A gold processing plant in Burkina Faso called us after their newly installed 500 kW generator failed repeatedly during startup. Every time the jaw crusher and ball mill tried to start simultaneously, the generator’s circuit breaker tripped. Production stopped. The shift crew sat idle for three hours while electricians scratch their heads.

The problem was not the generator — it was the sizing. Whoever calculated the power requirement had added up nameplate ratings without accounting for motor starting currents, harmonic distortion from the VFD-driven conveyor, or the altitude derating at their 1,200-meter site elevation. The result was a generator that was 35% too small for the actual starting demand.

Sizing a China diesel generator set for a mining processing plant is one of the most technically demanding calculations in the power generation industry. At Tesla Power, we have done this for copper, gold, lithium, and iron ore operations across Africa and South America. Here is exactly how to get it right.

Why Mining Plant Sizing Is Uniquely Difficult

Commercial and residential generator sizing is straightforward — mostly lighting, HVAC, and plug loads with well-behaved power factors. Mining processing plants are a completely different beast for several reasons:

• Massive motor starting currents: A 75 kW crusher motor draws 375–525 kVA during the 5–10 seconds it takes to reach full speed. That is a 5–7x multiplier on the running load, and it happens every time you start the plant
• Dirty power profiles: Variable frequency drives (VFDs) on conveyors and pumps create harmonic distortion that causes additional heating in the generator’s alternator
• Cyclical load patterns: Processing plants run in stages — crushing, grinding, flotation, pumping — with loads that swing dramatically between phases
• Altitude and temperature: Many mining operations are at 1,000–4,000 meters elevation, where engine derating significantly reduces available power
• Continuous duty: Processing plants often run 18–24 hours per day during production seasons, pushing the generator into prime power territory

The Step-by-Step Calculation Method

Let me walk you through the complete calculation using a real Tesla Power project — a gold processing plant in Guinea with the following equipment:

Step 1: List Every Piece of Equipment

EquipmentQtyRunning kWPower FactorStarting MethodStarting kVA

Jaw crusher (primary)11100.85DOL (direct-on-line)770
Ball mill11600.82Soft starter480
SAG mill12500.85Soft starter625
Conveyor belt (VFD)330 each0.80VFDN/A
Slurry pump422 each0.83DOL132 each
Flotation cells (agitators)87.5 each0.85DOL45 each
Leaching tanks (agitaors)65.5 each0.85DOL33 each
Thickener drive211 each0.85DOL66 each
Compressed air system1370.85DOL222
Lighting and control—250.95N/AN/A
Water supply pumps218.5 each0.83DOL111 each

Step 2: Calculate Running Load

Total Connected Running Load:
110 + 160 + 250 + (3 × 30) + (4 × 22) + (8 × 7.5) + (6 × 5.5) + (2 × 11) + 37 + 25 + (2 × 18.5)
= 110 + 160 + 250 + 90 + 88 + 60 + 33 + 22 + 37 + 25 + 37
= 912 kW connected

Apply diversity factor (not all equipment runs simultaneously in all processing stages):

• Crushing stage: crusher + conveyors + lighting = 260 kW (diversity 1.0 — all must run)
• Grinding stage: SAG mill + ball mill + conveyors + slurry pumps = 562 kW
• Processing stage: flotation + leaching + thickener + compressed air + pumps = 298 kW

Maximum simultaneous running load: 562 kW (grinding stage — the peak demand)

Step 3: Calculate Worst-Case Starting Scenario

The critical moment is when the largest motor starts while other equipment is already running. We need to determine: running load + largest motor start = required generator capacity.

Worst-Case Starting Calculation:
Running load (excluding SAG mill): 562 – 250 = 312 kW
SAG mill running kVA: 250 / 0.85 = 294 kVA
SAG mill starting kVA (soft start, 2.5x): 250 / 0.85 × 2.5 = 735 kVA
Running kVA of other equipment: 312 / 0.84 = 371 kVA
Total during SAG start: 371 + 735 = 1,106 kVA peak demand

Step 4: Apply Derating Factors

The plant is at 1,200 meters elevation with ambient temperatures reaching 42°C:

• Altitude derating: 1% per 100m above sea level = 12% derating for 1,200m
• Temperature derating: 2% for each 5°C above 40°C standard = 0.8% (minor)
• VFD harmonic derating: 10% additional derating for harmonic content
• Total derating factor: 1.12 × 1.008 × 1.10 = 1.24 (24% total derating)

Required Generator Capacity:
1,106 kVA × 1.24 derating = 1,371 kVA minimum
Add 15% growth margin: 1,371 × 1.15 = 1,577 kVA

Recommended: Two 800 kVA Weichai generators in parallel

See our detailed industrial sizing guide.

