In short. A generator is selected by working through the application, not by picking a kVA from a list. Two facilities with the same connected kW can need very different generator systems because their largest motor, starting method, power factor, load sequence, duty, ambient conditions and continuity consequence differ. Reddy Generators supplies, installs and commissions diesel and gas generator systems from Secunderabad, and every proposal starts with the load, the site and the duty before any model is named.
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By capacity
By duty and type
Every package is offered with the canopy, controller, AMF/ATS panel, cabling, installation and commissioning as required; makes and models are confirmed against your load and site.
Why kVA alone is not a specification
The usual enquiry is a single number: how many kVA do you need. It is rarely enough. A 200 kVA requirement for a commercial building with lifts and air conditioning, a 200 kVA requirement for a rice mill with a 90 kW direct-on-line huller motor, and a 200 kVA requirement for a data room full of UPS rectifiers are three different machines. The first needs a standard alternator and a good AMF panel. The second needs an alternator with high motor-starting capability or a larger frame. The third needs an alternator rated for nonlinear load with an oversized neutral and a controller that tolerates the UPS walk-in. Buying any of them as a generic 200 kVA set produces a generator that starts and runs but does not do the job. The kW and kVA guide explains why real power, apparent power and power factor must all be stated.
The selection chain
Generator selection runs in a fixed order, and model selection is the last step rather than the first.
| Step | Question answered | What it decides |
|---|---|---|
| Application and critical load | Which loads must run during an outage and for how long | Scope of the generator and whether UPS is also needed |
| Running demand | Steady kW and kVA with diversity applied | Minimum continuous rating |
| Starting and transient demand | Largest motor, its starting method, UPS and drive content | Alternator frame and transient margin |
| Duty | Standby, prime or continuous under ISO 8528-1 | Engine rating and service regime |
| Site | Ambient temperature, altitude, dust, indoor or outdoor, noise limits | Derating, cooling, enclosure and exhaust design |
| Electrical system | Voltage, phase, frequency, earthing, fault level, paralleling | Alternator winding, neutral arrangement, switchgear |
| Controls and verification | AMF, synchronising, monitoring, test and acceptance | Controller, panel and commissioning plan |
The generator sizing guide walks through the first three steps in detail, including motor starting and the allowances for growth.
Select by configuration
Once the requirement is defined, the physical configuration follows from the site. Diesel generator sets remain the default for standby and project power in India because of fuel availability and transient response, with gas sets considered where piped gas and long running hours justify them. Stationary sets form part of the permanent installation and are engineered with their room, fuel storage, exhaust and switchgear. Mobile and trailer sets are configured for relocation between sites and carry their own earthing and distribution questions with every move. Open sets are installed in an engineered room that provides cooling air, exhaust and noise control; acoustic enclosed sets package those functions in a factory canopy and are the usual answer for outdoor installation in Indian cities, where CPCB noise norms require 75 dB(A) at one metre for sets up to 1,000 kVA. Containerised systems serve large projects that need protection, transportability or integration of several sets with switchgear.
Select by power band and duty
Power bands are a navigation aid, not a stock list. Sets under 15 kVA serve shops, clinics and small offices; 15 to 125 kVA covers most commercial buildings, small factories, pumping stations and construction sites; 125 to 500 kVA covers hospitals, mid-size industry, hotels and large pumping; 500 kVA to 2 MVA and above serves large industry, data centres and paralleled plants. Across every band the duty rating is the more important choice. Standby rating applies where grid supply normally exists and the set runs during outages; prime rating applies where the set is the main source for long periods at variable load; continuous rating applies to constant base load. Running a standby-rated set as the main supply at a site with poor grid is the most common duty error in Telangana and Andhra Pradesh, and it shows up as early overhauls. The standby power page and the prime power page set out the definitions.
