First Commissioning of a Generator: Settings and Measurements

Generator commissioning: the settings and measurements that decide long-term reliability

The generator is on its plinth, the cables are connected and the tank is full. Everyone wants to hear the engine fire and move on. But generator commissioning is where you decide, for years ahead, how the set will behave during a real power outage. It also decides whether you will notice when something starts to drift.

In this guide we go through the whole process: pre-start checks, controller and transfer switch settings, the load bank test and the commissioning report. At the end there is a checklist you can print and take to the handover.

---

In short

Generator commissioning is a controlled procedure, not just “firing it up”. It includes:

• checking fluids, fuel and the battery,
• measuring insulation resistance and phase rotation,
• setting the protection limits and timers in the controller,
• testing the automatic transfer switch (ATS) with a simulated mains failure,
• running the set under real load.

The results you record in the commissioning report become the baseline for diagnostics over the generator’s whole life. The most common causes of later failures are a skipped load test, wrong phase rotation and controller settings left at factory defaults.

---

How does generator commissioning differ from a normal start?

A normal start shows that the engine runs. Commissioning checks that the whole power system works as designed: engine, alternator, controller, ATS, installation and loads.

Think of it as the check before a long road trip. An engine can idle smoothly on the driveway, and the car can still struggle up a hill with a trailer. A generator that hums nicely at no load can lose frequency when a pump starts. It can also trip on a protection because someone left a factory limit in the controller.

In our experience, most issues reported in the first year of operation are not equipment faults. They come from what was set, or skipped, on commissioning day. The good news is that all of it can be checked in a single working day.

Step 1: Pre-start checks before you press “start”

This stage looks unremarkable, but it protects the engine from the most expensive mistakes. We always work through it with a list, even when the generator comes straight from the factory.

Fluids and fuel

• Engine oil: level between MIN and MAX on the dipstick, grade as specified by the engine manufacturer.
• Coolant: level and concentration. The coolant must give frost protection for the site conditions. A generator in an unheated container in a Nordic winter needs different protection from one in a hospital plant room.
• Fuel: clean, free of water and suitable for the season. The fuel system must be bled. Air in the lines is the classic reason a “brand-new generator won’t start”.
• Leaks: check fuel, oil and coolant connections before starting, then again after a few minutes of running, when the system is warm and under pressure.

Battery and starting system

The battery is the most common cause of a failed emergency start across the industry. At commissioning we measure:

• Resting voltage: about 12.6–12.8 V for a fully charged 12 V battery, and about 25.2–25.6 V for a 24 V system. These values are approximate and depend on battery technology.
• Voltage drop during cranking: if a 12 V system drops well below about 10 V while cranking, the battery, connections or cable cross-sections need attention [TO VERIFY: limit per engine and controller manufacturer documentation].
• Mains-powered battery charger operation: a standby generator spends most of its life on standby, not running.

Engine block heater

On standby sets, the block heater keeps the engine at a temperature where a fast start and load acceptance are not a shock to it. We check that the heater has power, that the thermostat works and that the block is actually warm. A hand on the casing or an infrared thermometer is enough.

Air, exhaust and surroundings

• Air inlet and outlet must be unobstructed. A generator “breathes” a volume of air that surprises many clients.
• The exhaust system must be gas-tight. It should discharge away from windows, building ventilation intakes and occupied areas.
• In a container or plant room, check that hot air from the radiator does not loop back to the inlet. This recirculation causes overheating that nobody sees in a short test, but it shows up after an hour of running in July.

Step 2: Electrical measurements before the first start

This part belongs to a qualified electrician. The scope of testing follows the regulations and standards that apply to the installation [TO VERIFY: applicable standards for the project, e.g. IEC 60364-5-55 / 60364-6 or local equivalents]. Below we describe what matters for the generator’s reliability.

Alternator insulation resistance

An alternator that sat in storage for a long time, travelled in humid air or waited weeks on site may have picked up moisture. Measuring winding insulation resistance before the first start is cheap insurance.

An important practical note: before testing with an insulation tester, disconnect the automatic voltage regulator (AVR) and any electronics that cannot withstand the test voltage. We have seen an AVR damaged exactly this way on handover day, which is a particularly poor start to a relationship with new equipment. The minimum resistance value, and how to dry the windings if the result is too low, are given by the alternator manufacturer [TO VERIFY: minimum value and test voltage per alternator documentation].

Earthing and protection against electric shock

The electrician checks the bond between the generator frame and earth, the continuity of protective conductors and the effectiveness of protection in the earthing system used on site. Details such as how the alternator neutral is connected, or whether the ATS switches the neutral, come from the installation design. That design should be on hand at commissioning, not in the designer’s drawer.

