Generator SizingCalculator for India

The calculator follows the IS 8528 / ISO 8528 two-test method used by Greaves, Kirloskar, Cummins and Caterpillar. You select your equipment from a library of 80 typical Indian industrial loads, and the engine computes (a) the steady-state running kVA after applying a diversity factor, and (b) the worst-case starting surge kVA when your largest motor inrushes while everything else is already running. It then takes the larger of the two, derates for site altitude and ambient temperature per IS 13364, adds a future-expansion reserve, and rounds up to the nearest standard kVA bracket. Finally, it recommends the smallest CPCB IV+ Greaves model whose rated kVA meets that requirement.

kVA (kilo-volt-amperes) is the apparent power a generator can deliver - it accounts for both real power (kW, what does useful work) and reactive power (kVAR, needed by inductive loads like motors and transformers). The relationship is kW = kVA × power factor. Indian generators are rated in kVA at 0.8 PF by convention, so a 100 kVA genset delivers 80 kW of real power into a typical industrial load. Sizing in kVA is the right approach because the alternator's heating limit is set by current, which depends on apparent power, not real power.

Three reasons. First, IS 8528 recommends sizing for future load growth - most Indian industrial sites add equipment within 3-5 years of installation. Second, generators run most efficiently at 70-85% of their rated load; running at 100% continuously shortens engine life and increases fuel consumption. Third, real-world transient overloads (motor restarts, capacitor switching, fault clearing) need headroom beyond steady-state load. For critical applications like hospitals and data centres we recommend 35-40% reserve.

An induction motor draws 6-8 times its full-load current at the moment of starting (Direct-On-Line / DOL start), at a very low power factor (~0.3-0.4). For a few seconds the apparent power demand can be 8-10x the running kVA. If the generator can't supply this surge, the engine RPM drops, the voltage collapses, and the motor either fails to start or burns out. That's why the calculator separately computes the surge kVA scenario - generators are often sized by the largest motor's starting requirement, not by total running load. Soft-starters and VFDs reduce this surge to roughly 2.5x and 1x respectively.

Diversity factor is the ratio of average simultaneously-operating load to total connected load. Not every motor, AC, or light is on at the same instant - even in a busy factory. Typical values: residential 0.4-0.6, commercial offices 0.6-0.8, light industry 0.7-0.8, heavy manufacturing 0.75-0.9, continuous-process plants (cold storage, pharma) 0.85-0.95, and warehouses 0.4-0.65. Choosing a value that's too high oversizes the genset (wasting capex and burning fuel inefficiently); too low risks tripping under peak load. The calculator's industry presets pre-set a sensible default per industry type.

Yes. Above 1000 metres above mean sea level, the engine loses approximately 1% of rated output for every additional 100 metres because of reduced air density (less oxygen for combustion). For most Indian sites in the plains (Delhi-NCR, Bhiwadi, Jaipur, Chennai, Mumbai) altitude derating is negligible. For Bengaluru and Pune (~900 m) it's still under 1%. Hill stations (Shimla, Darjeeling) need ~5% extra capacity, and high-altitude installations like Leh-Ladakh need 25-30% extra. The calculator applies this derating automatically based on your selected altitude.

Alternators are rated at 40°C ambient per IS 13364 / IEC 60034-1. Above 40°C the insulation system degrades faster, so the alternator must be derated to keep winding temperatures within Class H/F limits. Approximate derating: 96% at 45°C, 93% at 50°C, 88% at 55°C, 83% at 60°C. Outdoor canopy installations across most of India regularly see 50°C or higher inside the canopy during summer, so 7-12% derating is normal. The calculator's default is 50°C - adjust it down only if your genset will be installed indoors with proper ventilation.

Alpha Diesels is an authorized Greaves Cotton dealer, and we calibrated this tool against the verified Greaves CPCB IV+ technical brochure (25 models from 5 kVA to 2250 kVA). That lets us guarantee the recommended model's specifications - engine type, alternator make, fuel consumption, dimensions - are accurate to the manufacturer's data sheet. The sizing engine itself follows industry-standard IS 8528 methodology, so the kVA number is brand-neutral and equally valid if you choose to source from another OEM. We're transparent about this and the recommendation is always backed by the underlying calculation, never the other way around.

