Urban Distribution Networks

Distribution inside the urban load centre

Urban networks are made up of large numbers of 10 kV substations feeding housing estates, mixed-use complexes, offices and municipal facilities directly. They stay energised all year, the load curve swings between day and night and light-load periods are long, so no-load loss behaves as a fixed cost and takes a significant share of annual energy losses.

Space in cities is scarce: equipment ends up in basement substation rooms, podium levels or beside landscaped areas, under constraints on footprint, noise, fire protection and appearance. Outages for maintenance are hard to schedule once a substation is in service, which is why urban networks favour fully sealed, maintenance-free transformers and assemblies that can sit inside the load centre.

What urban substations have to cope with

The difficulty is not the rating of a single unit but the number of units and their running hours: hundreds of distribution transformers operate between light and medium load for years, and every fixed loss is multiplied by those hours.

• Long light-load periods at night and on holidays, so no-load loss weighs heavily on annual consumption
• Strict noise and fire-protection limits in substation rooms, basements and residential areas
• Tight sites that call for compact layouts and short construction schedules
• A largely cabled network: both ring-main and terminal supply arrangements must be possible
• Scattered substations and limited maintenance staff, so long maintenance-free intervals are required

Equipment selection therefore has to answer three questions at once: are the annual losses low enough, does the equipment fit on site, and will it need frequent attention once energised?

Coreda's approach for urban networks

We build the configuration around low no-load loss, compact prefabrication and maintenance-free operation, combining transformer, MV switchgear and LV distribution into a substation package that suits the site.

Recommended configuration:

• SCBH19 amorphous-alloy dry-type transformer: grade 1 energy efficiency, amorphous-alloy core with vacuum-cast epoxy resin and class H insulation, flame-retardant and explosion-proof — suited to basement substation rooms and load centres in tall buildings.
• SBH25 amorphous-alloy oil-immersed transformer: wound amorphous-alloy core in a fully sealed corrugated tank (ONAN), no-load loss roughly 1/3 to 1/4 of a silicon-steel S13 unit of the same rating and noise about 5–10 dB(A) lower.
• YBM European-style prefabricated substation: MV switchgear, distribution transformer and LV distribution assembled in the factory, small footprint and short installation time, to GB 17467—1998.
• GGD and GCS LV assemblies: fixed or withdrawable cubicles depending on the number of feeders, covering incoming, feeder and reactive-power compensation duties.

The three families combine freely by substation size: dry-type transformers indoors, complete prefabricated substations outdoors and in industrial parks, and like-for-like replacement to bring losses down step by step in retrofit projects.