Radial, loop and network distribution merits

A radial system feeds the loads from one end only. A loop (ring) system feeds each load from two directions through a closed or normally-open ring. A network (mesh) system interconnects many feeders and transformers on the secondary side, so each load has several supply paths.

 Radial:   S ===+===+===+  (one path)

 Loop:     S ===+===+===+
           |            |   (two paths)
           +============+

 Network:  S1 ==+===+===+== S2
                |   |   |
              ==+===+===+==  (mesh, many paths)

Radial system

Merits

• Simplest and cheapest system, with the lowest initial cost.
• Simple protection (fuses, OC relays) and easy operation.
• Easy to plan and extend.

Demerits

• Low reliability: a fault cuts off all consumers beyond it.
• The far-end consumers get low voltage and suffer voltage fluctuation as the load changes.
• High losses on long feeders.

Loop (ring) system

Merits

• Each load has two supply paths. A faulty section is isolated and supply is restored from the other side, giving good reliability.
• Better voltage regulation and lower losses, because the load current divides between the two paths.
• Maintenance can be done without long outages.

Demerits

• Higher cost (extra conductor, sectionalizing switches, RMUs).
• More complex protection (directional relays) when the loop is operated closed.
• Each section must be sized for the full load when the loop is fed from one side.

Network system

Merits

• Highest reliability: a single feeder or transformer outage causes no interruption.
• Best voltage regulation and lowest losses, since the load is shared among many paths.
• Good flexibility for load growth, and the transformers share load efficiently.

Demerits

• Highest cost: many interconnections, network protectors and more transformers.
• Complex design, protection and fault-current coordination; high fault levels.
• Justified only for very high load density.