hello there ; I have several questions about the 3-phase transformer connections and I will be really grateful if any one could help .... I've learnt that there are several types of 3-phase transformer connections which are in general ; the (Wye-wye) , ( Wye-Delta ) , (Delta-Delta ) , ( Delta-Wye ) , and Open Delta but I got a bit confused with the VA relation for each ....I also have read in a book that the VA rating of Open-delta configuration is = 0.58 of ( Delta-Delta ) rating , how this relation been derived in the first place !? and what's the different between each configuration and another , I know that only 2 transformers have to be used for Open-delta configuration , and 3 transformers for the rest configurations .... what if the current ratings for each winding increased , could the open-delta configuration work as well as the Delta-Delta configuration !? what about a transformer with capacity of 60 KVA what total 3-phase power can be obtained in each of the ; (Wye-wye) , ( Wye-Delta ) , (Delta-Delta ) , ( Delta-Wye ) , and Open Delta !? thanks in advance .