HVDC link earthing 1

[Foudrette]

Hello,

I would like to know what is the best way of earthing of a HVDC cable (connecting to converter stations in a monopolar mode). The way of laying is to place the screened underground power cable close to the screened return cable.
I have seen that in some cases, it was solidly earthed at both ends and in other cases the single point earthing was used.
What is in your opinion the best solution ? Advantages, disadvantages.
Total length of cable is above 30km.

Thanks for all of your help and...Merry Christmas !

Foudrette

 

[cuky2000]

The return current in monopolar application is the earth. Therefore, the return cable could represent significant saving in the initial capital investment of the project. On the other hand, for short lines this obvious saving need to be carefully evaluated again the mitigation effort to solve environmental issues, additional installation required and possible reduction in system reliability/availability as follow:
- Corrosion acceleration in pipelines and other underground metallic objects even at considerable distance is a concern for inland installation. For submarine crossing, there is a possibility to generate poison chlorine gas.
- Additional real state and O&M cost required maintaining the electrodes at each converter station.
- The system reliability of the monopolar system solely relies on the single cable availability while in bipolar designs the system could be operated in monopolar mode temporarily.

 

[Foudrette]

Thank you very much for your detailed explanations.

I understand that if environment is a big issue for the involved project, we need to install an underground return cable.
We plan to ground such cable systems at both ends as no induced currents are generated under DC. But, I have seen in another case that it was grounded at only one end (Swepol project). I wonder why ?

If you have any idea please let me know,
With my best wishes,

Foudrette

 

[cuky2000]

The primarily reason to ground the system at one end is because the ground resistance is normally much lower than the metallic resistance. If both ends are grounded, the current will follow the least resistance path creating the environment effect described in the above post.
Grounding one end provide reference voltage and simplify the requirement for DC commutating switching devices and their duty during high-speed transfer from bipolar to monopolar operation mode.
I hope this could help to clarify your question

Marry Xmas + Prosperous 2005.

 

[Foudrette]

Thank you very much Cuky !

Now I see the explanation, it seems obvious to me !
But however, I was looking for an explanation for a long time, I have read many papers, but unfortunately nothing about the earthing was described.

Thanks a lot once again,
Foudrette