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SUBSTATION

Indoor 11 kV to 400 V distribution substation single line diagram

This substation single line diagram shows an indoor 11 kV to 400Y/230 V distribution substation for a building. An 11 kV utility cable enters an SF6 ring main unit load-break switch, then passes through a transformer fuse to a 630 kVA cast-resin transformer. A 1000 A low-voltage air circuit breaker supplies the main distribution bus.

UPDATED 2026-09-23
TYPESld
USE-CASESubstation
EXAMPLEIndoor 11 kV to 400 V distribution substation single line diagram
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CASE ANALYSIS

Scenario

This indoor package substation feeds a building LV distribution bus from an 11 kV cable via an RMU and cast-resin transformer.

Key decisions

  • Indoor MV isolation: An SF6 RMU load-break switch receives the 11 kV cable supply.
  • Transformer branch: A 63 A fuse protects the 630 kVA transformer primary.
  • Dry transformer: Cast-resin construction suits an indoor equipment room.
  • LV main protection: A 1000 A ACB feeds the 400Y/230 V distribution bus.
  • Building feeders: Lighting, power, and HVAC loads are independently protected.

When to reuse this

Use this for a building-scale indoor substation concept. Room ventilation, fire strategy, protection settings, and local MV standards must be verified.

FAQ

Frequently asked questions

Why use a cast-resin transformer indoors?01
It avoids liquid dielectric fluid and is commonly selected for indoor applications.
What is the RMU switch used for?02
It provides compact medium-voltage switching and isolation at the cable incomer.
Does a transformer fuse replace all protection?03
No. Final protection design must coordinate MV fuses, LV breakers, and upstream utility devices.
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