05-09-2012, 03:44 PM
Lightning Protection of Distribution Lines by Long Flashover Arresters (LFA)
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.4bstract -
The paper describes a new method of
lightning protection of overhead distribution lines by
Long Flashover Arresters (LFA) which were invented
and developed by the authors. The LFAs are low - cost
arresters which are installed in parallel or in series to
the line insulators.
An Insulator with characteristics LFA (ILFA) is also
presented. With the use of LFAs or ILFAs the number
of line outages may be drastically reduced, The LFA
principle, its main applications and some laboratory test
results are presented.
INTRODUCTION
Outages of overhead power lines due to lightning strokes
is one of the main causes of shortages of electric supplies
and economic losses of power utilities.
A previous study [ 11 has concluded that widely separated
pole-top arresters can effectively protect a distribution line
from induced-voltage flashovers.
In order to prevent arc fusion of insulated conductors on
distribution lines due to lightning flashovers it is
recommended to install an arrester at every insulator.
Millions of metal - oxide arresters are already installed in
Japan and more will be installed in the future [2].
The main problem of using pole-top arresters is their
high cost. For mass application of arresters for 1ightn.ing
protection of overhead distribution lines an arrester must
be cheap, reliable with no need for maintenance.
MAIN APPLICATIONS
Fig. 1 presents an LFA installed on a distribution pole. A
piece of rigid insulated coaductor (it can be a steel rod
covered with insulation) is connected to the pole with a
clamp. A metallic tube is placed over the insulated
conductor in its middle part. The metallic tube forms with
the line conductor a sparkover air gap, S.
The insulated conductor is at the same potential as the
pole Due to relatively big capacitance between the metallic
tube and the insulated conductor the tube is practically at
the same potential as the pole. Therefore an overvoltage
which appears between the line conductor and the pole
will be also applied between the metallic tube and the line
conductor. If the overvoltage is large enough, the sparkover
gap S will breakdown and the overvoltage will be applied
between the metallic tube and the insulated conductor to its
insulation.
DISCUSSION
Effective protection of distribution lines against lightning
overvoltages is best achieved when arresters of any type
(metal-oxide, protector tubes, etc.) are placed at each pole
aiid phase. For protection of lilies with insulated conductors
it is also necessary to install arresters in parallel with each
insulator [%I.
Due to the high cost of metal - oxide arresters some other
options were investigated, for example placing one arrester
at each pole, or three arresters every third pole etc. It is
obvious that these alternatives are less effective than the
installation of arresters at each insulator.