage exists in the center of the city. If there is a fault in any feeder, the whole circuit will be affected.

b. Ring main distribution system

This system designed like a closed ring. Each load junctions were constructed one after another. Electricity is provided from two supply sources in different places for each load junctions. If one gets faulted, the other can be used to get power supply. This system is used in places where low and medium voltage is required. In this way there may be a chance of low voltage fluctuations happening for the consumers. Power supply can be provided by more than one feeder. Reliability can be generated by supply of electricity through each of the two feeders.

c. Grid or interconnected distribution system

More than one power plants and sub-stations are connected in series feeders are called as ‘Interconnected distribution system.’ It is also called as grid. In this system, the power plant and sub-station are connected together, and the voltage is reduced to 33KV, by using transformer. This method increases the reliability and efficiency. Electricity can be provided from different power plants during high power consumption.

Service lines

Service line is low length connecting conductor. These service lines act as conductor between distribution pole and consumer.

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