×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Verifying Transformer Rating

Verifying Transformer Rating

Verifying Transformer Rating

(OP)
I have a power transformer marked
KVA = 2501/2800/3250/3500
Class ONAF
55/65 deg

Is it correct that the 2501/2800 are ratings at 55/65, no fans, and the 3250/3500 are 55/65 with fans?

RE: Verifying Transformer Rating

(OP)
To expand - an existing transformer rated as shown above is the GSU for a 1.6MW/2.0 MVA genset. We wish to add a second identical genset, and I have stated a larger GSU is required. Others have challenged stating because generators are operated at close to unity pf (0.95-.0.99 pf leading) per interconnect agreement, total generation with two generators will remain below the 3500 KVA FA rating of transformer. Shouldn't the transformer be rated for full range of generator capability curve?

RE: Verifying Transformer Rating

Yes, you have the ratings correct.

As to sizing - it depends. As long as the transformer is adequately protected and it is felt that the rating will not be exceeded, I be OK with one xfmr. Obviously a second transformer would allow for more flexible loading, greater reliability, and probably extend the life of both transformers, it would represent a major expense. I'd design the system so it can be added later.

RE: Verifying Transformer Rating

(OP)
Thanks dpc.

To confirm - you are indicating you'd consider tying both the existing and new generators (total output 3.2 MVA/0.8 pf) through the single, existing 3500 KVA transformer, provided protection was configured to ensure transformer ratings were not exceeded? This would end up decreasing the overall KVA/reactive capability of the facility, although in normal operation this should not be an issue. As the existing GSU and gear is already installed, designing for a future connection would also involve some expense. I am guessing the mgmt. will elect to leave the existing xfmr and interconnecting switchgear line up as is. I had envisioned a second or new, larger transformer.

RE: Verifying Transformer Rating

Adding a second transformer is a major cost. Replacing the existing transformer with a larger one could work, but is still a major expense. Just allow space and possibility for the second, if possible. I don't see how you can justify the cost a new transformer at this time, based on my understanding of the project. Also, transformer ratings can be exceeded in some situations.

RE: Verifying Transformer Rating

(OP)
thanks again. The only justification would have been a need to match the MVA / pf capabilities of the generator, however if not required by the utility and adequate transformer protection provided, then I see the logic in using the existing unit.

RE: Verifying Transformer Rating

Money is always a factor. Just don't paint yourself into a corner.

RE: Verifying Transformer Rating

Hi all,

when talking about genset ratings keep in mind that acc. to ISO 8528-1 'Application, ratings and performance' only 'Continuous Power (COP)'-rated genset are capable of delivering 100% of nameplate power on a 24/7 basis. Others like 'Prime Power (PRP)' usually are either limited to 70% on average over a 24-h-period or have limited running hours per year (500hrs at 100% for a 'Limited-Time running Power (LTP)'-rated genset). So except for COP-Operation the transformer may be downsized w/o compromising its life expectancy.
Load factors may also be different between manufacturers and deviate from the ISO standard.

Johannes

RE: Verifying Transformer Rating

(OP)
Which KVA value does the %impedance apply to? I assume in this case the 2500 KVA value?

RE: Verifying Transformer Rating

If this is an ANSI rated tranformer, the impedance is based on the lowest kVA rating.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources