--- title: "Substation classification and 11 kV schematic" subject: "Industrial Power Distribution and Illumination" chapter: 4 key: "semester_6/industrial_power_distribution_and_illumination:substation-classification-11kv-schematic" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/substation-classification-11kv-schematic site: BCT Engineering --- # Substation classification and 11 kV schematic Industrial Power Distribution and Illumination · Chapter 4: Distribution Substation of Industrial Plant - Asked in: 2073 Magh, 2+6 marks - 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-11kv-schematic - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-4 ## Question Classify the distribution substation of industry according to service and design. Draw and explain the schematic diagram of a distribution substation of a typical industry from 11 kV to end use. ## Short answer By service: step-down, switching, converting, PFC substations. By design: outdoor (pole/plinth), indoor, compact. Schematic: 11 kV feeder → LA → AB switch → DO fuse → metering → 11/0.4 kV Dyn11 transformer → LT breaker → MDB → MCCBs to SDBs for motors (400 V) and lighting (230 V), plus APFC panel. ## Answer #### Classification of industrial distribution substations **According to service** - Step-down (transformer) substation: 11/0.4 kV or 33/11 kV. - Switching substation: only switchgear, no transformer. - Converting substation: AC to DC or frequency conversion. - Power factor correction substation: capacitor banks. **According to design** - Outdoor: pole-mounted (single pole), H-pole (double pole, up to about 250 kVA), plinth-mounted (above 250 kVA). - Indoor: equipment inside a building. - Underground and packaged/compact (kiosk) substations. #### Schematic diagram from 11 kV to end use ```text 11 kV overhead feeder (utility, NEA) | [LA] lightning arresters (3 nos) | [AB] air-break / gang-operated isolator | [DO] drop-out fuse (or HT VCB + relay) | [HT metering CT/PT] (for HT consumers) | (TR) 11/0.4 kV, Dyn11 transformer | neutral + body earthed [ACB / MCCB] LT main breaker + LT meter | ======== MDB 400 V, 3-ph 4-wire busbar ======== | | | | MCCB MCCB MCCB MCCB | | | | SDB-1 SDB-2 SDB-3 APFC panel (motors) (lighting) (sockets) (capacitors) | | | MCB/MPCB MCB MCB/RCCB | | | 400 V M 230 V lamps 230 V outlets ``` #### Explanation 1. **11 kV incoming** line from the utility feeder. 2. **Lightning arresters** protect the transformer from lightning and switching surges. 3. **AB switch** isolates the substation (off-load) for maintenance. 4. **DO fuse** (or VCB with overcurrent and earth fault relays in bigger plants) protects the transformer from internal faults and overloads. 5. **HT metering** for energy billing of HT consumers. 6. **11/0.4 kV Dyn11 transformer** gives 400 V line and 230 V phase voltage with a solidly earthed neutral. 7. **LT ACB/MCCB** is the main LT switch and protection; LT meters show current, voltage and energy. 8. **MDB** busbars divide power into feeders with MCCBs; an **APFC panel** improves power factor. 9. **SDBs** near each shop feed **motors** (through starters and overload relays) at 400 V and **lighting and sockets** at 230 V through MCBs and RCCBs. 10. **Earthing** of neutral, equipment bodies and arresters completes the system. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a classification by service? A. Pole, plinth and underground B. Step-down, switching, converting and power factor correction substations C. Indoor and outdoor only D. Single-phase and three-phase Answer: B. Pole, plinth, indoor and underground relate to design. (Key point: Classification by service) 2. What size separates H-pole from plinth-mounted substations? A. About 25 kVA B. About 1000 kVA C. About 50 kVA D. About 250 kVA Answer: D. H-pole up to 250 kVA, plinth above 250 kVA. 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