In short. The Power Engineering Centre is a library of practical guides for sizing, specifying, installing and testing diesel generator systems in Indian conditions. Each guide covers one engineering question, from load inventory and kW to kVA conversion through motor starting, voltage and frequency dip, harmonics, cabling, protection, fuel and commissioning, and links to the next question in the chain. Use it to prepare a sound enquiry, check a vendor proposal or train a new engineer.
What the centre is for
A generator is equipment. Reliable power is a system that includes the loads, the transfer scheme, the cables, the protection, the fuel, the room and the people who maintain it. Most generator problems we are called to in Telangana and Andhra Pradesh were caused not by a faulty machine but by an early decision made with incomplete information: a set sized on connected load rather than demand, a chiller started on a lightly loaded alternator, a UPS fed from a set with a small alternator, or a room with no path for hot air to leave.
The guides in this centre exist to make those decisions visible before equipment is ordered. They are written for plant electrical engineers, consultants, facility managers and business owners. They do not replace manufacturer sizing software, a protection study or a competent site review, but they tell you what those studies must answer.
The engineering chain from load to supported system
Every generator project passes through the same questions, whether it is a 25 kVA set for a clinic or a 2 MVA paralleled plant for a pharmaceutical unit. The order matters, because each answer feeds the next.
| Step | Question to answer | Guide to use |
|---|---|---|
| 1. Load | What runs, when, and what must stay on during an outage? | Load inventory |
| 2. Units | What is the apparent power demand in kVA, and at what power factor? | kW to kVA guide, power factor guide |
| 3. Transients | What is the hardest start or block load the set must survive? | Motor starting, starting kVA, voltage dip, frequency dip |
| 4. Rating | Which rating category, derated for site, carries that duty? | Generator sizing |
| 5. Power quality | Will UPS, drives and LED loads distort the waveform or heat the alternator? | Harmonics and THD, UPS and non-linear loads |
| 6. Distribution | What current flows, what cable is needed and what voltage reaches the load? | Generator current, cable sizing, voltage drop |
| 7. Protection and earthing | Does protection clear faults selectively, and is the neutral correctly earthed? | Protection coordination, earthing and neutral grounding |
| 8. Fuel and room | How many hours of fuel, how much air, how much heat? | Fuel consumption, fuel runtime, room ventilation |
| 9. Proof and care | How is the installation tested and kept ready? | Commissioning checklist, maintenance planning |
Skipping a step only moves the answer to the day the generator is first asked to carry the load. The first two steps are covered in load inventory and kW to kVA conversion, and the rating decision in generator sizing.
Indian site conditions that change the numbers
Catalogue ratings are stated at reference conditions, usually 25 degrees Celsius air intake and 100 metres altitude. Hyderabad summers reach 42 to 45 degrees Celsius in the shade, and a generator room or canopy in the sun runs hotter. Expect a derating of a few percent on engine output for high ambient, and more where the room is poorly ventilated. The Deccan plateau at 500 to 600 metres is within most manufacturers’ altitude allowance, but confirm it on the engine data sheet.
Indian LV distribution is 415 V three-phase and 230 V single-phase at 50 Hz, with a solidly earthed neutral at the DISCOM transformer. Monsoon outages are frequent but short, so standby sets accumulate many starts and few hours, which is hard on batteries and encourages carbon build-up from low-load running. New diesel sets up to 800 kW must meet CPCB IV+ emission norms, which changes exhaust design, fuel quality requirements and cost.
Screening calculations and where they stop
Most guides include a simple formula and an illustrative worked example. These are screening tools that tell you whether a proposal is in the right range and what to ask next. The central ones are worth memorising.
kVA = kW / PF, and I = (kVA x 1000) / (1.732 x V) for a balanced three-phase load
Here kW is real power, PF is power factor, kVA is apparent power, I is line current in amperes and V is line-to-line voltage in volts. A 200 kW load at 0.8 PF is 250 kVA and draws about 348 A at 415 V (illustrative). That is correct arithmetic, not a generator selection, because it ignores starting transients, harmonics, derating and future load.
Three things must come from verified data rather than from a formula: the engine’s load acceptance, the alternator’s motor-starting and non-linear load capability, and the protection settings for the actual fault levels. Where a guide reaches that boundary, it says so.
How to use the centre for a real project
Consider an injection moulding unit near Patancheru that wants standby power with automatic restart of the machines (illustrative). Build the load inventory with each machine’s heater, hydraulic motor and auxiliaries, and mark which machines may restart together. Convert to kVA at a measured power factor rather than an assumed 0.8. Find the hydraulic motor with the highest starting current and check whether it starts direct-on-line or through a soft starter. Estimate the starting kVA and use the voltage dip guide to decide what dip the controls and contactors tolerate. Choose a standby or prime rating, apply the ambient derating, then check fuel autonomy and room ventilation. Finally, use the commissioning checklist to write the acceptance test before the set arrives, so the vendor demonstrates the actual restart sequence under load. Done this way, the enquiry contains what a supplier needs to quote responsibly, and the acceptance criteria are fixed before the commercial discussion starts.
Which guide answers which problem
If a set trips or lights dim when a compressor starts, read motor starting, starting kVA and voltage dip. If a UPS goes to bypass on generator, read harmonics and THD and frequency dip. If voltage at the machine is low, read generator current and voltage drop. If a set overheats in summer, read room ventilation and ambient derating. For transfer, paralleling or switchgear, start with integrated power systems.
Common mistakes
- Sizing on the sum of nameplates instead of measured or diversified demand, which produces a set two sizes too large that then runs at 20 percent load and wet-stacks.
- Treating a kW to kVA conversion as a final rating, so the largest motor is never checked and the set stalls on the first restart.
- Specifying the generator and leaving cables, transfer switch and earthing to a separate contractor, which produces a system nobody has reviewed as a whole.
- Accepting a catalogue transient claim without an agreed site test, which leaves the owner with no evidence when the UPS rejects the supply.
- Ignoring ambient and room conditions, which turns a correctly rated set into an under-rated one every April and May.
What to send us
If you want us to work through this chain with you, send a load list or a recent electricity bill with maximum demand, a note of the largest motors and how they start, the location and the type of premises, the hours of outage you need to cover, and photographs of the proposed generator location and the existing main panel. If a set already exists, add a photograph of the nameplate. We will identify which questions are already answered and which need data or a site visit. Send your application engineering enquiry.
Questions engineers ask
Where should I start if I only have a rough idea of the load?
Start with the load inventory guide and the most recent electricity bills, which give the recorded maximum demand in kVA. The bill gives the running demand; the inventory tells you about starting events and which loads must stay on. Those two together give a defensible first estimate.
Can I rely on the formulas in these guides for a purchase decision?
Use them to check that a proposal is in the right range and to frame questions. The final rating should be confirmed with the manufacturer’s sizing data for the specific engine and alternator, because transient performance and harmonic capability differ between packages of the same kVA.
Do the guides apply to CPCB IV+ generators?
Yes. The electrical engineering is unchanged. CPCB IV+ affects exhaust aftertreatment, fuel and lubricant specification, low-load operation and service intervals, and the relevant guides note where those differences matter.
How do I use the centre to compare competing quotations?
Write down your load, largest starting event, acceptable voltage and frequency dip, fuel autonomy and site conditions first, then ask each supplier to show from manufacturer data how their package meets each item. A quotation that cannot be mapped to those points is incomplete, whatever its price.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.