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Lightning and Power
Transmission Lines
EE ---
Term Paper
By ---
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Outline of Presentation
The Thunderstorm
The Lightning Discharge (Stages)
Lightning Currents and RelatedParameters
Protection of Power-Transmission
Effect of Lightning on PowerTransmission systems
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The Thunderstorm
Global Distribution of Thunderstorms
The Thundercloud
Point-Discharge Currents
The Lightning Discharge
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Global Distribution of
Thunderstorms
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The Thundercloud
Two main classes: heat storms and
frontal storms
Heat storm in tropics and mountainareas
Frontal storms in temperate regions
Characterized by the electrical charge ofwater droplets.
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Point-Discharge Currents
Electrostatic field distribution about vertical
lightning conductor (could induce lightning
discharge)
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The Thundercloud continued
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The Lightning Discharge
(Stages) Temporal Development of Flash to
Ground
Mature Stage The Leader Stroke
The Dart Leader
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The Lightning Discharge
(Stages) continued
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Lightning Currents and
Related Parameters Lightning Currents
Average lightning current amplitude is 25kA (lowest 2kA, highest
recorded 270 kA)
Frequency of Lightning Discharges (flashdensity)
Varies from place to place
Measured in thunderstorm days andlightning flash density
Lightning flash density for Greece = 3.7(most recent data)
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Protection of Power-Transmission
Systems
Reasons for Protection
Avoid power disruptions
Lightning protection methods
The Air Terminal (overhead conductors)
Tower Impedance (ability of tower to resist lightning)
The Buried Earth System (underground grid of
conductors)
Protective Leakage Paths-Pipe-Pipe Gaps (utilizes a gapbetween
conductors)
Underground Cables (Utilizes insulation of the earth)
Lightning Arresters (acts as over-voltage release valves)
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Effect of Lightning on Power
Transmission systems
Lightning Location
Prediction of Lightning Activities
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Lightning Location
Use of magnetic link locators, lightningcounters location within
country-widenetworks
Recorded by Meteorological Services andPower distribution
companies over time
Empirical formula for calculation of lightning
flash density correlate well with actual flashdensity obtain
from magnetic counters (mostrecent data obtained from Greece
andJapan)
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Prediction of Lightning
Activities Prediction based on a variety of methods
Modeling of lightning parameters
Prediction based on neural networks Prediction based on fuzzy
neural networks
All based on data obtained from lightning
location from meteorological and power
services.
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Prediction based on Fuzzy
Neural NetworksNew technique used in Japan
Gave better prediction of lighting strike
compared to neural networks Limitations: only predicts lightning
strike few
hours before the strike.
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Conclusions
Thunderstorms occur at highest at the equatorial beltand
decreases towards the poles. Local thunderstormactivity varies from
year to year.
Lightning data is available from the meteorologicalservices of
countries in the form of flash maps showingisokeraunic lines, i.e.
lines joining areas have the samenumber of thunderstorm days.
The mechanism of light formation and dischargeinvolves
electrical charging of water droplets within a
cloud leading to a dipole. The electrical field thusproduces
causes a cloud to cloud lightning discharge ora cloud to earth
discharge.
The average lightning current of about 25 kA.
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Conclusions continued
The earth flash density varies in different parts
of the world with the earth flash density
estimated at 1 to 2 flashes per 10 thunderstorm
days.
A variety of protection mechanism exist for the
lightning protection of transmission lines
including ground conductors(air terminals),
counterpoise , pipe-pipe gap, down-lead,grounding systems,
underground cables and
lightning arresters.
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Conclusions continued
Traditional methods of lightning monitoringinclude the use of
magnetic link directionfinders and lightning counters.
Correlation between lightning data obtainedfrom meteorological
lightning networks andthose obtained using standard formula
showgood agreement.
More modern methods have focused on lightingprediction using
neural network and fuzzyneural network techniques, but these
onlyprovide prediction a couple of hours before thelightning
strike.
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End of Presentation
Thank You
