Lightning Radiated Electric Fields and Their
Contribution to Induced Voltages
M. G. Sorwar and I. G. Gosling
Nanyang Technological University
School of EEE, Nanyang Avenue
Singapore 639798
Abstmct- During the return stroke, the radiated electric
field from a lightning channel contains vertical and horizontal
components of electric fields, which are both responsible
for producing transients in power lines, telecommunication
lines, and electronic circuitry of communication and control
systems. This paper analyses the characteristics of the vertical
and horizontal components of electric field depending on
different parametric conditions of the return stroke. Lightning
induced voltages on an overhead telecommunication
line are also calculated for different elemental fields. The numerical
results show that horizontal electric field (HEF) produces
high ringing of fields at distances far from the strike
point, and plays an important role in producing induced
voltages in the vicinity of the lightning channel. The radiation
and the induction components of fields are found to be
responsible for the change in polarity of induced voltages.
I. Introduction
Lightning is a natural source of electrical intcrference. It
is caused by an accumulation of charge on clouds, which,
when sufficient potential (minimum 3 x 106V to maximum
1Ol0V) is reached with respect to the ground, breaks down
the air insulation gap and a discharge spark results. During
lightning discharge a pulse current with fast rise time and
high peak moves between ground and cloud with a high
velocity. This moving current pulse radiates electromagnetic
radiation of very high energy into the surrounding
medium. The radiated electric field comprises two component
fields: the vertical electric field (VEF) and the horizontal
electric field (HEF). Both the VEF and the HEF
are important in coupling calculations, for example to determine
the lightning induced overvoltages appearing on
electric utilities’ or telecommunication lines when lightning
occurs nearby. Much research has been conducted to investigate
the coupling effect in power or telecommunication
lines due to lightning radiated electric fields[l-81. However,
it is important to investigate the role of elemental fields
in producing induced overvoltage. Firstly, we analyse the
characteristics of the elements of both fields as a function
of strike distance. The change in electric fields for different
channel heights and observation point heights of the
return stroke are also calculated. Finally, the individual
contributions of the elemental fields in producing induced
voltages in an overhead telecommunication line is considered
within the scope of this paper. The integro-differential
expressions for electric fields at a point above the ground
havc been solved using the integral equation method. The
induced voltage calculation follows the model of Agrawal
et al.[l] to consider both the VEF and the HEF.
0-7803-5057-W99~$10.00 0 1999 IEEE
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