Last Updated on May 7, 2022 by Admin
The phrase “when lightning strikes” is frequently used as a euphemism for an uncommon occurrence when lightning strikes. Every year, institutes such as IMD publish the Monsoon date. Lightning strikes are common during monsoon rain; however, the most dangerous lightning strikes occur during pre-monsoon or untimely rain. Read more to know about what is lightning and its impact on buildings and what are remedial actions to avoid the impact.
Lightning, as the name implies, is a dazzling flash of light created by electrical discharges that occur all over the world, whether in urban areas, rural areas or even in open fields. In theory, lightning is caused by a charge imbalance between thunderclouds and the ground or the clouds themselves.
The majority of lightning strikes occur between clouds, with the rare exception of lightning striking the earth. In the blink of an eye, a lightning strike might deliver thousands of mega-amperes of current.
Lightning is most likely to strike the closest point on Earth to it, which has a large potential for positive charges. In other words, a towering building, structure, electrical tower, or even trees that may discharge electricity to the ground are considered the closest point
What is lightning and how is it formed?
Lightning is a massive electrical discharge that originates in clouds or the atmosphere. In-cloud lightning, which accounts for the bulk of lightning incidents, occurs wholly within a cloud or clouds or between a cloud and the air, according to the National Severe Storms Laboratory. When negative electricity from the atmosphere combines with the positive charge of an object below, deadly cloud-to-ground lightning strikes occur.
When the electrical charge in the atmosphere is less than a hundred yards from the ground, objects like trees and buildings emit sparks to meet it. When those sparks meet, the resulting channel causes a massive electric current surge that goes rapidly downhill, culminating in the flashing bolt we know as lightning.
Lightning travels at the speed of light, or 186,000 miles per second, according to NASA. Lightning can strike anywhere outside, but it is most likely to do so near water or towering, isolated objects like trees. It’s important to keep in mind, however, that the tallest object isn’t always the target.
How does lightning affect the building property?
Lightning is caused by a high-intensity impulse current that travels through a gaseous environment (the atmosphere) before reaching a solid, more or less conductive medium (the ground). These impacts are mostly classified into two categories:
- Thermal effects: The quantity of charge associated with lightning strikes is linked to these outcomes. They result in fusion points melting holes of various sizes at the impact site of high resistivity materials. A high amount of energy is emitted in the form of heat when a substance is a poor conductor. The heating of the material’s water vapor causes a sudden increase in localized pressure, which could cause it to explode.
- Effects due to the initiation: Depending on the grounding network and soil resistivity, a significant increase in the ground potential of the installation will occur in the event of a lightning strike. There will also be potential differences between distinct metal components. As a result, special care must be taken when constructing earth rods and interconnecting metal structures adjacent to conductors.
- Acoustic effects – thunder: Thunder is caused by the electrodynamic forces creating a quick increase in pressure (2 to 3 atmospheres) in the discharge channel during a lightning strike. The length of the ionized channel determines how long a thunderclap lasts. The spectral components released by the shock wave propagate perpendicular to the channel at high frequencies. Because low-frequency propagation is omnidirectional, an observer will hear various types of rumbling or claps depending on the distance and orientation of the consecutive channels used by the lightning flash.
- Luminous effects: An observer’s retina is violently sensitized by a nearby lightning strike. For several seconds, the eye is blinded and vision is lost.
- Electrodynamic effects: The high magnetic field of the lightning current causes electrodynamic effects between conductors and other parts. This produces large mechanical forces, both attracting and repulsive, which are amplified when the conductors are near together or the current is high.
- Electrochemical effects: Because lightning strikes are so brief (in comparison to stray ground currents), their effects are minor and have no effect on earth rods.
Electrical equipment is becoming increasingly vulnerable to transient overvoltage induced by lightning as the use of sensitive electronics grows. The overvoltage is either caused by the atmosphere or by industry. The most dangerous is atmospheric overvoltage, which is caused by three primary factors:
- Conduction: An overvoltage that propagates along a conductor that has been directly struck by lightning. The majority of the lightning energy is disseminated across the entire network, making this effect even more devastating. This problem can be rectified by installing an appropriate device that can handle high currents.
