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BACK FLASHOVER

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by

raj shekhar

on 17 October 2014

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Transcript of BACK FLASHOVER

BACK FLASHOVER
CONTENTS
1.Introduction to lightning and its charecteristics
2.Types of impacts on transmission system
3.Back Flashover & its magnitude calculation
4.Parameters affecting backflashover voltage
Tower footover resistance
Striking distance
Peak of lightning current
Front time & Tail time
5.Effects of surge on sytem
6.Protection methods
7.Future scope
8.Conclusions
9.What do we need to do as engineers
INTRODUCTION TO LIGHTNING
CHARACTERISTICS OF LIGHTNING
EFFECTS OF LIGHTNING
TWO TYPES OF IMPACTS
BACK FLASHOVER
CALCULATION OF BACK FLASHOVER VOLTAGE
EFFECTS OF SURGE DUE TO B.F.O
METHODS OF PROTECTION FROM
BACK FLASHOVER
FUTURE SCOPE
WHAT DO WE (ENGINEERS) NEED TO DO
a brilliant electric spark discharge in the atmosphere, occurring within a thundercloud, between clouds, or between a cloud and the ground
Static Electricity
Ultra-High Voltage Generation
The Discharge
Surface Dispersion
Basic Laws of Electricity

Static Electricity
Separation and storage of electrical charge
A spark is an extremely small lightning discharge



Ultra-High Voltage Generation
Surface of earth is normally negatively charged
Top of storm clouds are positively charged
Forces nearby earth to become positively charged
Develops a multimillion-volt potential

Clouds send negative charged leaders down

Earth sends positive leaders up
From grounded sharp metal objects



Conducting path when leaders meet
Unidirectional (DC) current flow
Voltage potential 100 to 1,000 million volts
Current range 10,000 to 200,000 amperes
Duration from 1 microsecond to 1 second
BASIC LAWS OF ELECTRICITY

Lightning creates magnetically induced current in all metal items within its influence
The longer the wire, greater the current
The closer the strike, greater the current

Any impedance to current flow results in
Build up of high voltage at that location
Resulting in arc-over to reach ground
Ignites flammable material
Vaporizes metal of insufficient cross-section

Suges , flash overs
Back flashovers
Damage to trees,humans,animals,property
Damage to power system
Back flashover is a phenomenon in which flashover takes place from tower structure to the conductor across the insulator
IF the earth resistance of tower is considerable and is struck by lightning then voltage build across the tower top will be
Damage to the crucial equipment
Damage of conductors due to excess heating due to high current flow
Temporary blackouts

Surge Arrestor
Usage of superconductors
Proper switchgear setup
Proper insulation co ordination is very important
PARAMETERS AFFECTING BACKFLASHOVER DUE TO
LIGHTNING

Tower foot resistance
Striking distance
Peak of lightning current
Front time of strike
Tail time of strike
Parameters of ground system
Impact on ground wire
Impact on conductor directly
Research on insulation coordination
Develop better standards
Improvement of existing methods
Better design to minimize flashover is requiered
Reduce cost of insulation by reducing BIL
Improve insulation standards

STRIKING DISTANCE
EFFECT OF FOOT RESISTANCE
PEAK OF LIGHTNING CURRENT
FRONT TIME & TAIL TIME
CONCLUSION
High tower foot resistance will lead to more backflashover
High line currents will lead to more backflashover
High Front time will raise the backflashover
Tail time has no significance effect
A
PRESENTATION
BY
G.RAJASHEKHAR REDDY
[10621A0216]
K.AKSHAY KUMAR
[10621A0223]
FACTORS AFFECTING
Full transcript