500 kW Onshore Wind Farm: 800 kVA Box Transformer (0.69/35 kV) + 35 kV Collector + 110 kV Step-up Deep-Read
1×500 kW WTG · 800 kVA box transformer (0.69/35 kV) · 35 kV collector · 10 MVA 110 kV step-up · ±1 Mvar SVG
1 · TL;DR Conclusion
Conclusion: this 500 kW onshore wind farm (1 × 500 kW WTG) uses an 800 kVA one-turbine-one-transformer box transformer (0.69/35 kV) → a 35 kV collector (1 feeder) → a 110 kV step-up main transformer + ±1 Mvar SVG + 35 kV collector switchgear — configurator total ≈ $491,625 (FOB), EPC ≈ $640,850, 9 yr payback, 10.6% IRR, 181% 25-yr ROI (feasibility-level).
- •1×500 kW WTG → 800 kVA box transformer (0.69/35 kV, engine "Combined dry-type"); one-turbine-one-transformer topology
- •35 kV collector, 1 feeder (≤10 turbines/feeder); step-up main transformer 10 MVA 35/110 kV (engine floor — a real 0.5 MW farm ties in at 35 kV directly)
- •±1 Mvar SVG for grid-code reactive support (PF ±0.95 continuous) + 35 kV collector switchgear + RMU-SF6
- •Generation 1,040,250 kWh/yr (P50, CF≈24%), P90 986,906 kWh, revenue $83,220/yr @ $0.08/kWh PPA
- •Economics: $640,850 EPC, 9 yr payback, 10.6% IRR, 181% 25-yr ROI
2 · Solution Overview
An onshore wind farm is a 100% generation-export case: the turbine generates at 0.69 kV, a box transformer (one-turbine-one-transformer) steps up to 35 kV, a collector feeder gathers output, and a step-up main transformer raises it to 110 kV for transmission. The configurator's generation-export mode models and prices the whole chain.
3 · Design Process & Rationale
1. Requirement identification
500 kW onshore wind, 100% grid export, no local load; the explicit generationExport flag triggers generation-export mode instead of consumer-side distribution modelling.
2. Source sizing
One 500 kW WTG (turbMw 0.5); installed 500 kW, effective supply 400 kW (0.8 factor), 100% renewable share.
3. Generator voltage
The 0.69 kV machine terminal is LV and cannot transmit far — it must be stepped up on-site, which is exactly why one-turbine-one-transformer exists.
4. Box transformer selection
500 kW ÷ 1.0 PF × 1.05 margin = 525 kVA → 800 kVA standard tier (0.69/35 kV); at 35 kV the small machine is classed "Combined dry-type" by the engine.
5. Collector design
35 kV single feeder (30 MVA feeder limit → ≤10 × 800 kVA boxes/feeder); this case has 1 turbine → 1 feeder.
6. Step-up & POI
Step-up main transformer 35/110 kV (engine floor 10 MVA) + 110 kV POI; a real 0.5 MW farm usually ties in at 35 kV — 110 kV applies to multi-turbine utility farms.
7. Reactive & power quality
Grid connection needs PF ±0.95 continuous (GB/T 19963), so a ±1 Mvar SVG is added; turbine harmonics/flicker handled by SVG + filters.
Pain Points → Solution → Evidence
A wind farm has no local load — sizing it as a consumer distribution system understates the export-side equipment.
Generation-export mode models the full WTG→box→collector→step-up chain with PPA-based economics.
genPlant mode active; 100% renewable share; PPA revenue $83,220/yr.
Grid code demands LVRT and ±0.95 PF — a passive plant trips off on any voltage dip.
±1 Mvar SVG provides continuous dynamic reactive + LVRT support, with collector feeder protection.
BOM includes SVG ±1 Mvar (PF ±0.95 continuous); aligned with GB/T 19963.
One-turbine-one-transformer means many small boxes — the wrong tier over-builds cost or overloads.
