4 MW Green-Hydrogen Power: N+1 35 kV Feed + 4055 A APF + SVG Deep-Read
2×SCB13-4000/35 N+1 · APF 4055 A + SVG ±1 Mvar + PFC 1000 kvar · 35 kV · THDi 88% treated
1 · TL;DR Conclusion
Conclusion: this 4 MW green-hydrogen plant uses 35 kV dual feeds + 2×SCB13-4000/35 dry transformers (N+1) + a 4055 A active power filter (APF) + ±1 Mvar SVG + 1000 kvar PFC. Rectifier THDi of 88% is treated to pass; configurator total ≈ $1,524,603 (APF priced on application), LV fault 69.56 kA → 80 kA breaking (feasibility-level).
- •2×4000 kVA dry transformers N+1; 84% loading after one-unit loss (pass), 2 s transfer ≤ 15 s allowed
- •Electrolyzer rectifier load 3500 kW (88% nonlinear), THDi 88% → 4055 A APF + ±1 Mvar SVG + 1000 kvar PFC
- •500 kW VFD compressor/pump start, ±1 Mvar SVG suppresses voltage flicker
- •LV fault 69.56 kA → 4000 A MNS bus, 80 kA breaking; MV 35 kV at 25 kA
- •≈2,917,501 kWh/yr losses ($489,427/yr)
2 · Solution Overview
A green-hydrogen plant's core load is the electrolyzer rectifier: purely nonlinear, large, and continuous, so harmonics are the top problem, while VFD auxiliaries add impact and reactive swings. This scheme pairs 35 kV infeed + N+1 transformers + active filtering + dynamic VAR to build a high-power, low-harmonic, high-continuity supply.
| Source | Role | Share kW | Share |
|---|---|---|---|
| Grid 35 kV | base | 3200 kW | 100% |
3 · Design Process & Rationale
1. Requirement identification
A 4 MW hydrogen plant = 3500 kW electrolyzer rectifier (pure nonlinear) + 500 kW VFD auxiliaries (H2 compressor, cooling pumps). Continuous, harmonic-sensitive — a classic high-power nonlinear-load case.
2. Load grading & classification
Whole site as grade-2 (loadGrade2=4000); nonlinear 88% (3500/4000), impact 500 kW (VFD start). Demand 3200 kW (Kd=0.8).
3. Voltage level choice
4 MW continuous load exceeds economical 10 kV delivery → 35 kV infeed (KYN61-40.5 MV switchgear) to cut line current and losses.
4. Transformer sizing
3200 kW ÷ 0.8 PF = 4000 kVA; N+1 → 2×SCB13-4000/35 dry-type (indoor, fire-safe, low-noise), 84% loading after one-unit loss.
5. Harmonic & reactive mitigation
Rectifier THDi ≈ 88% far over the limit → 4055 A APF active filter to remove THDi; VFD impact + VAR swings → ±1 Mvar SVG; base reactive → 1000 kvar capacitors with detuned reactors.
6. Protection & breaking
LV fault current 69.56 kA (large 4000 kVA dry transformer) → 80 kA LV switchgear; MV 8.2 kA → 25 kA. Multi-level overcurrent grading 0.3/0.2 s, selectivity 13.6× satisfied.
7. Secondary & monitoring
61850 comms + DC auxiliary + SCADA for rectifier-transformer temperature, APF/SVG status and real-time power-quality monitoring to keep hydrogen production continuous.
