How rapidly do EMFs reduce with distance from powerlines?
18.1 At public inquiries industry bodies have provided data showing rapid fall off based on ideal theory. Under ideal conditions of perfect balance in the three phases of a circuit, and further under perfect balance between two circuits on a phase-transposed double-circuit line, magnetic fields can be shown to tend ultimately (asymptotically) to an inverse-cube relation with distance, but this isn’t achieved in practice. The idealised assumptions are clearly broken, with loss of phase- and circuit-balance. That makes a lot of difference at far distances. Nevertheless, there is sufficient balancing, with its partial cancellation of fields, that the theoretical calculations match measured data within the first 100 metres. 18.2 National Grid’s EMF expert John Swanson has kindly posted (2008, on www.emfs.info ) some helpful notes on the rates of fall-off of magnetic fields from powerlines with distance from the lines. The notes confirm that the ideal inverse-cube fall-off is not achieved f
