Free module. This page is free to read. It does not ask you to sign in. It does not offer a class or a call. Use the edition of each standard named in the contract. Questions: hello@transformerpath.com.
Volume 14 is the thermal model, the loading guide, and the decision taken hour by hour. This module separates the nameplate from an overload. It does not authorise a load above the plate, and it does not quote a percent of rated current as universally safe. IEC 60076-7 is the loading guide in IEC practice. IEEE has its own loading guide. Use the one the contract and the operator’s procedure name. This page does not merge them.
What the plate already promised
Rated power is the continuous power at rated voltage and rated frequency under the cooling method printed next to that power. An ONAN value and a higher ONAF value are two promises. The higher one is available when that stage is running, not whenever someone wishes the unit were larger. Ambient and altitude sit under the assumptions of the temperature-rise standard. A site hotter or higher than those assumptions is not the site the plate was written for, even if the kilovolt-amperes match.
The limit that ages the paper is the hot spot, not the average winding temperature and not the top oil alone. Paper aging speeds up as that hot spot rises. A short peak can be carried on the thermal mass of the oil and the windings. A peak that is repeated every day is no longer an emergency. It is the new duty, and it needs to have been designed and guaranteed as a duty. Ancillary equipment — bushings, tap-changer contacts, and current transformers — can be the limit before the winding is. A loading decision that looks only at the winding temperature has not looked at the whole unit.
An overload is a decision you record
If an operator loads above the plate, the record should show the power, the duration, the cooling stage that was running, the ambient, and which guide was used. A scorch mark found years later cannot be interpreted without that record. The paid module works the thermal model. This module only refuses two mistakes: treating the forced-cooled power as the self-cooled power, and treating an emergency loading as if it had no life cost.
- Read the cooling stage beside the power. Do not borrow the fan-cooled number with the fans stopped.
- Hot-spot temperature, not the average, is what ages the paper.
- A daily peak is a duty. An emergency is occasional. They are not the same guarantee.
- Bushings, tap changers, and current transformers can limit the load before the winding does.
The thermal calculation and the guide’s loading tables stay on the paid plan, in the edition you cite.
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