Pain Points → Solution → Evidence
Electrolyzer rectifier harmonics trip the grid and derate transformers
4055 A APF active filter + detuned reactors + 12-pulse rectifier guidance
V6: THDi 88% treated to pass by APF
VFD auxiliaries cause starting impact and VAR swings → voltage flicker
±1 Mvar SVG dynamic VAR (<10 ms response)
500 kW VFD impact → SVG fast response; $70,000 in the BOM
A single fault at 4 MW blacks out the whole plant
35 kV dual feeds + N+1 dual transformers + auto-transfer
N-1 pass (84% after one-unit loss), 2 s transfer ≤ 15 s
Continuous operation means high loss energy cost
SH15 amorphous upgrade + HV-side metering management
$489,427/yr losses
4 · Key Parameter Deep-Read
| Parameter | Value | Basis | Impact & Boundary |
|---|---|---|---|
| Transformer capacity | 4000 kVA ×2 (SCB13, 35 kV) | 3200 kW ÷ 0.8 PF = 4000 kVA; N+1 → 2 dry units | 84% loading; dry-type is fire-safe and low-noise indoors Above ~3800 kVA demand, step to 5000/6300 |
| Incoming voltage | 35 kV | 4 MW continuous load exceeds economical 10 kV delivery | MV current only 66 A, big cut in line loss and drop Needs a 35 kV supply point, else step down on site |
| Harmonic mitigation | APF 4055 A + detuned reactors | Rectifier THDi 88%, 6-pulse characteristic orders 5/7/11/13 | THDi passes, protects transformer and metering APF 4055 A priced on application; recommend 12-pulse rectifier |
| Dynamic VAR | SVG ±1 Mvar | 500 kW VFD impact + VAR swings | <10 ms response suppresses voltage flicker Staged with 1000 kvar capacitors (SVG fast + caps steady-state) |
| LV breaking | 80 kA (Icu) | Fault current LV 69.56 kA | MNS bus 4000 A, 1.1× breaking margin Confirm actual system fault level with grid |
| MV breaking | 25 kA (Icu) | Fault current HV 8.2 kA | KYN61-40.5 vacuum switchgear, 3× margin 35 kV side needs dedicated protection settings |
| Annual losses | 2,917,501 kWh ($489,427) | 84% loading + line loss (88% nonlinear amplifies) | Dominates opex and drives amorphous upgrade Real loss under harmonics exceeds fundamental estimate — measure on site |
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
35 kV infeed → dual transformers (84% loading) → 4000 A LV bus → rectifier/electrolyzer 3200 kW + VFD auxiliaries; system loss 333.05 kW (10.41%), of which line 317.52 kW and transformer 15.53 kW — the high loss under harmonics is clear.
Power quality & harmonics
6-pulse orders 5/7/11/13 dominate, THDi 88%; the 4055 A APF removes THDi, ±1 Mvar SVG suppresses flicker and 1000 kvar caps cover base VAR — three stages bring THDi to pass.
Fault & protection
Rehearses 80 kA breaking under a 69.56 kA LV fault plus multi-level grading (downstream 0.1 s, upstream 0.3 s), with 61850 and DC auxiliary — a single fault never escalates.
Loss & cost
2,917,501 kWh/yr ($489,427).
Other views (shown): LCC (life-cycle cost) · Voltage profile · Scheme features · Environmental derating
7 · Economics & Payback
Equipment total ≈ $1,524,603 (the 4055 A APF is priced on application); no PV/BESS so no generation payback model. Economics center on operation: 2,917,501 kWh/yr losses ($489,427/yr). The $70,000 SVG and $27,000 PFC are one-off investments buying grid harmonic compliance and continuous-run reliability.
8 · FAQ
What transformer size for a 4 MW hydrogen plant?
Why 35 kV instead of 10 kV infeed?
How are rectifier harmonics handled?
What's the difference between SVG and capacitors?
What happens on a power outage?
How much does the scheme cost?
Are operating losses high?
What is the LV fault level and breaking?
Are the rectifier and isolation transformers in the quote?
Special Considerations
- The rectifier transformer and isolation transformer (for the electrolyzer DC bus) sit in the electrolyzer-package / specialist design scope — the configurator models the 35 kV→0.4 kV AC distribution plus harmonic mitigation, and does NOT price the rectifier/isolation transformers themselves.
- The 4055 A APF is an extra-large rating priced on application (excluded from total); prefer a 12-pulse rectifier to suppress the 5th/7th at source and sharply cut APF size.
- Transformer loss under harmonics exceeds the fundamental estimate — for continuous duty use a K-factor transformer or extra margin, and verify THDi by measurement.
- LV 69.56 kA fault needs 80 kA breaking; arc-flash 5.86 cal/cm² (Cat 2) — a formal IEEE 1584 study is required before PPE selection.
- Feasibility-level estimate; drawings pending a licensed design institute. Rectifier/isolation/DC-bus selection must be coordinated with the electrolyzer OEM.
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