Phase rotation: a small detail that runs motors backwards

This is our favourite in the “small mistake, big consequence” category. If the generator’s phase sequence (L1–L2–L3) does not match the mains, three-phase motors will run in reverse after transfer to standby power. Pumps stop pumping, fans suck instead of blow, and scroll compressors can be damaged.

Phase rotation is measured with a phase rotation meter at the ATS terminals, once on the mains side and once on the generator side. The measurement takes two minutes. Fixing the consequences of skipping it takes considerably longer.

Step 3: First start and no-load running

The generator starts. The first few minutes are for observation, not for a performance test.

What we measure and watch:

At this stage we are not judging whether the generator “can handle it”. We are only making sure it is healthy and ready for load.

Step 4: Controller settings that decide reliability

A modern generator controller has dozens of parameters. In our sets this is usually ComAp or DEIF. Most factory defaults are sensible. A few, however, need to be set deliberately for the site and recorded in the report. They decide whether the generator behaves predictably on the day it is really needed.

Protection limits

Protections guard the engine and alternator. Set too tight, they cause nuisance shutdowns. Set too loose, they put the equipment at risk. At commissioning we mainly check:

• low oil pressure (warning and shutdown),
• high coolant temperature (warning and shutdown),
• overspeed: shutdown when engine speed exceeds a set limit, typically some percent above rated speed [TO VERIFY: limit per engine manufacturer],
• under/overvoltage and under/overfrequency, with suitable time delays,
• overload and short circuit on the alternator side,
• low fuel level: an early warning that leaves enough time to order a delivery.

Good practice is to test critical protections functionally. For example, simulate the sensor signal and check that the generator responds, rather than trusting that “it’s in the parameters”.

Automatic operation timers

The exact values depend on the site. In a data centre with a UPS, fast transfer matters, but the UPS buys a few minutes. On a site without a UPS and with sensitive loads, the priorities are different. That is why we never leave these timers at their defaults without talking to the site operator.

Speed governing: isochronous or droop?

An isochronous governor holds 50 Hz regardless of load. Droop governing lets the frequency fall slightly as load increases. That can be needed for some types of parallel operation, among other cases. A single standby generator usually runs isochronous. In parallel systems, the mode follows from the load-sharing concept and is set together with synchronisation.

Communication and alarms

A controller that knows about a problem and tells no one is like a smoke detector without a battery. At commissioning it is worth setting up:

• alarm forwarding (SMS, email, BMS, remote monitoring),
• a list of who gets notified and who does what for each alarm,
• event logging in the controller, which makes later diagnostics much easier.

Step 5: ATS test, the real dress rehearsal

The automatic transfer switch (ATS) detects a mains failure, starts the generator and transfers the loads. At commissioning we simulate a real mains failure, ideally by opening the mains supply rather than just pressing “test”.

We check:

1. that the generator starts after the set delay,
2. how long it takes from mains failure to supplying the loads,
3. that all loads behave correctly: motors turn the right way, process controllers don’t lose their place, and the UPS moves from battery to generator supply,
4. that after mains return the ATS waits the set time and transfers back correctly,
5. that the generator runs its cool-down, stops and returns to standby.

On one project for a manufacturing plant, everything went perfectly except one detail. The air compressor had its own controls, which waited for a manual reset after a voltage loss. The generator did its job, and the compressor waited politely for a human. Things like this only show up in a real test, which is exactly why you run one.

Step 6: Load bank test, or why the generator has to actually work

This is the most frequently shortened part of commissioning, and also the most revealing. A generator with no load is like an athlete warming up on the bench. It looks good, but we don’t know how it will run.

Why light loading harms a diesel engine

A diesel engine running for long periods at very light load never reaches proper combustion temperature. Unburnt fuel and soot build up in the exhaust and on the piston rings. This is called wet stacking. A common rule of thumb is that extended running below about 30% of rated output encourages it [TO VERIFY: recommended minimum load per the specific engine manufacturer].

That makes the load test at commissioning important for two reasons. It confirms that the generator delivers its power. And it shows straight away whether routine test runs can be done on real load. If they can’t, it’s worth planning periodic tests with a load bank.

What does a stepped load test look like? Example for a 200 kVA generator

Take a 200 kVA generator. At a power factor of cos φ = 0.8, its active power is:

200 kVA × 0.8 = 160 kW

We run the test in steps, on a resistive load bank or on the site’s real loads:

The times are examples. Agree the test scope with your supplier and designer. For sites with special requirements, such as hospitals and critical infrastructure, it may be set by tender documents or sector requirements.

