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Tony S

Loss of 1Ph to a 3Ph transformer:

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Tony S

Loss of 1Ph to a 3Ph transformer:


So what happens if a 3 phase transformer tries to run on 2 phases?


I’ve drawn a 11/.433kV Dyn11 transformer showing the actual phase relationship between primary and secondary windings.



The LV outputs being:

l1→l2 = 433V

l2→l3 = 433V

l3→l1 = 433V

l1→N = 250V

l2→N = 250V

l3→N = 250V


Loose one of the MV primary phases (in this case red) both L3→L1 and L1→L2 become series windings





The offload LV outputs now being:

l1→l2 = 0V

l2→l3 = 375V

l3→l1 = 375V

l1→N = 125V

l2→N = 125V

l3→N = 250V



©Tony S


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