The following connection schemes of the power distribution system are generally employed:

Radial Distribution System

In a radial distribution system, separate feeders radiate from a single sub-station and feed the distributors at one end only. A single-line diagram of a radial system for AC distribution is shown in the figure.

Here substation supplies power to a distributor AB at end A through feeder OC. This system is only employed when power is generated at low voltage and the substation is located at the center of the load.

Advantages of Radial System

• Its initial cost is minimal.
• It is the simplest distribution system.

Disadvantages of Radial System

• The end of the distributor nearest to the feeding end would be heavily loaded.
• The consumers are dependent on single feeder and distributor. Therefore, when a fault occurs on the feeder or distributor, the supply is cut off to all the consumers who are on the side of the fault away from the substation.
• The consumers at the far end (B) of the distributor would be subjected to serious voltage fluctuations because of changing the load on the distributor.

Due to the above limitations, this system is used for short distances only.

Ring Main Distribution System

In this system, the feeder closes on itself i.e. it forms a complete ring hence the name ring main system. The figure shows the ring main system, where BCDAB is the closed feeder supplied by the sub-station S at point B. The various distributors are connected to points A, C, and D of the feeder.

Advantages of Ring Main System

Each distributor is supplied via two feeders, for example, the distributor connected at point C is fed via feeders BC and BADC. This reduces the voltage fluctuations at the consumer’s terminals to some extent.

The system is more reliable since each distributor is fed via two feeders. In the event of a fault on any section of the feeder, the continuity of supply can be maintained. For instance, suppose a fault occurs at any point F of section CD of the feeder, then section CD of the feeder can be isolated for repairs, and at the same time continuity of supply is maintained to all the consumers.

Interconnected Distribution System

An interconnected distribution system is a type of electrical power distribution system where multiple power sources or substations are linked together to create a closed loop.

This system provides several advantages over traditional radial distribution systems, where power flows from a single source to consumers.

In an interconnected distribution system, the feeder loop is energized by two or more than two generating stations or substations. The breakers or switches are strategically placed at various points in the loop. These breakers can be used to isolate faulted sections of the system, minimizing the number of customers affected by an outage.

The figure shows the single-line diagram of an interconnected distribution system, where the closed feeder ring ABCA is supplied by two generating or substations S₁, and S₂, at points X and Y respectively. Distributors are connected to the feeder at points A, B, and C.

Advantages of Interconnected Distribution Systems

Improved Reliability: In the event of an outage on one section of the loop, power can still be delivered to customers from the other direction. This ensures a more reliable supply of electricity to consumers.

Reduced Losses: By having multiple power sources, interconnected systems can help to reduce energy losses that occur during transmission over long distances.

Load Balancing: Interconnected systems allow for better load balancing between different substations, which can improve overall system efficiency.

Integration of Renewable Energy Sources: Interconnected systems can more easily integrate renewable energy sources, such as solar and wind power, which can be variable and intermittent.

Interconnected distribution systems are becoming increasingly common in urban and suburban areas, where there is a high demand for reliable electricity. They are also well-suited for industrial facilities and critical infrastructure, where outages can be disruptive and costly.

While interconnected distribution systems offer several benefits, there are also some considerations to be aware of. The initial cost of installing an interconnected system can be higher than a radial system. Additionally, the added complexity of the system can require more sophisticated control and monitoring systems.

Design Considerations of Distribution System

The main elements of a distribution network are the feeders and distributors. To maintain the required voltage at the terminals of a consumer, proper care has to be taken while designing these elements.

Feeder design: While designing a feeder, the main consideration is its current carrying capacity. The voltage drop consideration is relatively unimportant. The reason is that the voltage drop in a feeder can be compensated by using voltage-regulating equipment placed at the substations.

Distributor design: While designing a distributor, the main consideration is the voltage drop in it. The current carrying capacity consideration is not that much important. The reason is that the distributor supplies power to the consumers and there is a statutory limit to the voltage fluctuations at the consumer’s terminals. Hence the size and length of the distributor are designed in such a way that the voltage at the consumer’s terminals is within the permissible limits.