400 kW Hospital Power: Dual Supply + N+1 Dry Transformer + 200 kVA UPS + 500 kVA Diesel
2× SCB13-400/10 N+1 · 500 kVA diesel · 200 kVA/15 min UPS · medical IT isolation
1 · TL;DR Conclusion
Conclusion: a 400 kW hospital uses 2×SCB13-400/10 dry transformers (N+1) + a 500 kVA standby diesel + a 200 kVA/15-min UPS — $200,667 equipment total. 10 kV dual supply with auto-transfer (2 s switch) + medical IT isolation keeps grade-1/critical loads alive at 84% transformer loading under N-1.
- •N+1 redundancy: 2× SCB13-400/10 dry transformers — one outage still carries 84% of demand (N-1 verdict: pass).
- •Dual supply: 10 kV grid + 500 kVA standby diesel — auto-transfer in 2 s < 15 s allowed outage.
- •200 kVA online UPS (15 min / 40 kWh) rides through ms-level outages for 120 kW medical-IT / ICU loads.
- •Medical IT isolation (ES710) + arc-flash protection (ARB6, Cat 1) + fire dedicated circuit with end-transfer ATS.
- •Transformer TCO: upgrading to SH15 amorphous alloy saves ≈ $694/yr (payback ≈ 1.2 yr at 84% loading).
2 · Solution Overview
A hospital is the most demanding reliability load: operating rooms, ICU and life-support tolerate no interruption, so the whole facility is designed as grade-1 (400 kW), with 320 kW critical and 120 kW medical-IT sensitive load. The scheme stacks 10 kV dual supply + auto-transfer + diesel + UPS, plus medical IT isolation and equipotential grounding, meeting IEC 60364-7-710 for group-2 medical locations.
| Source | Role | Share kW | Share |
|---|---|---|---|
| Grid 10 kV | base | 320 kW | 100% |
| Diesel 400 kW | backup | 0 kW | 0% |
| UPS 200 kVA | backup | 0 kW | 0% |
3 · Design Process & Rationale
① Classify the load first (400 kW → grade-1 & critical)
Split 400 kW into lighting 60 kW, power 280 kW, sensitive 120 kW (medical IT / ICU), critical 320 kW, fire 60 kW. Per IEC 60364 the whole hospital is grade-1 (400 kW); the 320 kW critical load mandates an emergency source — the basis for dual supply + diesel + UPS.
② Dual supply + emergency-source mix
10 kV grid (base) + 500 kVA diesel (standby/backup) + 200 kVA UPS (backup). allowedOutage = 15 s drives diesel auto-transfer in 2 s; the 120 kW sensitive load needs ms-level, hence the 200 kVA online UPS.
③ N+1 transformer redundancy
Demand 320 kW / 0.9 PF ≈ 356 kVA → 2× SCB13-400/10 dry-type (N+1). Dry-type is chosen for indoor fire safety (no oil); N+1 keeps 84% loading after one unit trips.
④ LV distribution + bus-tie + transfer switches
MNS LV switchgear with incoming + bus-tie + feeder panels; ATS-630 (grid/diesel), STS-630 (UPS static transfer), GATS-630 (grade-1 end-transfer), FATS-630 (fire end-transfer).
⑤ Protection & selectivity
50/51 coordination (incoming 0.6 s → transformer 0.3 s), arc-flash ARB6 (Cat 1, 1.58 cal/cm²); LV short-circuit 14.15 kA → 25 kA breaking (1.8× margin).
⑥ Medical IT isolated system
The 120 kW medical-IT loads (OR, ICU) sit on an isolated power supply ES710 with insulation monitoring — first fault alarms but does not trip; a 20 kVA operating-room UPS is quoted per project.
⑦ Fire + grounding + reliability checks
Fire load 60 kW on a dedicated circuit with end-transfer ATS; TN-S equipotential grounding (18 rods); EPS 60 kW emergency lighting; N-1 verdict pass.
Pain Points → Solution → Evidence
Even a 15-second outage can interrupt surgery or a ventilator
10 kV dual supply + auto-transfer (2 s) + 200 kVA UPS (15 min ride-through)
nMinus1 verdict pass, switchTimeS 2 s < allowedOutageS 15 s; upsBattery runtimeMin 15
A first earth fault tripping the medical-IT circuit would interrupt surgery
Medical IT isolated supply (ES710) with insulation monitoring — alarm on first fault, no trip
BOM includes 'Medical IT isolated power supply ES710' + 'Medical IT isolation system'
A single transformer failure would black out the whole hospital
2× SCB13-400/10 N+1 — one unit out still serves 84% of demand
nMinus1 loadingPctAfter 84%, verdict pass
4 · Key Parameter Deep-Read
| Parameter | Value | Basis | Impact & Boundary |
|---|---|---|---|
| totalKw (connected load) | 400 kW | sum of all equipment rated power | drives transformer / genset / UPS sizing demand 320 kW at Kd 0.8 |
| loadGrade1 / loadCritical | 400 / 320 kW | IEC 60364 grade-1 = hospital | mandates dual supply + emergency diesel + UPS grade-2/3 = 0 — everything is grade-1 |
| allowedOutage | 15 s (s15) | grade-1 supply requirement | diesel ATS in 2 s; sensitive load gets UPS medical IT needs ms-level → UPS bridge |
| transformer redundancy | N+1 (2× 400 kVA) | SCB13 dry-type, indoor | 84% loading after N-1 single = 80% loading but no redundancy |
| loadSensitive (medical IT) | 120 kW | OR + ICU + life-support | 200 kVA UPS + isolated supply ES710 scales linearly with OR count |
| largestMotorKw / start mode | 37 kW / soft | HVAC chiller / air-handling | soft-start limits voltage dip larger motors → VFD |
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 (N-1)
Click 'Grid failure': diesel takes over in 2 s, terminal voltage holds; N-1 scenario: one transformer out still 84% loading (verdict pass).
Power quality
Medical IT + UPS deliver clean supply to sensitive loads; THDi 15% on the LV side, online double-conversion UPS removes grid disturbance.
Fault & protection
14.15 kA LV short-circuit → 25 kA breaking (1.8× margin); arc-flash Cat 1 (1.58 cal/cm²); main protection 0.6 s.
Other views (shown): Load flow · Voltage · Losses · Fault & protection · Environment
7 · Economics & Payback
Equipment total $200,667 (feasibility-level). This is grid + diesel + UPS — no PV/storage, so the financial case is availability, not energy savings. Two quantifiable levers: transformer TCO (SH15 amorphous alloy saves ≈ $694/yr, payback 1.2 yr) and losses (3.8 kW ≈ $9,918/yr at $0.12/kWh).
8 · FAQ
What transformer does a 400 kW hospital need?
Why N+1 instead of a single 630 kVA?
What UPS size for the operating room?
How fast does the diesel take over after a mains outage?
Is medical IT isolation mandatory?
How is the fire load handled?
Dry-type or oil-immersed transformer for a hospital?
What does this scheme cost?
How do I cut the transformer energy bill?
Special Considerations
- Medical IT isolation (ES710) and operating-room UPS are 'price on application' (poa) — excluded from the total, quote separately.
- The 500 kVA diesel carries 400 kW grade-1 at ≈ 100% loading — verify the load profile and reserve expansion margin.
- Ssc (grid short-circuit 500 MVA) is assumed — confirm actual fault level with the utility for final protection & cable settings.
- Arc-flash Cat 1 (1.58 cal/cm²) is preliminary — a formal IEEE 1584 study by a qualified engineer is required before permits.
- Drawings are schematic deliverables pending design-institute refinement; all figures are feasibility-level estimates.
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