Friday, July 11, 2008
Wednesday, July 9, 2008
Lightning Protection system
Protection Methods Of Lightning systems.
The highest point of the facility is, in general, the most vulnerable to a direct lightning strike. Lightning rods or air terminals are needed to capture the strike to a proffered point, and to safely conduct the energy to ground to minimize the risk of damage. The number of terminals required, and their placement, is determined by the chosen lightning protection design method.
The placement of the terminals, whether conventional or active, is a critical part of lightning protection design process. Since 1750’s the most popular methods of lightning protection have involve sharp vertical rods (Franklin), horizontal and vertical conductors. Or combination of both. Only if air terminals are placed in the optimum location on the structure makes it possible to achieve an efficient and reliable lightning protection system. Historically a number of methods have been employed, some of which are still in common use, such as cone of protection Mesh and rolling sphere methods.
Cone of protection
The cone of protection is a simple geometrical construction that assigns a zone of protection to a vertical conductor. On a structure protected by Franklin rods using this design method, it is not usual to find location where lightning has struck well with in the supposed zone of protection
The highest point of the facility is, in general, the most vulnerable to a direct lightning strike. Lightning rods or air terminals are needed to capture the strike to a proffered point, and to safely conduct the energy to ground to minimize the risk of damage. The number of terminals required, and their placement, is determined by the chosen lightning protection design method.
The placement of the terminals, whether conventional or active, is a critical part of lightning protection design process. Since 1750’s the most popular methods of lightning protection have involve sharp vertical rods (Franklin), horizontal and vertical conductors. Or combination of both. Only if air terminals are placed in the optimum location on the structure makes it possible to achieve an efficient and reliable lightning protection system. Historically a number of methods have been employed, some of which are still in common use, such as cone of protection Mesh and rolling sphere methods.
Cone of protection
The cone of protection is a simple geometrical construction that assigns a zone of protection to a vertical conductor. On a structure protected by Franklin rods using this design method, it is not usual to find location where lightning has struck well with in the supposed zone of protection
Mesh Method (faraday cage) 
The mesh or Faraday cage method consists of series of horizontal air terminations (Copper tape), which are bonded to vertically descending down conductors. The structural steel if bonded may also be used to conduct the lightning impulse.
The mesh or Faraday cage method consists of series of horizontal air terminations (Copper tape), which are bonded to vertically descending down conductors. The structural steel if bonded may also be used to conduct the lightning impulse.
The picture opposit shows a labortory demonstration of the method, ( DON'T TRY AT HOME !)
Rolling spare method
Rolling spare method
The rolling sphere method is undoubtedly the most common recommended method in codes of practice. It is based on the electromagnetic model, which released the striking distance to the peak current delivered by the lightning strike. To apply this technique, an imaginary sphere, typically 45 m in radius (the striking distance), is rolled over the structure. All structure surface points that contact with the sphere and deemed to be protected, as shown in the diagram.
In order to determine weather lightning protection system is necessary, the following should be considered.
· Prevalence of thunderstorms and lightning protection system.
· Construction of the building
· Height of the building
· Relationship with other building or structures.
· Utilization and contents of building
· Type terrain.
· Regardless of the location, all the buildings and structures higher than 50m should have a lightning protection system.
Elements of a Lightning protection system.
Air Terminal
The primary function of an air terminal or termination system is to capture the lightning strike to a preferred point, so that the discharge current can be safely directed through the down conductor(s) to the grounding system.
The Down conductor
The function of a down conductor is provide a low impedance path from the air termination to the ground system so that the lightning current can be safely conducted to earth, without the development of excessively large voltage.
In order to reduce the possibility of dangerous sparking (side-flashing), the down conductor route(s) should be as direct as possible with no sharp bends or stress points where inductance, hence impedance, is increased under impulse condition.
The Grounding System
The grounding system must have a low impedance to safely disperse the energy of the lightning strike. Because the lightning discharge consists of high frequency components, we are particularly concerned with the frequency dependent electrical parameter of a grounding system- impedance- as well as low resistance grounding.
A disconnect link should be fitted in each of the down conductors to facilitate testing. The disconnect link should be a bi-metal connector for aluminum networks.
All metalwork on, or around, a structure should be bonded to the lightning protection system. Metallic drainpipes, fire escape ladders, metallic fencing, etc. should be bonded to the lightning protection system at the top and the bottom.
Tuesday, July 8, 2008
How a thunder storm Develops
A thundercloud commences with the development of a cumulonimbus thunder cloud. The cloud is typically formed by rapidly raising humid air, which becomes electrified due to convection and precipitation effect. This is accompanied by wind speeds up to 200km/h.
