The BritNed grid cable

[Cantata]

You've probably heard about the 'BritNed' power cable that is being laid from the Isle of Grain (Medway entrance) to the Netherlands, the idea being to connect the two countries grids together and pump power in either direction as required. Actual cable-laying has just begun.
Instead of AC, as used on overhead grid cables, this is going to be HVDC, direct current.
Won't this generate a stupendous magnetic field around the cable that will affect compasses etc for quite a large distance?
Any experts out there with an answer?

 

[MoodySabre]

From this website

"The earth’s magnetic field originates from large convective DC currents in its interior. This natural magnetic field varies from between 30 to 60 μTesla for different latitudes on the earth’s surface. The same type of magnetic field is produced by an HVDC Light cable, and is not considered unhealthy to the human body.

A DC cable will generate a magnetic field of between 5 and 10 μTesla one meter above the ground surface. This will then be superposed to the natural magnetic field of the earth, which is much the same as saying that the magnetic effect from a DC cable corresponds to traveling from the south to the north of the earth. This is not considered dangerous from a magnetic point of view."

Is that a no? Sounds like a no.

 

[Cantata]

"A DC cable will generate a magnetic field of between 5 and 10 μTesla one meter above the ground surface"
Doesn't it depend on the strength of the current flowing??

 

[MoodySabre]

Try this then (from a different website):

"2.2 Low magnetic field
HVDC Light® cables are laid in pairs, usually close together. As they carry the same current levels in opposite directions, the static magnetic fields from the cables largely cancel each other out. Figure 2 demonstrates a bipolar DC system in which currents are flowing in opposite directions. Cancellation occurs where the magnetic fields (as denoted by the blue and red arrows) overlap. The resulting magnetic field decreases rapidly toward zero with distance from the cables.

Figure 2: Diagram of a bipolar DC system.

(Can't get this on here but it is two wires side by side and the field from one rotates clockwise and the other anti-clockwise)

The resulting static magnetic field is similar in magnitude and character to the Earth’s natural magnetic field. Static fields, by definition, do not fluctuate (unlike the fields associated with AC transmission lines) and do not induce currents in nearby objects as fluctuating magnetic fields are known to do."

Back to painting the house, trying ignore blue skies, sunshine, sparkling seas and gentle breeze

 

[Cantata]

Oh all right, I'm off to Tesco for the weekly shop then and I'll stop worrying.

 

[shmoo]

That is how the cables between Folkstone and France work and I have watched the compass carefully going over them (and the cutlery in the galley) - no effect whatever. Dull really.