500 kW Truck Battery-Swap Station: 8×120 kW DC Chargers + 250 kW/1161 kWh Peak-Shaving BESS
8× DC120 kW · SCB13-400/10 · 250 kW/1161 kWh BESS · 400 A APF + SVG
1 · TL;DR Conclusion
Conclusion: an 8-bay truck battery-swap station (8×120 kW DC chargers, 960 kW installed) runs on one SCB13-400/10 transformer + a 250 kW/1161 kWh peak-shaving BESS + a 400 A APF — $264,418 equipment total. The BESS shaves 250 kW×4 h (≈ $47,450/yr at $0.13/kWh spread) so the 960 kW fleet stays within a 500 kW connection.
- •8× 120 kW DC fast-charge bays (960 kW installed) — demand-limited to 500 kW (350 kW at Kd 0.7) via charger power-sharing + BESS.
- •250 kW / 1161 kWh BESS peak-shaves 250 kW×4 h; ≈ $47,450/yr arbitrage at $0.13/kWh spread (feasibility-level).
- •400 A APF (APF-403A) + ±1 Mvar SVG handle THDi ≈ 80% from the DC rectifier chargers.
- •SCB13-400/10 single transformer at 92% loading — economical but thin headroom (watch the 5–7% cascade voltage-drop warn).
- •BESS EPC ≈ $212,500 vs ≈ $47,450/yr shaving → ≈ 4.5 yr simple payback (demand-charge avoidance adds more).
2 · Solution Overview
A truck battery-swap station is the classic 'high-power DC fast-charging + peak-shaving BESS' case: 8 swap bays each with a 120 kW DC charger (960 kW installed), yet only a 500 kW grid connection — via charger power-sharing + a 250 kW/1161 kWh BESS that shaves the peak under the demand limit. The DC rectifier stack injects THDi ≈ 80%, requiring a 400 A APF + SVG.
| Source | Role | Share kW | Share |
|---|---|---|---|
| Grid 10 kV | base | 100 kW | 29% |
| BESS 250 kW / 1000 kWh | variable | 250 kW | 71% |
3 · Design Process & Rationale
① Size the charger fleet, not just the load
8×120 kW = 960 kW installed, but swap duty cycles are staggered → Kd 0.7 → 350 kW demand → 500 kW grid contract.
② Peak-shaving BESS instead of a bigger connection
250 kW/1161 kWh (4 h) BESS shaves the peak 250 kW×4 h, holding grid at 500 kW and cutting demand charges — no need for a 960 kW MV dedicated feeder.
③ Nonlinear load → harmonic mitigation
DC fast chargers are 6-pulse/Vienna rectifier loads; 400 kW nonlinear (80%) → THDi up to 80% → 400 A APF (APF-403A) + ±1 Mvar SVG.
④ Impact load from swap inrush
150 kW impact (battery-swap step load) — LV feeders sized for inrush; chargers soft-start / staggered switching.
⑤ Transformer sizing
350 kW demand / 0.92 PF ≈ 380 kVA → SCB13-400/10 (single) at 92% loading — economical but thin headroom.
⑥ MV/LV distribution + protection
KYN28A-12 MV + MNS LV switchgear, 8 charger feeders (YJV 25 mm²), 50/51 coordination, 14.15 kA LV short-circuit → 25 kA breaking.
⑦ EMS + BMS orchestration
EMS-1161 coordinates charger power-sharing + BESS charge/discharge against a real-time demand cap; SCADA + BMS communication.
Pain Points → Solution → Evidence
8 chargers at once (960 kW) would trip a 500 kW connection
charger power-sharing + 250 kW BESS peak-shaving caps grid draw at 500 kW
capacitySummary renewablePct 71%, supplyMix storage shareKw 250 of 350 kW demand
DC rectifiers inject THDi ≈ 80%, overheating cables and transformers
400 A APF + ±1 Mvar SVG hold PCC THD under 5%
BOM APF-403A ($14,605) + SVC/SVG ±1 Mvar ($32,200)
The 350 kW peak inflates the demand-charge bill
BESS shaves 250 kW×4 h → ≈ $47,450/yr at $0.13/kWh spread
economic.shaving annualSaving 47450, invest 212500
4 · Key Parameter Deep-Read
| Parameter | Value | Basis | Impact & Boundary |
|---|---|---|---|
| totalKw | 500 kW | grid connection / contracted demand | sets transformer + BESS sizing installed fleet 960 kW > 500 kW — diversity + BESS bridge the gap |
| loadNonlinear | 400 kW (80%) | DC fast chargers are rectifier loads | APF + SVG required THDi up to 80% uncompensated |
| loadImpact | 150 kW | battery-swap step load | feeder + transformer inrush margin high impact → soft-start / staggered swap |
| kd (demand factor) | 0.7 | staggered swap duty cycles | 350 kW demand from 500 kW connected higher simultaneity → larger transformer |
| storageUse | peak-shaving + demand | shave peak & cut demand charge | 250 kW/1161 kWh BESS (4 h) 4 h storage duration matches the peak window |
| avgPf | 0.92 | DC chargers with PFC front-end | 350/0.92 = 380 kVA → 400 kVA transformer lower PF → larger transformer + PFC |
5 · Drawing Deep-Read
The following drawings are shown for reference (full set in the configurator “View design document”):
6 · Operation Demo (Deep-Read)
Load flow / voltage
Drag the load slider at 350 kW demand to see I²R losses and the cascade voltage drop (5–7% warn); doubling load roughly quadruples losses — why headroom matters.
Power quality
THDi 80% uncompensated → APF to < 5%; SVG compensates the charger reactive power dynamically.
Peak-shaving economics
250 kW×4 h shave at $0.13/kWh spread = $130/day ≈ $47,450/yr → ≈ 4.5 yr simple payback vs $212,500 BESS EPC.
Other views (shown): Load flow · Voltage · Losses · Peak-shaving economics · Power quality
7 · Economics & Payback
Equipment total $264,418 (feasibility-level). The economics live in the BESS: 250 kW/1161 kWh shaves 250 kW×4 h at $0.13/kWh spread ≈ $47,450/yr, against ≈ $212,500 BESS EPC → ≈ 4.5 yr simple payback (plus demand-charge savings where applicable). Honest caveat: at a flat tariff with no demand charge, pure energy arbitrage may not pay back — the BESS's real value is demand-cap avoidance + letting the 960 kW fleet run on a 500 kW connection, plus backup.
8 · FAQ
8×120 kW = 960 kW, why only a 500 kW connection?
What BESS size for peak-shaving?
Do DC fast chargers need harmonic filtering?
Is 400 kVA enough for 500 kW?
How much does the BESS save, and when does it pay back?
Why is there a voltage-drop warning?
How is the swap inrush handled?
Single or N+1 transformer?
What does the whole scheme cost?
Special Considerations
- Cascade voltage drop 5–7% (warn) — enlarge the feeder cable or raise PF for the farthest charger bays.
- THDi up to 80% on DC charger feeders — the 400 A APF + SVG are mandatory, not optional.
- Ssc (500 MVA) and grid-code for BESS interconnection are assumed — confirm with the utility.
- All figures are feasibility-level estimates; drawings are schematic, pending design-institute refinement.
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