Metrics to characterise time varying potential gradient disturbances caused by corona ions from high voltage power lines.

J C Matthews and D L Henshaw

High voltage power lines are known ionise the air producing corona ions which can be carried by the wind away from the line in clouds of space charge. This causes a modification of the Earth’s natural potential gradient (PG). Corona ions are implicated in two hypotheses to explain the increase of childhood leukaemia found within 600 m of high voltage power lines [Draper et al. 2005]. Charged ions can attach to aerosols in the atmosphere, including pollutants, increasing their charge state. If pollutants with an increased charge state are inhaled, it is suggested that they are more likely to deposit in the lung due to image charge effects [Henshaw 2002]. The Earth has a natural PG caused by global thunderstorm activity keeping the ionosphere at a raised potential compared to the ground. This causes a natural fair weather PG in the region of ~ 100 V m-1. In precipitation, or when there is cloud cover, the PG is more changeable. Fluctuations caused by corona ions have been hypothesised to affect human circadian rhythms inhibiting the body’s natural defences [Henshaw et al. 2008].

A fixed site monitoring station has been installed near to a 400 kV high voltage power line which measures the vertical PG fluctuations caused by corona ions. This monitoring station continuously records the PG at 1 s intervals and allows the time structure to be compared in different conditions. As there is a large volume of information, metrics need to be chosen that can be compared to the weather conditions in order to ascertain what effect the weather has on the production and transport of corona ions.

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