Vector Group Vs Price

Which country?

i have absolutely no idea, having zero knowledge in this field. i am eager to see experts give their responses...

But i think, is it logical ? If one was cheaper, why would anyone want to buy a more expensive one just for a neutral (or absence of one)? i await with bated breath....

The decision to go for DD/DD or DD/DY mainly depend on your requirement . If a step up transformer for EHT transmission ( 11kV to 220 kV or 400 kV )can be DD/ DD as the transmission is 3 phase 3 wire and there is no requirement of neutral . Where as in case of a 3 phase 11kV /430 V transformer for LT distribution transformer Neutral is a must as the distribution will be 3 Phase 4 wire system necessary to provide 230 V line (220/110 V in case where that voltage distribution system prevails)to neutral supply to single phase consumers .( Only if the complete load is purely 3 phase delta then DD /DD transformation system can be used.So it is not financial consideration but technical requirement by which decision is taken.

Who on earth are you getting quotes from?

A Dd transformer, needing no neutral terminal, is a simpler piece of equipment.

It also means cheaper? I'm asking because I have to change the vector group of 3 winding transformer from Dy5 Dy5 to Dy5 Dd0.

Get some proper quotes and find out!

In three phase transformer of 1:n ratio

for primary (V,I) there is (n.V, I/n) secondary in case of Delta-Delta.

(n.√3.V, I/(√3.n) Delta-Star.

(n.V/√3, √.I/n) Star-Delta.

(n.V,I/n) Star-Star.

These parameters are important while selecting capacity of transformer.

I think Yes,

Let us consider 2 MVA 6600V/440V trafo.

Pirmary current = 2000/1.732* 6.6= 174A

secondary current=2000/0.44=2600A

In case secondary is delta, line current is 2600A. But Each winding need to withstand 2600/1.732= 1501A

But in case secondary is star connected, each winding need to withstand 2600A.

So the increase in winding thickness increase the price.

Am i wrong or correct?

You are Wrong.

Your Formula for the 2ndary is missing the 1.732:

S = UxIx1.732 ==> I primary = 2000 x 1000 /(6600 x 1.732)

I secondary = 2000 x 1000 / (440 x 1.732)

Even though you got the answers correct in those lines.

The current in both cases will be the same in the windings.

Correct ! GA for you.

_Conclusion:

_{· In DD number of secondary turns in each winding would be higher than the DY by 1.732 times (according to the voltage induced (440/254V))}

_{· In DD secondary winding thickness would be lesser than DY (according to the current capacity(1501/2600A))}

_{These points also affect the price.}

Er.... more turns of less cross-section vs less turns of more cross-section....do you thing that copper will be less in one? If you do detailed calculations, you will realise that there is no free lunch in the world....both will be the same.

Yes Sir,

They do not affect the price much, but affect.

At low voltage, cost of conductor is the main concern.

At High voltage, cost of insulation is the main concern. (Delta winding voltage is √3 times higher than star- So insulation cost & thickness rises)