Both of us should be referred again not me alone. Flux density is very important in economical design and construction of transformer .Normally this is 1.7 T . when you say the voltage over zigzag is divided by 1.73 with the same number of turns, in fact you are saying that flux is also divided by 1.73 . in this case your transformer hasn’t been designed economically . However it can transfer 1.73 times its rated apparent power . I think both of us must come back university.