- Induction: due to the electromagnetic field emitted by a lightning strike It produces an overvoltage on conductors in a range proportionate to the lightning strike’s force and rate of speed fluctuation. As a result of the rapid current changes, the cables, and even the ducts that serve as aerials, may be subjected to destructive overvoltage. This is why burying the network does not ensure lightning protection.
- Rising up from the ground: When lightning strikes, an overvoltage might ascend from the ground, seeking a more favorable path to the ground. This can be addressed in part by
- Equipotential bonding between the metal structures and the ground of the complete structure installation.
- Implemented overvoltage protection on services
Protection of structure from lightening
Lightning protection systems, which consist primarily of lightning conductors (structural protection) and voltage surge protectors (overvoltage protection), provide excellent protection when properly defined and implemented.
A. External Protection
a. Protection system (lightning conductor)
These are designed to shield structures from direct lightning strikes. They avoid harm from the lightning strike and the related current circulation by capturing the lightning and running the discharge current to earth.
There are four different types of lightning conductors:
i. Single rod lightning conductor (franklin rods)
Depending on the size of the structure and the down conductors, these can have one or multiple tips. They are either directly connected to the installation’s earthing electrode (foundation) or, depending on the type of protection and national work norms, to a specific earthing electrode (lightning conductor earthing electrode) that is connected to the installation’s earth.
ii. Lightning conductors with spark over the device
The single rod has evolved into these. They have a sparkover device on the tip that creates an electromagnetic field, which helps them capture lightning and improves their effectiveness. On the same structure, many lightning conductors might be put. They, as well as their earthing electrodes, must be linked.
iii. Lightning conductors with meshed cage
The meshed cage is made out of a network of conductors that wrap around the outside of the building, enclosing its entire volume. At regular intervals on projecting locations, catcher rods (0.3 to 0.5 m high) are inserted into this network (rooftops, guttering, etc.). Down conductors connect all of the conductors to the earthing system (foundation).
iv. Lightning conductors with earthing wires
Above some buildings, outdoor storage areas, electric lines (overhead earth wire), and other structures, this system is used. These are covered by the sphere’s electrical geometric model.
b. Electro geometric model
The selection and placement of lightning capture devices necessitate a thorough examination of each site, with the goal of ensuring that the lighting “falls” at one of the predetermined spots (lightning conductors) rather than elsewhere on the structure. Depending on the sort of capture device, there are several ways to accomplish this (lightning conductor). The “electro geometric model” (or imaginary sphere model) method, for example, determines the spherical volume that is theoretically shielded by a lightning conductor based on the strength of the first arc’s discharge current. The greater the stream, the greater the chance of being captured and the larger the protected area.
c. Capture surface areas
When the protected site comprises multiple buildings or goes beyond the range of a single capture device (Lightning conductor), a protection strategy must be set up for the region, contrasting the various possible capture surface areas. When a site is made up of structures of various heights, it is always challenging to attain comprehensive coverage. By superimposing the protection plan over the area’s layout, it is feasible to see sections that are not protected, but it must also aid in in-depth study.
- Lightning strike probability by calculating the primary strike points (towers, chimneys, antennae, lamp posts, masts, etc.)
- The sensitive nature of the buildings’ equipment (Communication and computer equipment, PLCs, etc.)
- The businesses or the types of materials store’s potential risk (fire, explosion, etc.)
It’s also worth remembering that the numerous connections between buildings (computer networks, remote monitoring, communications, alarms, and power) might cause interference as a result of the electromagnetic field created by lightning or the voltage gradient created in the ground.
These connections can be safeguarded in two ways:
- Shielding or the usage of Faraday cages, which will guard against these fields while also maintaining the link’s equipotentiality (adjacent earthing conductor, twisting, conductor screen, etc.)
- Galvanic decoupling, which electrically separates buildings (optocouplers, fiber optics, isolation transformers, etc.).
d. Down conductors
These serve as a connection between the lightning conductor (rod, cage, or wire) and the earthing electrode. They are exposed to high currents and must have a sufficient cross-section (minimum 50 mm2 copper), be flat (HF current), be firmly fastened, and take the shortest route possible. There must be no abrupt angles or elevations.
