Transformer Connection T#21: Delta - Wye

Dennis Merchant video on transformer connections. This video goes with 4th year transformer connections unit in section 4-3 of the Merchant Job Training & Safety Program.

[@iowabuckinrut760]

Why are there 4 secondary terminals? Thanks

[@merchantjts]

Steven DeBerg sorry for the delay in getting back to you. I was on vacation. To answer your question, if a transformer has a secondary rating of 1:2, and a power rating of 167-500 kVA, then the secondary has four bushings. This transformer has a secondary rating of 120/240, and a power rating of 167 kVA, so it meets the criteria. On a smaller rating having three bushings, the four terminals A, B, C, and D, are all connected internally. The two coils are paralleled for 120 volt only operation. They are connected in series for 120/240 volt operation. The larger transformer uses four bushings externally because the stiffness of the large wire and the large size of terminals required. Hope this helps.