250 kW Office Building Power: 380 V LV Distribution + 80 kVA UPS + 80 kW Diesel Backup Deep-Read
380 V LV switchgear · 80 kVA online UPS (30 min) · 80 kW standby diesel · fire end-transfer ATS
1 · TL;DR Conclusion
Conclusion: this 250 kW office building uses 380 V LV distribution + an 80 kVA online UPS (30 min) for the 60 kW IT-room critical load + an 80 kW standby diesel for extended/fire backup — configurator total ≈ $102,229, 200 kW effective demand, selectivity pass, 25 kA breaking (3.1× margin), feasibility-level.
- •380 V LV direct feed (no MV transformer): 250 kW installed → 200 kW demand (0.8 diversity), stdKva 211
- •80 kVA (64 kW) online UPS, 30 min ≈ 39.8 kWh battery (384 VDC) — covers the 60 kW IT critical load at 107%
- •80 kW standby diesel (1×500 kVA 20-ft container, 3-day fuel) — critical + fire loads, compliance C3 pass
- •Fire load 30 kW on a dedicated circuit with end-transfer ATS (auto-added); selectivity 50/51 pass (Δt 0.5 s)
- •Equipment total $102,229; LV fault 8 kA → 25 kA breaking (3.1× margin); 37 kW motor soft-start dip ≤10%
2 · Solution Overview
An office building is a grade-2 commercial load where the real risk is the tenant IT room: servers and network gear tolerate no outage. This scheme uses 380 V LV distribution (no MV transformer) plus two-layer backup — an online UPS for millisecond continuity and a standby diesel for extended outage — with the fire load on a dedicated end-transfer circuit.
| Source | Role | Share kW | Share |
|---|---|---|---|
| Grid 0.38 kV | base | 200 kW | 100% |
| Diesel 80 kW | backup | 0 kW | 0% |
| UPS 80 kVA | backup | 0 kW | 0% |
3 · Design Process & Rationale
1. Requirement identification
250 kW office building: tenant power 150 kW, lighting 60 kW, sensitive 60 kW (IT), fire 30 kW. Largest motor 37 kW (HVAC/lift), soft start.
2. Load & grading
Whole building grade-2 (loadGrade2=250); IT room 60 kW classified critical (no outage); fire 30 kW dedicated (fireDedicated=yes).
3. Source mix
380 V grid (base) + online UPS (critical IT) + standby diesel (extended + fire). LV direct feed, no MV transformer.
4. UPS sizing
60 kW critical → 80 kVA (64 kW) online double-conversion, 30 min battery (39.8 kWh, 384 VDC), 107% coverage.
5. Diesel sizing
80 kW standby duty; the configurator selects 1×500 kVA 20-ft container (standard min unit, ~20% load, 3-day fuel).
6. Protection
LV 25 kA breaking (8 kA fault, 3.1× margin); 50/51 selectivity Δt 0.5 s pass; fire end-transfer ATS auto-added.
7. Secondary & starting
Modbus + multifunction meters + local HMI; 37 kW motor soft-start keeps bus dip ≤10%.
Pain Points → Solution → Evidence
The tenant IT room can't tolerate a second of outage
Online UPS 80 kVA + static switch, diesel for extended outage
UPS 30 min 39.8 kWh; diesel 3-day fuel; compliance C3 pass
Fire pumps and emergency lighting must run during a fire
Dedicated fire circuit + end-transfer ATS (auto-added)
V11 pass; fire 30 kW dedicated
Multiple sources complicate switching
EMS + ATS/STS automatic transfer (hybrid CR-01)
EMS $4,025 + STS $4,370 auto-added
Voltage drop and motor-start dips on LV
37 kW soft start + 185 mm² main cable
V1 pass (≤5%); V5 dip ≤10%
4 · Key Parameter Deep-Read
| Parameter | Value | Basis | Impact & Boundary |
|---|---|---|---|
| UPS capacity | 80 kVA (64 kW) | Covers 60 kW critical IT at 107% | 30 min ≈ 39.8 kWh (384 VDC) Add a second unit for N+1 tolerance |
| Diesel genset | 500 kVA (80 kW standby) | Standard 20-ft container min unit | 3-day fuel, ~20% load 500 kVA is oversized for 80 kW — verify a smaller unit |
| Demand | 200 kW (250 kW×0.8) | Diversity factor kd=0.8 | stdKva 211 Higher kd → larger cable/gear |
| LV breaking | 25 kA | LV fault ikLv 8 kA | 3.1× margin Confirm grid Ssc with the utility |
| UPS battery | 30 min / 39.8 kWh | backupTime=30 | 384 VDC 8×48V blocks Extend runtime → more Ah |
| Fire circuit | 30 kW dedicated | fireDedicated=yes | End-transfer ATS auto-added Confirm fire pump motor rating |
| Motor start | 37 kW soft start | Largest motor 37 kW | Bus dip ≤10% DOL would exceed the limit |
5 · Drawing Deep-Read
The following drawings are shown for reference (full set in the configurator “View design document”):
6 · Operation Demo (Deep-Read)
Reliability & backup
Shows grid loss → UPS millisecond takeover of IT → diesel start for fire/extended load; UPS 30 min covers critical IT, diesel 3-day fuel as backstop.
Fault & protection
A downstream fault trips only its feeder (Δt 0.5 s selectivity); fire circuits end-transfer to diesel — no site-wide blackout.
Energy flow
Grid 200 kW feeds power/lighting, UPS online double-conversion carries critical IT, diesel 80 kW standby — three-source status at a glance.
Economics
Equipment total $102,229 (LV panels + 80 kVA UPS + 500 kVA diesel + cables + secondary); no renewables so no payback/IRR — the value is reliability.
Other views (shown): LCC (life-cycle cost) · Voltage profile · Power quality · Scheme features
7 · Economics & Payback
Equipment total ≈ $102,229 (380 V LV switchgear + 80 kVA UPS + 500 kVA diesel container + cables + secondary, feasibility-level). With no renewable generation there is no payback/IRR — the value is reliability: the UPS carries the 60 kW IT load for 30 min and the diesel extends it to 3 days while backing the fire pumps. Adding rooftop PV would unlock a 6–12 yr payback path.
8 · FAQ
What transformer size for a 250 kW office building?
How big a UPS for the IT room?
Do I need a diesel genset?
How is the fire load handled?
What's the short-circuit / breaking capacity?
What's the total cost?
Voltage drop and motor starting?
Why no payback/IRR here?
380 V vs 10 kV feed — which is right?
Special Considerations
- No MV transformer (380 V LV direct feed) — losses / transformer TCO are N/A; the 0.38 kV connection assumes an existing upstream 10/0.4 kV transformer.
- The diesel is 1×500 kVA (standard 20-ft container) for only 80 kW standby duty (~20% load) — verify a smaller genset with the supplier or accept the standard unit.
- UPS 80 kVA (64 kW) covers the 60 kW IT critical load at 107%; add a second unit for N+1 single-failure tolerance.
- Fire load 30 kW on a dedicated circuit + end-transfer ATS (auto-added) — confirm the fire pump motor rating and soft-start.
- Feasibility-level estimate; drawings are schematic, pending a licensed design institute.
Turn this into your project
Open this exact scenario pre-loaded in the Power System Configurator, then generate the full design document or the operation & techno-economic assessment.
Open in Power System Configurator →Related Scenarios
One-Stop Supply of Conventional & Solar Power Equipment
From power distribution system design to solar energy — transformers, switchgear, substations and solar equipment, sized and quoted in one place. Use our calculators to get a complete bill of materials and FOB price.