Ground continuity conductor with multicore cables

[Power0020]

Currently came across a design for a solar power plant, a multi-core, armored 33 kV Cable is used.

I wonder that there is no ground continuity conductor running in parallel to the cables like single core ones. I can't locate any reference on that.

Multicore cables will, inherently have no circulating current I think, since the mag field is cancelling each other and all the three screens are touching each-other. The armour will be solidly bonded in both ends ( I think that, unless?), and fault currents will be divided between screens and parts of armour, if involved. (mostly, the screen will share more current, with less resistance compared with steel armour).

Any clues? codes?

 

[jghrist]

Magnetic fields are not completely cancelled because there is some distance between phases. There will be circulating current - it doesn't depend on the distance between bonding points between shields.

 

[Marmite]

If the screen is adequately rated for the fault current then you wouldn't need the ground continuity conductor for a multicore cable installation. Generally as your cable rating requirements increase you would move to single core cables, in which case for a given cable size you can get more out of it by using single point bonding than solid bonding of the screens. This requires a separate ground continuity conductor.

Regards
Marmite

 

[7anoter4]

Usually the three-core shielded cable it is destined for medium voltage 6-36 kV high resistance grounded neutral [10-25 A], so no short-circuit current will be expected in a ground fault case.
Circulating shield currents-in a both ends grounded-or build-up induced voltage in one point grounded shield or armor case are not expected if we talk about symmetrical three phase load.
For single core cable grounded at a single point see IEEE 575/1988 5.4.3 Parallel Ground Continuity Conductor.