A practical note: a resistive load bank has cos φ ≈ 1. A 200 kVA generator loaded to 160 kW on it delivers 160 kW, but not 200 kVA. Fully testing the alternator at apparent power needs a resistive-reactive load bank. For most sites, though, a resistive load bank gives a sufficient picture of engine performance.

What we record at each step

• phase-to-phase and phase-to-neutral voltages,
• current in each phase and the imbalance between them (a large imbalance usually points to uneven load distribution in the installation, not a generator problem),
• frequency,
• active and reactive power, and cos φ,
• oil pressure and coolant temperature,
• exhaust temperature, if the controller shows it,
• fuel consumption (approximate, from tank level or a flow meter),
• exhaust smoke: a brief puff of dark smoke on a load step is normal, persistent smoke is not.

Response to load steps

Dropping and applying load, for example stepping from 0 to 50% and back, shows how quickly the governor and AVR return to rated values. We measure the transient voltage and frequency dip and the recovery time. ISO 8528-5 defines requirements for these transients in performance classes such as G2 and G3 [TO VERIFY: required class per site specification and manufacturer data].

This matters most where the generator has to start large motors. Typical examples are pumping stations, cold stores and ventilation systems. A large motor started direct-on-line can draw several times its running current, and that never shows up in a load list “on paper”.

Step 7: The commissioning report, a document that pays off

A report sounds like paperwork. In practice it is the generator’s birth certificate and health record. If oil pressure under load is some percent lower in two years than at commissioning, the service engineer sees the trend straight away. Without a baseline, all that’s left is guesswork.

A good report includes:

• generator details: model, serial numbers of engine, alternator and controller, hour meter reading,
• results of pre-start checks and electrical measurements,
• a list of controller settings (protections, timers, test schedule), ideally as an exported configuration file,
• ATS test results with transfer times,
• the load test table,
• comments, defects and deadlines for fixing them,
• signatures of the handing-over and receiving parties.

Keep the report with the technical documentation and declarations of conformity. It also matters for warranty purposes. Every ElectroQuell generating set comes with a warranty of 12 months or 1,000 operating hours, whichever comes first. Documented commissioning and later servicing help everyone quickly establish what is happening if a question ever comes up.

The most common commissioning mistakes (from our practice)

1. No load test. “It started, it runs, sign it off.” This is the most common and the most expensive shortcut.
2. Unchecked phase rotation between mains and generator.
3. Factory controller settings left unadapted to the site, especially the ATS timers.
4. Periodic test runs with no load, set up “so they don’t disturb production”. A year later the engine shows signs of wet stacking.
5. Insulation testing with the AVR connected. See above. Better not to test this one empirically.
6. Alarms that go nowhere. The controller knows, the people don’t.
7. No operator training. The generator works, but nobody on shift knows what the amber light means or when to call.

Checklist: generator commissioning step by step

Print it and take it to the handover. If your answer to any item is “I don’t know”, that’s a good question for your supplier.

FAQ: common questions about generator commissioning

How long does generator commissioning take?
For a typical standby generator with an ATS, usually from a few hours to one working day. It depends on the scope of the load test and the complexity of the installation. Parallel systems and critical sites take longer.

Can the site electrician commission the generator alone?
Installation testing is done by a suitably qualified electrician. Controller configuration, the ATS test and the load test are best carried out together with the supplier or the generator service team, who know the settings and how the equipment behaves.

Is a load test necessary if the generator is only for standby?
Yes, that’s exactly when it matters most. A standby generator rarely runs, so commissioning day is one of the few chances to test it under real load in controlled conditions.

How often should a generator be tested after commissioning?
The usual approach is automatic weekly or monthly test runs plus periodic tests on load. The exact schedule depends on the manufacturer’s recommendations, the site’s requirements and whether testing on real load is possible.

What should I do if motors run backwards after transfer to the generator?
Stop those loads immediately and have an electrician correct the phase rotation on the generator side or in the ATS. This mistake should be caught during the ATS test at commissioning, which is why that test is a mandatory item on the checklist.

Are the commissioning results useful later on?
Very. Oil pressure, temperatures, voltages and currents from day one are the baseline. Deviations from them often reveal a developing problem before any alarm goes off.

A well-commissioned generator means years of peace of mind

Generator commissioning is a single day that shapes the years of operation that follow. Work through it with a checklist, record the results and tailor the settings to the site, and a power outage simply becomes the moment when the automatic system does its job.

At ElectroQuell we support clients from generator selection through installation to commissioning and service. Preparing to take over a generator, or want to check whether your commissioning was complete? Book a free 15-minute consultation. Send us your report or your load list, and we’ll tell you what else is worth checking.