Screened MV connection 1

[rzgpp]

Hi all!
It is not clear and I can't find instruction about core balance current transformer and screen connection of MV termination.Ground wires of cable are routed back throught Core balace current tranformer....do we need to do the same for cables which earth semiconductive layer of cable termination?Termination is Nexans euromold..
Thanks!

 

[7anoter4]

I think you have to do it, I'm afraid.

 

[mvcjr]

Good day!

My humble opinion:

A. If the ground wires are not routed back through the core-balance current transformer, the set-up could not detect phase-to-ground faults.

Total I = Ia + Ib + Ic + Ig = 0

B. If the ground wires are routed back through the core-balance current transformer, the set-up could detect phase-to-ground faults.

Total I = Ia + Ib + Ic + Ig - Ig ≠ 0

 

[davidbeach]

Oh, you can certainly detect and trip for ground faults if you don't route the grounds back through the CT. Ground faults here, there, and most anywhere except on the circuit in question. A bit of GPR putting a bit of current on the ground and you get a trip. Seen that several times over the years.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[7anoter4]

I agree with you, davidbeach !

 

[rzgpp]

Thanks all.Maybe I am not clear enought.Ground wire of power cable must be routed back throught core balance transformer...It is not clear for me.....ground wire of cable termination......from semiconductive layer of cable termination....do I need to route back?...or just connect to ground?

 

[7anoter4]

This CT will not "feel" the phase grounding, indeed, but there are other means to "feel" that.

 

[7anoter4]

At the second glance the conductive layer in the EUROMOLD picture it is the semiconductive layer on the conductor it self and it is not grounded. The semiconductor layer on the insulation under the shield is grounded together with the shield and this is connection to grounding[11] you have to introduce it back through the CT. I apologize for my confusing. This connection to ground [10] it is only to ground the EUROMOLD outer surface.

 

[7anoter4]

wrong sketch.

 

[rzgpp]

7anoter4..thanks..but my question is for [10] on this sketch.Do we need to route back wire from outer semiconductive surface?Is it better for relay protection ?

 

[7anoter4]

Certainty ,you don’t need.

 

[rzgpp]

Thanks a lot!