In short. Components that pass individual tests can still fail together. Integrated systems testing (IST) runs the whole chain, with utility loss, generator start, transfers, UPS behaviour and recovery, under realistic conditions. It is the evidence that the design works and the baseline for later checks.
The testing ladder
| Stage | What is tested |
|---|---|
| Factory acceptance | Individual equipment at the manufacturer |
| Site installation checks | Wiring, torque, labels, settings |
| Pre-functional tests | Each device energised and operated alone |
| Functional tests | Subsystems such as a generator with its ATS |
| Load bank tests | Capacity, cooling and stability at load |
| Integrated systems test | Whole chain, with failures injected |
| Ongoing periodic tests | Repeats of key tests over the system’s life |
Typical IST scenarios
- Utility loss with all systems normal.
- Utility loss with the first generator failing to start.
- Loss of one UPS or power path.
- Generator trip under load, with shedding.
- Transfer on and retransfer to utility.
- Black start from a dead bus.
- Loss of control power or a network failure.
- Failure during a maintenance state.
Test plan content
- Purpose and scope of each test.
- Prerequisites and safety measures.
- Step-by-step procedure with expected results.
- Acceptance criteria with numbers, such as maximum voltage dip and transfer time.
- Instrumentation: recorders, power analysers and time synchronisation.
- Rollback plan and responsible people.
Managing the risk of testing
Testing a live critical site carries risk. Control it by rehearsing on paper, testing before the load is live where possible, choosing low-risk windows, keeping a rollback ready, briefing all parties, and keeping the remaining systems healthy and verified. Some tests, such as opening the real utility supply, may be run first with dummy or load-bank loads.
What to record
- Waveforms or recordings of voltage, current and frequency during transfers.
- Time of each event and system response.
- Deviations, defects and their closure.
- Final settings and software versions.
Keep these as the baseline. When something changes, repeat the relevant test and compare. See FAT, SAT and functional acceptance.
Worked illustration
During IST of a data-room power system, the utility is opened with the load at 60 per cent. The generator starts, but the UPS rejects its supply because of frequency overshoot, staying on battery. The retransfer later causes a second short break. Both findings came only because the full chain was tested together. The fix was adjusting the generator governor and the retransfer logic, and the test was repeated and recorded.
Testing the system, not the parts
Each component can pass its test and the system can still fail, because failures often sit in the interfaces. Integrated systems testing exercises the full chain under realistic conditions.
| Test level | Scope |
|---|---|
| Component | Single device functions |
| Subsystem | Generator with ATS; UPS with battery |
| Integrated | All sources, switching, controls and loads together |
Integrated test sequence (illustrative)
- Verify baseline: all equipment healthy, alarms clear.
- Simulate utility failure on load (opening the incomer in a controlled way).
- Observe UPS transfer to battery, generator start, ATS transfer, UPS walk-in.
- Run on generator with the real or load bank load for the planned period.
- Return to utility and check recharge.
- Repeat for generator failure, UPS module failure and single-path loss.
Record
- Voltage, frequency and current at key points.
- Transfer times.
- Alarms and events generated.
- Deviations and corrective actions.
Risk management
Integrated tests carry risk, since a failure may cause an actual outage. Plan with a rollback procedure, spare capacity and the right people present. For high-risk sites, prove first on a test load bank. See load bank testing.
See commissioning.
Common mistakes
- Testing components but not the sequence.
- Never opening the real utility supply, so the transfer is never proven.
- Not recording measurements.
- Skipping retest after changes.
What to send us
Send the design, equipment list and acceptance requirements. Send your application details. See also failure simulation and recovery testing.
Questions engineers ask
What is an integrated systems test?
A test of the whole power chain together, including sources, transfer, UPS, controls and recovery, to prove they work as one system.
How often should IST be repeated?
After significant changes and at intervals agreed with operations, balancing risk and the value of the evidence.
Is a load bank test enough?
It proves capacity and stability but not the full transfer and control sequence.
Who should witness tests?
Representatives of the owner, operations, the designer and equipment suppliers.
This guide gives general principles. Test plans must be developed for the specific installation.