The end result is the separation of positive and negative charges as in figure 1. in approximately 90% of the cases the lower part of the thunder cloud is comprised of a thin concentrated layer of negative charge, and the upper part of the cloud consist of more diffuse positively region. The cloud base is typically 2-6 Km.
Charge electrified due to Convention and precipitation effect. As a result of the cloud electrification a quasi electric field is established between the cloud and ground. Pointed ground objects subjected to this ambient electric field emit varying amounts of point discharge or corona, and the resulting positive or negative ions drifts upwards to form a low density “ space charge” which extends from ground to cloud. This space charge reduces the electric field observed at ground level, typically from 50-60KV/m at heights of 500m, to 2-15 KV/m at the ground.
Within confines of ground to cloud, static electricity builds to an extent where on or more neutralizing discharge or flashes occur. These flashes can be in the form of an inter cloud or cloud to ground flashes.
The dramatic cloud to ground is of most concern. The dynamitic phase of lighting commences in the form of a luminescent downward leader from the base of the cloud, which proceeds in a series of steps and branches towards the ground. The protrusion of ground objects into a ambient field at the tip of the object. As the down leader approaches, it cause the electric field around points on the surface of the earth to increase rapidly, leading to the initiation of small upward streamers from the elevated points. Under the right conditions, the upward streamers thermalise and become competing upward leaders, which propagate toward the approaching down leader.
The ability of one ground point to develop an upward intercepting leader before other nearby competing points that can become the preferred strike point to successfully complete an ionized path between cloud and ground.
A small proportion of flashes transfer positive charge to ground (positive lightning). Typically 10% of lightning flashes are positive, although this can vary with latitude and season. The parameters for positive lightning differ considerably from their negative counterparts. Some of the main differences are that the:
· Strike phenomenon is absent (no subsequent strokes)
· Peak current higher ( ~ 2 x)
· Maximum rate of rise of current is less ( ~ 0.1 x)
· Total rise time is longer ( ~ 4 x)
· Stroke duration is longer ( ~ 4 x)
· Action integral (energy content) is higher ( ~ 10 x)
In summary, the main lightning discharge is characterized by a rapidly rising current (averaging about 30,000 Amps) with maximum values exceeding 200,000 Amps. This whole process is extremely rapid, typically occurring within milliseconds. The average energy released in a single discharge may be 55 kW hours. The danger lies in the extremely high rate of current rise (up to 1010 Amps per second) which can generate very high voltages, and also from the continuing current following the peak.
Without a proper intervention to capture and control the passage of this lightning energy to ground, cloud-to-ground lightning can be catastrophic.
The end result is the separation of positive and negative charges as in figure 1. in approximately 90% of the cases the lower part of the thunder cloud is comprised of a thin concentrated layer of negative charge, and the upper part of the cloud consist of more diffuse positively region. The cloud base is typically 2-6 Km.
Charge electrified due to Convention and precipitation effect. As a result of the cloud electrification a quasi electric field is established between the cloud and ground. Pointed ground objects subjected to this ambient electric field emit varying amounts of point discharge or corona, and the resulting positive or negative ions drifts upwards to form a low density “ space charge” which extends from ground to cloud. This space charge reduces the electric field observed at ground level, typically from 50-60KV/m at heights of 500m, to 2-15 KV/m at the ground.
Within confines of ground to cloud, static electricity builds to an extent where on or more neutralizing discharge or flashes occur. These flashes can be in the form of an inter cloud or cloud to ground flashes.
The dramatic cloud to ground is of most concern. The dynamitic phase of lighting commences in the form of a luminescent downward leader from the base of the cloud, which proceeds in a series of steps and branches towards the ground. The protrusion of ground objects into a ambient field at the tip of the object. As the down leader approaches, it cause the electric field around points on the surface of the earth to increase rapidly, leading to the initiation of small upward streamers from the elevated points. Under the right conditions, the upward streamers thermalise and become competing upward leaders, which propagate toward the approaching down leader.
The ability of one ground point to develop an upward intercepting leader before other nearby competing points that can become the preferred strike point to successfully complete an ionized path between cloud and ground.
