400 V overhead lines: magnetic field
see also:
400 V lines are mostly carried on wood poles with four (or sometimes
five) wires in a vertical array. At 400 V, the magnetic field depends
as much on the net current as on the load current.
The maximum field shown here is produced when the ground clearance
is the minimum allowed – 5.5 m. The maximum loads assumed
are 200 A load current and 10 A net current but higher values might
exceptionally be found.
Typical fields are lower than the maximum field because the clearance
is usually higher and the loads are usually lower. This graph is
for 8 m clearance, load current 50 A and net current 5 A.
Sometimes, the separate conductors are insulated and twisted together,
called “aerial bundled conductors” (abc). Then the fields
are even lower.
| 400 V open wire: |
400 V abc: |
 |
 |
This table gives some actual field values for the same conditions.
| |
magnetic field in µT at distance from centreline |
| maximum under line |
10 m |
25 m |
50 m |
100 m |
| 400 V |
wood pole |
vertical array 50 mm2 |
maximum |
clearance 5.5 m
single circuit
load 0.2 kA
net 0.01 kA@90° |
1.227 |
0.277 |
0.088 |
0.041 |
0.020
|
| typical |
clearance 8 m
single circuit
load 0.05 kA
net 0.005 kA@90° |
0.215 |
0.099 |
0.041 |
0.020 |
0.010 |
Note:
1. All fields calculated at 1 m above ground level.
2. All fields are given to the same resolution for simplicity of
presentation (1 nT = 0.001 µT) but are not accurate to better
than a few percent.
3. Supplies to single houses could be carried on different arrangements
of conductors which could produce different fields.
|
