Questions regarding induced voltage calculations per IEEE 575

[psmpsm]

Hi,

I'm currently trying to perform calculations for induced voltage on the following system:

138kV power cable in underground duct bank, flat formation, one phase per conduit, single point bonded, 8" spacing between conductors (8" between A/B, B/C, and 16" between A/C)

I was successful in performing the calculation for normal load current, emergency load current, three phase fault, and phase to phase fault scenarios. These calculations were performed per the equations in IEEE 575 standard - fairly straight forward.

However, when attempting the calculation for single phase fault to ground, I hit a roadblock.

In all the equations there is a parameter called "S" that refers to center to center spacing between conductors. This was 8" for my calculations.

However, for single line to ground fault, this "S" parameter becomes geometric mean spacing between each conductor and ground (the parallel ground continuity conductor).

My questions are as follows:

1) Since this PGCC will be laid such that it is touching the phase conductor, wouldn't "S" go to zero, and thus the entire induced voltage for single line to ground fault becomes zero as well?

2) The equations in IEEE 575 for calculating induced voltage assume that the PGCC is transposed such that 50% of the length of the conductor is on A phase, and then 50% is on C phase. In the design I'm looking at, it's more like 60% on A phase, and 40% on C phase. The standard doesn't really give an equation for that scenario, although it does say that a non transposed PGCC results in higher induced voltage in the phase conductors and higher circulating current in the PGCC. Is there any way to account for this in the calculation?

3) There does not appear to be an equation to calculating voltage for an internal cable fault. Is this found elsewhere?

Thank you!

 

[7anoter4]

I have not the last edition of 2014 of IEEE 575 with me but only the 1988 edition.
However, in this edition on para 5.4.3 Parallel Ground Continuity Conductor it is written [see attachment]. That means the conductor it is usually insulated. The 138 kV cable it is also insulated.
If I understood well the sense of fig.2 sketch the part referred to wide flat formation you have to install the PGCC halfway at 0.7*S on right of B cable and half a way on left side 0.7*S distance from the same phase B.

 

[7anoter4]

I am sorry. I forgot; I have 2014 edition indeed. However, the figure 2 is the same. Only instead of para. 5.4.3 Parallel Ground Continuity Conductor all I said it is written in para.6.3.3 Parallel ground continuity conductor.