WELCOME LIGHTNING PROTECTION USING LFA-M Submitted By:Somi.P. Chacko Class: S7-EEE Roll no: MCET CONTENTS. Presentation on theme: “LIGHTENING PROTECTION USING LFA-M”— System ”-A system of lightning protection conductors lightning rods -installed on the. effective and inexpensive method for lightning protection of medium voltage overhead distribution line is using long flashover arresters (LFA).
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When the cloud discharges to earth or to another cloud, negative charge on the wire is isolated as it can not flow quickly to earth over the insulator. From the line, current path may be over the insulators down to the pole to the ground. Its resistors assure application of the total arrestor-stressing voltage simultaneously to all the modules.
Before flash over, the uing resistance of the arrester can be assumed to.
The over voltage setup due to the stroke may be large enough to flashover this path directly to the ground. Takes place when clouds are charged to a high potential Electrical discharge between a cloud and earth A huge spark 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.
It protects from 0.
LIGHTENING PROTECTION USING LFA-M – ppt video online download
If the channel length is greater or equal to the module length, a flashover is assumed to have occurred for that particular module and the equivalent arrester resistance abruptly becomes equal to the resistance of the respective semi conductive cable section.
Where n 0 is the number of lightning outages on an LFA protected line caused by direct lightning strokes on the phase conductors and P I lcr is probability of a lightning current with steepness greater or equal to I lcr The efficiency of LFA lightning protection against direct lightning strokes can be expressed as the ratio of the number of lightning outages n 0 for unprotected line to n 0 for lines protected by LFA arresters.
As illustration, let us consider the operation of phase A arrester. An LFA mounted on the top phase must flash over before the top phase insulator.
Share to Facebook Share to Twitter. Are not stressed by operational voltage and do not require maintenance. Systems that provide an increased zone of protection Systems that eliminate lightning strikes altogether. Due to long flashover path, a flashover does not give rise to a power arc as the arc extinguishes when the power frequency current crosses zero. Each cable piece has a semi conductive core of resistance R. The rate of decrease of the critical gradient slows down for pfotection fault currents.
Provides a low-impedance path for the lightning current to lessen the heating effect.
LIGHTENING PROTECTION USING LFA-M
Where U l is the maximum operating line voltage; E cr is the critical gradient of the power frequency voltage that rules out PAF. In stroke A, the lightning discharge is from the cloud to the subject equipment e. As indicated before, the coordination of arrester LFA A is not depend on the grounding resistance because The pole does not get involved in the path of the lightning current until the insulator or the arrestors have flashed over.
The flashover length, L is greater for lines with wooden structures rather than steel or concrete structures, because wooden Cross-arm increases the flashover path. It keeps increasing at a still slower rate until time t 3.
Due to a special inner structure the LFA impulse flashover voltage is lower than that of the insulator and when subjected to lightning overvoltage the LFA will flashover before the insulator.
It was assumed to be equal to zero. Due to different propagation rates of flashover channels for lightning impulses of positive and negative polarity, the first module to flashover is module 1 with a flashover. If a positively charged cloud is above the line and induces a negative charge on the line by electrostatic induction.
From the short analysis presented above, it is clear that it is possible to improve the protection against lightning by increasing the length of lightning flashover path.
Due to long flashover path, a flashover does not give rise to a power arc as the arc extinguishes when the power frequency current crosses zero.
The direct stroke can be of two types 1. The voltage-time characteristics of the arresters and insulators can be approximated by the expression. For the protection of lines lkghtning direct lightning strokes, the arresters are connected between the poles and all of the phase conductors in parallel with the insulators.
Thus, t tr is larger than t cr.
A new simple, effective and inexpensive method for lightning protection of medium voltage overhead distribution line is using long flashover arresters LFA. In stroke B the lightning discharge occurs on the overhead line as the result of stroke A between the clouds.
The above calculation does not take into account the effect of near-by poise: The lightning protection failed. It is designated as LFA-M. Where k is the outage reduction factor of lightning outages caused by direct lightning strokes. How lightning is formed. The efficiency of LFA lightning protection against direct lightning strokes can be expressed as the ratio of the number of lightning outages n 0 for unprotected line to n 0 for lines protected by LFA arresters.
A heavy impulse current flows through the flashover channel, the pole, and the pole footing resistance resulting into a large sharp voltage rise at the cross-arm. Upload from Desktop Single File Upload. The cable pieces are arranged so as to form three flashover modules 1,2,3 as shown in figure1.