FAT Reports: What to Ask For and How to Read Them

The salesperson tells you: "Don't worry, the transformer passed all the tests." They send you a 3-page PDF — a table of green checkmarks. You sign the acceptance. The equipment arrives on site. Six months later, it fails.

When you trace it back, you discover the "test report" was an internal factory checklist — no measured values, no acceptance criteria, no reference to IEEE C57.12.90.

A misread FAT is more dangerous than no FAT at all: it gives you false confidence.

We've reviewed hundreds of FAT reports. The good ones run multiple pages, with numerical values, standard references, and a real inspector's signature. The bad ones are a checkbox table that wouldn't survive 30 seconds of scrutiny. This guide tells you how to tell the difference.

What a FAT Is — and Why It's Your Last Line of Defense

The Factory Acceptance Test is the complete suite of tests performed on a finished transformer before it leaves the factory and before it hits the ocean. It's your last chance to catch a problem before the equipment is on a container ship.

Once it leaves, the cost to correct a defect multiplies by a factor of 5 to 20.

The Tests You Must Demand (Per IEEE C57.12.90)

Routine Tests — Every Single Unit

For pad-mounted transformers specifically: IEEE C57.12.34 and ANSI C57.12.22 add requirements for the enclosed compartment design — including the integrity of the tamper-resistant enclosure, the bushing well interfaces for separable insulated connectors (loadbreak and deadbreak), and the parking stands.

Design Tests — When the Design Is Not Yet Certified

How to Read a Real FAT Report

A professional FAT report contains these elements. If any one is missing, you didn't receive a test report — you received an opinion.

1. Nameplate Data (Must Match Your Purchase Order Exactly)

Serial number. Rated kVA/MVA. Primary/secondary voltage (kV). Connection diagram. Impedance (%). Frequency (Hz). If any of these don't match your PO, the entire report is invalid.

2. Test Conditions

Ambient temperature during testing. Oil temperature (if applicable). Test power frequency. Which measurement instruments were used — including make, model, and calibration date.

3. Measured Values — Not "PASS / OK"

Every test must show: measured value (a number), acceptance criterion (a limit or tolerance), result (pass/fail), and the referenced standard clause.

4. Inspector's Signature

Name. Title. Date. Not a blurry "QC Department" stamp.

The Five Most Serious FAT Report Errors

Error 1: Checkmarks only, no values. Reject it. Demand measured numbers.

Error 2: Test frequency or conversion method is not stated. Some measurements are frequency-dependent, and an unexplained result cannot be audited. Ask which tests were performed at the rated frequency, whether any approved conversion method was used, and where the governing standard permits it.

Error 3: No temperature correction. Resistance and losses vary with temperature. The report must state the reference temperature (load loss typically at 75°C, insulation resistance typically corrected to 20°C).

Error 4: No acceptance criteria. Every measured value needs a criterion next to it: "≤ 65 K," "≥ 1,000 MΩ," "≤ 0.5% deviation." Without criteria, you don't know what passed and what didn't.

Error 5: No inspector's signature. A signature represents accountability. When something goes wrong, you need to know who to call.

Witnessed FAT vs. Remote FAT

For high-value orders, a witnessed FAT pays for itself — the travel expense is a fraction of the cost of receiving one defective unit.

What Happens When the FAT Fails

1. Document the non-conformance in writing — test number, measured value, expected value, acceptance criteria
2. Demand root cause analysis — manufacturing error, design error, or measurement error?
3. Require correction and re-test — at the manufacturer's expense
4. Do not accept "we'll handle it on site" — factory corrections are ten times cheaper and ten times faster

Pre-Acceptance Checklist: Before You Sign a FAT Report

• Nameplate data (kVA, kV, Z%, connection) matches my purchase order — line for line
• All IEEE C57.12.90 routine tests completed (resistance, ratio, polarity, no-load loss, load loss, applied potential, induced potential)
• Every test shows measured values — not "OK"
• Every test has explicit acceptance criteria
• Test frequency (50/60 Hz) is correct for my grid
• Report states the reference temperature for loss and resistance measurements
• Inspector's name, title, and signature are present
• Photos of the transformer during testing are attached
• For pad-mounted units: compartment integrity, bushing well interface, and parking stand verification included

Conclusion

The FAT is not a formality. It's your insurance that the transformer you paid for is the transformer you receive. A professional report runs multiple pages, contains numerical values, cites IEEE C57.12.90 clauses, references calibrated instruments, and is signed by a real human being. If what you received is a table of green checks with no numbers, you didn't get a test report — you got an opinion. And opinions don't survive a short circuit.

From TransformerGrid

TransformerGrid does not operate the factory test laboratory. We coordinate the FAT and review the report package between the buyer and the selected manufacturing partner: approved nameplate data, applicable standard and clauses, measured values, acceptance criteria, instrument calibration status, deviations, signatures, and supporting photos or live witness arrangements.

Our current verified manufacturing partner can provide FAT evidence for 50 Hz and 60 Hz projects, supported by KEMA documentation covering 250 MVA, 345 kV, and 60 Hz capability. The test method and test frequency must be confirmed for each required test rather than assumed from the destination frequency alone.

Do not accept a report made only of green checkmarks. Ask TransformerGrid to coordinate a relevant sample FAT report and a project-specific FAT review.

Related articles:

• Return to the Hub: How to Evaluate a Transformer Manufacturer
• Certifications and Qualification Documents
• Transformer Factory Visit Checklist
• Partial Discharge Testing During Transformer FAT