Lessons From a 400 kV Factory Test — What an Inspector Actually Checks
What an experienced inspector looks for during a 400 kV FAT — beyond simply observing the pass/fail of the headline tests.
A factory acceptance test is a verification, but an effective inspector uses it to learn about the unit and the manufacturer's process, not only to tick boxes.
First, understand the witnessed tests vs routine tests. Ratio, vector group, winding resistance, iron-loss and load-loss, impedance and insulation resistance are routine; impulse, temperature-rise and SFRA are the ones that reveal the design and build quality.
The temperature-rise test is where the inspector learns the most: it confirms the cooling design and the hot-spot allowance behind the guaranteed figures. Watch how the oil and winding temperatures track, and whether the calculated hot-spot dwells within the design margin.
An impulse test, if witnessed, is a process check as much as a pass check: the comparison of the reduced- and full-level transferred waveshapes (the neutral current on non-impulsed windings) is what actually detects an inter-turn breakdown — a clean crest does not prove the insulation is sound.
The inspector should verify the calibration and instrument connections behind every number, and confirm that the guaranteed figures (no-load, load loss, impedance) are within the contractual tolerance band before the unit is accepted.
Finally, record the evidence. A fat dossier with good traces and a clean SFRA fingerprint is worth far more than a pass in the acceptance letter — it is the baseline for the whole service life.
Related principle
Factory testing and type tests (see the Masterclass chapter on testing and IEC 60076).