×
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

Step-up transformer vector group

Step-up transformer vector group

Step-up transformer vector group

(OP)
Hi everyone,
I am trying to finalize the specification of a step-up transformer but I can't find a lot of information about vector group.
The existing step-down transformers of the installation are Dyn11 type. After a discussion with a transformer manufacturer his proposal was YNd11.
A rough description of the installation is [gen-set 0.4kV] - [step-up transformer 0.4/20kV] - [20kV line] - [step-down transformer 20/0.4kV] - [loads].

Thanks

RE: Step-up transformer vector group

There is not technical reason for using one vector group over another. US standards would have the high side leading the low side by 30°, which is YNd11 or Dyn11.

RE: Step-up transformer vector group

(OP)
Thanks jghrist for your answer.
Perhaps the question was not so clear. So, is there any regulation (or other tech restriction) which determine to use an exact vector group for the step-up trafo if the vector group of the step-down trafo (Dyn11) is known ?

RE: Step-up transformer vector group

A few things to consider would be:

- Are there any changeover supplies at the other end? If so, the phase shift degrees will need to be carefully coordinated to avoid mismatch of phasing between the two supplies at the receiving end
- Ground fault protection philosophy will also dictate the type of vector grouping. In the arrangement you have mentioned (having a YNd11), I presume the intention was to use the d11 for the 20kV side. If this is the case, grounding of the entire 20kV network is going to be challenging. You may need to consider corner point delta winding earthing or having earthing transformers installed. In my opinion, I would go with the 20kV side to be solidly or resistively earthed via an NER or NEX in which case a star winding is what I would prefer for the 20kV side

RE: Step-up transformer vector group

My understanding so far is delta connection is required on LV side of GSU to prevent the zero sequence current entering in to generator(as rotating machines have very little with stand capacity for zero sequence currents) on any LG fault on HV side. So in US YNd1 is usual connection for GSU and outside Ynd11.I have seen Ynyn GSU for small ratings, but never came across Dyn.

RE: Step-up transformer vector group

(OP)
Hi electrichie123, there is no changeover supplies. Step-up transformer is fed by a standby gen-set. YNd configuration means STAR connection in medium voltage 20kV side (I'll use solidly grounded neutral) and DELTA connection in low voltage 0.4kV side.

RE: Step-up transformer vector group

For large machines the LV delta is primarily there to allow high resistance earthing of the generator neutral point to ensure that any stator earth fault does not result in significant damage to a very high value asset. Phase-phase faults on the generator bus are rare because the output busbars are usually of the isolated phase type, and the GSU transformer itself is often a bank of single phase types.

The generator itself doesn't know or care about the GSU vector group, but the GSU vector group may be of significance if the station and unit auxiliary supplies are required to operate in parallel for any reason.

RE: Step-up transformer vector group

(OP)
Hi ScottyUK,
thanks for your answer. Consequently which is your proposal for my simple case ?

RE: Step-up transformer vector group

As I'm UK-based I guess I will go for YNd1 transformer, and earth the neutral point through a resistance to limit the earth fault to a few amps. I am assuming that you do not have any line-neutral loads on your generator, and I'm looking at this from the generator owner's perspective. The utility you connect to may well have the final say on the transformer - they may accept a zero sequence source from the star winding, or they may not. Without knowing how the 20kV system is designed to operate it is hard to be more specific.

RE: Step-up transformer vector group

LDKGR, the convention of transformer vector group representation is high voltage connection first(capital letter) followed by low voltage connection, clock number correspond to position with HV at 12 o'clock.
With delta on LV side, any LG fault on HV will be seen as a LL fault on LV. Scotty, my understanding is, UK you follow YNd11 for GSUs always. My understanding wrong? In India, we follow UK practice except where US consultants are involved where we use YNd1.

RE: Step-up transformer vector group

Hi prc,

There are few if any British generating plant manufacturers left, with the market now dominated by foreign companies - YNd1 isn't uncommon among the younger stations, especially those with North American links. I think the UK practice you refer to is that of the old CEGB, but now ownership of generation is fragmented there's no common standard. Dyn11 is the default vector group on the distribution system other than where 'unusual' types are required - typically star-star or star-interstar (zigzag) - for specific purposes.

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