Advice regarding cable routing on underground cable duct 1

[JuanBC]

Hello, I would greatly appreciate your advice on the following

Scenario:

- Standard: IEC
- Power cable type: Armoured XPLE/PVC 1.1 kV (LV)
- Routing: underground cable duct on concrete (Power and Instrument cables in different tubes BUT in same duct)

Question:

Shall I use PVC or galvanised steel tubes?
Why?

Some colleagues here are justifying the use of galvanized steel tubes to avoid "noise", but the cable is already armoured

Thank you very much!

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

 

[ScottyUK]

I'd use PVC tubes in an underground application. The real strength of the ductbank is the concrete surround, so the additional strength of steel adds little.

Galvanised steel tubes would help with capacitively coupled interference, but the steel armour will have a similar effect and the instrument cables should be shielded (if capacitively-coupled noise matters to the instrument guys).

Neither the steel tube, the steel armour nor the shield will help with magnetically-coupled interference but if you're using multicore power cables with all circuit conductors in one cable then the external magnetic field in the mid-field and far field is relatively low. For any magnetic interference the best solution is to keep the loop area small to minimise the external field, and the second-best solution is to get as far away from the magnetic source as possible.

 

[JuanBC]

Thank you Scotty.! Very clear as always

Any idea if there is an IEC standard related to this topic? Thanks!


JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

 

[7anoter4]

I agree with Scotty .For power cable we use 6" PVC 80 grade but for instrument and communication
cables we use steel. A grounding cable of bare 95 sqr.mm copper is following the duct and it is connected to the manhole cable rack and stairs. A distance of 250 mm center-line to center line has to be provided between ducts[or pipes] and no rebar beteen ducts is recommended-in order to avoid heating by induction. The outer side of the duct bank has to be reinforced.
In power stations-never-the less we are following IEC standard for cables- the U.S.A. standards as IEEE or ANSI are considered more suitable for cable duct bank.
IEC 60364-5-52 [it is close to BS7671, in my opinion] they are some indications.
You may start with-for instance:
NSTAR Electric CONSTRUCTION STANDARD ELECTRIC OPERATIONS ORGANIZATION
DISTRIBUTION DUCTBANK CONSTRUCTION AND MATERIAL

https://www.eversource.com/content/docs/default-source/ema---pdfs/c1100.pdf

 

[7anoter4]

Sorry.The "distance center line to center line" has to be only " the clearance".
Center line to center line will include the duct [pipe or conduit" overall diameter.

 

[JuanBC]

Thank you 7anoter! I'll start with that!

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"