bow72
Electrical
- Dec 24, 2009
- 1
Hello,
I am working on the design of a 50 MW generating facility on the USA connecting at 138 kV and need to specify the transformer rating. The facility can control p.f. to 0.95 so I decided to size the transformer up to 55 MVA. Now the issue comes with the ONAN and ONAF steps i define.
I am used to see in IEC that the ONAN is around 70% of the ONAF rating, so in this case a 40/55 ONAN/ONAF. But I see that the ANSI/IEEE practice usually has two ONAF steps and being 33% and 66% higher than the base ONAN rating, in this case 35/45/55 MVA ONAN/ONAF/ONAF. In this case the two transformers are relatively similar but the differrence is bigger for larger generating facilities.
My question is, how would you specify the transformer rating in this case?
thanks,
I am working on the design of a 50 MW generating facility on the USA connecting at 138 kV and need to specify the transformer rating. The facility can control p.f. to 0.95 so I decided to size the transformer up to 55 MVA. Now the issue comes with the ONAN and ONAF steps i define.
I am used to see in IEC that the ONAN is around 70% of the ONAF rating, so in this case a 40/55 ONAN/ONAF. But I see that the ANSI/IEEE practice usually has two ONAF steps and being 33% and 66% higher than the base ONAN rating, in this case 35/45/55 MVA ONAN/ONAF/ONAF. In this case the two transformers are relatively similar but the differrence is bigger for larger generating facilities.
My question is, how would you specify the transformer rating in this case?
thanks,