Grounding Concentric Neutral for 28kV Power Cable

[veman]

Hi,

We've found a relatively new cable installation where 2 underground feeders have been installed to service an industrial park. The cable is 750MCM Cu, 28kV concentric neutral, 3 conductors per circuit. The system voltage is 27.6kV. A separate 350 MCM Cu neutral has been installed and grounded at all switching locations.

The problem is, the concentric neutral has been connected to 3kV arresters at all locations, including the underground dip poles supplying the park. My thought is that each piece of cable should have one end of the CN solidly grounded and the other tied to an arrester to allow for the best ampacity and limit the induced shield voltage during a fault.

Any thoughts?? And thank you in advance....

 

[davidbeach]

A concentric neutral is strands of wire around the main insulation of the main conductor and is intended to be a current carrying conductor. May be 33% for use on 3 phase circuits or 100% for use on single phase circuits.

A shield is copper tape around the main insulation of the main conductor is NOT intended to be a current carrying conductor.

Your description of what you have is unclear. Do you have a concentric neutral or a shield?

 

[veman]

Our standard cable is concentric neutral. Sometimes we use the neutral for unbalance current and sometimes we open it at one end to increase the ampacity but this always involves us having to install a separate neutral conductor. I haven't seen this configuration we've found with both ends of the neutral open, connected to arresters....