CHAPTER strikes. The establishment and steady enhancing
CHAPTER 1 INTRODUCTION 1.1 Background Humankind runs over a few common disasters all around the world such as earthquake, snow slide, flood, and landslide and so on, which can be prevented.
Just safety measures are taken against these occasions are the reasons of which are known utilizing scientific knowledge, equipments and their applications. Predominantly, lightning is one of the natural phenomenon, which can cause severe damage to buildings and human life. Lightning kills and harms a greater number of people every year than sea hurricane or tornadoes. Lightning occurs when being a flow of electrical current between the earth and storm clouds, as varying charges of positive and negative polarity build up in the atmosphere during a storm. In a discharge, it should be understood that a channel, like a conductor wire is formed between cloud and ground. Through this channel, charge is transferred to ground. 90 percent of the cloud to ground discharges worldwide are initiated by downward-moving negatively charged leaders.
While negative charges are moving downwards (stepped leader), positive charges are induced on Earth. When the negative charges arrives near to the Earth where high electrical fields are developed, a bright, visible channel (return stroke) is formed from the ground up and the discharge occurs.The basic idea of a lightning protection system (LPS) reclaims to them middle of the eighteenth century with Benjamin Franklin. His electrical encounters prompted the creation of the lightning pole. He accepted this could help shield structures from lightning by connecting “upright rod of iron made sharp as a needle, and overlaid to counteract rusting, and from the foot of those rod a wire down the outside of the working into the ground”.Since the day, lightning has advanced to whole new level accordance to International Electrotechnical Commission (IEC) Standard 62305. It has been more than 200 years and still Franklin’s concept of a LPS is basically the same as the nowadays lightning protection system, which has the capacity to protect structures from lightning strikes. The establishment and steady enhancing of the interior lightning protection system is for the most part because of the progress of innovation that incorporates hardware working at low voltages which can be effortlessly harmed with an overvoltage.
As these hardware are inside associated and at last connected with outside line(s), the LPS has the objective to keep risky starting from occurring inside the structure, securing both valuable equipments and more importantly, human beings. 1.2 Problem Statement Lightning can risk human life; can make extreme harm structure and cause malfunction of supplies and equipments. It is one of the major reason of interference in power system because of its very huge current. Hence, it is important to have a solid lightning protection system (LPS) to limit hazards and harms because of lightning strikes. The engineering faculty building of University Tenaga Nasional (UNITEN) was installed with second ESE terminal system known as active 2D on year 2010 after the initial air terminal system failed to protect the building from lightning strikes on several occasions especially at BN.
However, the report from National Fire Protection Association (NFPA) demonstrates that the both air terminals again neglected to protect from another lightning strike after several years. 1.3 ObjectiveThere are three main objectives that will be satisfied by end of this projects as expressed below:· Minimize the bypass happening well within the guaranteed protection zone.
The parts of a building more likely to be struck by lightning are the edges and corners. Those regions are more vulnerable to lightning strikes. Hence, appropriate method needed to ensure the buildings are protected from lightning strikes.
· Improvise the current air terminal system in UNITENThe air terminals (rod) on top of the buildings are to provide protection for the area spread out below the structures. Number and height air terminals has to be determined through the calculation, to protect buildings and contents from damage caused by the intensely high currents of a lightning strike. · Increase the interception efficiency of the lightning strike towards the air terminals.Choosing the appropriate lightning protection level as stated in IEC-63205 standards from the risk assessment. 1.4 Scopes of Project There are several scopes have been set to ensure the task is executed within the proposed perspective and to ensure that this project will accomplish the objectives which have been mentioned earlier.
Those scopes are: 1. This research will be based on Conventional Lightning Protection system accordance to IEC – 63205 standards.2. The lightning risk assessment has been carried out to provide needed Level of protection for COE buildings.
3. The number and height of air terminals on building has been determined based on the level of protection and lightning interceptions efficiency.4. Appropriate method has been used to provide optimum protection for the buildings5.
The grounding system assessment has been done, where the grounding impedance will be affected by soil or water resistivity. 1.5 Thesis Overview The overview of this thesis follows the steps to accomplish the main objectives of the project. The thesis consist of 5 chapters such as the Introduction, Literature Review, Methodology, Results and analysis and conclusion.
