700 kW / 630 kVA Mine Power: 250 kW Four-Quadrant Hoist + SVG + Diesel Deep-Read
2×S13-M-630/10 N+1 · 250 kW four-quadrant hoist VFD · SVG · 500 kW diesel
1 · TL;DR Conclusion
Conclusion: this 700 kW mine uses 2×S13-M-630/10 oil transformers (N+1) + a 250 kW four-quadrant hoist VFD + SVG + a 500 kW standby diesel — configurator total ≈ $269,595, 94% N-1 loading (near limit), 250 kW hoist dip 2.7% on VFD vs 12.2% DOL (DOL fails), THDi 36% (feasibility-level).
- •2×630 kVA S13-M-630/10 (N+1), 94% loading after one-unit loss (pass, near limit — watch headroom)
- •250 kW four-quadrant hoist VFD: 2.7% dip; DOL would sag 12.2% and fail the 10% limit
- •SVG ($32,200) + 500 kW standby diesel keep hoist/ventilation/drainage continuous
- •THDi 36% from VFDs → detuned reactor + SVG/APF
- •Economics: $269,595 total; SH15 upgrade $336/yr, ~3 yr payback; losses 173,812 kWh/yr ≈ $20,857
2 · Solution Overview
A mine's electrical lifeline is the hoist, ventilation and dewatering: the hoist is four-quadrant (lifts on the way up, regenerates on the way down), ventilation and drainage run continuously, and a power loss endangers people underground. This scheme uses N+1 transformers, a four-quadrant hoist VFD, SVG and a standby diesel to keep the shaft safe.
| Source | Role | Share kW | Share |
|---|---|---|---|
| Grid 10 kV | base | 560 kW | 100% |
| Diesel 500 kW | backup | 0 kW | 0% |
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3 · Design Process & Rationale
1. Requirement identification
700 kW mine: 250 kW four-quadrant hoist, continuous ventilation/drainage, grade-1 250 kW (hoist), grade-2 300 kW (vent/drainage).
2. Load & grading
Hoist grade-1 250 kW (personnel safety); ventilation/drainage grade-2 300 kW; impact 350 kW, nonlinear 250 kW.
3. Source
10 kV grid + 500 kW standby diesel; diesel covers grade-1 250 kW (V9 pass), 20 ft container, 3-day autonomy.
4. Transformer sizing
560 kW ≈ 589 kVA → 630 kVA tier; N+1 → 2×S13-M-630/10, 94% loading after one-unit loss (near limit).
5. Hoist drive
250 kW four-quadrant VFD (2.7% dip); DOL would sag 12.2% and fail — VFD is mandatory; regenerative braking returns to the DC bus.
6. SVG & harmonics
36% THDi + 350 kW impact → SVG dynamic compensation + detuned reactor.
7. Protection
LV 22 kA / MV 28.9 kA, breaking LV 36 kA / MV 31.5 kA; selectivity 9.18×; modbus SCADA.
Pain Points → Solution → Evidence
DOL starting the hoist sags the bus 12.2% and trips other feeders
250 kW four-quadrant VFD, 2.7% dip
V5: DOL 12.2% ok=false, VFD 2.7% ok=true
Power loss traps miners underground
Standby diesel + ATS to hoist/ventilation
V9 pass (diesel 500 ≥ grade-1 250); 20 ft container, 3-day
VFD harmonics + regenerating hoist distort the bus
SVG + detuned reactor
THDi 36% (V6 warn), SVG $32,200
4 · Key Parameter Deep-Read
| Parameter | Value | Basis | Impact & Boundary |
|---|---|---|---|
| Transformer capacity | 630 kVA ×2 (S13-M) | 589 kVA → 630 tier; N+1 → 2 units | 94% after one-unit loss, near limit consider 800 kVA for headroom |
| Hoist drive | 250 kW four-quadrant VFD, 2.7% dip | VFD kst 1.3 vs DOL 6.5 | DOL 12.2% fails; VFD is mandatory four-quadrant regen needs braking resistor/feedback unit |
| Diesel | 500 kW standby | covers grade-1 250 kW (hoist) | 3-day autonomy, <15 s auto-start full-mine backup needs a larger set |
| Impact load | 350 kW | hoist acceleration surge | sets SVG size & start dip vent/drainage simultaneous start to verify |
| Harmonics | THDi 36% | nonlinear 250 kW / 700 kW | needs SVG active filtering target THDi ≤8% |
| Demand factor | 0.8 → 560 kW | installed 700 kW × Kd 0.8 | sizes transformer at real demand verify against hoist/vent duty cycle |
5 · Drawing Deep-Read
The following drawings are shown for reference (full set in the configurator “View design document”):
6 · Operation Demo (Deep-Read)
Reliability
N+1 94% after one-unit loss (near limit) + diesel auto-transfer ≤15 s covering grade-1 hoist 250 kW, keeping the shaft safe.
Fault & protection
LV 22 kA / MV 28.9 kA, breaking LV 36 kA / MV 31.5 kA; selectivity 9.18×, a downstream fault trips only its feeder.
Power quality
THDi 36% mitigated by SVG; hoist VFD dip 2.7% (DOL 12.2% fails), bus 0.981 pu.
Economics
$269,595 total; SH15 upgrade ~3 yr payback ($336/yr); losses 173,812 kWh/yr ≈ $20,857.
Other views (shown): LCC (life-cycle cost) · Power quality & harmonics · Voltage profile · Scheme features · Arc flash
7 · Economics & Payback
Equipment total ≈ $269,595 (2×S13-M-630/10 + hoist drive + ventilation/dewatering feeders + SVG + 500 kW diesel + modbus SCADA). No PV/BESS, so economics = capex + losses + transformer TCO: S13→SH15 amorphous upgrade saves ≈2,803 kWh/yr (≈$336/yr), ~3 yr payback; annual transformer+line losses ≈173,812 kWh (≈$20,857/yr). Diesel is standby-only. Hoist/ventilation/dewatering motors are POA.
8 · FAQ
What transformer for a 700 kW mine?
Why must the hoist be on a VFD?
What does four-quadrant mean?
How big a diesel?
How are ventilation and drainage powered?
How is 36% THDi handled?
What happens to miners on an outage?
What's the payback on a better transformer?
Is the price final?
Special Considerations
- N-1 94% loading after one-unit loss is near the limit — consider stepping the transformer to 800 kVA for headroom (V4/V13).
- DOL starting the hoist would sag 12.2% (>10% limit) — the four-quadrant VFD is mandatory, with braking resistor/feedback unit.
- If underground sections need explosion-proofing, add Ex equipment per hazardous zone separately (this scheme feeds the surface substation).
- 500 kW diesel covers grade-1 hoist 250 kW (V9 pass); full vent/drainage backup needs a larger set.
- Feasibility-level estimate; drawings pending a licensed design institute; confirm grid Ssc (500 MVA assumed).
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