In short. Generator commissioning is the structured proof that an installed set, its panel and its connections work as the design intended, under load and in automatic mode, before anyone relies on them. A set that starts is not commissioned. The checklist runs from pre-energisation inspection through no-load, load and transfer tests to a signed handover record, and each result is recorded against the scenario that was actually tested rather than implied for scenarios that were not.
Why a start-up is not a commissioning
Many sets in Telangana are handed over after a technician starts the engine, reads 415 V on the panel and leaves. The failures that follow are predictable: the AMF never sends a start signal because a sensing wire was left off, the set trips on the first motor start because the voltage dip was never tested, or the neutral is earthed at both the transformer and the alternator and the earth-fault relay trips on load. Commissioning exists to find those faults while the installer is still on site and before an outage finds them for you. It has a defined scope, a sequence, acceptance criteria and a record. The service itself is described under generator commissioning; what follows is the engineering content of the checklist.
Pre-energisation checks
Nothing is started until the installation has been inspected cold against the drawings. The items below apply to a typical diesel set with an AMF panel; a synchronising installation adds more.
- Foundation level and cured, anti-vibration mounts loaded evenly, no pipe or cable imposing strain on the set.
- Exhaust complete with flexible bellows, lagging, rain cap and a run whose backpressure has been estimated against the engine limit.
- Ventilation openings sized for radiator airflow plus combustion air, with hot air discharged away from the inlet.
- Fuel system flushed, tank clean, vent and return lines correct, water separator fitted, day tank level switches wired.
- Coolant mixed to specification, oil at the mark, battery electrolyte and terminals checked, charger connected.
- Earthing complete: body earth, neutral earthing arrangement as per the single-line diagram, earth resistance measured and recorded, with the neutral philosophy matching the earthing and neutral grounding design.
- Insulation resistance of alternator windings and outgoing cables measured and recorded before any voltage is applied.
- Cable terminations torqued, phase sequence verified at both ends, protection settings entered and recorded.
Running tests in sequence
| Stage | What is checked | Accept when |
|---|---|---|
| First start, manual | Cranking time, oil pressure rise, leaks, unusual noise, exhaust colour | Stable idle and rated speed, no leaks, pressures within manufacturer limits |
| No-load run | Voltage, frequency, phase balance, AVR stability, coolant temperature trend | 415 V and 50 Hz held within setpoint tolerance for 30 minutes |
| Protection functional test | Low oil pressure, high temperature, overspeed, emergency stop, overcurrent, earth fault | Each shutdown and alarm operates by simulation and is logged |
| Load test | Steps to 25, 50, 75 and 100 per cent, voltage and frequency dip and recovery, temperatures, fuel rate | Transient response within ISO 8528 class agreed, no overheating at full load for the specified duration |
| Automatic mode test | Mains fail, start delay, transfer, retransfer on mains return, cool-down and stop | Sequence completes unattended with timings recorded |
| Site load test | Largest motor start, UPS input, actual facility load | Loads start and run without nuisance trips |
Where the facility load is not available or cannot be interrupted, a resistive or reactive load bank substitutes for it, and load bank testing is the only way to prove full-load thermal performance in a new building that is still empty. A no-load voltage reading proves nothing about behaviour under load.
Testing the transfer system, not just the set
The AMF or ATS panel is where most commissioning failures are found, because it is where the generator, the DISCOM supply, the controller and the site wiring meet. The test must include a real mains failure simulated by opening the incoming breaker, not a button on the controller. Record the time from mains failure to generator breaker close, confirm the mechanical and electrical interlock prevents both sources closing together, test the retransfer delay so the site does not bounce back to an unstable supply, and check that the set runs its cool-down before stopping. On installations with a UPS, confirm the UPS rides through the transfer and that its battery charger does not pull the generator into an unstable condition when it reconnects. Panel logic is explained under AMF panels.
Recording the scenario, not just the result
A commissioning record that says “load test passed” is close to worthless a year later. The record should state the scenario: which load, for how long, at what ambient temperature, with which protection settings and which firmware version in the controller. If the set was tested to 75 per cent because the load bank available was too small, the record says so and the 100 per cent test is listed as outstanding. If a protection function was bypassed to complete a test, that is recorded and the bypass removed before handover, never left in place. The final pack should contain the as-built single-line diagram, the settings list, the insulation and earth resistance readings, the load test log, the AMF sequence timings, the outstanding items with owners and dates, and the signatures of installer and client. The start-up and handover service closes this pack, and the readings in it become the baseline for maintenance planning.
Related photographs and videos
Common mistakes
- Accepting the set on a no-load run; the first real outage reveals a voltage dip on motor starting or an overheating radiator that a load test would have exposed.
- Testing the AMF with the controller’s test button instead of opening the incoming breaker; the sensing circuit fault that stops the set starting in a real outage is never found.
- Leaving a protection function disabled to get through a test; the set later runs to destruction on low oil pressure.
- Earthing the alternator neutral without checking the transformer earthing; circulating neutral currents trip earth-fault protection under load.
- Filing a record without settings, firmware version or ambient conditions; the next engineer cannot tell what was proven and must repeat the work.
What to send us
Send the single-line diagram, the generator and panel nameplate photographs, the site drawings showing room, exhaust and fuel arrangement, a list of the largest motors and any UPS on the backed-up supply, and the date the site expects to take load. Tell us whether a load bank will be needed because the facility load is not yet available. We will return a commissioning scope and test plan matched to the installation. Request generator commissioning or a pre-handover check.
Questions engineers ask
How long should a full-load commissioning test run?
Long enough for coolant and oil temperatures to stabilise at full load, which usually means at least one to two hours at 100 per cent after the step tests, in the hottest ambient conditions practical. Shorter runs prove electrical output but not thermal capacity.
Can we commission without a load bank?
Only if the actual facility load is available, can be interrupted for testing and is large enough to reach the rated output. In a new building that is still empty, a load bank is the only way to prove full-load performance before handover.
Who signs off a generator commissioning in India?
The installer and the client’s engineer sign the test record. Depending on capacity and state rules, the installation may also need electrical inspectorate approval under the CEA regulations before it is energised, and the pollution control board consent conditions apply to emissions and noise.
What is the difference between commissioning and a routine load test?
Commissioning proves the whole installed system against its design for the first time, including wiring, protection, earthing and transfer logic. A routine load test later confirms the set still performs; it assumes the system was proven correct at the start.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.