Select by electrical system and installation
Indian installations are 415 V three-phase and 230 V single-phase at 50 Hz, but the electrical system still has to be specified: single-phase sets for small loads, three-phase for everything else, medium-voltage alternators at 3.3 kV, 6.6 kV or 11 kV for large plants, and 60 Hz only for export or specific equipment. The earthing arrangement, the fault level the switchgear must withstand, and whether the set will parallel with other sets or with the grid all shape the alternator and the controls. Installation then decides the rest: an indoor set makes the building part of the generator system through ventilation, exhaust routing and fuel storage, while an outdoor set must handle monsoon rain, 45 degree Celsius summers and dust. The integrated power systems page covers the panels, switchgear and paralleling that turn a set into a system.
What a complete generator package contains
An engine and an alternator on a base frame is not a generator system. The complete package includes the engine with its governor and emission equipment, the alternator with its AVR and excitation, the controller with protection and communication, the cooling system sized for the site ambient, the fuel system from bulk tank to injector, the exhaust system with silencer and backpressure within the engine’s limit, the acoustic enclosure or room, the batteries and charger, the AMF or synchronising panel, the cables and earthing, and the commissioning that proves it all works together. Each of these has its own page under the engine, alternator and controller architecture sections, and the generator finder helps narrow the configuration from a short description of the requirement.
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Common mistakes
- Choosing a set by kVA alone without stating the largest motor and its starting method. The set is too small for the start or oversized for everything else.
- Specifying standby rating for a site with unreliable grid supply. The engine runs far beyond its design hours and needs an early overhaul.
- Ignoring the UPS and drive content of the load. Voltage distortion upsets the equipment and the alternator runs hot on harmonic current.
- Treating the room, exhaust and fuel system as someone else’s scope. A correctly selected set becomes unreliable because it cannot reject heat or breathe.
What to send us
Send your load list or electricity bill with the maximum demand, the largest motor with its kW and starting method, and a note of any UPS or drives in the load. Add the site location, whether the set will be indoor or outdoor, the expected hours of running per month and the application. If you are replacing an existing set, a photograph of its nameplate and controller is the quickest start. Send your generator requirement.
Questions engineers ask
How do I work out the generator size I need?
List the loads that must run together, convert to kVA at their power factor, add the starting allowance for the largest motor, apply the derating for your site temperature and altitude, and add a margin of 10 to 20 per cent for growth. The result is then checked against the alternator’s motor-starting data before a frame is chosen.
What is the difference between standby and prime rated generators?
A standby-rated set is for outage duty where grid supply normally exists, with limited hours per year and no overload capability. A prime-rated set is for use as the main supply for unlimited hours at variable load, with a 10 per cent overload allowance for short periods, and is built and serviced accordingly.
Should I choose an acoustic enclosed set or an open set?
For outdoor or rooftop installation in a city, an acoustic enclosure is the practical way to meet the CPCB limit of 75 dB(A) at one metre. An open set suits a dedicated generator room that is designed for ventilation, exhaust and noise, and gives better service access in return for that room engineering.
Do new generators in India have to be CPCB IV+?
Yes. New diesel generator sets up to 800 kW sold in India must meet CPCB IV+ emission norms, which affects the engine, its aftertreatment and the fuel quality it needs. Sets above 800 kW follow separate emission requirements, and existing sets are governed by state pollution control board conditions.
Can you supply any brand of generator?
Reddy Generators works across the makes commonly installed in India, including Cummins, Kirloskar, Mahindra, Perkins, CAT and Greaves powered sets. The engine and alternator combination is chosen to fit the application, availability and service support rather than a brand preference.
New guides: what decides a generator’s price · how used sets are valued · exhaust pipes and stack height · 1 MVA generators.
Also in this section: the full-load current chart and used and refurbished generators for sale.
Generators by rating
- Under 15 kVA generators
- 15–50 kVA generators
- 50–125 kVA generators
- 125–250 kVA generators
- 250–500 kVA generators
- 500–1000 kVA generators
- 1–2 MVA generators
- 2 MVA and above generators
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.