FAT, SAT, SIT, and Pre-Energization Relay Testing: What Each Stage Must Prove

The labels FAT, SAT, SIT, commissioning, and pre-energization are often used as if they describe one activity. They do not. The useful question is not which label appears on the cover sheet; it is what uncertainty the stage removes and what evidence must exist before the next stage begins.

A stage is a boundary

Define each stage by its object, environment, inputs, outputs, and reviewer. A factory test may examine a configured relay panel with simulated signals. A site test may prove the installed wiring and device context. A system integration test may exercise interfaces among protection, automation, telecoms, and SCADA. A pre-energization test may focus on the final safe restoration and trip path.

ISA-105 and IEC 62381 provide a useful automation acceptance vocabulary, while protection-specific guidance from IEEE, IEC, and CIGRE adds the function and field-testing context. The standards should be used as anchors, not as permission to leave project boundaries ambiguous.

Factory acceptance testing

FAT should prove that the supplied equipment and configuration meet the approved design before shipment. Depending on the contract, this may include:

• device identity, hardware, firmware, and configuration review;
• relay logic, protection elements, alarms, and control functions;
• representative analog and binary cases;
• configured GOOSE, sampled-value, or other communications behavior in the test environment;
• report format, settings import, and evidence export;
• identified limitations, simulated interfaces, and open actions.

FAT cannot prove the station’s installed CT circuits, cable terminations, field network, breaker mechanism, actual time source, or site safety controls. Those boundaries should appear on the FAT exception list.

Site acceptance testing

SAT starts with the installed asset. Confirm the panel, wiring, test switches, grounding, CT and VT circuits, relay identity, settings, and communication connections. Re-run the cases whose result depends on installation rather than only on the factory configuration.

At SAT, a result needs enough context to answer:

• Was the approved configuration installed?
• Were the correct field terminals and test switches used?
• Did the measured quantities have the expected magnitude, phase, and polarity?
• Did the device respond at the expected terminal and through the intended output?
• Were alarms, blocking, permissives, and interlocks restored?

System integration testing

SIT is where interfaces are treated as part of the function. A line protection scheme may rely on a telecom channel, a breaker failure initiation, a remote permissive, a time source, and a SCADA indication. An IEC 61850 station may depend on SCL configuration, VLAN behavior, GOOSE subscriptions, sampled-value quality, and redundancy.

Test cases should be written as system behaviors, not just messages. Record the initiating condition, the expected sequence, timing or quality requirement, receiving function, output, and recovery behavior. A packet observed on a network is not by itself evidence that the protection function acted correctly.

Pre-energization checks

Pre-energization is the final controlled review of the installed scheme before the operating state changes. It should confirm that:

• all approved deviations are closed or formally accepted;
• test switches, links, and grounds are in the intended position;
• protection settings and active groups match the approved as-left record;
• trip, close, lockout, alarm, and interlock paths have been restored;
• communication channels and time sources are healthy;
• the operating authority has the required handover package.

This stage is not a second chance to discover that the design scope was incomplete. It is the final gate that the tested and approved state is the state being placed in service.

Build one evidence chain

Keep stage-specific results but connect them through stable asset and configuration identifiers. A FAT result should link to the design revision and the supplied package; SAT should link to the installed serial and settings; SIT should link to the interface configuration; pre-energization should link to the final as-left state.

ProtectionAI can help assemble that chain, flag missing stage evidence, and draft a handover report. It should not collapse simulated FAT evidence into field proof or declare an open exception harmless. The responsible engineer decides whether an exception is closed, accepted, or escalated.

References

• International Society of Automation. (n.d.). ISA-105 standards for automation systems acceptance testing. https://www.isa.org/standards-and-publications/isa-standards/isa-105-standards
• CIGRE Working Group B5.45. (2015). Acceptance, commissioning and field testing techniques for protection and automation systems (Technical Brochure No. 637). https://www.e-cigre.org/publications/detail/637-acceptance-commissioning-and-field-testing-techniques-for-protection-and-automation-systems.html
• Institute of Electrical and Electronics Engineers. (2023). IEEE guide for power system protection testing (IEEE Std C37.233-2023). https://standards.ieee.org/ieee/C37.233/6676/
• International Electrotechnical Commission. (2022). IEC TR 61850-10-3: Communication networks and systems for power utility automation — Part 10-3: Functional testing. https://webstore.iec.ch/en/publication/61395