I’m not so sure but i believe it has to do with number of poles and combining the 3 phases in that way and then perhaps a manner to make or provoked waves to Bounce along the tubes like if it was an antena like Ron said few time ago… I thing the alternator had the coils arranged on the other phases like shorting ckr or like an unbalanced 3 phase system so it cause a dc flow… I imagine using a y alternator as a kind of load feeding the other alternator