Lightning strike counters can be installed on the conductors. The lightning conductor down conductor(s) should be connected to the bonding systems on each floor in structures with several stories. The voltage difference between the down conductors and the internal exposed conductive portions could create a spark over through the building’s walls if this is not done.
Due to the increase in its high-frequency impedance, the circulation of the HF lightning current may produce a substantial voltage surge in the down conductor (several hundred kV). The effects of lightning current circulation in down conductors can be minimized in the installation by: – Increasing the number of down conductors to divide the current and limit the impacts produced by lightning current circulation
- Ensuring that the building’s down conductors are linked to the bonding systems on all floors.
- Developing equipotential bonding systems that include all conductive elements, including inaccessible ones, such as fluid pipes, protection circuits, concrete reinforcements, metal frames, and so on.
- Keep conductors away from sensitive places and equipment (computing, telecommunications, etc.).
e. Earthing system
This is a critical component of lightning protection: all exposed conductive parts, which are interconnected, must be connected, and the system must be capable of discharging the lightning current without causing a voltage spike in the earthing system or the surrounding ground. In terms of the discharge of the high-frequency lightning current, the low-frequency resistance value of the earthing electrode is less essential than its form and size, even though it must be low enough (10 O).
Each down conductor must, in general, terminate in an earthing electrode, which can be made up of conductors (at least three) buried at least 0.5 m deep in a crow’s foot arrangement or earth rods, preferably in a triangle configuration. When possible, increasing the number of down conductors and connection points (each level) and hence the overall scale of the equipotential bonding system is always recommended.
At the same time, the earthing system must be capable of discharging the lightning currents in order to keep the bonding system’s voltage rise as low as possible.
When the equipment to be protected is particularly sensitive (electronics with 0 V referenced to the bonding network, telecommunications, computing shielding, etc. ), when an effective high-frequency earthing electrode cannot be established (for example, rocky ground), or when the scale of the installation is such that there are numerous voltage feedback points, additional measures must be taken to provide protection against a high-frequency voltage rise in the b.
B. Internal protection
a. Active and passive protection of the installation
Fuse and circuit breakers, which are the most often employed safety devices, are too sluggish in comparison to the phenomena of lightning and cannot safeguard electrical or electronic equipment from overvoltage induced by lightning. This necessitates the use of voltage surge protectors. Active surge protection is provided by voltage surge protectors. However, they are only truly effective when carefully and precisely installed: model selection, positioning, connection, and so on. Other physical parameters of the installation (size, equipotentiality, earthing system, circuit isolation, etc.) are other determining variables in addition to this initial need. The term “passive protection” is used to put them all together. Surge protectors for voltage are also used to protect equipment.
- Overvoltage threats from operations may occur statistically more frequently than lightning-caused overvoltage. Despite their reduced energy level, this overvoltage can harm a huge amount of equipment.
- Against electromagnetic interference up to several hundred kilohertz in frequency, such as interference induced by inductive or capacitive loads starting often, or even the operational modes of some devices (repetitive starting of welding stations, high-pressure washers, contactors, radiators, air conditioning units, heaters, etc.).
Despite their modest energy level, these types of overvoltage can hasten the aging of very sensitive equipment (computers, modems, TVs, HiFi systems, etc.). The goal of voltage surge protectors, on the other hand, is not to:
- Filters must be employed to protect equipment from high-frequency interference.
- Protect and install from momentary overvoltage caused by high or low voltage supply defects, such as neutral breaks.
b. Lightning strike withstand equipment
Regardless of how the lightning strike’s energy enters the installation, it creates overvoltage and current levels that are dependent on the installation’s construction and where the energy is created. The requirement to safeguard equipment from overvoltage must be based on a comparison between the potential value of a lightning strike based on installation conditions and the equipment’s impulse voltage withstands value (overvoltage category).
Although lightning is an important and necessary aspect of the earth’s ecology, it can also be devastating. It’s sometimes difficult to comprehend why some areas appear to be prone to lightning. Because they represent the shortest path from a cloud to Earth, very tall objects are frequently targeted. Lightning’s inability to find a rapid and easy path generally results in injury, destruction, and flames. A good lightning protection system can assist in providing that path, lowering the risk of damage to people or animals.
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