--- title: "Substation classification and indoor substation" subject: "Industrial Power Distribution and Illumination" chapter: 4 key: "semester_6/industrial_power_distribution_and_illumination:substation-classify-indoor" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/substation-classify-indoor site: BCT Engineering --- # Substation classification and indoor substation Industrial Power Distribution and Illumination · Chapter 4: Distribution Substation of Industrial Plant - Asked in: 2073 Bhadra, 4 marks - Video: [Comparison Between Indoor and Outdoor Substation | Selection of Site for Substations](https://www.youtube.com/watch?v=8yvPi53lkLY) — IB TECHNICAL CLASSES - 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-classify-indoor - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-4 ## Question Classify the distribution sub-station of industrial plant according to service and design. Describe the functions and operating characteristics of indoor substation with proper schematic diagram. ## Short answer By service: step-down, switching, converting, PF correction. By design: outdoor, indoor, underground, packaged. Indoor substation houses all equipment indoors: HT room with isolator, VCB, relays; transformer room steps voltage; LT room with ACB, MDB, MCCBs, APFC panel. Characteristics: weather-protected, safe, load-centre location, but costlier, needs ventilation and fire protection. ## Answer #### Classification of industrial distribution substations **By service**: step-down (11/0.4 kV) substation, switching substation, converting substation (AC/DC), power factor correction substation. **By design**: outdoor (pole-mounted, H-pole, plinth-mounted), indoor, underground and packaged (compact/kiosk) substations. #### Indoor substation: functions and operation All equipment is inside a building, divided into HT room, transformer room and LT room. ```text 11 kV cable in | [Isolator]-[VCB + relay] HT room | (TR) 11/0.4 kV TR room | [ACB]== MDB ==[MCCBs] LT room |-[APFC] v to SDBs ``` - **HT room**: isolator and VCB with overcurrent and earth-fault relays switch and protect the incoming 11 kV supply. - **Transformer room**: steps down to 400/230 V; oil pit and fire wall for oil units, or dry-type for fire safety; ventilation louvres. - **LT room**: ACB incomer, busbars, MCCB feeders, meters and capacitor bank distribute power to SDBs. **Operating characteristics**: protected from weather and dust, safe and compact, can be placed at the load centre; but costlier, needs ventilation and fire protection, and is limited to about 33 kV. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which are classification by design? A. Step-down, switching, converting B. Single-phase and three-phase C. HT and LT only D. Outdoor, indoor, underground and packaged substations Answer: D. Service classes are step-down, switching, converting and PF correction. (Key point: Design classes) 2. What are the three rooms of the indoor substation? A. Battery, fuse and relay rooms B. HT room, transformer room and LT room C. Control, generator and store D. Metering, lighting and panel rooms Answer: B. HT incomer isolator and VCB; transformer; then ACB and MDB. (Key point: Rooms) 3. What is a characteristic of indoor substation operation? A. Cheapest and unlimited voltage B. Needs no fire protection C. Exposed to dust D. Protected from weather and dust, can be at load centre, but costlier and needs ventilation Answer: D. Limited to about 33 kV. 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