500 kcmil Static Umbilical submarine cable for FPSO (Floating production storage and offloading) 2

[Oblsss]

Hello everyone,

I came across the attached specification for MV power cables used in FPSO applications.
My experience is limited to the onshore industry and I can not find the use of the 6 ground wires located in the interstices between the 3 MV shielded power cores.

A large fault current could have been dealt with the use of large cross-section metallic shields or even in combination with the cable armor via a semiconductive armor bedding layer.
I was thinking that they can be used to make an equipotential bonding of a large number of metal parts that are not connected to a common earth grid.

Is there anyone who knows the theory behind these cables design or can refer me to a document that describes the electrical characteristics of an application that uses them?
Ι am trying to find alternative designs that could be used as this specification is quite old.

Thank you in advance,

George

 

[Oblsss]

Any information you can provide me would be greatly appreciated.

Please feel free to ask if you need any further information.

Thank you in advance,

George

 

[FacEngrPE]

Shovel and mining cable, also used for crane (ship loading, and shipbuilding yards) trailing cable has a similar construction. Example

https://generalcable.com/na/us-can/products-solutions/specialty/mining-cable.

These products top out at about 15kV

https://www.nsw.com/en/cable/submarine-power-cable/

has some illustrations that look similar to the ones in your cut sheet. There is also a statement that implies marine cable is mostly custom built.

I think you should assemble a short list of vendors you think you can work with, sent them the requirements, and see what they respond with. Once you get to custom cable in reasonable run lengths all sorts of things are possible. Early in the process you should determine what standards apply to the landing points. One end might be NEC, the other end might be USCG, or API, it might be important to your requirements.

Fred

 

[jraef]

The theory behind having the multiple nested ground conductors is based on having a fixed symmetric geometry of the ground conductor's relationship to the power conductors. Fixed geometry cable (cable that keeps the spacing and orientation of the individual conductors constant) offers significant advantages over asymmetric conductors, including reduced cross-coupling noise and insulation stress. I don't know all the details, but I do know that the basics are involved with Transmission Line Theory if you want to research that.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Oblsss]

Thank your for the answers!

@jraef

[highlight #FCE94F]is based on having a fixed symmetric geometry of the ground conductor's relationship to the power conductors. Fixed geometry cable (cable that keeps the spacing and orientation of the individual conductors constant) offers significant advantages over asymmetric conductors, including reduced cross-coupling noise and insulation stress.[/highlight]

I'm not sure I understand what you are describing, however everything you mention can be achieved solely with a three-core cable with metal shielding/concentric neutral per core.
If you see the attached pdf, the cable in question already uses a copper tape per core as a metal shield which would have resulted in a symmetric cable both geometrical and electrically speaking.

Am i missing something?

George

 

[cuky2000]

Is not uncommon to design an umbilical cable with full neutral size for application with a VFD pump or another motor load. One of the reasons for the oversize neutral is to reduce the impedance to mitigate electromagnetic interference (EMI), high-frequency electrical noise, minimize peak overvoltage due to static capacitance, avoid potential neutral overheating, and other safety and performance considerations, especially for longer cable length.

Below is an illustration of the cable indicating that just the grounding cable represents 72% of the 500 kcmil phase conductors. If the armored cable is added and other smaller grounding tapes, there is a good possibility that the cable is rated 100% neutral similar to the phase conductor.
The enclosed link and the illustration below contain some of the features used for an umbilical application that we hope helps to clarify some of your inquires.

 

[Oblsss]

@cuky2000

Excellent summary of the subject in the attached slide.
I have noticed the specific notes in other threads as well, i.e. "abe's Personal notes".

Forgive me for being "rude", but is there a way you can share them with us?

Thanks for the answer,

George