Design a reliable power supply for hospitals, schools, stadiums and airports — transformer sizing, N / N+1 / 2N redundancy, automatic transfer switch, emergency (EPS) lighting and standby diesel, with BOM and single-line diagram.
Public facilities carry life-safety loads that must never lose power. This calculator sizes a dry-type transformer supply for the building type, applies N / N+1 / 2N redundancy, and configures the emergency power chain — ATS, EPS fire lighting and standby diesel — per GB 50052, GB 51309 and GB 50016.
online double-conversion · IEC 62040 · quoted per project
1
Fire pump feeder (dedicated)
120 kW
dedicated fire pump supply · GB 50016
1
📐 Single-line diagram
⚙️ Electrical schematic (protection & metering)
⛳ Grounding grid layout
🔌 Cable schedule & routing
🗄 Switchgear arrangement
🛡 Protection configuration
📋 Protection settings
Circuit
Protection
Setting
Time
Standard
HV incoming 10 kV
50 instantaneous
739 A
inst
IEC 60255-151 / IEEE 242
HV incoming 10 kV
51 overcurrent
111 A
0.5 s
IEC 60255-151 / IEEE 242
HV incoming 10 kV
51N earth-fault
18 A
0.5 s
IEC 60364-4-41
Transformer 1600 kVA
87 differential
18 A
inst
IEEE C37.91 / GB/T 14285
Transformer 1600 kVA
49 thermal overload
89% of rated
alarm 90%
IEC 60076-7 / IEEE C57.91
LV incoming 0.4 kV
50 instantaneous
18475 A
inst
IEC 60947-2
LV incoming 0.4 kV
51 overcurrent
2771 A
0.3 s
IEC 60947-2 / IEC 60255
LV incoming 0.4 kV
51N earth-fault
462 A
0.3 s
IEC 60364-4-41
LV bus-tie
50/51 overcurrent
2771 A
0.3 s
IEC 60947-2
Ward 1
50/51/51N (MCCB)
Ir 193 A - Im 1402 A - Ig 35 A
0.1 s (grading)
IEC 60947-2 / IEC 60255
Ward 2
50/51/51N (MCCB)
Ir 193 A - Im 1402 A - Ig 35 A
0.1 s (grading)
IEC 60947-2 / IEC 60255
Ward 3
50/51/51N (MCCB)
Ir 193 A - Im 1402 A - Ig 35 A
0.1 s (grading)
IEC 60947-2 / IEC 60255
Ward 4
50/51/51N (MCCB)
Ir 193 A - Im 1402 A - Ig 35 A
0.1 s (grading)
IEC 60947-2 / IEC 60255
Ward 5
50/51/51N (MCCB)
Ir 193 A - Im 1402 A - Ig 35 A
0.1 s (grading)
IEC 60947-2 / IEC 60255
Ward 6
50/51/51N (MCCB)
Ir 193 A - Im 1402 A - Ig 35 A
0.1 s (grading)
IEC 60947-2 / IEC 60255
+7 more feeders
50/51/51N (MCCB)
per feeder load
0.1 s (grading)
IEC 60947-2
Settings are illustrative starting points — confirm with a protection coordination study per IEC 60255 / IEEE 242.
📚 Calculation book
CALCULATION BOOK
1600 kVA - 10kV/0.4kV - N+1 - illustrative
1. Load calculation
Standard: IEC 60076 - IEC 60364-5-52
Parameter
Formula
Value
Connected load
P = sum(kW)
1,500 kW
Demand factor
Kd
0.9
Demand power
Pd = P x Kd
1,350 kW
Power factor
cos(phi) before -> after
0.95 -> 0.95
Design apparent power
Sd = Pd / cos(phi)
1,421 kVA
Transformer loading
Sd / Srated
89%
2. Short-circuit calculation
Standard: IEC 60909
Parameter
Formula
Value
System impedance (pu)
Zs = S / Ssc
0.32% (on 1600 kVA base)
Transformer impedance
Zt = Z%
6%
Total impedance
Z = Zt + Zs
6.32%
LV prospective Isc
Isc = In / Z
36.5 kA
HV prospective Isc
Isc = Ssc / (sqrt(3) x V)
28.9 kA
Breaking check
Icu >= Isc
LV 50 kA (1.4x margin) PASS
3. Voltage drop
Standard: IEC 60364-5-52 Annex G
Parameter
Formula
Value
Main feeder
dU = sqrt(3) x I x L x R / V
300 mm2 - dU 0.90% @ 60 m
Limit
max 3%
within limit
Transformer volt. reg.
dU ~ loading x Z% x sin(phi)
1.7% at full load
4. Reactive power / harmonics
Standard: IEC 61921 (PFC) - IEEE 519 (harmonics)
Parameter
Formula
Value
Required compensation
Qc = Pd x (tan1 - tan2)
0 kvar
PFC bank
standard step
0 kvar
Detuned reactor
p = 6%
n/a
5. Grounding
Standard: IEC 60364-5-54 earthing arrangements and protective conductors LV earthing target 10 ohm (TN systems); 4 ohm used as a conservative design target - target 4 ohm
Parameter
Formula
Value
Single rod resistance
R1 = rho/(2 x pi x L) x ln(4L/d)
39.6 ohm
Rods required
n = R1 / (target x 0.8)
13 rod(s) <= 4 ohm
Rod spec
dia x length
20 mm x 2.5 m
This calculation book is illustrative it consolidates the computed values with the referenced standards. A licensed engineer must verify and seal final design documents for construction.
