Difference between AA/FA and AFA

[IncredibleGreg]

I've been studying for the NETA 2 exam and during my reading of the different types of transformers (here: https://testguy.net/content/184-Tran...ms-and-Methods) I noticed two similar but different classifications. The AA/FA and AFA classes are almost identical, except it specifies that the AA/FA type will typically have two different load ratings, one for AA and one for FA.

My question is, are there any more differences that should be noted between the two? Are there any physical differences that, if you were to look at a transformer that was either AA/FA or AFA, would you be able to tell the difference between them without looking at the nameplate?

[NBatson]

I've been studying for the NETA 2 exam and during my reading of the different types of transformers (here: https://testguy.net/content/184-Tran...ms-and-Methods) I noticed two similar but different classifications. The AA/FA and AFA classes are almost identical, except it specifies that the AA/FA type will typically have two different load ratings, one for AA and one for FA.

My question is, are there any more differences that should be noted between the two? Are there any physical differences that, if you were to look at a transformer that was either AA/FA or AFA, would you be able to tell the difference between them without looking at the nameplate?

Below is a summary of some common examples:


Class

Description


AA
Ventilated, self-cooled transformers. These transformers have ventilation ports located in outside walls of the enclosure. There are no fans to force air into and out of the enclosure with typically no external fins or radiators. Cooler air enters the lower ports, is heated as it rises past windings, and exits the upper ventilation ports.

AFA
Self-cooled (A) and additionally cooled by forced circulation of air (FA). These transformers have ventilation ports for fan inlets and outlets only. Normally, there are no additional ventilation ports for natural air circulation.

AA/FA
Ventilated, self-cooled (same as Class AA). These transformers have a fan or fans providing additional forced-air cooling. Fans may be wired to start automatically when the temperature reaches a pre-set value. These transformers generally have a dual load rating, one for AA (self-cooling natural air flow) and a larger load rating for FA (forced air flow).

ANV
Self-cooled (A), non-ventilated (NV). These transformers have no ventilation ports or fans on the enclosure and is not sealed to exclude migration of outside air, but there are no provisions to intentionally allow outside air to enter and exit. Cooling is by natural circulation of air around the enclosure. This transformer may have some type of fins attached outside the enclosure to increase surface area for additional cooling.

GA
Sealed with internal gas (G) and self-cooled (A). These transformers typically have a gas, such as nitrogen, SF6, or freon, to provide high dielectric and good heat removal. Cooling occurs by natural circulation of air around the outside of the enclosure. There are no fans to circulate cooling air; however, there may be fins attached to the outside to aid in cooling. The enclosure is hermetically sealed to prevent leakage.

Maybe this helps??

[samair99]

Below is a summary of some common examples. Maybe this helps??

Did you just copy this from the testguy article in the first post?

Far as I know the main difference is the automatic fan control and dual ratings. AFA is a single kva rating with fans running all of the time. AA/FA has a rating with no fans running and a higher rating with fans running.

[NBatson]

Did you just copy this from the testguy article in the first post?

Far as I know the main difference is the automatic fan control and dual ratings. AFA is a single kva rating with fans running all of the time. AA/FA has a rating with no fans running and a higher rating with fans running.

My fault I some how missed that link! From what I have gained from our transformer guy what you are saying is correct. So to refer to the original question...

In my mind there shouldn't be a physical difference between AFA and AA/AF. Like you said one runs all the time and the other operates under a temp sensor and kicks on with the higher load.