Radial, ring & mesh
The key idea
A radial network feeds every customer along exactly one path — cheap and simple, but one fault darkens everything downstream. Rings and meshes add second paths: faults hurt less, and protection has to work harder.
The idea
Every network is built from three basic shapes:
Radial — a tree. Power flows outward from the source along branches that never rejoin. Most distribution feeders are radial: cheapest to build, easy to protect (current only ever flows one way), simple to analyze. The cost: every element is a single point of failure for everything beyond it.
Ring — a loop. The feeder returns to the source, so every bus can be fed from either direction. A faulted section is switched out, and the rest of the ring keeps everyone else on supply. Many urban networks run as rings — often open rings: built as a loop, but operated radially with one normally-open point that closes when a fault makes it useful.
Mesh — many loops. Transmission networks interconnect everything with everything, so the loss of any one line — or several — leaves the power a way through. Maximum resilience, maximum analytical complexity: flows divide among parallel paths according to impedance, and only a power flow can say how.
Try it
Place the same fault on a radial feeder, then on the ring, and compare who stays on supply.
buses off supply: 2 of 3
2 buses are off supply. On a radial feeder, everything downstream of the fault goes dark until the repair is done. Switch to the ring and place the same fault.
Why it matters
- Shape sets the customer minutes lost. On the radial feeder, a mid-feeder fault takes everything downstream off supply until the repair is done. On the ring, the same fault costs one section.
- Shape sets the protection problem. Radial protection is a one-way street graded from the far end back to the source. Close a ring and current can flow either way — the scheme now needs direction awareness, and the grading exercise doubles.
- Accidental shape changes are real faults in waiting. A ring closed by mistake shows up as a loop in the topology; a mesh operated as if radial hides parallel paths that carry real current. See islands & topology for the reverse problem.
See it in Phasor
Phasor's Graph Space shows the shape directly: a radial feeder straightens into a tree, and every loop is detected and marked — so an intended ring and an accidental one are equally visible. Decide for each loop whether it belongs.