🔧 Secondary schematic (control & signal)
🔩 Terminal strip (typical)
🛡️ Redundancy & emergency power
Parameter
Value
Building type
Hospital
Design factor
1× (life-safety + 100% medical load, no reduction)
Cable & grounding pricing:Cable conductors and grounding are priced from the confirmed cables-trays-grounding price reference (per-metre copper YJV; aluminium remains POA). The main copper busbar is POA — its length is project-specific.
Busway (high-current feeders):For LV feeders above ~2500 A, a busway (母线槽) trunking system is recommended instead of parallel cables.
Design factor (explicit):Hospital applies a 1× design/coincidence factor to the entered load (life-safety + 100% medical load, no reduction) — entered 1,500 kW becomes 1,500 kW design load.
Redundancy:2N topology — two independent paths, each sized for 100% load (fault-tolerant).
Emergency power:critical level: automatic transfer switch for dual source; EPS for fire/emergency lighting (GB 51309); standby diesel genset for life-safety loads (GB 50016).
Load classification:Hospitals and airports carry life-safety (first-class) loads requiring dual independent sources — GB 50052 classifies load by importance.
Hospital critical loads:Operating theatres and ICU need a medical IT isolated power supply (IEC 60364-7-710) and an online UPS; the fire pump has a dedicated feeder (GB 50016). These are included as separate line items for hospitals.
Pricing:ATS, EPS and standby diesel gensets are priced from the catalogue price reference; medical IT panels, OR UPS and fire pumps remain quoted per project (POA).
How it was calculated
How the sizing works
Total load is the building load adjusted for cooling and auxiliary. The transformer is sized at the target power factor; N+1 / 2N redundancy sets the number of parallel units and independent paths. The emergency level (basic / standard / critical) determines whether an ATS, EPS and/or standby diesel generator is added.
Applicable standards
Sizing references GB 50052 (power supply design and load classification), GB 51309 (fire emergency lighting), GB 50016 (building fire protection) and IEC 62040 (UPS for critical loads).
Frequently asked questions
What redundancy do hospitals require for power supply?
Hospitals are first-class important loads under GB 50052 and need two independent utility supplies plus an emergency source (diesel or EPS) that restores critical circuits in seconds. Life-support and operating rooms use 2N topology with UPS. The calculator models building type, redundancy (N+1/2N) and emergency level to size the full plant.
How is emergency power restored in public buildings?
An automatic transfer switch (ATS) detects supply loss and transfers to a standby diesel generator, which starts and reaches full load in 30-60 seconds. For millisecond-critical loads, a UPS bridges the gap. GB 50052 classifies the emergency level; the calculator sizes ATS, diesel/EPS and battery backup per the building's load class.
What is the typical load density of a hospital or stadium?
Hospitals run 60-120 W/m2 (up to 150 W/m2 with imaging), schools 30-60 W/m2, offices 50-80 W/m2, and stadiums 60-100 W/m2 plus floodlighting peaks. The calculator's 1500 kW default models a mid-size hospital; total demand sets the Transformer and emergency ratings.
What transformer size does a 1500 kW hospital need?
A 1500 kW hospital at 0.95 pf needs about 1580 kVA, so select 2x800 kVA or 2x1000 kVA for N+1/2N redundancy. Hospitals often run two transformers with automatic bus-tie so either can carry critical load. The calculator selects standard IEC 60076 ratings and applies the chosen redundancy level.
What is an EPS and how does it differ from a UPS?
An emergency power supply (EPS) is an inverter-based backup for lighting and life-safety loads, transferring within 0.25-5 seconds — slower than a UPS (0-10 ms) but cheaper per kVA and built for motor and lighting duty. UPS serves electronics that cannot tolerate any interruption. The calculator selects EPS for emergency lighting and UPS for critical IT.
What power quality rules apply to public buildings?
Public buildings must limit harmonic distortion per IEEE 519 (5-8% THD at PCC) and maintain Power Factor above ~0.9 to avoid utility penalties. LED lighting and VFD HVAC drives inject Harmonics, so detuned capacitors or APFs are common. The calculator checks pf and harmonic share and sizes compensation accordingly.
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Results are engineering estimates for reference. Final design must be confirmed by a licensed local engineer against site conditions and applicable codes. Prices are FOB Qingdao (EXW) and do not include freight, duty or installation.
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