In short. An application engineering enquiry starts with the decision you need to make and the condition that prompted it: a motor that will not start, a voltage dip that resets equipment, a planned load addition, a transfer that drops the UPS, or a choice between paralleling and one larger set. Send the existing system details, load data and drawings, and say which figures are measured and which are assumed. The review then targets the real question.
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Begin with what the power system must achieve
A generator should never be selected as an isolated machine. It works inside an electrical system and must respond to the actual load, its starting characteristics, power factor, harmonics, duty cycle, the environment, the changeover philosophy and the protection system. So the useful first question is not which generator, but what the power system must achieve and what is stopping it today. Application engineering is the structured review that turns that question into a technical direction before equipment is bought, installed, hired, upgraded or repaired.
Typical questions we are asked
| Problem or decision | What the review examines | Typical outcome |
|---|---|---|
| Motor will not start or set trips on start | Starting kVA, starting method, alternator reactance, governor response | Soft starter or VFD, staged starting, or larger alternator |
| Voltage dip resets equipment | Load step size, AVR response, sensitive loads | Load sequencing, AVR or PMG upgrade, UPS ride-through |
| Load addition on existing set | Measured demand, spare capacity, derating | Confirm headroom, add a set, or load shedding |
| Single large set or paralleled sets | Redundancy, load profile, maintenance windows | N+1 arrangement or single set with rental backup |
| UPS drops load on transfer | Transfer time, UPS input window, generator frequency stability | Adjusted transfer delays, UPS settings, governor tuning |
| Generator overheating or derating | Ambient, ventilation, altitude, exhaust back-pressure | Room airflow changes or a different set |
The hardest moment, not the final load
The generator must support the hardest credible operating moment, not just the final steady load. That moment is usually a large motor start or a block load applied after transfer.
Starting kVA = sqrt(3) x V x I(start) / 1000
V is the line voltage in volts and I(start) is the motor’s starting current in amperes. Worked example (illustrative): a 37 kW pump motor at 415 V with a full-load current of about 68 A, started direct-on-line at around 6.5 times full-load current, draws about 440 A, so starting kVA is about 1.732 x 415 x 440 / 1000, roughly 316 kVA. On a 250 kVA set that will cause a deep voltage dip, while a soft starter limiting current to about three times full load cuts the starting demand to roughly 150 kVA. The detailed method is in motor starting and the dip consequences in voltage dip.
Existing basis: measured, specified or assumed
Include the load schedule, equipment identities, single-line diagram and supply arrangement. Then label each figure. A measured value from a power analyser is evidence; a nameplate value is a specification; a guessed diversity factor is an assumption. Mixing them without labels produces a confident wrong answer. Where records are incomplete, say what is missing so that the next step closes the gap instead of treating an estimate as confirmed. For existing generators, the engine and alternator nameplates, controller model and recent run data are as important as the load figures; see generator engine architecture.
Derating for Telangana conditions
Generator ratings are normally stated at reference conditions defined by the manufacturer, often around 25 to 40 degrees ambient and near sea level. A set in a hot, poorly ventilated room in Hyderabad in May may see intake air well above 45 degrees, and the engine may need to be derated by a few percent or more according to the manufacturer’s curve. Tell us where the set stands, how air reaches it and the hottest conditions on site, because derating can move a marginal selection to the next rating.
What the assessment delivers
An enquiry begins a discussion about inputs, deliverables and responsibilities; it does not produce an automatic design or a technical sign-off. Depending on scope, the output may be a short technical note answering one question, a sizing recommendation with stated assumptions, a list of studies required, or a site visit with measurements. Where a formal load flow, short-circuit or protection coordination study is needed, we say so and explain why. Mechanical and electrical integration, ventilation, fuel, earthing and controls are reviewed as applicable, and testing or commissioning requirements are identified. Related support is listed under application assessment and engine service.
Common mistakes
- Asking which generator to buy before stating the problem; the answer fits the question asked and not the plant’s real constraint.
- Sending connected load as running load; the recommended set is much larger and runs lightly loaded.
- Omitting starting methods of large motors; the dip analysis is wrong by a factor of two or more.
- Presenting assumed figures as measured; the review builds on them and the conclusion fails on site.
What to send us
Send the project location, a description of the problem or decision, the existing generator and electrical system details with nameplate photographs, the load list with starting loads and methods, control and transfer arrangements, and any drawings, single-line diagrams or analyser readings you have. Mark which figures are measured. Phone or WhatsApp 098852 01608, or contact Reddy Generators through the form with the files attached.
Questions engineers ask
Do I need a site visit for an application review?
Not always. A clear problem statement with nameplates, drawings and measured data can often be answered remotely. Motor-starting failures, overheating and transfer problems usually benefit from measurements on site.
Can you review a consultant’s generator specification?
Yes. We check the rating basis, motor-starting assumptions, derating, transfer arrangement and installation requirements against the load and site, and report any gaps.
Is one large generator better than two smaller ones in parallel?
Two paralleled sets give redundancy and better efficiency at low load, at the cost of synchronising controls and more maintenance. A single set is simpler and cheaper. The load profile and the cost of an outage decide it.
Can a soft starter let me use a smaller generator?
Often, because it reduces starting current. The set must still handle the reduced starting kVA and any harmonics the starter produces, so the combination should be checked.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.