Hello all, I've been reading up on both potential and current polarization for directional phase relays in, "Power System Relaying" by Stanley H. Horowitz and Arun G. Phadke and I am confused as to how the direction of the fault (i.e. into or out of the line) is obtained. In potential polarization they mention how a grounded wye-grounded/open-delta voltage transformer is and the polarization potential is connected across the open-delta. For a ground fault, zero sequence voltage of 3Eo will be present across the open delta connection, but how does this indicate direction, that is, whether the fault is into our out of the line? The magnitude of the zero sequence voltage will be larger if the fault is closer in, but it still does not tell me on which side the fault resides. How is this deduced? In current polarization they discuss how they use the current in the neutral of a wye-grounded/delta power transformer. They then go on to say, "If the current is positive, current flows up the neutral; if negative it flows down the neutral." This is AC current we are talking about right, so it oscillate back and forth at the system frequency right? Are they implying the direction of power flow when they refer to positive or negative current? What is considered positive current and what is considered negative and what is the basis for these designations? Thanks again!