Each chapters provide explanation on all the procedure in order to complete the project. Chapter 1 : IntroductionThis chapter provides an overview of occurrence of lightning phenomenon and background of conventional lightning rod. The problem statements and objectives of the project have been discussed in this section as well. Chapter 2 : Literature ReviewThis chapter presents a complete literature review about modern day Lightning Protection System (LPS) and methods of protecting any structures from lightning strike. The literature review also covers the placement of air terminals and ground electrodes to give less impedance path to discharge at ground.
Chapter 3 : MethodologyThis chapter discuss about the methods and techniques which have been used to complete the project. This chapter also presents about the work flow of the project. Chapter 4 : Results and AnalysisThis chapter will cover all results from calculation and estimation that have been done in achieving the main objectives including the Computer aided programs which have been utilized throughout the project. The analysis of these results will be discussed clearly through this part. Chapter 5 : Conclusion and RecommendationChapter five will explain the findings from previous chapters with recommendation in order to further develop which can considered to implement on COE buildings. Chapter 2 Literature Review 2.
1 Introduction Despite of the fact that occurrence of lightning phenomenon has discussed in chapter 1 earlier, yet it still impotent of explaining in detail about many of the basic concept of lightning stoke. Hence this chapter presents a detailed literature review about modern day lightning protection system. The objective of this chapter is to provide brief explanation on the methods that have been using worldwide to protect the structure and safety of occupants from lightning strikes. All the methods that will be discuss in this section comply the IEC-62305 standards. The chapter also covers the placement of air terminals and ground electrodes to provide less impedance path to discharge at ground. 2.2 Lightning Phenomena As a matter of fact, it has been known for decades about the conditions for event of lightning however the correct procedure of lightning development has never been confirmed.
There are a lot of myth and misconceptions of lightning occurrence. Modern science have acknowledged speculations are about partition of electric charge inside a cloud and creating electric field. Moreover, recent researches prove that ice, hail and semi solidified water drops also contribute during the formation of lightning. However, the modern day science are still incapable of predicting the time and location the lightning strike. There is an unstable environment in a thunderstorm. When there is a storm, solid updrafts and downdrafts frequently happened and proximately near each other. The updrafts bring little fluid water beads from the lower district of tempest up to stature of 70000 feet, far over the solidifying level while downdrafts will cut down ice and hail from the upper area of the tempest. The warmth discharging will happen when solidified water droplets slam into hail and ice.
The surface of hail will keep slightly hotter than its encompassing condition because of the warmth and a delicate hail will be developed. At the point when the fragile hail crashes into ice particles and water droplets, the electrons accumulate on the dropping particles and shared off the climbing particles. From that point onward, a thundercloud with positively charged at upper part and negatively charged at bottom part was accumulate since the electrons bring negative charges.
From electricity perspective, the unlike charges will pull in each other and minimize the insulation gap. An electric field will be delivered between upper and lower portion of the thundercloud when the positive and negative charges inside a same cloud start to separate. As the partition separate between the two charges grows bigger, the electric field strength increase gradually. In any case, a lot of charges are expected to form lightning since atmospheric layer is a decent insulator which counteracts stream of electric. Lightning will be form just if the quality of electric field is adequate to overpower the insulation quality of atmospheric layer.
At the point when a thundercloud is moving, it will gather another pool of molecule with positive charge along the ground that is in its way of movement since the earth is positively charged. The height of object from the earth surface influences the positive charge of the ground. The structures with greater heights such as tall building and skyscrapers have more positive charges. Then, a channel of negative charge otherwise called stepped leader will be formed from lower part of the thunderstorm toward the ground. It advances toward the ground in a progression of quick advances that happens so quick and not visible to human eyes. As stepped leader comprise of negative charges approaches the earth, positive charges additionally accumulate in the ground or in the any objects near to the ground. Then, the upward rising positive charge known as streamer will begin to move upward into the air through building or tree from ground.
It approaches the stepped leader in the air from decent distance from ground and they may collide each other at a height roughly equivalent to the length of a football field. An entire directing pathway is formed once there is a contact between stepped leader from the thundercloud and streamer starting from the earliest stage. In this way, a return stroke is formed which carries a huge current (bright bolt) and this underlying strike is trailed by a couple of secondary strikes. 2.3 Types of lightning Researches shows that, there are a few types of lightning and the most well-known kinds of lightning are cloud to ground, intra-cloud, between cloud and ball lightning. 2.3.
