--- title: "Classification of industrial distribution substations" subject: "Industrial Power Distribution and Illumination" chapter: 4 key: "semester_6/industrial_power_distribution_and_illumination:substation-classification-service-design" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/substation-classification-service-design site: BCT Engineering --- # Classification of industrial distribution substations Industrial Power Distribution and Illumination · Chapter 4: Distribution Substation of Industrial Plant - Asked in: 2071 Bhadra, 8 marks; 2071 Magh, 8 marks (asked 2 times) - Video: [LECTURE-11|| electric substation, classification, comparison.](https://www.youtube.com/watch?v=GAZkun9sGZg) — VISHNU CHANDRAN - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/substation-classification-service-design - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-4 ## Question What is distribution substation? Classify and explain briefly the distribution sub-stations in an industry, according to service and design. ## 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. ## Answer 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) | Type | Description | Typical use | |---|---|---| | Pole mounted (single pole) | Transformer up to about 25–100 kVA on one pole with LA, DO fuse | Small 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 kVA | Medium and large industries | | Indoor | Transformer, HT and LT switchgear in a separate room | Polluted, coastal, crowded or high-load plants | | Underground | In basement or vault | City centres, high-rise buildings | | Packaged / compact (kiosk) | RMU, transformer and LT panel in one metal enclosure | Quick 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does a distribution substation do? A. Receives power at 11 or 33 kV and steps it down to 400/230 V for consumers B. Steps up generator voltage for transmission C. Converts AC to DC for traction D. Only switches feeders without any transformer Answer: A. It provides step-down, switching, protection and metering for the plant. (Key point: Definition) 2. What distinguishes a switching substation? A. It converts AC to DC B. It steps down 11 kV to 400 V C. It has no transformer, only switches and breakers D. It houses only capacitor banks Answer: C. It connects or sectionalises incoming and outgoing feeders without changing voltage. (Key point: Switching substation) 3. A transformer on a platform between two poles is what type and up to what size? A. H-pole, up to about 250 kVA B. Single pole, up to 250 kVA C. Plinth, up to 25 kVA D. Kiosk, above 1000 kVA Answer: A. H-pole substations typically carry up to 250 kVA (sometimes 315 kVA). (Key point: H-pole limit) 4. Why is an indoor substation chosen despite higher cost? A. It is cheaper and easier to extend B. It needs no ventilation C. It is protected from dust, pollution and weather and suits crowded or polluted sites D. It cools better than outdoor types Answer: C. Indoor types cost more (building, ventilation, fire protection) but are safe and compact. 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