Turns out no zero sequence current flows on the high side for an unbalance or open conductor on the low side. The open conductor problem turns out to be a nasty symetrical components problem. Thanks everyone for their help.
If I have an unbalance condition (not a phase to ground fault but an unbalance, say an open phase conductor) on the low side of a grounded wye-delta distribution transformer (distribution system is impedance grounded through a zig-zag grounding transformer) how can I sense this unbalance? Will...