Recommended Weichai Configuration for Mining Processing Plants

• Engine: Weichai WP12.480, 12-cylinder, turbocharged, intercooled, rated for continuous prime power
• Rated Power: 640 kW / 800 kVA (Prime), 704 kW / 880 kVA (Standby)
• Alternator: Leroy-Somer LSA 50.1, brushless, IP23, H-class insulation, heavy-duty damper winding for harmonic loads
• Controller: ComAp InteliGen NT with parallel synchronization, load-dependent start/stop, motor starting management, and GSM remote monitoring
• Fuel Consumption: 138 L/h at 75% load per unit — strong Weichai generator fuel efficiency
• Fuel Tank: 1,500L base-mounted + 5,000L remote day tank
• Cooling: 50°C ambient rated oversized radiator with coolant pre-heater for cold starts
• Air Filtration: Three-stage system — cyclonic pre-cleaner + heavy-duty dry filter + safety filter with dust indicator
• Canopy: Heavy-duty mining grade, 2.5mm steel, anti-vibration mounting, marine-grade exhaust
• Dimensions: 3800 × 1600 × 2200 mm
• Weight: 4,200 kg
• Raw Materials: Q235B structural steel, hot-dip galvanized fasteners, copper busbars, high-density rock wool 75mm, polyester powder coat 200µm
• Service Mode: Tesla Power provides commissioning supervision, operator training, maintenance contracts, and 24/7 remote support

Motor Starting — The Technical Detail That Kills Undersized Generators

Understanding motor starting behavior is critical for mining power requirements:

• DOL (Direct-On-Line) starting: Draws 5–7x running current. Simple, cheap, but creates massive voltage dip. Only suitable for small motors (<22 kW) on generator power
• Star-Delta starting: Reduces starting current to 2–3x running. Requires 3-contactor configuration. Common for medium motors (22–75 kW)
• Soft starter: Reduces starting current to 2–3.5x with smooth acceleration. Best option for large motors (75–250 kW) on generator power. Adds $1,500–$5,000 per motor
• VFD (Variable Frequency Drive): Near-unity starting current. Ideal for conveyors and pumps. Creates harmonics that require alternator derating

Tesla Power sizing rule: the generator must be capable of starting the largest motor while maintaining voltage dip below 25% and frequency dip below 5%. If it cannot, you need a larger generator or motor starting aids.

Tools for Accurate Power Calculation

• ETAP PowerStation: Professional software for load flow analysis, short circuit, motor starting, and harmonic studies. Cost: $5,000–$25,000 annual license
• SKM Power*Tools: Similar to ETAP, widely used by mining engineering firms
• Cummins Power Suite: Free tool for generator sizing (works for Weichai comparisons too)
• Power factor meter: Fluke 43B or equivalent for measuring actual power factor at existing installations
• Clamp meter: Measure actual running current on each motor to verify nameplate data

Frequently Asked Questions

Q1: Should I size for all motors starting simultaneously?

No — that would result in a massively oversized and expensive generator. Size for the worst-case scenario: the largest motor starting while all other running equipment is at full load. Implement a staggered starting sequence that prevents multiple large motors from starting at the same time.

Q2: How does altitude specifically affect my generator sizing?

At 1,200 meters, a 800 kVA generator effectively delivers only about 708 kVA. The derating formula: effective power = rated power × (1 – altitude/1000 × 0.01). For high-altitude mines, we compensate by specifying turbocharged engines with oversized radiators and intercoolers. Learn about altitude effects on fuel consumption.

Q3: Do VFDs on conveyors require special generator sizing?

Yes. VFDs create harmonic currents (primarily 5th and 7th harmonics) that cause additional heating in the alternator. Standard practice is to derate the alternator by 10–15% for VFD loads, or specify an alternator with a damper winding and reinforced winding insulation. Tesla Power always specifies oversized alternators for mining plants with significant VFD content.

Q4: Is it better to have one large generator or two smaller ones in parallel?

For mining processing plants, two parallel units (N+1 configuration) is almost always the better choice. Benefits include: redundancy (if one unit fails, the plant keeps running), flexibility (run one unit during low-demand maintenance periods, both during peak production), and lower capital risk (if your production forecast is wrong, you have not over-committed to a single oversized unit).

Q5: How often should I recalculate my power requirements?

Annually, or whenever you add equipment to the processing plant. Mining operations expand frequently — a new thickener, an upgraded crusher, or additional flotation cells can push your load beyond the generator’s capacity. Tesla Power offers free power audits for existing clients to verify their generator sizing remains adequate.

Correct generator sizing for mining processing plants prevents costly downtime and protects your equipment from damage. Tesla Power provides complimentary sizing calculations for all mining project inquiries — send us your equipment list and receive a detailed recommendation within 24 hours.