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Substation classification and indoor substation

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.

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.

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.

 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.

✓ Answer checked by Claude Opus 5.5 (high effort)

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