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What is lightning equipotential bonding?
The lightning equipotential bonding can be explained as bonding of conducting parts to the Lightning Protection System either by connecting them directly or through Surge protection devices in order to reduce the differences in potential caused during the lightning strikes. This prevents from dangerous sparking that may occur between the external Lightning Protection System and other components.
Metal installations like gas pipes, water pipes, air pipes, heating pipes, shafts of lifts, crane supports etc. shall be bonded together and to the LPS at ground level.
Lightning equipotential bonding should be integrated and coordinated with other equipotential bonding in the structure as shown in the picture above.
When the building height exceeds 30m, equipotential bonding is performed at 20m level height and also at every 20m above that. That is, on such cases the external down conductors, internal down conductors and metals parts are to be bonded.
The conductors used for bonding to the earth-termination system should meet the cross - sectional area requirements as specified by IS/IEC 62305 - part 3 and is independent of class of Lightning Protection system.
Characteristics of flexible metal tubes
1. The outside of the flexible metal tube is wound by a metal band, so it has excellent flexibility.
2. The outer metal strip of the flexible metal tube has corrosion resistance, tensile resistance and wear resistance.
3. The inner wall of the insulating resin layer of the flexible metal tube can withstand high temperatures.
Location of Installation:
Flexible metal conduits are primarily used in dry applications although FMC is available with a UV resistant polymer that makes it watertight. Appropriate liquid tight fittings are required when using this type of conduit in a wet application.
Flexible metal conduits can be installed in most of the same places that rigid conduits are installed.
What is the difference between metal conduit and Flexible Metal Conduit?
Metal conduit is generally a metal conduit, which can transmit liquid and withstand a certain pressure.
Flexible Metal Conduit is a metal spiral sleeve, which is generally used as a wire protection sleeve. The Electrical Flexible Conduit Factory will explain the differences between them in detail.
1. Different definitions
Metal hose: Metal hose is an important component in the connecting pipeline of modern industrial equipment. Metal hoses are used for wires, cables, wire and cable protection tubes for automation instrument signals, and civilian shower hoses with specifications from 3mm to 150mm. Small-caliber metal hoses (inner diameter 3mm-25mm) are mainly used for the protection of sensor lines and industrial sensor lines of precision optical rulers.
Flexible metal casing: Flexible (metal) wire protection casing (now known as flexible metal conduit), the basic type of KZ material is a special insulating resin layer on the inner wall made of hot-dip galvanized steel tape on the outer layer. The basic type is covered with plastic soft polyvinyl chloride, and the flame-retardant KVZ is covered with soft flame-retardant polyvinyl chloride on the basic type.
Ultra-small-diameter metal wire protection sleeve (inner diameter 3mm-25mm) is mainly used for the protection of precision optical ruler's sensor circuit and industrial sensor circuit protection. It has good softness, corrosion resistance, high temperature resistance, wear resistance and tensile strength.
2. Different applications
Metal hose: used to protect various equipment signal lines, transmission wires and cables, and fiber optic cables. Armored optical cables, precision optical rulers, optical measuring instruments, medical instruments, wire protection tubes for machinery and equipment; applicable to public telephones, remote water meters, door magnetic alarms, and other equipment that requires safety protection of wires;
Protection tubes for various small wires; protection tubes for various computer, robots, etc. network cables. PVC protective film for solar equipment.
Flexible metal casing: used as wire, cable, and wire protection cable for automatic instrument signals, specifications from 3mm to 130mm.
① Good flexibility and convenient construction;
② Suitable for construction connection in complex situations;
③ It can be deformed freely, and it has certain rigidity and firmness and is not easy to be damaged;
④ Combined with other waterproof materials, thermal insulation materials and fireproof materials, it can play the function of material use.
What is a lightning flash?
According to IS/IEC 62305 Part-1, lightning flash can be defined as the discharge of charges between the cloud and the earth consisting of one or more strokes.
