500 kW Airport Power: 400 Hz GPU + Runway Lighting + UPS on a Dual-Feed N+1 Scheme
2×SCB13-500/10 N+1 · 400 kW diesel standby · 150 kVA UPS (15 min) · 400 Hz GPU bridge
1 · TL;DR Conclusion
Conclusion: this 500 kW airport uses a 10 kV feed + 2×SCB13-500/10 dry transformers (N+1), with a 400 kW standby diesel and a 150 kVA UPS covering 100% of the grade-1 runway/ATC load. The 400 Hz GPU bridge drives THDi to 30%, so the 150 kvar PFC is detuned and an APF is recommended — configurator total ≈ $456,014 (feasibility-level).
- •2×500 kVA SCB13 dry transformers N+1; 84% loading after one-unit loss, within the 60–85% band
- •Dual-supply chain: grid 10 kV + 400 kW diesel + 150 kVA UPS = 550 kW backup, exactly covering grade-1 (500) + fire (50)
- •400 Hz GPU converters put 150 kW nonlinear (30% THDi); 150 kvar detuned PFC prevents resonance, an APF clears the limit
- •150 kVA UPS (120 kW, 15 min, 384 Vdc) holds ATC/comms across the 2 s diesel transfer
- •Short-circuit 28.9 kA (MV) / 17.6 kA (LV); 300 mm² cable passes thermal check (44 mm² min)
2 · Solution Overview
An airport is a grade-1, high-reliability site: runway/approach lighting, ATC and comms cannot go dark. This 500 kW scheme combines a 10 kV utility feed, N+1 dry transformers, a 400 kW standby diesel and a 150 kVA UPS, with the 400 Hz ground-power (GPU) bridge load modelled as a 150 kW nonlinear source.
| Source | Role | Share kW | Share |
|---|---|---|---|
| Grid 10 kV | base | 400 kW | 100% |
| Diesel 400 kW | backup | 0 kW | 0% |
| UPS 150 kVA | backup | 0 kW | 0% |
3 · Design Process & Rationale
1. Requirement identification
An airport is grade-1 — runway lighting, ATC and comms must not lose power; the 400 Hz GPU bridge is a variable-frequency nonlinear load. We set: allowed outage ≤15 s, fire load on a dedicated circuit, and UPS-backed sensitive loads (ATC/radar).
2. Load classification
All 500 kW is treated as grade-1 (airport practice): critical 300 kW, nonlinear 150 kW (400 Hz converters), sensitive 150 kW (ATC), fire 50 kW. This profile drives the source mix and harmonic treatment.
3. Source & mix
Dual-supply structure: grid 10 kV as base (100%), plus a 400 kW standby diesel and a 150 kVA UPS forming the emergency chain — 550 kW backup = grade-1 (500) + fire (50); V9 check reports 100% coverage.
4. Transformer sizing
Apparent demand Sd=400/0.95≈421 kVA → 500 kVA tier; for single-unit-failure continuity we select N+1 → 2×SCB13-500/10 dry-type (indoor, oil-free, fire-friendly), 84% loading.
5. Distribution & protection
MV KYN28A-12 incomer → 2 dry transformers → MNS LV bus (with bus-tie). Protection uses 50/51 overcurrent with 0.3/0.2 s grading; all 5 coordination pairs pass.
6. Reactive & harmonics
Target PF 0.95 needs 150 kvar (4×38 kvar detuned banks). The 400 Hz drives push THDi to 30%, far over the 15% limit: detuned reactors only prevent amplification — an APF is needed to actually clear it.
7. Reliability & special requirements
N+1 keeps 84% loading after one-unit loss; the diesel takes over within 2 s while the UPS holds ATC for 15 min; runway lighting and indoor GPU circuits are fed separately to avoid interference.
