What is the average field from a transmission
line?
The various graphs and tables
of fields from power lines show calculations for “typical”
values of current. An alternative is to take actual loads where
these are available.
The following table gives more detail on the average magnetic field
at various distances from National Grid lines. These figures were
calculated from one year’s worth of recorded load data and
are the average for a representative sample of 43 different lines
(a mixture of 275 kV and 400 kV).
| Distance m |
0 |
50 |
100 |
200 |
300 |
| Average Field µT |
4.005 |
0.520 |
0.136 |
0.034 |
0.015 |
Because these fields are calculated from actual load data, they reflect the actual degree of unbalance between the two circuits of a transmission line. More on the effect of unbalanced currents.
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