Types of lightning discharges:
In general, there are four types of lightning discharges. The different types are shown in Figure 1.
1) Intra cloud discharges
2) Cloud to Cloud discharges
3) Cloud to Ground discharges and
4) Ground to Cloud discharges
Among these, more than 50% of the lightning flashes occur within the cloud and only the remaining flashes occur from cloud to ground
Cloud to Ground discharge:
During 45% of cloud to ground flashes, the cloud is positively charged at the top, leaving negative charges at the bottom. So, the lightning starts as a negative leader from the cloud and discharges to the ground. In the remaining 5% flashes, the cloud to ground discharges is initiated as a positive leader from the cloud as the cloud is negatively charged at the top, leaving positive charges at the bottom.
Ground to Cloud discharge:
There are a few extremely rare flashes moving from ground to cloud, are found to occur in high mountain tops and man-made structures that are extremely tall.
Introduction:
Lightning is a natural phenomenon and it cannot be avoided whereas the damages due to lightning can be reduced by providing proper lightning protection system (LPS). A Lightning Protection System consists of both the external and internal lightning protection system. An External LPS provides protection against physical damages whereas an internal LPS provides protection for electrical and electronic systems
Overall Lightning Protection System:
External Lightning Protection System:
An External Lightning Protection System will provide protection to the buildings and structures from the damages due to direct lightning strikes.
An external Lightning Protection System is intended to
1) Safely capture the lightning flash. (Air terminal system)
2) Conduct the lightning current safely from air terminal to the earth. (Down conductor system)
3) Dissipate the lightning current into the earth. (Earth termination system)
Internal Lightning Protection System:
The function of the internal LPS is to protect electrical and electronic equipment inside the structure from the lightning impulse surges by using equipotential bonding or a separation distance along with surge protection devices.
Some of the major sources of transient over-voltages are as follows
1) Lightning strikes on a structure.
2) Lightning strikes near the structure.
3) Lightning strikes on a transmission line.
4) Lightning strikes near a transmission line.
Physical damages due to lightning strikes on the structure shall be protected by using an External Lightning Protection system whereas the electrical equipment shall be protected from lightning impulse currents by using Surge Protection Modules.
The damages of electrical and electronic equipment are either caused by the lightning strikes on the power lines or by the induction due to the impulse currents. Hence this can be classified as the indirect effects of lightning strikes. The indirect effects of lightning strikes are shown below in Figure3.
The protection against the failure of internal systems due to lightning impulse current limits.
The system to be protected shall be located inside Lightning Protection Zone 1(LPZI) or higher. The protection measures for any LPZ shall comply with IS/IEC 62305-4.
Introduction:
A lightning strike is a natural phenomenon of sudden discharge of charges from a highly concentrated cloud or any object. Lightning cannot be avoided, rather the damages can be reduced with proper preventive measures. The complete protection includes a properly designed and executed external and internal lightning protection system.
Lightning Protection System:
The designing of a lightning protection system can be divided into 2 major parts,
1. Risk assessment
2. Designing
Risk assessment:
Risk assessment measures the risk due to lightning strikes and the probability of damages. IS/IEC 62305 -2 explains the damages due to lightning strikes, the source of such damages, losses due to lightning and the corresponding risks.
The damages caused by the lightning strike as specified in IS/IEC 62305 part 2 are as follows.
1) Loss of human life / Injury (D1)
2) Physical damage (D2)
3) Electrical /Electronic components (D3)
We have already explained about the sources of damages, losses, risks and risk components in our previous articles.
Design of lightning protection system:
IS/IEC 62305 -3 has given the procedure for designing lightning protection for both external as well as internal system.
Lightning design shall be done with respect of class of lightning protection system.
The position of the air termination system shall be designed by using the following placement methods as specified by IS/IEC 62305-3
1) Protection Angle Method
2) Rolling Sphere Method
3) Mesh Method
The distance between down conductors will depends on the class of lightning protection. IS/IEC 62305 has given the arrangement of earth termination system.
