Quick Answer
The Factory Acceptance Test (FAT) verifies that switchgear meets contract specifications before shipment. The Site Acceptance Test (SAT) verifies correct installation and integration before energization. Both are required for critical power infrastructure — skipping either increases the risk of costly commissioning failures or early-life equipment failures.
| Parameter | Factory Acceptance Test (FAT) | Site Acceptance Test (SAT) |
|---|---|---|
| When performed | Before shipment, at manufacturer's facility | After installation, before energization |
| Who performs | Manufacturer's test team + customer witness | Commissioning engineer + manufacturer rep (if contracted) |
| What is tested | Equipment in isolation, factory settings | Complete installed system including external connections |
| IEC reference | IEC 62271-1 Clause 8 (routine tests) | IEC 60364 / project specification |
| Duration | 1–3 days per lineup | 2–5 days per lineup |
| Typical cost | $2,000–$8,000 travel + expenses | $5,000–$20,000 (commissioning engineer fee) |
Factory Acceptance Test (FAT): What It Covers
The FAT is conducted at the manufacturer's facility with the switchgear fully assembled as it will be shipped. The customer's representative (and any third-party inspector) witnesses each test and signs the test record. A complete FAT for medium voltage switchgear includes the following test categories:
1. Visual and Mechanical Inspection
Before any electrical test is performed, the complete switchgear lineup is inspected against the approved drawings:
- Nameplate data (voltage rating, current rating, frequency, serial number) vs. contract specification
- Panel arrangement and bus configuration vs. approved single-line diagram
- Cable entry/exit points, gland plate dimensions, and bushing arrangements
- Earthing (ground) conductor sizing and termination points
- Interlocking mechanism operation — all mechanical interlocks verified against the interlocking scheme document
- Painting and finish quality: no chips, rust, or bare metal on external surfaces
- Gasket integrity on all weather-sealed enclosure joints (for outdoor equipment)
- Breaker draw-out mechanism: smooth operation through TEST, DISCONNECTED, CONNECTED positions
2. Wiring Verification
Secondary wiring (protection relay circuits, control circuits, metering circuits) is verified against the approved schematic diagrams:
- Point-to-point wiring continuity check: each connection verified against the wiring diagram
- Wire number and terminal block labeling vs. diagram
- CT and VT polarity verification — critical for directional protection relay elements
- Control power supply fuse ratings and alarm contact wiring
- SCADA communication wiring continuity (IEC 61850, Modbus RTU, DNP3)
3. High Voltage (HV) Withstand Test
The HV withstand test is the most critical electrical FAT test. It verifies insulation integrity of the primary circuit:
| Rated Voltage (kV) | AC Withstand (1 min) | Lightning Impulse (BIL) | IEC Reference |
|---|---|---|---|
| 7.2 kV | 20 kV | 60 kV peak | IEC 62271-1 Table 1 |
| 12 kV | 28 kV | 75 kV peak | IEC 62271-1 Table 1 |
| 17.5 kV | 38 kV | 95 kV peak | IEC 62271-1 Table 1 |
| 24 kV | 50 kV | 125 kV peak | IEC 62271-1 Table 1 |
| 36 kV | 70 kV | 170 kV peak | IEC 62271-1 Table 1 |
Test sequence: Apply test voltage for 1 minute with the circuit breaker open (between live bus and earth), then with the circuit breaker closed (across open contacts). No flashover or breakdown is an acceptable result. Partial discharge measurement per IEC 62271-204 may be added for GIS or sealed-pressure switchgear.
4. Insulation Resistance (IR) Test
Using a 2,500V or 5,000V DC Megger, measure insulation resistance between:
- Each phase and earth (breaker open and closed)
- Phase-to-phase
- Secondary circuits: control wiring to earth, CT/VT secondary to earth
Acceptance criteria: Primary circuit IR ≥ 1,000 MΩ at 2,500V DC (typical minimum; check project specification). Secondary circuit IR ≥ 100 MΩ at 500V DC.
5. Protection Relay Testing
Protection relay testing at FAT verifies that relay settings entered in the relay match the approved relay setting schedule, and that the relay correctly trips the circuit breaker within the specified time:
- Overcurrent (50/51): Inject test current at 1.05× and 2× pickup. Verify trip time at each level matches TCC curve.
- Earth fault (50N/51N): Same procedure as overcurrent, using residual current circuit in test set.
- Directional elements (67/67N): Verify correct directional characteristic with test set producing both fault current and polarizing voltage.
- Differential (87) for transformer protection: Verify operating characteristic and slope setting.
- Breaker failure (50BF): Initiate trip signal, block main CB, verify BF timer operates correctly.
6. Circuit Breaker (VCB) Operational Test
Verify the vacuum circuit breaker operates correctly across all operating modes:
- CLOSE and OPEN via local control (HMI panel push-buttons)
- CLOSE and OPEN via remote control (simulated SCADA signal)
- CLOSE and OPEN via protection relay trip signal
- Spring charging motor operation and timing (time to recharge after OPEN: ≤10 seconds typically)
- Anti-pumping relay function (verify breaker does not reclose immediately after trip)
- Mechanical operation counter reading
- CB timing test (if required by specification): measure OPEN time, CLOSE time, and contact bounce with timing relay test set
7. Auxiliary Function Verification
- Indication lamp test (all LED/lamp indicators illuminate correctly)
- Alarm and trip relay contacts verified against hardwired alarm and trip scheme
- Measured values accuracy (current transformer ratio, energy meter reading vs. test set reference)
- Heater and thermostat operation (if installed for cold climate applications)
- Lock and key system operation (if specified)
Site Acceptance Test (SAT): What It Covers
The SAT is conducted after the switchgear is installed at the project site, cabling completed, control wiring terminated, and before the system is energized with live voltage. The SAT scope is typically broader than the FAT because it includes all external connections that were not present during the FAT.
