Effect of neutral reactance on transient overvoltages (high resistance grounding)

[brainsalad]

Greetings:

Attached is a picture of the zero sequence network of a solid ground fault with high resistance grounding (from EPRI "Grounding and Lighting Protection")

Practically speaking, if the resistor/xfmr was connected to the neutral through a long cable (say 5kV, 2/0, 200'), would its shunt capacitance (zero sequence capacitance) contribute to the total 3Ico ("3-phase") charging current? This charging current (3Ico) is from the two unfaulted phases. Could the neutral shunt capacitance formed by the cable (which only becomes charged upon the fault creating V_ng=V_ll from V_ng=0) be modeled by a capacitor in parallel with Xco in the attached figure?

If anyone has the ABB T&D book, Chapter 14, page 521, fig. 48 (sorry could not upload), does this plot indicate that such a neutral cable shunt capacitance can be neglected in 3Ico (Xco)? Thanks for your thoughts.

 

[odlanor]

NO! X0 does not include Xc0
Xo only include ractance of resistor and transformer
If X0 = 0 we have fig 47 values as fig 48 values;

fig. 47
X axe
ratio kW/kVA : 1.0
Yaxe
unfaulted phase: 260V
neutral to gtound: 165V
faulted phase: 120V

fig. 48
X axe
Xo/R0 ratio: 0
Yaxe
unfaulted phase: 260V
neutral to gtound: 165V
faulted phase: 120V