Lightning cannot be avoided, rather the damages can be reduced with the help of well-designed and executed Lightning Protection System. LPS usually consists of both external and internal lightning protection system.
An external Lightning Protection System consists of,
1. Air terminals
2. Down conductor
3. Earthing system.
Test Joint:
Test Joints act as the intersection of down conductor and the earthing system. The down conductor will be terminated at the Test joints whereas the connections to the earthing system begins at the test joints. Test joints will be provided on each down conductors.
At normal operating conditions the test link will remain in closed position. During the time of inspection, the test link or test joint in every down conductor can be used to isolate the earthing from the lightning protection system.
The test joints will be used for inspecting both the continuity of the down conductor, air terminal interconnections and the earth electrode resistance values
Introduction:
The components of Lightning Protection System (LPS) are exposed to direct lightning strikes and corrosive atmosphere. The materials should have high current withstanding capacity and they should be less corrosive. The current carrying capacity depends on the cross sectional area and the materials should be selected based on the local environment.
A material which is most preferable for some site conditions might be the least preferred material for other site conditions due to its chemical properties. Apart from the corrosion of materials due to the local environment, the contact of two dissimilar materials also leads to galvanic corrosion. Hence, IS/IEC 62305 suggests the materials that can be used for different corrosive environments and it has provided the minimum cross sectional area required for different materials of LPS Components.
Minimum Cross sectional area of different materials:
The minimum cross-sectional area of different materials suggested by IS/IEC 62305-3 are as follows.
Protection against corrosion:
Aluminium has very good electrical conductivity but it more prone to corrosion on soil and concrete medium. Hence, they can be used for air terminal and down conductor systems above the ground level and connected to earthing system of Gl/Copper/SS using proper bimetallic connectors. The fasteners or sleeves for aluminium conductors should be made of similar metal and it should have adequate crosssectional area to withstand the adverse weather conditions.
What is lightning equipotential bonding?
The lightning equipotential bonding can be explained as bonding of conducting parts to the Lightning Protection System either by connecting them directly or through Surge protection devices in order to reduce the differences in potential caused during the lightning strikes. This prevents from dangerous sparking that may occur between the external Lightning Protection System and other components.
Metal installations like gas pipes, water pipes, air pipes, heating pipes, shafts of lifts, crane supports etc. shall be bonded together and to the LPS at ground level.
Lightning equipotential bonding should be integrated and coordinated with other equipotential bonding in the structure as shown in the picture above.
When the building height exceeds 30m, equipotential bonding is performed at 20m level height and also at every 20m above that. That is, on such cases the external down conductors, internal down conductors and metals parts are to be bonded.
The conductors used for bonding to the earth-termination system should meet the cross - sectional area requirements as specified by IS/IEC 62305 - part 3 and is independent of class of Lightning Protection system.
Introduction:
Lightning is one of the most destructive phenomena of nature. It can cause damage to humans, structures, electrical and electronics equipment. Currently, due to global warming, the entire world is moving towards Renewable Energy, and Solar Panels are at high risk due to the possibility of destruction by lightning strikes because of its elevation and the widespread vacant land areas chosen for the installation of such structures. Redesigning or modification of Lightning Protection System post the installation of these structures isn't advisable as it would attract heavy expenses and hence a properly designed LPS as per relevant standards mandatory. Lightning could strike and cause damage to the solar panels either directly or indirectly. External protection of solar panel against direct lightning strikes needs an air terminal to intercept the lightning strike, a down conductor to provide a dedicated path and an efficient earthing system to dissipate the lightning current in to the earth. The internal protection of solar panels needs an appropriate surge protection device to protect these solar panels from getting damaged from a surge current caused due to lightning strikes.
The external lightning protection shall be provided by any of the following two methods.
