Single core MV cable armour and Shield

[vinod]

One of the project specs. requires that "Armour and Shield of all single core AC power cables shall be grounded at one end only?. I understand it is to do with circulating current but can't visualize real problems for power cables if laid in trifoil formation.
What will happned If I connect armour and Shield together to ground?
What is the defferance between armour and shield?

 

[dicklaxt]

I don't recall ever using well in fact even seeing a shielded,armored 1/c MV cable..........single core/conductors are shielded and are normally pulled into conduit.I have seen them triplexed and installed in cable tray.

Shield is over the individully conductor to reduce stresses and armor is for physical protection,,,,,,,,,the armored is usually grounded via the terminator as conduit is to a hub etc,shilrds are usually terminated with a stress cone

Small cables, ie:Multipair instrument cables will often have individual shields and overall armor.

dick

 

[dicklaxt]

I don't recall ever using well in fact even seeing a shielded,armored 1/c MV cable..........single core/conductors are shielded and are normally pulled into conduit.I have seen them triplexed and installed in cable tray.

Shield is over the individully conductor to reduce stresses and armor is for physical protection,,,,,,,,,the armored is usually grounded via the terminator as conduit is to a hub etc,shields are usually terminated with a stress cone.

Small cables, ie:Multipair instrument cables will often have individual shields and overall armor.

dick

 

[dicklaxt]

This link may be of some help



http://www.okonite.com/engineering/shielding.html

 

[vinod]

Thanks Mr Dick

 

[rcwilson]

In Canada where they use TECK cable a lot and in the IEC world, single conductor power cables are the norm in larger sizes and most have a metal jacket. The CEC has special probvisions for termianting the cables to prevent circulating currents.

Laying cables in trefoil won't do any good because the armour is around each conductor. It would be like placing three conduits in trefoil arrangement with a 1/c cable in each conduit and expect that to cancel circulating currents. (Except the conduit is a better path for induced currents compared to the thinner spiral armor).

 

[Maders]

What will happned If I connect armour and Shield together to ground?

If your system has zero sequence ground fault protection, directly connecting the armor to the shield could compromise it.