The engine sizes the box on turbine rating/PF/margin and picks the standard tier.
525 kVA raw demand → 800 kVA standard tier, one-turbine-one-transformer.
4 · Key Parameter Deep-Read
| Parameter | Value | Basis | Impact & Boundary |
|---|---|---|---|
| Box transformer | 800 kVA (0.69/35 kV) | 500 kW ÷ 1.0 PF × 1.05 margin = 525 kVA → 800 kVA tier | One-turbine-one-transformer; small 35 kV machine classed "Combined dry-type" >3 MW turbines switch to "Oil-immersed combined box" |
| Collector voltage | 35 kV | collectorKv=35 (kept when ≥35) | 30 MVA feeder limit → ≤10 boxes/feeder <35 kV drops to 10 kV collection |
| Step-up main transformer | 10 MVA (35/110 kV) | Total collector 0.8 MVA → engine floor 10 MVA | 110 kV POI Real 0.5 MW ties 35 kV directly; 110 kV is for multi-turbine farms |
| SVG rating | ±1 Mvar | 25% of 500 kW = 125 kvar → 1 Mvar min tier | PF ±0.95, LVRT support ≥1 Mvar engine floor |
| Annual P50 | 1,040,250 kWh | 500 kW × 8760 h × CF 0.25 × 0.95 | $83,220/yr @ $0.08/kWh P90 = 986,906 kWh (CV 0.04) |
| Capacity factor | ≈24% | Wind full-load 2190 h (8760×0.25) × 0.95 | Drives 10.6% IRR Highly site-specific wind resource |
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
WTG 500 kW → 0.69 kV terminal → 800 kVA box up to 35 kV → collector feeder → 110 kV step-up → grid export, 100% online.
Reactive & power quality
±1 Mvar SVG continuous dynamic reactive, PF ±0.95; turbine harmonics/flicker handled with the SVG.
Fault & protection
LVRT support on dips, staged collector feeder protection, step-up differential — a single fault does not trip the whole farm.
Economics
1,040,250 kWh/yr, $83,220/yr; $640,850 EPC, 9 yr payback, 10.6% IRR, 181% 25-yr ROI.
Other views (shown): LCC (life-cycle cost) · Power quality & harmonics · Voltage profile · Scheme features · Environmental derating
7 · Economics & Payback
Equipment FOB ≈ $491,625 (WTG $352,500 + box transformer $37,000 + step-up $29,500 + SVG $50,000 + HV switchgear $16,750 + RMU $5,875; collector network & switchgear are POA); EPC ≈ $640,850. Annual 1,040,250 kWh → $83,220/yr @ $0.08/kWh PPA; 9 yr payback, 10.6% IRR, 181% 25-yr ROI.
8 · FAQ
What box transformer for a 500 kW wind turbine?
Why a 35 kV collector?
What size 110 kV step-up transformer?
What is the payback?
Why is an SVG needed?
How much energy per year?
Is this one-turbine-one-transformer?
What does $491,625 cover?
Why is stdKva 500 while the box is 800 kVA?
Special Considerations
- Step-up main transformer is engine-floored at 10 MVA (smallest 35/110 kV tier); a 0.5 MW single-turbine farm should realistically tie in at 35 kV — 110 kV step-up is for multi-turbine utility farms. Feasibility-level, pending design institute.
- The priced BOM step-up is YB-630/10 (10 kV, the engine's PV-oriented generic step-up); the wind 35/110 kV collector/step-up scope (collector switchgear + main transformer) is POA — reconcile with the design institute.
- LVRT / grid code (GB/T 19963) is not explicitly modelled in the engine — confirm fault-ride-through requirements with the grid operator.
- Collector network and collector switchgear are line items without unit price (POA) — the total is conservative.
- Receiving-side calcs (10/0.4 kV short-circuit, load flow, arc flash, N-1) are stale in generation-export mode — ignore them; plant-side data is in windCalc/genPlant.
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