1) Non-Isolated Lightning Protection System
2) Isolated Lightning Protection System
Non-Isolated Lightning Protection System:
Reference: NBC 2016 Part 8 Clause 11.5.1.7
Air terminal height: less than 0.5m
Positioning method: Rolling Sphere Method
Max. distance between air terminals: 15m
Protected Region: (12X9) m using 2 air terminals
As the influence of the shadow of Lightning arrestor arrangement on the solar panel could hamper the performance of the entire solar system, the height of the LA should be restricted to less than 0.5m above the solar panel.
Isolated Lightning Protection System:
Reference: NFC 17-102/2011
Air terminal height: > 5m above solar panels
Radius of Protection: 107m
As we said early, the shadow effect of the solar panel arrangement could affect the performance of entire solar panel. So, we will maintain safe separation distance between LPS and solar panel for avoiding those effects. This separation distance between the solar panel and the Lightning Protection System shall be calculated based on the following parameters. Height of the supporting mast. Latitude and Longitude of the site. Time of operation and Seasonal variation
The transmission lines are more to lightning strikes because of the following reasons,
1) Directly exposed to atmosphere,
2) Higher than other structures,
3) Higher charge concentration as they are earthed at every pole,
4) Lower earth resistance
The ground wires at the top of transmission lines act as a shield and protect the live lines from lightning strikes.
The transmission lines are protected from lightning strikes by taking measures like adding overhead ground wires, reducing the tower foot resistance, adding counterpoise wires, increasing insulation, etc.
The overhead ground wires protect the transmission lines from direct lightning strikes. A ground wire is a conductor that runs in parallel to the line conductor and is placed at the top of the tower structure as shown in the picture below.
The ground wire is placed over the tower in such a way that all the lines are placed well within the shielding angle of the ground wires. The height of the shielding earth wire depends on the width of the cross arm.
Since the earth wires are exposed are directly exposed to extreme weather conditions, it should possess sufficient mechanical strength
Telecommunication System:
Telecommunication plays a major role in the industrial revolution which we are currently undergoing - INDUSTRY 4.0. Industrial automation involves communication of the each and every machine with the central hub which helps to monitor and analyse the issues even without direct intervention. The automation is even extended to individual homes which results in SMART HOMES. Thus, the telecommunication devices have become very essential components of our day-to-day life.
Overall Lightning Protection System:
The towers used for telecommunication will be taller than the remaining structures in the premises to avoid the obstacles and interference to the signals which will be transmitted received through the antenna. These metallic towers are more prone to lightning strikes because of their position and height of the structures and the electronic devices used for transmitting and receiving the data are very sensitive to impulse surges. Hence a complete lightning protection system is very essential for the telecommunication towers to provide uninterrupted and efficient service. The complete protection includes,
1) Properly designed and executed external lightning protection system.
2) Installing Surge protection devices for both power line and data line and
Introduction:
Heavy duty stacks are smoke or vent stack more than 75 feet high, and in which the cross sectional area of the flue more than 500 square inches. The guidance provided by UL for protecting the Heavy-Duty Stacks in the application guide is as follows.
Challenges in Protection:
Since stacks are very high structures, they are more prone to lightning strikes. The chances of side flashes to the stacks are also high. Hence care should be taken on designing the proper lightning protection system and installation should be made as per the design to provide protection to the structure and the people within the zone.
In addition to the height of the stacks, the one more important factor that has to be considered while designing the protection sys em of stack is material selection. Since the stack acts as vent for flue gases, the materials used on the top of stack (air terminal) are more prone to corrosion.
Hence the material should possess good corrosion resistance property.
Corrosion Zone:
The top 25 feet of a stack is generally the high corrosion zone and hence a minimum of 1/16 inch coating of lead should be provided for terminals, mounting brackets and conductors.
The components used in the upper 25 feet shall be made of materials like copper, copper alloy. bronze or stainless steel.
Aluminium components are prohibited in this installation.
Designing:
All components shall be designed by considering Class Il protection. The materials of air terminals on stacks shall be solid copper, copper alloy, stainless steel or monel metal