| Lightning
Protection Using LFA-M
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Introduction
A
new simple, effective and inexpensive method for lightning protection of medium
voltage overhead distribution line is using long flashover arresters (LFA). A
new long flashover arrester model has been developed. It is designated as LFA-M.
It offers great number of technical and economical advantages. The
important feature of this modular long flashover arrester (LFA-M) is that it can
be applied for lightning protection of overhead distribution line against both
induced overvoltages and direct lightning strokes. The induced over voltages can
be counteracted by installing a single arrester on an overhead line support (pole).
For the protection of lines against direct lightning strokes, the arresters are
connected between the poles and all of the phase conductors in parallel with the
insulators.
Lightning is an
electrical discharge between cloud and the earth, between clouds or between the
charge centers of the same cloud. Lightning is a huge spark and that take place
when clouds are charged to at a high potential with respect to earth object (e.g.
overhead lines) or neighboring cloud that the dielectric strength of the neighboring
medium(air) is destroyed. TYPES OF LIGHTNING
STROKES There are two main ways in which
the lightning may strike the power system . They are 1.
Direct stroke 2. Indirect stroke Direct
Stroke In direct stroke, the lightning
discharge is directly from the cloud to the an overhead line. From the line, current
path may be over the insulators down to the pole to the ground. The over voltage
set up due to the stroke may be large enough to flashover this path directly to
the ground. The direct stroke can be of two types 1.
stroke A
2. stroke B In stroke A, the lightning
discharge is from the cloud to the subject equipment(e.g. overhead lines). The
cloud will induce a charge of opposite sign on the tall object. When the potential
between the cloud and line exceed the breakdown value of air, the lightning discharge
occurs between the cloud and the line.
In
stroke B the lightning discharge occurs on the overhead line as the result of
stroke A between the clouds. There are three clouds P,Q and R having positive,
negative and positive charge respectively.
Charge on the cloud Q is bound by cloud
R.If the cloud P shift too nearer to cloud Q,Then lightning discharge will occur
between them and charges on both these cloud disappear quickly. The result is
that charge on cloud R suddenly become free and it then discharges rapidly to
earth, ignoring tall object.
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