CPCB IV+ is India's strictest emission norm for diesel gensets, mandatory for all new installations from 1 July 2023. It requires Common Rail Direct Injection (CRDI) engines, optimised after-treatment (often Selective Catalytic Reduction with DEF/AdBlue), and significantly cleaner NOx, PM, CO, and HC emissions. If you're buying a new genset for any commercial or industrial site in India today, it must be CPCB IV+ compliant - no exceptions. The calculator only recommends CPCB IV+ models. Older CPCB II units can still legally operate but cannot be newly installed.

DOL (Direct-On-Line) is simplest and cheapest, used up to 7.5 kW (10 HP) - surge is 6-8x running current. Star-Delta is the traditional method for 7.5-37 kW motors - surge drops to ~2.5x but only works for low-inertia loads (pumps, fans). Soft-starters (electronic) work for any load type and reduce surge to 2-3x with smooth ramping. VFDs (Variable Frequency Drives) eliminate inrush entirely (1x) and add energy savings on variable-load applications, but cost more. The calculator lets you override the default starting method per item to see how genset size changes - frequently a VFD on the largest motor lets you drop one full kVA bracket.

For preliminary budgeting, yes - the IS 8528 methodology and verified equipment values give you a sizing answer that's within ±10% of a full engineering study for typical loads. For final purchase decisions on installations above 250 kVA, or for critical-load sites (hospitals, data centres, continuous-process plants), we recommend a free Alpha Diesels site survey. Our engineers will measure actual load profiles with a power analyser, verify cable sizing and earthing, check installation site for ventilation and acoustics, and issue a stamped sizing report you can share with consultants and lenders.

Wattage values are cross-referenced against IS 12615 (motor efficiency standard), BIS HVAC tables, ASHRAE chiller data, and named manufacturer catalogs (Crompton Greaves, ABB, Siemens, Bharat Bijlee for motors; Atlas Copco, ELGi, Kirloskar Pneumatic for compressors). Where a value is a typical industry estimate rather than a specific datasheet number - for instance, CNC machines, pharma equipment, hotel kitchen loads - we mark the item with a tilde (~) so you know to verify against your nameplate. For binding sizing decisions, always share your equipment nameplate ratings with our team for a refined calculation.

Use the appropriate industry preset to pre-load typical equipment, then refine quantities to match your project. Mixed-load buildings need extra attention to (a) lift and elevator surge - modern ACVF lifts surge less than older Y-Δ lifts; (b) chiller compressor inrush - water-cooled centrifugal chillers can surge 5-7x running kW unless soft-started; (c) life-safety loads (fire pumps, emergency lighting) which must run on the same genset; and (d) higher reserve (35%) for hospitals because trips can endanger patients. The calculator's hospital preset bakes in these conservative defaults.

Set the future-expansion reserve to 30-40% instead of the default 25%. This sizes the generator one or two standard kVA brackets above your day-one load, leaving headroom to add machines without replacing the genset. The trade-off: a larger genset has higher upfront cost and runs less efficiently at light load, so don't oversize beyond actual likely growth. If you're confident about specific future additions (e.g., a second CNC line in 18 months), it's better to add those items to the calculator now at quantity 1 with a starting method assumed.

Yes for single-phase loads - the equipment library marks each item as 1Φ or 3Φ. If your total load is genuinely single-phase (small shops, offices under 25 kVA), select Greaves's small portable / Mech series at the recommendation step. For backup-only applications (where the genset only runs during grid outages, not as prime power), the IS 8528 'Standby' rating applies - typically 10% above the Prime rating from the same model. The Greaves catalog uses Prime rating per ISO 8528 throughout, which is the conservative (correct) choice for sizing. Standby-only sites can effectively buy one bracket smaller, but most Indian industrial sites with frequent outages should size on Prime rating to be safe.