Transformer test report: free site test template (Excel and PDF)
Deskely Completions team Singapore
Before a power transformer is energised on site, it is inspected and tested to show it arrived undamaged and was installed correctly. The transformer test report records the visual checks, insulation resistance, turns ratio, winding resistance and the protection devices.
This page gives you a free transformer test report in Excel and PDF. The Excel version works out the polarisation index, the ratio error and the winding resistance imbalance for you.
- Compare site results with the factory test report, not only with fixed limits.
- Turns ratio is normally expected within ±0.5 % of the nameplate ratio.
- Winding resistances should be close between phases once corrected to the same temperature.
- Test the Buchholz relay, temperature and pressure devices through to alarm and trip.
The site tests
| Test | What it shows |
|---|---|
| Visual and mechanical checks | No transport damage or leaks, oil level, accessories fitted, earthing, bushings, tap changer. |
| Insulation resistance and PI | The condition of the insulation between windings and to earth. See the insulation resistance guide. |
| Turns ratio (TTR) | The ratio on every tap matches the nameplate; finds shorted turns and wrong tap connections. |
| Winding resistance | Loose connections, broken strands or tap changer contact problems show as imbalance. |
| Vector group and polarity | The phase relationship matches the nameplate, so the transformer can be paralleled and protected correctly. |
| Oil breakdown voltage | The dielectric strength of the oil sample (oil-filled units). |
| Protection devices | Buchholz relay, pressure relief, oil and winding temperature devices operate to alarm and trip. |
The template
Enter the nameplate ratio and the measured ratios per tap and the sheet works out the largest error and marks it against ±0.5 %, the tolerance IEEE C57.12.00 gives for the turns ratio. For winding resistance it shows the imbalance between phases; your specification sets the limit.
Before you energise
Transformer tests are pre-commissioning checks: they sit with the pre-commissioning checklist for the substation and feed the ready for commissioning certificate. See substation commissioning for the order of work around them.
In Deskely, the test results are recorded against the transformer's tag on a tablet and checked against the expected values as they are entered.
The Deskely products for this
Frequently asked questions
What tests are done on a transformer before energising?
Visual and mechanical checks, insulation resistance and PI, turns ratio on every tap, winding resistance, vector group, oil breakdown voltage for oil-filled units, and function tests of the protection devices.
What is the acceptable turns ratio error?
Normally within ±0.5 % of the nameplate ratio, the tolerance in IEEE C57.12.00.
Why compare with the factory test report?
Because the factory values are the transformer's own baseline. A change since the factory test points to damage in transport or installation.
Is the template free?
Yes. Download the Excel or PDF version and adapt it to your project.
- In production since 2014
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