Transformer Selection 1

[hanksmith]

When selecting a transformer for a job does the connection have to be taken into account, Dy1 Dy11, ect..., this transformer is for a 2.5MVA 13.8kv/600

I have done some reading and I can only find information telling me that this matters when hooking up transformers in parallel, if it's just a single transformer it does not really matter.

If someone could point me to some other reading materials or information that would be great.

Thanks
Hank

 

[jghrist]

See The Whys of the Wyes at

http://www.geindustrial.com/publibrary/checkout/38652.30055.7762.44019/generic/GET-3388B.pdf

 

[majesus]

Wow, what an excellent document, and I love the title:
"The Whys of the Wyes"

Thanks

 

[davidbeach]

Hank, if you are in North America, the ANSI standard configuration (and I think Canada pretty much goes along with ANSI standards) is that the low side lags the high side by 30[°]. Unless you have some very specific problem to solve you would be best off not messing with that relationship.

 

[ELEP]

jghrist,
Very usefull document,
thnkx.

 

[hanksmith]

Ok,

Little more on this subject.

The senior engineer in the office is saying we have to evaluate the whole system to ensure we select the right vector relationship between the transformers. He says that if we don't do the analysis we could have inductive motor loads acting as generators. I didn't really understand this and skimming through that article didn't really help.

Senior engineer won't just say that the Dyn11 is standard and that's what we are using.

Any other input?

Thanks
Hank

 

[burnt2x]

hanksmith,
Goggle "tranformer connections". Or this attachment might help.

 

[jghrist]

The 600 volt motors don't care what the phase angle of the 13.8 kV system is. If there is no possibility of paralleling with another source, then the phase relationship doesn't matter as long as the phase rotation is not changed. The phase rotation is not be changed with different vector groups. There are system grounding considerations between Dy and Yd, but this doesn't seem to be an issue.

What exactly does the senior engineer say needs to be evaluated about the system? What analysis is he talking about?

 

[hanksmith]

jghrist, this is my biggest problem, I don't really know what he is asking for, if I knew I would have posted a better question or even tried opening a textbook. He talks like this is common knowledge and every electrical guy should know it.

Lets me ask another question.

Working with a clients power system. They currently have a 115kV to 13.8kV, 20MVA transformer installed, with a few 13.8kV to 600V 2.5MVA existing transformers. The have asked us to build a small plant with mostly inductive motor loads, biggest load being about 200HP, in doing this we are to specify a 13.8kV to 600V transformer in the 2.5MVA. What steps do I have to take to ensure a properly specified transformer for this system.

If I have missed anything that is critical to helping me out please let me know.

Thanks again.
Hank