Pain Points → Solution → Evidence
Runway lighting cannot go dark — one feed loss must not black out the airfield
Dual supply + N+1: grid + 400 kW diesel + 150 kVA UPS emergency chain
V9: 550 kW backup = grade-1 500 + fire 50 (100%); V4 N-1 84% loading pass
400 Hz GPU converters distort the bus and overheat the capacitor bank
150 kvar detuned reactors prevent resonance, plus an APF to clear the exceedance
Load profile THDi 30% (150/500 kW nonlinear), far over the 15% limit
ATC/comms glitch during the grid-to-diesel transfer
A 150 kVA UPS (15 min) bridges sensitive loads seamlessly
UPS 150 kVA/120 kW · 15 min · 384 Vdc · 97 Ah, spanning the 2 s transfer
Indoor substation oil/fire risk
SCB13 dry-type transformer (oil-free, flame-retardant)
transModel SCB13-500/10 dry-type — indoor, fire-friendly
4 · Key Parameter Deep-Read
| Parameter | Value | Basis | Impact & Boundary |
|---|---|---|---|
| Transformer capacity | 500 kVA ×2 (N+1) | Sd=400/0.95≈421 kVA → 500 kVA tier; N+1 → 2 units | 84% loading, economical; no outage on single-unit loss Rise to 630 kVA if demand >450 kW |
| Backup coverage | 550 kW (diesel 400 + UPS 150) | grade-1 500 + fire 50 = 550 | V9 100% backup, zero loss for critical loads Add diesel/UPS if critical load grows |
| THDi | 30% | 400 Hz converters are a concentrated nonlinear load (150 kW) | Over the 15% limit; detuned PFC + APF required APF rating finalised from the harmonic spectrum |
| UPS rating | 150 kVA / 120 kW | Holds ATC/comms (sensitive) for 15 min | 384 Vdc battery 97 Ah, zero-gap transfer Add battery strings for longer runtime |
| N-1 loading | 84% | Sd 421/500 after one-unit loss | 2 s transfer ≤ 15 s allowed, verdict pass Single unit may overload as load grows |
| Short-circuit | MV 28.9 / LV 17.6 kA | 500 MVA fault level + uk=4% transformer | HV 31.5 kA / LV 25 kA breaking (1.1×/1.4× margin) Confirm actual fault level with grid (toConfirm: ssc) |
| PFC | 150 kvar (4×38) | avgPf 0.85 → pfTarget 0.95 gap | PF compliant, less transformer loading & loss 400 Hz harmonics — detuned to prevent 5th/7th amplification |
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 400 kW demand → MV switchgear → two SCB13 transformers → LV bus → 14 feeders (runway / GPU / ATC). The dual transformers share ~42% each; on one-unit loss the survivor carries 84%.
Fault & transfer
On grid loss the diesel synchronises within 2 s while the UPS holds ATC for 15 min; a feeder fault trips only that feeder (0.1 s) with the upstream 0.3 s holding — selectivity holds.
Power quality & harmonics
The 400 Hz bridge puts THDi at 30%; compare the harmonic spectrum before/after detuned-reactor + APF treatment to quantify the cause and fix of “harmonics burn capacitors”.
Losses & electricity cost
Dry-type losses p0=1.16 / pk=4.88 kW, ≈102,071 kWh/yr (≈$12,249 @ $0.12/kWh); an SH15 amorphous oil unit would save ≈7,434 kWh/yr but trades away the oil-free safety.
Other views (shown): 24h operation · Voltage profile · Scheme features · Environmental derating
7 · Economics & Payback
Configurator equipment total ≈ $456,014 (feasibility-level, incl. 2×SCB13-500/10 dry transformers, MV/LV switchgear, 500 kVA containerised diesel, 150 kVA UPS, 150 kvar PFC and cables). Economics centre on the reliability premium plus losses: ≈102,071 kWh/yr ($12,249); an SH15 amorphous oil unit would save ≈$892/yr, but indoor airports prefer oil-free dry type — safety over efficiency.
8 · FAQ
What transformer size for a 500 kW airport?
Why dry-type for an airport?
How big a standby diesel for an airport?
What is a 400 Hz GPU and why does it affect the design?
How long does the UPS hold?
What backs the runway lighting?
Why N+1 dual transformers?
Is 30% THDi a problem?
What does the airport package cost?
Special Considerations
- System fault level defaults to 500 MVA — confirm the actual value with the grid company (affects protection settings & cable thermal; toConfirm: ssc).
- THDi ~30% is over the limit; detuned reactors only prevent amplification — add an APF to actually clear the warning.
- All 500 kW is treated as grade-1; if some terminal loads can be de-rated, the diesel/UPS backup (and cost) can shrink.
- Feasibility-level estimate; drawings pending a licensed design institute, not construction documents.
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