Fields from underground DC cables

We give here graphs of the typical static magnetic fields produced by underground cables.  More on sources of static fields and on static fields generally.

These calculations are for a typical design of cable such as would be used in the UK to connect an undersea cable to the convertor station.  This design has two cores, spaced 0.5 m, 1 m deep, carrying 2000 A at +/- 500 kV.  (These are typical for underground cables.  Subsea cables would typically have the same electrical characteristics but would be spaced further apart.)

 graph of field from hvdc cable

This field combines with the earth's static magnetic field, which has a magnitude of about 50 µT in the UK.  How the two fields combine depends on the relative direction of the fields, which in turn depends on the direction of the cable.  The following graph is for the cable running north-south:

 graph of combined field

see also the effect of this field on compasses.

For this particular cable and this particular orientation relative to the earth's field (taken as exactly 50 µT) the values are:

 

 magnetic field in µT at horizontal distance from centreline
0 m5 m10 m20 m
+/-500 kV, 2 kAdirect buried0.5 m spacing 1 m below groundfield from cable49.236.911.920.50
combined field from cable and earth's field96.945.7748.4049.56
compass deviation / degrees012.72.00.3