What does OA stand for on older transformers

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Just curious to find out what OA stands for on older transformers, this isn't a homework assignment its 1st to answer the right answer in my class gets $5 bucks lol. I been googling and been getting closer to the right answer but I need to know what it stands for.
 

GoldDigger

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I guess any way to research the question is OK!

My edumacated guess is that OA stands for OilAir (oil transfers heat to fins cooled by air), both with only natural circulation (no pumps, no fans.)

The modern nomenclature for exactly the same rating would be ONAN where the N goes with each to mean Natural circulation.
If you used an oil pump and cooling fans (of a capacity specified elsewhere) the code would be OFAF and the power rating for the same core temperature rise will be greater than the OA (ONAN) rating.

Again, just a guess, but I think you could collect on that.

Credit where credit is due: https://www.eng-tips.com/viewthread.cfm?qid=21127
 
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my instucter said there was a different meaning to that instead of that, i found that earlier but was wrong. i did happen to stumble on some really old news paper where it kind of gave it a diferent meaning like:
OA may stand for ampere-turns of the transformer coil on the stator. OA represents the field flux produce by the current flowing through the feild winding on the stator. the rotor ampere-turns (A'c) are obtained by adding vectorially OA' (=v' OA, v' denoting the leakage of the coefficient) ande OC. I found this in a electrical journal from 1906. hit or miss still worth a shot to figure out.
 

Jraef

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That definition is a bit too esoteric for my taste.

In the most COMMON interpretation, OA was an earlier ANSI term for the cooling of a transformer NOT being required to have fans to facilitate it. And GoldDigger was correct as to the definition. OA = Oil/Air, meaning the cooling method is oil dissipating into air naturally by convection, so the transformer would just have a tank and a radiator, with the oil circulating in the radiator by virtue of the heat rising from the radiator due to convection, pulling oil in the bottom and back into the transformer from the top. In that older ANSI nomenclature, the choices in oil filled transformers were OA, FA and FOA, where OA was as described above, FA stood for Fan Assisted (for the radiator), and FOA stood for Forced Oil Fan, where there is a circulating pump for the oil inside of the tank, then fan assisted cooling for the radiator. These transformers often came with different ratings based on those cooling methods, i.e. 30/40/50MVA OA/FA/FOA, meaning that with no fans on, it was 30MVA, turn on the fans and you can get 40MVA, then on the circulating pump AND the fans and you can get 50MVA out of it.

The newer (ANSI) IEEE Std C57.12.00 - 2010 designations are a little more comprehensive and separate the cooling medium from the method;

Cooling methods
A = air cooling,
O = oil cooling,
K, L = cooling with synthetic fluid,
W = water cooling

Cooling mode
N = natural (convection) cooling,
F = forced (fan assisted) cooling,
D = directed cooling (directed oil flow)

Then there are two sets of designation letters, the first two are the INTERNAL cooling method, the second two are the EXTERNAL cooling method for the oil. So the older OA designation would now be ONAN meaning Oil Natural cooling internal, meaning the transformer is oil filled, but there is no pump to circulate the oil; then Air natural cooling external, meaning there is a simple heat radiator for the oil on the outside, no fans.
 

jim dungar

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OA may stand for ampere-turns of the transformer coil on the stator. OA represents the field flux produce by the current flowing through the feild winding on the stator. the rotor

Well seeing how a standard transformer does not have stator and rotor windings, I would guess you may have misunderstood your resource.

As far as transformers are concern, the information from Jraef and GoldDigger is correct, and has been for some 70 years.
 

Hv&Lv

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my instucter said there was a different meaning to that instead of that, i found that earlier but was wrong. i did happen to stumble on some really old news paper where it kind of gave it a diferent meaning like:
OA may stand for ampere-turns of the transformer coil on the stator. OA represents the field flux produce by the current flowing through the feild winding on the stator. the rotor ampere-turns (A'c) are obtained by adding vectorially OA' (=v' OA, v' denoting the leakage of the coefficient) ande OC. I found this in a electrical journal from 1906. hit or miss still worth a shot to figure out.

I’m assuming from you occupation it’s Substation technician apprentice.
hang in there, this is a great resource for all fields, including substations.
When you get an answer like above, understand there is no animosity involved, just look up the resource and learn the trade.
i don’t think anyone on here has been right every time.



Electricity hasn’t changed in all the years from 1906, but seriously, get a newer journal...:p

OH, write down the stuff in Jraefs post. Look at all the transformer data plates in the field. Those with pumps, fans, and just fins, and see what he was writing about.
 
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