How to Read a Transformer Nameplate (and Order the Right Accessories)
If you can read the nameplate, you can order the right accessories without guessing. This guide is written for procurement officers and field engineers who receive a photo of the tank sticker and need to turn it into a parts list.
Every oil-immersed power transformer carries a nameplate with the data that decides which accessories fit. You do not need to be an electrical engineer to use it — you only need to know which four or five fields matter for accessories.
1. The fields that decide your accessory list
| Nameplate field | What it tells you for ordering |
|---|---|
| Rated power (kVA / MVA) | Sets the relay, valve and indicator sizes. Larger units need larger bore diameters and higher gas-volume settings. |
| Voltage ratio (e.g. 11 kV / 0.4 kV) | Confirms the insulation class and which connecting flanges apply. |
| Cooling class (ONAN / ONAF / OFAF) | The most important field for accessories. Forced-cooling units (ONAF/OFAF) need an oil flow relay; ONAN units do not. |
| Frequency (50 / 60 Hz) | Matters for cooling fans and some motors — confirm before ordering export units. |
| Vector group / impedance | Usually not needed for accessories, but keep it on file for the quote. |
2. Cooling class — the shortcut
The cooling code is the single fastest way to know what you need:
- ONAN — natural cooling only. You need gas relay, pressure relief valve, oil level indicator, breather. No oil flow relay.
- ONAF / OFAF — forced cooling. Add an oil flow relay and cooling-fan assemblies to the list above.
3. Worked example (illustrative)
A nameplate reads S11-M-630/10, 630 kVA, 10/0.4 kV, ONAN, 50 Hz. From this you can quote: one QJ-type Buchholz relay (matched to the conservator pipe bore), one YSF pressure relief valve, one UZF oil level indicator, one YC moisture absorber, plus gasket set and standby silica gel.
The figures above are an illustrative example to show the method. Exact model numbers, bore diameters and gas-volume settings are confirmed per order — see the TBD* notes on each product page.
4. What to send us
A clear photo of the nameplate is usually enough to start a quote. If you also have the conservator pipe diameter and the mounting flange drawing, the offer will be exact on the first pass.
FAQ
Q: My nameplate is faded / in another language. Can you still help?
A: Yes. Send the photo — often the model number and kVA are enough, and we will ask only the few missing fields.
Q: Do I need the factory's original part numbers?
A: Not necessarily. Transformer accessories are largely standardised by bore, pressure and mounting; we cross-reference to the right QJ / YSF / UZF type.
Q: 60 Hz export unit — any trap?
A: Cooling fans and some solenoid parts must be rated for 60 Hz / the local voltage. Always state the destination market in the inquiry.
Send us the nameplate photo
We return a priced parts list with datasheets within one business day.