Diesel Generator Sizing Calculator — Calculate DG Set KVA for Industrial Loads
Calculate required DG set KVA from running load, motor starting kVA, and generator loading factor.
Calculator
No signup required. Results are indicative—verify for your standards.
Running kVA: 150.0 kVA
Motor starting kVA: 211.8 kVA (starting scenario: 326.5 kVA)
Governing load: 326.5 kVA
Minimum generator kVA: 435.3 kVA
Select: 500 kVA genset
Est. fuel consumption at target load: 90.0 L/hr
Formula
Running kVA = Σ (kW / PF) × Demand factor. Starting kVA = Running kVA (excl. starting motor) + Motor starting kVA (DOL: 6× rated; Y-Δ: 2×; VFD: 1.2×). Generator kVA ≥ max(Running kVA, Starting kVA) / loading factor.
Example calculation
Running loads: 120 kW motors (PF 0.85) + 30 kW lighting = 141.2 + 30 = 171.2 kVA × 0.85 demand = 145.5 kVA. Largest DOL motor: 30 kW → starting kVA = (30/0.85) × 6 = 211.8 kVA. Total at start = (145.5 − 35.3) + 211.8 = 322 kVA / 0.75 = 429 kVA → select 500 kVA genset.
Engineering notes
Motor starting kVA (not running kVA) usually determines generator size for industrial loads with large motors. Standard genset ratings (kVA): 15, 25, 40, 62.5, 82.5, 100, 125, 160, 200, 250, 320, 400, 500, 625, 800, 1000, 1250 kVA. Fuel consumption: 0.25–0.33 L/kWh at 75% load (0.8 PF). AMF (Auto Mains Failure) panel with ATS (Auto Transfer Switch) required for automatic changeover. Specify sound attenuated enclosure (acoustic canopy) for built-up area installations — typical noise levels: open set 100–105 dB(A) at 1m; acoustic canopy 70–80 dB(A). Include 48-hour fuel tank for extended outages.
When to use this calculator
- Factory standby power — size a DG set to supply critical loads during grid power failure
- Remote site prime power — size genset for continuous power where grid is unavailable
- Hospital and data centre — calculate emergency power for life-safety and critical IT loads
- Construction site power — temporary power for tools, lighting, and welding on a construction project
- Solar hybrid system — size DG set as backup to a solar + battery system for night and overcast periods
Frequently asked questions
- How do I calculate DG set KVA requirement?
- Step 1: List all loads connected to the generator (kW and PF). Step 2: Running kVA = Σ(kW/PF) × demand factor. Step 3: Identify the largest motor that starts DOL. Starting kVA = (motor kW / PF) × 6 (DOL) or × 2 (star-delta) or × 1.2 (VFD). Step 4: Generator kVA ≥ (running kVA − motor rated kVA) + motor starting kVA. Step 5: Divide by loading factor (0.75) and select next standard rating.
- What size diesel generator do I need for a 50 kW load?
- For a 50 kW load at PF 0.8: running kVA = 50/0.8 = 62.5 kVA. At 75% loading: generator kVA = 62.5/0.75 = 83 kVA → select 82.5 or 100 kVA. However, if there is a large motor (say 22 kW DOL): starting kVA = (22/0.85) × 6 = 155 kVA. Total = (62.5 − 25.9) + 155 = 191.6 kVA / 0.75 = 255 kVA → you would need a 250–320 kVA genset, not 100 kVA. Always check motor starting load.
- What is the fuel consumption of a diesel generator per hour?
- Typical diesel fuel consumption at 75% load: 7.5 kVA genset: ~1.5–2 L/hr; 25 kVA: 4–6 L/hr; 62.5 kVA: 10–13 L/hr; 125 kVA: 19–24 L/hr; 250 kVA: 38–47 L/hr; 500 kVA: 75–90 L/hr; 1000 kVA: 150–175 L/hr. At ₹95/L diesel: 125 kVA at 75% load ≈ 21 L/hr = ₹2,000/hr running cost. Specific fuel consumption (L/kWh) improves at higher loading — avoid running generators below 40% load for extended periods.
- What is the difference between standby KVA and prime KVA for a generator?
- Standby (emergency) KVA rating: for use when the main grid fails; allows 10% overload for 1 hour per 12 hours, with average load not exceeding 70% of standby rating. Not for continuous use. Prime KVA: for continuous operation as the main power source, unlimited hours. Always 10–15% lower than standby KVA for the same engine. For most industrial standby applications, specify standby KVA. For remote sites without grid, specify prime KVA.