400 kW Commercial Complex: 380 V PFC + Fire/Emergency Load Grading
S13-M-400/10 · 100 kvar PFC · 200 kW diesel fire backup · 3-tier load grading
1 · TL;DR Conclusion
Conclusion: this 400 kW commercial complex uses a 10 kV feed + a single S13-M-400/10 transformer, with 100 kvar PFC on the 380 V side raising PF to 0.95. Loads are graded in three tiers, and fire/emergency (80 kW grade-1 + 80 kW fire) is 100% covered by a 200 kW standby diesel — configurator total ≈ $99,100 (feasibility-level).
- •400 kVA single S13 transformer: 84% loading, economical across commercial load swings
- •100 kvar PFC (4×25): PF 0.85→0.95, avoids power-factor penalties
- •3-tier grading: grade-1 80 + grade-2 120 + grade-3 200 kW, fire/emergency on dedicated circuit
- •200 kW diesel backs 100% of fire/emergency (160 kW) with end-transfer ATS
- •SH15 amorphous upgrade saves 2,015 kWh/yr (≈$241), 8.7 yr payback
2 · Solution Overview
A commercial complex is a mixed LV lighting + power load: lighting 150 kW, power 180 kW, sensitive 40 kW, fire 80 kW, with large diurnal/seasonal swings. The scheme uses a 10 kV feed, a single oil transformer, 380 V GGD distribution, 100 kvar PFC and three-tier load grading, with fire/emergency backed by a diesel.
| Source | Role | Share kW | Share |
|---|---|---|---|
| Grid 10 kV | base | 320 kW | 100% |
| Diesel 200 kW | backup | 0 kW | 0% |
3 · Design Process & Rationale
1. Requirement identification
A commercial complex has volatile load dominated by lighting/HVAC/retail equipment, plus fire pumps and emergency lighting. We set: fire load on a dedicated circuit with end-transfer, normal retail loads graded tier-3.
2. Load grading
Three tiers: grade-1 80 kW (fire/emergency/critical), grade-2 120 kW (lifts/key retail), grade-3 200 kW (general lighting/shops). Grading drives the source mix and backup scope.
3. Source & mix
Grid 10 kV is the only base supply; fire/emergency (grade-1 80 + fire 80 = 160 kW) is backed by a 200 kW diesel, V9 reports 100% coverage, with end-transfer ATS on fire circuits.
4. Transformer sizing
Sd=320/0.95≈337 kVA → 400 kVA tier, single S13-M-400/10 oil unit (commercial norm, cost-first), 84% loading.
5. Reactive compensation
Central 100 kvar (4×25 kvar) on the 380 V side raises PF 0.85→0.95, cutting transformer loading and PF penalties — the key cost saver in commercial distribution.
6. Distribution & protection
MV KYN28A-12 incomer → single transformer → 380 V GGD bus. 50/51 overcurrent with 0.3/0.2 s grading; all 5 coordination pairs pass.
7. Fire & emergency
Fire load on a dedicated circuit with end-transfer: fed from the LV bus normally, taken over by the 200 kW diesel within 2 s on grid loss, meeting fire codes.
Pain Points → Solution → Evidence
Commercial load swings drop the power factor and trigger utility penalties
100 kvar automatic PFC on the 380 V side raises PF to 0.95
pfcConfig: 100 kvar · 4×25 kvar · target pf 0.95
A fire/emergency outage is a safety incident
Dedicated fire circuit + end-transfer, 200 kW diesel backup
V9: 200 kW backup ≥ grade-1 80 + fire 80 = 160 kW (100%)
High transformer losses inflate the power bill
Upgrade to SH15 amorphous-alloy to cut no-load losses
TCO: S13→SH15 saves 2,015 kWh/yr (≈$241), 8.7 yr payback
Single transformer means one failure blacks out the building
Normal retail loads accept short outage; fire/emergency is diesel-backed
N-1 single verdict fail, but fire/emergency backupCoverPct 100%
4 · Key Parameter Deep-Read
| Parameter | Value | Basis | Impact & Boundary |
|---|---|---|---|
| Transformer capacity | 400 kVA ×1 | Sd=320/0.95≈337 kVA → 400 kVA tier | 84% loading, cost-first Rise to 500 kVA or dual if demand >360 kW |
| PFC | 100 kvar (4×25) | avgPf 0.85 → pfTarget 0.95 gap | PF compliant, no PF penalty Auto step-switching for volatile commercial load |
| Load grading | 80 / 120 / 200 kW | grade-1 fire/emergency, grade-2 lifts, grade-3 retail | Backup covers only grade-1+fire, controlling cost Add diesel if grade-1 load grows |
| Fire backup | 200 kW diesel | grade-1 80 + fire 80 = 160 kW need | V9 100% coverage, end-transfer ATS Size fire pumps per fire codes |
| N-1 redundancy | None (single) | Normal retail load accepts short outage | Fire/emergency is diesel-backed on transformer loss Use N+1 dual if continuity is critical |
| Short-circuit | MV 28.9 / LV 14.2 kA | 500 MVA fault level + uk=4% | HV 31.5 / LV 25 kA breaking Confirm actual fault level with grid |
5 · Drawing Deep-Read
The following drawings are shown for reference (full set in the configurator “View design document”):
6 · Operation Demo (Deep-Read)
Energy flow
Grid 320 kW demand → MV switchgear → S13 transformer → 380 V LV bus → shop/lighting/lift/fire feeders. Commercial load swings diurnally; the 100 kvar PFC steps automatically to hold PF ≥0.95.
Fire & emergency
On grid loss the 200 kW diesel takes over fire pumps/emergency lighting within 2 s (end-transfer), showing the fire circuit never loses power through the transfer.
PF & reactive
Show the 100 kvar stepping: banks switch out at low load (avoid over-compensation) and in at peak, holding PF at 0.95 and offsetting penalties.
Losses & electricity cost
Oil-type losses p0=0.33 / pk=4.3 kW, ≈78,878 kWh/yr (≈$9,465); SH15 amorphous saves 2,015 kWh/yr (≈$241), 8.7 yr payback.
Other views (shown): 24h operation · Voltage profile · Scheme features · Environmental derating
7 · Economics & Payback
Configurator equipment total ≈ $99,100 (feasibility-level, incl. S13-M-400/10 transformer, MV/LV switchgear, 100 kvar PFC, 200 kW diesel and cables). Economics centre on PFC and losses: 100 kvar raises PF to 0.95, offsetting penalties; ≈78,878 kWh/yr losses ($9,465), with SH15 amorphous saving $241/yr at 8.7 yr payback.
8 · FAQ
What transformer size for a 400 kW commercial complex?
Why is PFC important for commercial?
How is fire/emergency load secured?
What is load grading?
What happens on a single transformer failure?
What does the commercial package cost?
Is the SH15 amorphous upgrade worth it?
How is the 380 V PFC sized?
Special Considerations
- System fault level defaults to 500 MVA — confirm with the grid company (toConfirm: ssc).
- Single transformer has no N-1 redundancy — only fire/emergency is diesel-backed on transformer loss; use N+1 dual for critical continuity.
- Fire pump sizing must follow local fire codes; the configurator assumes 80 kW fire load.
- Feasibility-level estimate; drawings pending a licensed design institute, not construction documents.
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