Electric Power Distribution System Topologies: Radial, Ring, Parallel & Interconnected
An electric power distribution system can be classified based on the configuration of its feeder connection schemes, also known as distribution topologies. The four most commonly used configurations are:
- Radial distribution system
- Parallel feeders distribution
- Ring main distribution system
- Interconnected distribution
Note: Other variations exist, but these four are the most widely implemented.
[Also read: Classification of distribution systems according to number of phases and wires involved.]
Radial distribution system
This system is used only when the substation or generating station is located at the center of the consumer zone. In this system, different feeders radiate from a substation or a generating station and feed the distributors at one end. Thus, the main characteristic of a radial distribution system is that the power flow is in only one direction. Single line diagram of a typical radial distribution system is as shown in the figure below. It is the simplest system and has the lowest initial cost.
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| Image credit: Wikimedia commons |
Key Characteristics:
- Power flows in one direction only
- Simplest and least expensive configuration
- Low initial cost
Drawbacks:
- Low reliability – a fault in the feeder will result in supply failure to associated consumers as there won't be any alternative feeder to feed distributors
- Maintenance leads to service interruption
Parallel feeders distribution system
The above-mentioned disadvantage of a radial system can be minimized by introducing parallel feeders. The initial cost of this system is much more as the number of feeders is doubled. Such system may be used where reliability of the supply is important or for load sharing where the load is higher. (Reference: EEP - Distribution Feeder Systems)
Key Characteristics:
- Improved reliability
- Better load-sharing in high-demand areas
Drawbacks:
- High initial cost due to doubling of feeders
Ring main distribution system
A similar level of system reliability to that of the parallel feeders can be achieved by using ring distribution system. Here, each distribution transformer is fed with two feeders but in different paths. The feeders in this system form a loop which starts from the substation bus-bars, runs through the load area feeding distribution transformers and returns to the substation bus-bars. The following figure shows a typical single line diagram of a ring main distribution system.
Ring main distribution system is the most preferred due to its following advantages.
Advantages of ring main distribution system
- There are fewer voltage fluctuations at consumer's terminal.
- The system is very reliable as each distribution transformer is fed with two feeders. That means, in the event of a fault in any section of the feeder, the continuity of the supply is ensured from the alternative path.
Interconnected distribution system
When a ring main feeder is energized by two or more substations or generating stations, it is called as an interconnected distribution system. This system ensures reliability in an event of transmission failure. Also, any area fed from one generating stations during peak load hours can be fed from the other generating station or substation for meeting power requirements from increased load.
Key Characteristics:
- Redundant power sources in case of failure
- Load sharing between substations during peak demand
- Highly suitable for dense metro areas
Summary Comparison
| Distribution Type | Reliability | Cost | Power Flow | Best For |
|---|---|---|---|---|
| Radial | Low | Low | One-directional | Small towns, rural areas |
| Parallel Feeders | Moderate | High | One-directional | High-load, industrial zones |
| Ring Main | High | Moderate | Bidirectional | Urban & residential areas |
| Interconnected | Very High | Very High | Multi-directional | Metropolitan grids |