ONAN/ONAN/ONAN?
ONAN/ONAN/ONAN?
(OP)
Reviewing a transformer spec (230/69/12.47 kV, 167 MVA single rating) and noticed the following verbiage:
"Class... ONAN/ONAN/ONAN or ONAN/ONAF/ONAF at Contractor's option"
Seems curious to me that they would suggest three stages of non-forced oil and air. The engineer that put this together is not available for questions, and I was wondering if anyone out there might suggest reasons why the ONAN/ONAN/ONAN rating was provided. ONAN or ONAN/ONAF/ONAF would seem the more accurate way to put this.
"Class... ONAN/ONAN/ONAN or ONAN/ONAF/ONAF at Contractor's option"
Seems curious to me that they would suggest three stages of non-forced oil and air. The engineer that put this together is not available for questions, and I was wondering if anyone out there might suggest reasons why the ONAN/ONAN/ONAN rating was provided. ONAN or ONAN/ONAF/ONAF would seem the more accurate way to put this.






RE: ONAN/ONAN/ONAN?
RE: ONAN/ONAN/ONAN?
http://www.onan.com/na/pages/en/products/powergeneration/index.cfm
RE: ONAN/ONAN/ONAN?
BLadewig, you may be wrongly assuming that the person who stated the ONAN/ONAN/ONAN was stating it correctly/correctly/correctly. My guess is that they were considering the triple voltage levels as a candidate for three separate cooling ratings. Otherwise there is no reason I can think of to state the cooling levels 3 times. If they had listed it twice, i.e. ONAN/ONAN, that might have been to match the MVA rating at two separate temperature rises, for example 100/112 MVA ONAN/ONAN 55/65 C rise. But since you say it has a single MVA rating I can think of no reason to indicate the ratings as you described. I would write it off to someone not following standard rating conventions.
RE: ONAN/ONAN/ONAN?
RE: ONAN/ONAN/ONAN?
RE: ONAN/ONAN/ONAN?
The ONAN/ONAN/ONAN part still sounds wacko to me.
RE: ONAN/ONAN/ONAN?
RE: ONAN/ONAN/ONAN?
So my question (like the original question) is this: how can we have three stages of naturcal circulation oil/natural circulation air (ONAN). I can understand multiple stages/ratings of forced cooling where the fans or pumps can switch on in banks, but I don't understand multiple stages/ratings of forced cooling.
RE: ONAN/ONAN/ONAN?
1. IEEE Std 141-1993 IEEE Recommended Practice for Electric Power Distribution for Industrial Plants,
Table 10-11 Classes of Transformer Cooling Systems, on page 509
would state for the above transformer:
OA/FA/FOA = Liquid immersed, self-cooled/forced-air, forced-liquid-cooled/forced-air, forced-liquid cooled, which is difficult to interpret since FOA stands for liquid-immersed, forced-liquid-cooled with forced-air-cooled.
RE: ONAN/ONAN/ONAN?
http://grouper.ieee.org/groups/transformers/subcommittees/performance/WG_C57_12_00/PCS_C571200_Proposed_Changes.pdf
for correlations "in progress"
RE: ONAN/ONAN/ONAN?
C57.12.00 Section 5. Rating Data, and Table 2 – Cooling Class
Designations.
Present Designations (2000) Previous Designations
ONAN OA
ONAF FA
ONAN/ONAF/ONAF OA/FA/FA
ONAN/ONAF/OFAF OA/FA/FOA
ONAN/OFAF OA/FOA
ONAN/ODAF/ODAF OA/FOA∗/FOA∗
OFAF FOA
OFWF FOW
ODAF FOA∗
ODWF FOW∗
∗ Indicates directed oil flow per Table 9, Note 2 of IEEE Std. C57.12.00 – 1993.
RE: ONAN/ONAN/ONAN?
RE: ONAN/ONAN/ONAN?
They wanted to also provide the option of building the transformer without any forced cooling, and apparently sort of followed suit with the above format. There are no multiple-temperature rises spec'd. So I don't think it's necessarily wrong to write ONAN/ONAN/ONAN, just maybe not preferable. Out of curiosity, when you have no forced cooling then you really don't have different output stages, right? It wouldn't be a 100/133/167MVA transformer, but rather a 167MVA one.
RE: ONAN/ONAN/ONAN?
RE: ONAN/ONAN/ONAN?
By the way, the trend for new units is to ignore the 55C rating and only specify a 65C rating. But some people prefer to use only the 55C rating and operate their transformers cooler, thereby extending their life (the transformers, not the engineers).
RE: ONAN/ONAN/ONAN?