LIGHTNING PROTECTION USING LFA-M
CONTENTS INTRODUCTION WHAT
IS A LIGHTNING STROKE? TYPES OF LIGHTNING STROKES. WHAT IS LFA-M? HOW LIGHTNING AFFECTS OVERHEAD TRANSMISSION? HOW CAN IT BE PROTECTED? CONCLUSION
Lightening can be serious….not only for overhead lines but also for human lives….
WHAT IS LIGHTNING STROKE? Lightning
is an electrical discharge between cloud and earth, between clouds or between the charge centers of same cloud.
Lightning
is a huge spark that takes place when clouds are charged to a high potential with respect to earth object (e.g. overhead lines) or neighboring cloud such that the dielectric strength of the neighboring medium (air) is destroyed.
TYPES OF LIGHTNING STROKES DIRECT
STROKE INDIRECT STROKE
DIRECT STROKE
Lightning discharge is directly from cloud to 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.
DIRECT STROKE- types
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. STROKE-B – Lightning discharge occurs on overhead line due to stroke-A.
INDIRECT STROKE
Results from electrostatically induced charges on the conductors.
(+ve) ly charged cloud induces (-ve) charge right under the cloud on the line and (+ve) charge away from it.
When cloud discharges to earth, (-ve) charge rushes along both directions in form of travelling wave.
Most common.
PREVIOUSLY…. Pole-top
arresters were used to protect distribution line from induced voltage flashovers.
It
was recommended to install an arrester at every insulator.
Very
costly.
What is LFA-M?
Long flashover arrestors are those devices which capture the high voltage sparks resulting out of lightening.
”M” indicates that LFA-M is for the protection of medium overhead transmission lines.
It can be applied for lightning protection of overhead distribution line against both induced over voltages 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.
Performance data of LFAM10-0,4 Voltage rating, kV 10 Flashover length, cm 40 1.2/50 μs impulse flashover voltage, kV 120 Impulse protection level, kV* 500 Switching overvoltage impulse withstand voltage, kV 100 Power frequency withstand voltage, kV - clean dry .................. - clean wet ................. - polluted wet, at 20 μS specific surface conductance .................. 70 40 30 Arc extinction current at
How does LFA-M protect the overhead lines?
First, a lightning impulse causes a spark over of the spark gaps Next, the semiconducting core of the upper cable piece, whose resistance , carries the high potential to the surface of the lower piece at its middle. Similarly, the semiconducting core of the lower piece of the same resistance applies the low potential 0 to the surface of the upper piece, also at its center. Thus the total voltage is applied to each flashover module at the same moment, and all the three flashover modules 1, 2 and 3 are assured conditions for simultaneous initiation of creeping discharges which,with respective modules flashed over, develop a single long flashover channel
CONCLUSION
The LFA-M is a simple, low weight and convenient apparatus.
THANK YOU
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