Pre-SAT Requirements
Before beginning the SAT, verify the following are complete:
- Switchgear installation inspected and approved by site electrical supervisor
- All cable installation complete — power cables pulled, terminated, and compression lugs torqued to specification
- All secondary cable terminations complete at control panel terminal blocks
- Earthing (grounding) system continuity verified: switchgear earth bar connected to site earth grid
- Control power supply (125V DC or 48V DC from battery charger/UPS) connected and available
- Protection relay settings loaded and verified against approved setting schedule
- IEC 61850 GOOSE and SCADA communication tested (loopback or system controller test)
SAT Test Sequence
Step 1: Insulation resistance test (repeat from FAT)
Mega-test all power cables at the switchgear termination, with the far end of each cable isolated (transformer HV terminals open-circuited, bus-bar isolation maintained). This verifies the cables survived installation without nicking or damage.
Step 2: CT/VT secondary wiring continuity and polarity
Inject low-current test signal into each CT primary and measure secondary response to confirm correct polarity, correct ratio, and correct connection to protection relay inputs. This is critical — a reversed CT polarity will cause directional protection elements to operate in the wrong direction.
Step 3: Protection relay secondary injection
Repeat key relay element tests with test current injected at the relay terminals (not through the CT — at the secondary wiring level). This verifies correct connection of CT secondaries to relay inputs, correct scaling (CT ratio), and correct trip circuit wiring to the breaker trip coil.
Step 4: End-to-end protection trip test
The most critical SAT test: from the protection relay, initiate a simulated fault, verify the fault causes the relay to issue a trip signal, verify the trip signal travels through the DC trip circuit and operates the CB trip coil, and verify the CB opens within the specified time. Then verify all remote annunciations (SCADA alarm, bay controller, HMI panel) receive the trip signal correctly.
Step 5: Breaker interlock verification (site conditions)
Repeat all mechanical and electrical interlock tests from the FAT checklist, now including all site-specific additions: cable connection bay interlocks, bus-coupler interlocks (if applicable), transformer tap changer interlocks (if applicable), and access door interlocks.
Step 6: SCADA/HMI system integration test
Verify all status signals (breaker position, protection alarm, metering values) are correctly received by the SCADA system. Test all remote control commands from SCADA to switchgear (CLOSE, OPEN, RESET). Verify communication failure alarm is raised when the communication link is disconnected.
Step 7: Pre-energization final check
Before applying live voltage:
- Phase rotation confirmed with phase rotation meter at incoming cable terminations
- All temporary earthing removed — verify earthing log
- All test equipment disconnected
- All access doors and panels closed, bolted, and padlocked
- Safety zone established per site electrical safety rules
- SAT report signed by witness and commissioning engineer
FAT and SAT Documentation Requirements
A complete FAT/SAT documentation package typically includes:
| Document | FAT | SAT |
|---|---|---|
| Test procedure (approved before testing) | Required | Required |
| Test record sheets (all readings, signed) | Required | Required |
| Test equipment calibration certificates | Required | Required |
| HV test instrument calibration | Required | Required |
| Non-conformance reports (NCRs) for any failed tests | If applicable | If applicable |
| NCR resolution/corrective action records | If applicable | If applicable |
| Witness sign-off sheet | Required | Required |
| Final FAT/SAT certificate | Required (before shipment) | Required (before energization) |
| As-built drawings (any site modifications) | Not applicable | Required |
All FAT/SAT records should be retained for the life of the equipment — typically 20–30 years. These records are essential for future maintenance, fault diagnosis, and regulatory audits.
Most Common FAT Non-Conformances
Based on our experience completing 500+ FATs at NAIJI Electric, the most common issues discovered during witness FATs are:
- Wiring errors in CT circuits (25% of NCRs): Incorrect CT polarity wiring, reversed A and C phase CTs, or missing earth connection on CT secondary. Usually corrected within 2–4 hours on site.
- Protection relay settings not loaded (18%): Test engineer relies on default settings instead of the approved setting schedule. Always request the setting schedule before the FAT and verify all elements against it.
- Missing mechanical interlocks (15%): A specified interlock (e.g., cable compartment door cannot open with breaker closed) was not installed or does not operate as specified. Usually requires a workshop modification.
- Nameplate errors (12%): Serial number, voltage rating, or current rating on the installed nameplate differs from the contract specification. Administrative correction required.
- Insulation resistance below 1,000 MΩ (8%): Usually caused by contamination from the manufacturing process (metal filings, moisture). Clean and re-test — usually clears the next day after cleaning and drying.
NAIJI Electric FAT/SAT Process
NAIJI Electric conducts witnessed FATs at our production facility in Ningbo. Standard FAT services include:
- Full FAT test procedure provided to the customer 2 weeks before the FAT date for review and approval
- Calibrated test equipment (Megger, relay test sets, HV Withstand tester) — calibration certificates provided
- Dedicated test engineer for the full FAT duration
- Signed test records and FAT certificate issued on the final day
- Digital documentation package (PDF + Excel) provided within 3 business days after FAT completion
- Non-conformance correction within the agreed timeline before shipment authorization
For SAT support, our commissioning engineers are available for on-site deployment to projects in Southeast Asia, Middle East, Africa, and Europe. Contact our project team for FAT scheduling or SAT commissioning support pricing.