SOLUTION

The main criterion for the selection of the size of a distribution for a radial distribution system is station is located in the center of the load.

According to the scheme of connection, the distribution system may be classified as:

(a) Radial system

(b) Ring main system

(c) Inter-connected system

Radial System

1. If a distributor is connected to the supply system from one end only, it is called a radial system of distribution.
2. This is also true for the feeders i.e. if a feeder is connected to the supply system from one end only that feeder is called a radial feeder.
3. The main characteristic of a radial distribution system is that the power flow is in only one direction.
4. There are combinations of one distributor and one feeder, connecting that distributor to the substation.
5. In distributor 1 is connected only at one end to the substation through a feeder at point A. Similarly, the other feeder is feeding distributor 2, only at one point B.

Advantage of Radial System

• Simple in operation
• Low initial cost
• Useful when the generation is low voltage
• Radial system is preferred only when the station is located in the center of the load

In a radial distribution system, for a given length (l) and area of cross-section (A), the resistance of the conductor is given by

$R = frac{{rho l}}{A}$

Voltage drop is given by V = IR

In order to reduce the voltage drop, the size of the conductor must be increased (for a fixed given length) so that the resistance of the conductor is reduced. Hence rated voltage can be maintained at the load terminal.

Disadvantages of Radial System

1. The end of the distributor near to the substation gets heavily loaded.
2. When load on the distributor changes, the consumers at the distant end of the distributor face serious voltage fluctuations.
3. As consumers are dependent on a single feeder and distributor, a fault on any of these two causes interruption in supply to all the consumers connected to that distributor.