Concentric Neutral vs Tape Shield MV Cable

[Amex12]

I have a 100m underground cable run that needs to carry ~500A. We have the option of going with concentric neutral cable or tape shield. Couple of questions in evaluating cable selection and bonding methods:

1. If I go with the concentric neutral cable option, can I unground the one end to get more current and run a GCC/ECC alongside the cable? I know induced voltage is always a concern but this seems like a short cable run.
2. If I go with the tape shield cable option, do I have to unground one end even if I am running a GCC/ECC alongside the cable?

 

[Palletjack]

1. If your going to do that I wouldn’t waste the money on concentric cable.
The concentric N is designed to be current carrying.
2.You don’t have to, but there could be voltage away from the grounded end. At 300’, I would ground both ends and buy cable large enough for 500A without worrying about circulating currents.

 

[7anoter4]

The shield grounding methods are provided in IEEE Std 575/2014.
6.3.1 Shield/sheath standing voltages
Values of sheath standing voltage can be found using Figure 1.
As an example, for a typical circuit having a conductor current I = 1000 A and S/d = 2
where
S is the center-to-center cable spacing
d is the mean sheath diameter
You have a 100m underground cable run that needs to carry ~500A.
Underground cable routing may be direct-buried or in ductbank. Let's say it is 35 kV 3 single-core cables in single duct in a duct bank.
According to IEEE 835 /1994 [the base of NEC] page 682 [xlpe or epr insulated 90oC rated copper conductor one circuit triplex] it has to be 750 MCM [380 mm^2].
The cable dimensions are : conductor diameter 1", insul.thick 0.345", ins.core 1.75" [shield dia] and ov.dia 2.09".
If it's about triplex s/d=1.19
According to IEEE std 575/2014 fig.1 the built-up voltage for 1000 A current it is 100 V/km for 500 A and 100 m this voltage will be only 5 V.
For 10" distance s/d= 10/1.75=5.7 , 220 V/km and then 11 V [since it is less than 200 V in my impression you don't need to do anything.]
So, what's the problem?

 

[Amex12]

thanks @palletjack and @7anoter4 for the responses.

It sounds like you both are suggesting that leaving one end ungrounded and running a GCC/ECC should be safe. However, what about for fault currents? If the fault current is say 10 kA, wouldn't the voltage stress at that time be 20x the normal induced voltage and can the cable withstand this?

 

[Palletjack]

I suggested grounding both ends…

 

[7anoter4]

The voltage for 0.1 km cable at 10kA will be 100 V for triplex and 220 V for 250 mm distance between cables [center line-to-center line].
The insulation of the overall jacket is tested all the time with 7-10 kV AC on spark tester as per UL 1072 Table 28.1 for PVC
Table 28.1 A-C spark-test potential in kilovolts for a nonconductive jacket over insulation shielding, a metal sheath, or armor

 

[7anoter4]

In my opinion, single-point grounding and the ungrounded end well insulated [for rated voltage BIL] it is better never less the continuity grounding conductor will carry the short-circuit current back and will produce another shield induced voltage of 150 to 300 V. Both ends grounding will produce shield losses and the shield has to withstand the short-circuit current [thermal stability].