1 Cloud to ground lightning Cloud to ground lightning is one of the most dangerous and risky kind of lightning that can make serious harm to the objects or even put human life into risk. It happens when there is a discharge from bottom part of the thundercloud which is negatively charged and approached the ground which contains positive charges. This kind of lightning generally tall structures, for instance, tower, building, media transmission radio wire, and tall tree. It has shown a lot of light threating evidence. Since it can cause serious damage to objects and human life, cloud to ground lightning is the most dangerous type of lightning of all. 2.
3.2 Intra-cloud lightning Intra-cloud lightning occurs due to inverse charges between area in a similar thundercloud and it will release from pool with negative accuses to the pool of positive charges. In any case, it can cause visible lightning flash that indistinguishable as cloud to ground kind when it surpasses the limit of the cloud. 2.3.3 Inter-cloud lightning Inter-cloud lightning occurs between two different clouds and it does not touch the ground since it is a cloud to cloud lightning.
This type of lightning forms because there are opposite charges between clouds and it travels from point of negative charge at a cloud to point of negative charge in another cloud. 2.3.4 Ball lightning Ball lightning is a very rare event and it visible once in a while as a reddish lambent ball. However the shading might be differed. It moves horizontally in the air and shows up through sparkling circle only for a few seconds. 2.4 Introduction to Lightning Protection System (LPS) The lightning studies and Lightning Protection system (LPS) starts in mid-1750 with Benjamin Franklin, who found that the emission from sharp-tipped rod would be able to avoid lightning harm by releasing jolted clouds.
In 1753, he understood that a tall metal rod associated with a reasonable down conductor ended in ground could be utilized to conduct lighting strikes (huge current) and dispersed to earth safely with no harm to the structure. From there on that, he held the essential capacity of the sharp-tipped pole was as a preventer of lightning. The main purpose of a lightning rod is to provide protection to structure by directing the lightning strike (huge current) to discharge at earth.
The scientific concept for conventional rod or Franklin rod Lightning protection system are stated in Appendix L of the 1997 Edition of National Fire Protection Association (NFPA) 780 , which explains a system that gives a less resistive way to channel the large current of lightning to dispersed at ground, preventing harm to the structure and it occupants. 2.4.1 Categories of Lightning Protection System (LPS) The modern day Lightning Protection System (LPS) can be divided into two classes. One provides protection against indirect lightning strike while the second one is to prevent direct lightning strike. 2.
4.1.1 Protection against direct lightning strike (Primary Protection) The most common harms caused by direct lightning strike are the burning of structures and the event of crack on the surface of the building especially at the corner of the building. Therefore, primary protection is essential to secure all structures under its claimed protection zone from being straightforwardly struck by lightning.
The primary protection able to avoid causalities or loss of human life by attracting the downward leader before it strikes individuals and other lower points near to the ground.The primary protection consists of 3 main components such as lightning rod, down conductor and earth electrode. The lightning rods are made to intercept the lightning strikes and act as a lightning receptors, which can be found in various structures, for example, watch wires on High Voltage (HV) overhead lines or air terminal at the highest point of the any structures. They are well earthed to keeping in mind the end goal is to channel the large current to the ground, either by one conductor (regularly a copper strip) or by a few according to the preference. The earth electrode, which must be especially well made to give a low impedance way for the lightning current, is regularly formed by a few, independently buried conductors. 2.4.
1.2 Protection against indirect lightning stroke (secondary protection) The secondary protection components offers protection against the impacts of indirect lightning and sudden increase in power frequency as well. Surge arrestor for Low Voltage (LV) systems, channels and wave absorber to constrain either the impulse voltage or the power transmitted form under this category.
The surge arrester is one of the secondary protection segments. It is expected to shield types of well-equipped structures from being influenced by lightning strokes. Typically, indirect lightning stroke will cause impacts to the overhead cables and transmission lines, for example, the high frequency coaxial cable, power lines and media transmission lines. A voltage surge will be created and spread in the system and may reach connected types of devices in the surrounding.
This voltage surge can likewise be created by acceptance because of the electromagnetic radiation of the lighting streak. Indirect lightning stroke can cause a few consequences, for example, pre mature aging of the components, demolition of printed circuit loads up, hardware malfunction, data loss along the line. Besides the primary and secondary protection as said above, there is other protection type that is identified with the communication and exchanged systems must not be overlooked as well. Both of these system will be influenced by surges like the LV, the main diverse being that the worthy surge level is always lower.
