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Lightning --- A Case Study
Dr Anil Kumar Tripathy , faculty GHITM Puri , Odisha
Abstract---- Concept behind Lightening are a discharge of electricity & involve a very high
electrical energy discharge and may put an adverse effect to structural damage , machinery
/equipment and puts fatal effect to human beings and animal life when comes in contact . The
paper gives an ample of ideas related to protection, effect and provides a solution for the cause
behind it.
Keywords: Lightening origination, Charge separation, Cloud cover factor, Temperature
Gradient, Effects, Protection Provider Mechanism, etc.
1. Introduction--The mechanisms behind lightning are a discharge of electricity & involve a very high
electrical energy discharge caused by the difference in potential between clouds or between
the clouds and the ground. Clouds are formed in the upper atmosphere. The air around the
lightening heats the air forming a channel with temperature 0f 30,000 0k and currents are
more than 20 kA in 80% of cases and can reach in the region of 200 kA (or even more) with
rise times of a few microseconds (source CIGRE – Electra no. 41 and 69).
II. MECHANISM OF LIGHTNING
The mechanism behind lightening is based on separation of charges of the thunderstorm which
carries a positive charge on top & negative charge on bottom. The ground below the storm also
develops a positive charge. As a result there exist differences in electrical potential which is
caused for freezing of water to form ice crystals due to thermo-electric effect. In this process
electrons flow from colder to warmer areas due to thermal gradient (electrical gradient). Since
electrons carry a negative charge, the ice crystal then has a negatively charged core and a
positively charged outer edge. A positive charge develops in the ground below the storm. When
a lightning bolt jumps from one place to another, it originates in an area of negative charge and
moves to an area of positive charge. The flow of electricity between the two then reduces some
of the difference in electrical potential. Electricity may flow up and down the channel several
times in the course of a single lightning strike. Depending on the direction in which the charge
develops (cloud-to-ground or ground-to-cloud) and whether the charge is negative or positive,
there are four different types of ground lightning strike.
i.
ii.
iii.
iv.
Negative cloud-to-ground
Positive ground to cloud
Positive cloud to ground
Negative ground to cloud
--
--
--
+
+
+++++ ++++++
- - - - - - -- - - - - - - - - -
Negative
Positive
Cloud - to- ground -toGround
cloud
Positive
cloud -toground
Negative
ground - tocloud
III. EFFECTS OF LIGHTNING
Further sub divided into direct and indirect effects.
A) Direct effects (strikes on structures)
The simplest way to catch up structural effect will follow a path to ground layer through either
lightning protection system or metallic path. In another way it may put directly strike to
Electrical appliance (power lines, antennas, antenna feeders and overhead telephone cables) as
well as mechanical services like water and gas piping. It may put a fatal state to human beings.
Mechanism --At the point of contact, lightning generate
a. Thermal effects caused by the electric arc
b. Thermal and electrodynamics effects induced by circulation of the lightning current
Protection against the direct effects of lightning is based on catching the current and
discharging it to earth (lightning conductor, catcher rods, etc).
B) Indirect effects
Indirect effects of lightening may leads to damage in three ways
voltages as
caused by transient over
- a. By conduction process which may put direct lightning strikes on lines (power,
telecommunications, TV, etc.) entering or exiting buildings
- b. By feedback process from earth via the earthing system, the protective conductors and the
exposed conductive parts of equipment
- c. by induction process in the installation's conductive elements (structure of the building, etc.)
and internal lines (power, telecommunications, etc.)
The effects of lighting can be felt by induction within a 1 km radius, and by conduction
(feedback from earth and strikes on lines) within a radius of more than 10 km.
Statistically, damage to electrical installations and equipment is mainly the result of the indirect effects of lightning
strikes and over-voltages from operations, against which it is important to provide protection by installing voltage
surge protectors.
Mechanism – In two ways
1.
When lightning current falls on a lightning conductor causes an overvoltage between the
earthling system and the internal lines within the installation. Through distribution network
overvoltage spreads to neighboring installations & strike hits the ground near the building
directly via their earthing electrodes so as equip all installations supplied by the same LV
network with voltage surge protectors
During the period of lightening, (discharge current) it generate a field of Electric and magnetic
component where radiation is received and forming appropriate aerial, which becomes induced
current. Thus there makes a linkage between lightening conductor to the conductors in the
structure.
2.
4. PROTECTION OF STRUCTURE FROM LIGHTNING
A) External protection
a. Passing the discharge current (during lightning) to earth. The main protection behind
lightening effect can be protected by doing proper earthing .
b. Uses of proper capture device may leads to protection of unshaped structural size (wider
area), current density should be higher with probability of capture area.
c. Some specific techniques such as shielding technique, Galvanic decoupling methods may be
adopted to protect a total coverage area having different heights of tall building & Electric as
well as magnetic effect .
d. It is strongly recommended for buildings having many floors, that the lightning conductor,
down conductor(s) is connected to the bonding systems on each floor to avoid a spark over
through the walls of the building due to the voltage difference that occurs between the down
conductors and the internal exposed conductive parts. The consequences in the installation of the
effects caused by circulation of the lightning current in the down conductors can be minimized
by:
- Increasing the number of down conductors in order to divide the current and limit the effects
caused
- Ensuring that the down conductors are interconnected with the bonding systems on all floors in
the building
- Creating equipotential bonding systems incorporating all conductive elements
e. Enhance the system in such a way that it must be must be capable of discharging the
lightning current, avoiding a voltage rise in the earthing system itself and the surrounding
ground. We must follow the scientific and objectively obtaining installation of voltage feedback
points, to provide protection against high frequency voltage rise in the circuits interconnected
with it.
B) Internal protection
a. Voltage surge protectors serve better rather than fuses and circuit breakers in case of
protection towards electric and electronics equipment due to lightening from over
voltage.
b. Protect equipment against high-frequency interference, for which filters must be used.
c. Protect an installation against the risks of temporary over voltages due to faults on the
high or low voltage supply, such as neutral breaks.
5. CONCLUSION
Due to complexity nature of lightning generation, an ample idea
has been suggested in its transmission path, path of destruction
(Short or long), fatal effect to man & animal, adverse effect in
relation to its Structural view, mode of destruction, places for prone
to lightening. The one and only one solution is a good lightning
protection system helps to provide that path, thus reducing the
probability that damage will occur to people or animals etc .
REFERENCES
[1] Golde, R.H., lightning protection, 1973
[2] IEEE standard 1100, IEEE Recommended practice for Powering
And grounding sensitive electronic equipment (Emerald book).
[3] National fire protection Association 780, Standard for the
Installation of lightning protection systems, NFPA, 1997&2000.
[4]Uman, Martin A and Krider, E. Philip,” Naturally and
artificially Initiated lightning,” SCIENCE, 27 October 1989,
volume 246
[5] Principle of lightning protection by Phillip R Tompson
[6] Abdel-Salam, M. et al, Lightning Protection Using Energised,
Franklin RodsAssiutUniversity, IEEE 1995.
[7] Allen, N.L., On the Performance of Active and Passive
Terminations in LightningProtection, University of Leeds.
[8] Petrov, N.I. et al, Determination of the Striking Distanceof
Lightning to EarthedStructures, University of WalesCollege of
Cardiff, the Royal Society 1995.
[9] Kunal Patel-- Protection Measures of Lightning Effect on Building
[10] Power guide –A complete set of technical documents –Protection against
lightning effect --R World Headquarters and International Department
87045 Limoges Cedex - France