Underground feeder economical in urban areas

In dense urban areas, underground distribution is often unavoidable for space and safety reasons. When the full costs are counted, it can also be cheaper per unit of load served than overhead lines, while in rural areas the opposite holds.

Why it is a necessity in urban areas:

• Streets are narrow and buildings close, so it is hard to keep pole and conductor clearances from balconies and windows.
• The public safety risk of bare conductors is high.
• Appearance matters (city centres, heritage zones such as Kathmandu Durbar Square).
• Many feeders and transformers must fit into a small space.

Why it can be economical in urban areas:

1. High load density (MW/km²): one cable route serves a large load over a short length. The high cost per km is spread over many kW, so the cost per kW is low. In rural areas the load is small and scattered, so the cost per kW of cable is very high.
2. Short feeder lengths: urban feeders are a few km long, while rural feeders run tens of km. Cable cost grows with length.
3. Overhead is costly in cities too: overhead lines there need short spans, special poles, covered conductors or ABC, tree trimming and more frequent repairs.
4. Reliability value: fewer faults and less outage time mean less lost revenue (kWh not sold). Urban commercial and industrial customers have a high cost of interruption, and loop or ring-main cables restore supply quickly.
5. Lower losses and maintenance: cables have lower reactance, less theft and fewer weather-related faults. These savings over 40 years or more offset the higher first cost.
6. Land value: no pole space or right-of-way is needed on costly urban land.

So, for the same total load, an underground network has a much lower life-cycle cost per kW in an urban area than it would in a rural area. Rural areas, with low density, long distances and cheap open land, remain economical with overhead lines.