EGX_PROD_n6923390_191_Hollett_Road,_Noosaville_L53_SP163571

      J&P Richardson Industries Pty Ltd         -13-


5.0   METHODS FOR REDUCING MAGNETIC FIELD LEVELS


5.1   Background

      Magnetic field strength of a powerline is a function of a number of variables, including the
      current through the transmission circuits, the distance from the line, and the physical and
      electrical geometry of the conductors. As the current through the transmission lines
      changes with time, the associated magnetic field is a continuously changing parameter.

      The Electric Field strength is a function of the physical attributes of a line and the voltage to
      which the line has been energised. As such, the Electric field strength at a particular point
      will remain at the same order of magnitude over time.


5.2   Increasing distance from source

      As the magnetic field strength decreases as distance from the source increases, the
      separation from the distribution line to the habited areas should be maximised as far as
      practicable.

      It is noted that the net separation is a function of both the lateral and vertical ( ie due to
      conductor height ) offsets.


5.3   Conductor geometry and phase configuration

      Different arrangements of phase conductors can produce different magnetic field strengths
      for the same line current. Equilateral triangular arrangements tend to be the most
      favourable, producing more field cancellation than the common flat arrangements.

      With multi-circuit lines the careful placement of conductors with respect to phase can
      significantly reduce the net magnetic field. The example often used is the double circuit
      vertical construction diagonally phased (A-B-C on one side, C-B-A on the other).


5.4   Conductor compactness

      The compactness of a line can reduce the resultant magnetic fields by enhancing the field
      cancellation effect between the phases.


5.5   Load current reduction and balancing

      Load current can be reduced by supplying the load fed through the subject circuit by using
      an alternate route or increasing the supply voltage. These options are rarely available.


5.6   Undergrounding

      Undergrounding can be effective at reducing magnetic fields due to the very compact
      positioning of the respective phase conductors. However, because undergrounding is far
      more expensive than overhead construction, it does not often fall into the category of
      prudent avoidance.



      Hollett Road EMF Study                                                             V1.0