Skip to main content

Single line diagram from 11 kV to end use

Short answer

The SLD shows 11 kV feeder, lightning arresters, AB switch, drop-out fuse, 11/0.4 kV Dyn11 transformer, LT breaker, MDB, SDBs, and final circuits. Components: LA diverts surges, AB isolates, DO fuse protects transformer, transformer steps down, LT breaker protects secondary, MDB distributes, SDBs feed loads, APFC corrects power factor.

Draw a neat single line diagram of a 11 KV start from 11 KV to end use 230 V. Explain briefly about each component.

The single line diagram (SLD) shows, with one line for all three phases, how power flows from the 11 kV utility line through the distribution substation to the 230 V end users.

Single line diagram

 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

Function of each component

  1. 11 kV incoming feeder: overhead line (or HT XLPE cable) from the utility (NEA) substation.
  2. Lightning arresters (LA): one per phase, connected between line and earth; divert lightning and switching surges to ground and protect the transformer insulation.
  3. AB switch / isolator: gang-operated, off-load switch for isolating the substation for maintenance; operated only after the load is removed.
  4. Drop-out fuse (DO) / HT VCB: protects the transformer and the 11 kV line from transformer faults. Large industrial substations use a VCB or SF₆ breaker with overcurrent and earth-fault relays.
  5. HT metering (CT/PT): for HT consumers, measures energy in kWh, kVAh and maximum demand for billing.
  6. Distribution transformer 11/0.4 kV, Dyn11: steps voltage down to 400 V line / 230 V phase; delta HV blocks triplen harmonics, star LV gives a neutral for single-phase loads. Neutral and tank are earthed separately.
  7. LT main breaker (ACB/MCCB): main switch and overload/short-circuit protection on the secondary; LT energy meter, ammeter and voltmeter.
  8. Main distribution board (MDB): copper busbars that feed outgoing circuits through MCCBs or switch-fuse units.
  9. APFC panel: automatic capacitor bank that keeps power factor near 0.95–0.99, reducing current and penalty charges.
  10. Sub-distribution boards (SDB): located near load centres (each shop or floor); they have MCCB/MCB incomers and MCB outgoings.
  11. Final circuits: MCBs, RCCBs/ELCBs, motor starters (DOL, star-delta) for 400 V motors, and 230 V lighting and socket circuits between one phase and neutral.
  12. Earthing system: separate earth electrodes for transformer neutral, body/equipment and lightning arresters; protects people and lets protection operate.

Single-phase end users are balanced across R, Y and B phases so the transformer is equally loaded.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Industrial Power Distribution and Illumination chapter 4 questions →