# Use of 3 phase transformers which are ∆-Y connected and Y-∆ connected

Different literatures say different things regarding ∆-Y and Y-∆ 3 phase transformer connection...

Some say that ∆-Y is used for step down and Y-∆ is used for step up while others say just the opposite things...

Depending on this step up and step down ability they are used in transmission and distribution of power... So please can anyone explain me what are ∆-Y and Y-∆ actually used for(which for step up and which for step down) along with a mathematical reason... Thanks in advanced!!

• Looks to me that your second source is internally contradictory. On the two pages it calls both arrangements step-down. I'd be suspicious. Oct 9, 2018 at 18:16
• It's a transformer and can be used (with the appropriate turns ratio) for step-up, step-down or 1:1. Oct 9, 2018 at 18:41
• So please can you explain me what you know... I am in great turmoil regarding this issue as I cannot make it out as to what shall be the answer actually... Oct 9, 2018 at 18:41
• I just have - it's anything you design it to be. Oct 9, 2018 at 18:42
• For the same winding on each leg, the wye-delta has a 'built-in' step-down ratio of sqrt(3) and delta-wye the same step-up, reinforcing the claim of the first source, but there's no practical reason that you need to keep all the coils similar, so other factors, including the availability of a neutral for separating out single phase supplies can overrule this advantage. Oct 9, 2018 at 20:40