Calculating and measuring fields from power lines

If you know the geometry of the line and the currents (or voltages for electric fields) it is possible to calculate fields quite accurately.

Often, it is acceptably accurate to approximate the conductors as infinitely long straight lines and to approximate the currents as exactly balanced (the three currents in the three phases exactly equal).

If necessary, however, you can model the actual sag of the conductors and the actual currents in each conductor (more on unbalanced currents). The results from this exercise are shown here. The red dots are the measured magnetic field, the blue line the calculated magnetic field for the same instant of time. This comparison has been published in a scientific journal.

Power-line calculations and measurements are usually performed for 1 m above ground.  This is for a sound scientific reason explained here.

If you want to calculate fields yourself we provide dimensions for some common UK power line designs here.