2.5 Lightning Protection methods Basically lightning protection technique can be categorized in to two, as below:a) Attracts the lightning stroke towards the rod and it act as a sacrificial device, such as Franklin Rod (FR) and Early Streamer Emission (ESE).b) Act as lightning prevention air terminal (lightning elimination) such as Charge Transfer System (CTS) Dissipation Array System (DAS). The Franklin rod is viewed as a lightning collector, as it is the end for a lightning strike in the area. The ESE is likewise thought to be a collector as well since it expands the upward streamer by outline of the end of the bar. The CTS is considered as prevention kind as it keeps the event of lightning strike by neutralizing the charge with multi-pointed electrodes.
2.6 Conventional and Non- Conventional lightning rods The conventional Lightning protection system comprise of three fundamental parts: an ordinary lightning conductor bar at a suitable points or areas on the structure to block the lightning, a conductor fitted between the terminal and the grounding system to pass the lightning current into the earth, and the down conductor convey the lightning current into the earth. With legitimate installation, this system is said can give lightning connection point and ways for the lightning current to take after from the connection points into the ground without making any damage to the structure. The conventional rod and commonly known as franklin rods are the most conventional Lightning protection system with spikes on top in various shape and configuration. Those spikes on top are highly conductive metal and mainly made of copper of stainless steel .These types of devices are passive in nature and act as sacrificial device.
The conventional rod act in accordance with standards. However, the major drawbacks of these type of conventional rods is, it only provides small protection zone. Hence, more than one conventional rods are required to give optimum protection to structures with greater in width, length and height.
The examination for further developed terminal was sought after because of the downsides of FR, for example, extremely constrained scope zone, which is conditioned, just by the height and needed protection level and for greater measurement installation number of bars with mesh network must be worked out. As needs be, present day Lightning protection system practices have followed and modified Franklin’s guideline in order to increase the protection zone. These days, a new approach suggested by scientist and researchers, which is known as Early Streamer Emission (ESE) LP system has been presented in advertising for around ten years. This system as per lab thinks about completed in numerous nations is said to give a more compelling protection against a lightning strike. The inventors and manufacturers had additionally made this as a claim. Nonetheless, solid quantitative data about the relative execution of ESE lightning rod contrasted with Conventional Lightning Rod (CLR) under comparable conditions are as yet inadequate. In this way, the adequacy of these advancements still stays open to being researched more.
ESE types of non-conventional terminals are available in the market in different shapes and configurations. Figure shows few examples of nonconventional lightning rods (such as ESE type of terminal, Dynasphere and DAS) that are manufactured by different manufacturers. Nowadays Non-Conventional terminals are widely accessible in global market in various shapes and designs. Figure …. shows few types of nonconventional lightning rods, (such as ESE sort of terminal, Dynasphere and DAS) that are fabricated by various designers: 2.7 Lightning Parameters The data about lightning parameters are essential in deciding lightning protection level (LPL) for a lightning protection system (LPS). Lightning current and lightning ground flash density are two key factors in determining lightning protection level.
Lightning current is utilized to decide the measurement of lightning protection system since the peak value of the lightning current is identified with impacts of lightning strike. Besides, the gradient of lightning current head influences the induced voltage because of lightning strike. In the meantime, ground flash density is number of lightning flashes to the ground for a unit zone in a unit of time and communicates in term of ground stroke per kilometer square every year. The magnitude of the lightning current is a critical parameter in planning a lightning protection system despite the fact that total protection against the lightning strike is unpredictable because of high electric potential and quick ascent time of a lightning strike. Lightning protection system will make a way for high lightning current that makes harm to the buildings channels to ground.
Basically, there are four lightning protection levels and each of them relates to various estimations of the lighting parameter. The need or requirement for the structure to be ensured will influence by the choice of lightning protection level. The maximum tolerable hazard should constantly more than the risk of harm to the structure because of an immediate lightning strike.
The yearly recurrence of the direct lightning strike to the structure, Nd will be utilized to assess the danger of harm to the structure. 2.8 Fixed Angle method There is an assumption been made by the researchers and scientists, which is the air terminal can capture all the lightning strike from making a direct contact with the buildings, only if the air terminal can keep up a specific geometrical connection by methods for partition separate and differ in term of height to the protected structure. The easiest technique to apply those presumption is utilizing fixed angle method where the edge, ? is portrays as a slanted line that secure all objects underneath it. Both 30° and 45° are the most commonly used for beta angle, ?. The downside of this fixed angle method is, it’s only applicable for structures with symmetrical dimension or roof –mounted structures. 2.9 Rolling sphere method