Lightning is an abrupt electrostatic discharge that occurs between clouds or from clouds to the earth. It is accompanied by a flash. Charges build up in clouds during storms and separate, with negative charges near the ground and positive charges higher up. When enough charge builds up, electrons move toward the positive charges, ionizing the air and allowing discharge along a path of least resistance in a zigzag pattern. Upward and downward leaders form until they meet, causing a stroke and releasing a large amount of heat and producing the flash and thunder. Lightning arrestors safely guide the current from a strike to ground to dissipate the energy.

1. LIGHTNING
An abrupt electro-static discharge
 from cloud to cloud or,
 from cloud to earth
 accompanied by a FLASH
Separation and Accumulation of Electrical
Charges in the clouds via micro- and macro-
physical
During rain storms Clouds get electrically
charged

9. LIGHTNING…
• Negative charges are near and +ve charges
away from, the ground
• When the charges build up enough Electrons
tend to move towards the +ve charges
• air gets ionized and the discharge path
becomes a plasma with high conductivity
• This discharge is in jumps called “stepped-up
leaders”

10. How lightning occurs ?
• The movement is along the path of “least
resistance” and hence Zig-Zag Form
• When electrons approach the +ve charges,
leaders (called streamers) develop towards
the center of positive charge
• Downward leaders start from the clouds and
upward leaders from the earth
• The two leaders join causing a “stroke”

11. How lightning occurs ?
• Up leaders causing strokes are called return
strokes
• Point of intersection of two leaders (about 10~
30M from the center of the +ve charges” is
the “center of the stroke
• Large amount of heat is dissipated, producing
FLASH & THUNDER

12. Lightning parameters
• Cloud potential - very small to 100 MV
• Charge in a cloud - very small to > 300 C
• Lightning flash - Has many strokes – upto 40
-Typically 4 to 5 strokes/Flash
- Peak current is highest for the first stroke
• Current in a lightning discharge to ground -
negative stroke – 200 kA
positive stroke – 300 kA
• Rate of rise – 1011 A/s (max) = 100 kA/μs
• More than 70% of the strokes are negative
• Number of strokes/second – 2000 to 5000 (all over the
world)

14. Lightning characteristics
• 1 ~ 100 kA Current
• Few hundred micro second duration
• Very rapid current rise (up to 1010A/sec)
• Average Dissipated Energy ~ 55 KW Hr
• Velocity : 1/3 speed of light
• Rise is fast 1~ 50 µS ec
• Decay is slow: Time for half the max. value
50~250 µ sec

15. Characteristics Lightning
Fast Rise of
current
means:
Inductance of
wires and skin
effects of the
conductors

16. Characteristics Lightning..
• Frequency of thunderstorm occurrence 0.1T ~
0.2 T, Where T: Number of thunderstorm
days/year/sq.Km)
• Only some thunderstorms are dangerous
• Lightning is purely a random phenomenon
• Researches being conducted for diverting
lightning

17. Protection scheme
• Capture the lightning strike.
• Safely convey this energy to ground
• Dissipate energy into a low impedance
grounding system
• Bond all ground points together.
• Protect incoming AC power feeders.
• Protect low voltage data/telecommunications
circuits.

18. Function of lightning arrestor
The purpose of an arrestor is to
• launch a successful up-leader before any other
point on the structure to be protected
• There by “Guide the charges to discharge
through a safe passage to the ground, and
dissipate the energy”

19. Lightning Arrestors Models..,
• Lighting Rod (Franklin Rod)
• Rolling Sphere
• Parabolic-like lightning charge “Collection
Volume” method
• A conducting Rod (Franklin Rod) with sharp tip
protrudes the installation.
• It offers a “Cone of Protection” as shown in
another slide

21. MOV
• metal oxide varistor (MOV) is
an electronic component with a
significant non-ohmic current-
voltage characteristic
• The name is for variable
resistor
• When triggered by high voltage,
they will shunt the current
• Often used to protect circuits
against excessive transient
voltages

22. MOV…
• stacks of MOV as the nonlinear element
• virtually no current to flow during steady state
operation and very large amounts to flow
during over voltages
• 90% of all MOVs: ZnO
• The disks-shaped blocks of ZnO are made by a
process involving grinding, mixing, pressing,
and sintering
• number of disks depend on dielectic
properties of the material

28. Surge protection

31. Thank you