WG C4.28 Extrapolation of measured values of power frequency magnetic fields in the vicinity of power links

Background :

In the past few years, important works have been conducted within CIGRE SC C4, aiming at characterizing ELF magnetic fields (TF C4.205) and improving measuring techniques (TF C4.203).  Nevertheless, magnetic fields measurements (even when following the best recommended practices as established by CIGRE) are only a limited sample, a “photography” of the magnetic environment at a given time.

As a matter of fact, measurements are not sufficient to describe all the characteristics of magnetic fields with regard to human exposure. In practice, the question often raise about the meaning of measured values, and their adequacy to describe or define the “real” level of exposure. Therefore, a “post-processing” of the measured values is often needed to offer a more complete answer to the question of the exposure of people neighboring power lines.  This means that measured values have to be extrapolated to other values which are supposed to be more relevant in characterizing people’s exposure to EMF.  The first question is therefore to determine the relevant reference value(s) of the current flow: in addition to general considerations developed by CIGRE TF C4.205, particular cases such as mixed overhead/buried lines have also to be considered.   

Moreover, even if the magnetic fields is directly related to the current flowing in a power line, the extrapolation is simple only when the line configuration is simple (i.e. single circuit lines) and when its geometry does not change with its temperature (such as for buried cables). In the contrary,  there are many situations where a simple linear extrapolation based on values of flowing currents would result in important biases, such as double circuit overhead lines with different currents in the circuits, or “low” overhead lines, for which the sag variation due to the increase of the conductors temperature must be taken into account.

Scope :
  1. To discuss the possible values of the current flow to be used as reference for extrapolating measured values of power frequency magnetic fields   
  2. To propose different extrapolation methods  applicable to simple (single buried lines) or complex  (multiple circuits) configurations.
  3. To assess the various correction factors and uncertainties to be associated with the different extrapolation methods.
Deliverables :

Report to be published in Electra or technical brochure with summary in Electra

Convener: P. Rojas (Brazil)

Progress Report 2013 (pdf, 57kB)


Progress Report 2014 (ppt, 369kB)