A small proportion of flashes transfer positive charge to ground (positive lightning). Typically 10% of lightning flashes are positive, although this can vary with latitude and season. The parameters for positive lightning differ considerably from their negative counterparts. Some of the main differences are that the:
· Strike phenomenon is absent (no subsequent strokes)
· Peak current higher ( ~ 2 x)
· Maximum rate of rise of current is less ( ~ 0.1 x)
· Total rise time is longer ( ~ 4 x)
· Stroke duration is longer ( ~ 4 x)
· Action integral (energy content) is higher ( ~ 10 x)
In summary, the main lightning discharge is characterized by a rapidly rising current (averaging about 30,000 Amps) with maximum values exceeding 200,000 Amps. This whole process is extremely rapid, typically occurring within milliseconds. The average energy released in a single discharge may be 55 kW hours. The danger lies in the extremely high rate of current rise (up to 1010 Amps per second) which can generate very high voltages, and also from the continuing current following the peak.
Without a proper intervention to capture and control the passage of this lightning energy to ground, cloud-to-ground lightning can be catastrophic.
Lightning - History and Discovery
Every year millions of dollars are spent by various companies to get suitable protection against surges that resulted from faulty earthing conditions and lightning.
Lightning is a phenomenon that has no prevention methods invented so
far. However protection and damage reduction methods have existed with in the last two centuries.
Lightning existed as an unknown mysterious” fireballs “falling from the sky high, until the mid 18th century, when a scientist Benjamin Franklin solved the mystery by proving to the worl
d with his world famous Kite experiment that lightning is produced simply by an interaction of two unlike charges. Hence it is simply a discharge of a fully charged electric cloud to the ground earth mass.
Inventors have invented several methods of protections and accessories, that are utilized to shield the gigantic electric current that flows in a lightning or fault earth, are readily available in the existing market.
In a world of increasingly sophisticated buildings and equipment, lightning is a constant risk. Telecommunication sites and buildings are considered as high-risk area for lightning and faulty earth due to sophisticated equipments that are used in the industry. There for in general all telecommunication stations should be provided with an appropriate Earthing and lightning protection system designed to safeguard against, or reduce the risk of a lightning strike, or an electrical fault becoming a hazard to personnel, equipment, or structures.
Lightning is a phenomenon that has no prevention methods invented so
far. However protection and damage reduction methods have existed with in the last two centuries.
Lightning existed as an unknown mysterious” fireballs “falling from the sky high, until the mid 18th century, when a scientist Benjamin Franklin solved the mystery by proving to the worl
d with his world famous Kite experiment that lightning is produced simply by an interaction of two unlike charges. Hence it is simply a discharge of a fully charged electric cloud to the ground earth mass.Inventors have invented several methods of protections and accessories, that are utilized to shield the gigantic electric current that flows in a lightning or fault earth, are readily available in the existing market.
In a world of increasingly sophisticated buildings and equipment, lightning is a constant risk. Telecommunication sites and buildings are considered as high-risk area for lightning and faulty earth due to sophisticated equipments that are used in the industry. There for in general all telecommunication stations should be provided with an appropriate Earthing and lightning protection system designed to safeguard against, or reduce the risk of a lightning strike, or an electrical fault becoming a hazard to personnel, equipment, or structures.
An Introduction to My Self
In every cubic centimeter above, on, and below the earth exist millions of living cells. Each cell struggles to reproduce and survive, along the way incurring mutations. Every mutation is a step in the surreal and unseen dance of evolution - a dance the Digital Life Laboratory's Avida project attempts to recreate artificially. Evolutionary programs and transcendent algorithms are what fascinate me most.
Born in GD.Atoll (most southern part of the Maldives), my family migrated to the capital city (Male’) while I was 6 months old. My first school was Male’ English School (MES), where I completed my primary grade studies.
When I reached the standard 8 (Where Studies for GCSE O’Level commences), I was transferred to Majeediyya School.
Once I completed my A’level’s I joined Dhiraagu as a technician, and for the past 10 years I have worked Dhiraagu and currently I am holding the post of Assistant Engineer. I have responsibility to design and maintain electrical system protection, which includes grounding, surge protection and lightning protection systems. Apart from this, I am also responsible for operation and maintenance of all the power system, which includes day to day fault maintenance as well as routine maintenance of the power system elements.
It is when completing my Diploma in Mechanical engineering at Subang Jaya of Malaysia; I became fully aware of the passion for the engineering, a passion embedded in a world of creativity and enthusiasm. The endless patterns of numbers and theories which define all the aspect of the real world that we live. Nothing is as captivating as an unsolved problem. My curiosity for Engineering leads me to new insights and projects every day. My destiny was sealed to become an expert engineer in my field.
I want to be challenged. I want to stretch my mind to the limit, to maximize my ability, to work so hard towards a purpose that I will cry tears of frustration alongside those of success, yet I call my self SUPER MAN..
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