Skip to main content

Classification of industrial distribution substations

Short answer

A distribution substation steps down 11/33 kV to 400/230 V for consumers. By service: step-down, switching, industrial, converting, power factor correction. By design: pole-mounted (up to 250 kVA), plinth-mounted (above 250 kVA), indoor, underground, and packaged/kiosk. Choice depends on load, space, environment, and cost.

What is distribution substation? Classify and explain briefly the distribution sub-stations in an industry, according to service and design.

A distribution substation is the substation that receives power at primary distribution voltage (11 kV or 33 kV) and steps it down to utilization voltage (400/230 V) for the consumers, with switching, protection and metering equipment. In an industry it is the point where the plant takes supply from the utility and distributes it to all shops.

Classification according to service

  1. Step-down (transformer) substation: 11/0.4 kV or 33/11 kV; the common type in industries.
  2. Switching substation: no transformer; only switches and breakers that connect or sectionalise incoming and outgoing feeders (e.g. HT switchboard in a large plant with several transformers).
  3. Industrial substation: dedicated to one large consumer; may have HT metering, multiple transformers and HT motor feeders.
  4. Converting substation: AC to DC (electrolysis, traction, DC drives) or frequency conversion (induction furnaces).
  5. Power factor correction substation: houses capacitor banks or synchronous condensers.

Classification according to design (construction)

TypeDescriptionTypical use
Pole mounted (single pole)Transformer up to about 25–100 kVA on one pole with LA, DO fuseSmall workshops, rural loads
H-pole (double pole)Transformer on a platform between two poles, up to 250 kVA (sometimes 315 kVA)Small and medium industries
Plinth / foundation mounted (outdoor)Transformer on a concrete plinth with fencing, above 250 kVAMedium and large industries
IndoorTransformer, HT and LT switchgear in a separate roomPolluted, coastal, crowded or high-load plants
UndergroundIn basement or vaultCity centres, high-rise buildings
Packaged / compact (kiosk)RMU, transformer and LT panel in one metal enclosureQuick installation, limited space

Brief explanation

  • Outdoor substations are cheaper, easy to extend and cool well, but need fencing and more space and are exposed to weather.
  • Indoor substations are safe, compact, protected from dust and weather and suitable near the load centre, but cost more (building, ventilation, fire protection).
  • Pole-mounted types are the cheapest; equipment is LA, AB switch, DO fuse, transformer and LT distribution box.
  • Package substations are factory-tested and need little site work.

The choice depends on load (kVA), space, environment, safety, reliability and cost.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Industrial Power Distribution and Illumination chapter 4 questions →