Lightning Protection Systems and Earthing Quizzes
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Questions and Answers

What is the main characteristic of the Type A earthing arrangement?

It consists of horizontal or vertical earth electrodes connected to each down conductor fixed on the outside of the structure.

Describe the layout of the Type B arrangement in an earthing system.

Type B arrangement features a fully connected ring earth electrode around the structure's periphery, in contact with soil for at least 80% of its length.

What role do foundation earth electrodes play in earthing systems?

Foundation earth electrodes, installed in the concrete foundation, augment the Type B arrangement and may use steel reinforcing foundation mesh.

Why is a separation distance important in the design of external lightning protection systems (LPS)?

<p>A separation distance minimizes the risk of partial lightning current entering the structure through conductive parts.</p> Signup and view all the answers

What does BS EN/IEC 62305 recommend regarding earth termination systems?

<p>It recommends a single integrated earth termination system combining lightning protection, power, and telecommunication systems.</p> Signup and view all the answers

What is the primary role of an internal LPS?

<p>The primary role is to prevent dangerous sparking within the structure due to lightning discharge currents.</p> Signup and view all the answers

What happens if lightning discharge strikes a lightning conductor too close to structural metal parts?

<p>It can bridge the gap, introducing partial lightning current into the structure and causing potential hazards.</p> Signup and view all the answers

How does the Type B arrangement differ from the Type A arrangement?

<p>Type B uses a ring electrode around the structure, while Type A connects individual electrodes to each down conductor.</p> Signup and view all the answers

What is the primary objective of an earthing system in electrical installations?

<p>To maintain a zero potential or zero voltage of all non-current carrying parts to prevent lethal shocks.</p> Signup and view all the answers

How does the BS EN/IEC 62305 series of standards relate to structural lightning protection?

<p>It acknowledges the need for integrating structural lightning protection with transient overvoltage and surge protection for equipment.</p> Signup and view all the answers

What role do surge protective devices (SPDs) play in lightning protection systems?

<p>SPDs provide a practical cost-effective means of protecting systems during lightning electromagnetic pulse (LEMP) activity.</p> Signup and view all the answers

List two purposes of earthing as mentioned in the specifications for S&T installations.

<ol> <li>To afford safety to personnel against shock. 2. To protect equipment against high voltages.</li> </ol> Signup and view all the answers

What can happen if non-current carrying parts of an electrical system are not earthed?

<p>If electrified, a person touching those parts could receive a lethal shock.</p> Signup and view all the answers

Why is it important to eliminate or limit voltages and currents caused by electromagnetic interference (EMI)?

<p>To ensure the safe and reliable operation of equipment.</p> Signup and view all the answers

What is one way that earthing provides a return path in electrical systems?

<p>By earthing protective devices like surge arrestors and lightning dischargers.</p> Signup and view all the answers

How does earthing facilitate the operation of protective devices in power supply systems?

<p>It provides a path for heavy fault currents to ensure effective and quick operations.</p> Signup and view all the answers

What is the significance of the hemisphere of radius L when considering electrode to earth resistance?

<p>The hemisphere of radius L represents the exclusive soil portion required for each electrode, influencing the calculation of electrode to earth resistance.</p> Signup and view all the answers

How does the separation distance of electrodes affect the electrode to earth resistance, and what is the optimal distance mentioned?

<p>The electrode to earth resistance can be halved if the electrodes are separated by a distance of 2L.</p> Signup and view all the answers

In the formula for plate electrode resistance, which parameter has the most significant effect on the resistance?

<p>The length L has a major influence, while thickness T has a minor influence on the electrode to earth resistance.</p> Signup and view all the answers

What approach did engineers adopt to address the limitations of using large area earthing plates?

<p>Engineers began using electrode-grids for substations to effectively reduce high 'electrode to earth' resistance.</p> Signup and view all the answers

What primary materials compose Earth enhancement material?

<p>Graphite and Portland cement.</p> Signup and view all the answers

List two methods to reduce earth resistance outlined in the content.

<p>Adding salt, charcoal, and sand mixture, and burying the ground electrode as deep as possible are two methods to reduce earth resistance.</p> Signup and view all the answers

What is the resistivity range of surface soil such as loam, according to the provided table?

<p>The resistivity of surface soil, loam, etc. ranges from 1 to 50 Ohm-m.</p> Signup and view all the answers

What is the maximum resistivity allowed for Earth enhancement material?

<p>Less than 0.2 ohm-meters.</p> Signup and view all the answers

Why is a maintenance-free earth system recommended when managing multiple earth systems?

<p>A maintenance-free earth system is recommended to simplify tracking and treatment across a large number of systems.</p> Signup and view all the answers

Why should Earth enhancement material not dissolve or leach over time?

<p>To maintain its conductivity and to avoid polluting the soil or local water table.</p> Signup and view all the answers

What is the resistivity of clay soil as per the given information?

<p>The resistivity of clay soil ranges from 2 to 100 Ohm-m.</p> Signup and view all the answers

What characteristic of Earth enhancement material ensures that it does not require water to maintain its effectiveness?

<p>It shall not depend on the continuous presence of water.</p> Signup and view all the answers

What are the thermal stability requirements for Earth enhancement material?

<p>It must be thermally stable between -100 C to +600 C.</p> Signup and view all the answers

What kind of treatment or replacement does Earth enhancement material require over time?

<p>It requires no periodic charging treatment nor replacement and maintenance.</p> Signup and view all the answers

What must be done to excavated soil before using it as backfill around an electrode?

<p>It should be sieved to remove any large stones and well compacted.</p> Signup and view all the answers

List three materials that should not be used as backfill for earthing electrodes.

<p>Sand, salt, and cinders.</p> Signup and view all the answers

How does moisture content below 20 percent affect soil resistivity?

<p>Below 20 percent moisture, soil resistivity increases very abruptly with a decrease in moisture content.</p> Signup and view all the answers

What is the normal range of moisture content in soil throughout different seasons?

<p>Normal moisture content ranges from 10 percent in dry seasons to 35 percent in wet seasons, averaging about 16 to 18 percent.</p> Signup and view all the answers

What depth should earth electrodes be installed in cold climates?

<p>In cold climates, earth electrodes should be installed at least 2 meters below the frost line.</p> Signup and view all the answers

Why is temperature only a minor factor affecting soil resistivity above freezing point?

<p>The temperature coefficient of resistivity is negligible above freezing, having minimal impact on resistivity changes.</p> Signup and view all the answers

Explain the effect of freezing temperatures on soil resistivity.

<p>Below 0°C, water in the soil begins to freeze, causing a tremendous increase in soil resistivity.</p> Signup and view all the answers

What are the recommended types of soil for constructing earth pits?

<p>Preferred soil types include wet marshy ground, clay loam, damp sand, and peat in that order of preference.</p> Signup and view all the answers

What happens to soil resistivity when moisture content falls slightly below 20 percent?

<p>A difference of a few percent moisture below 20 percent can cause a marked increase in soil resistivity.</p> Signup and view all the answers

What is the resistivity change rate per degree Celsius at 20°C?

<p>At 20°C, the resistivity changes by about 9 percent per degree Celsius.</p> Signup and view all the answers

What types of ground conditions should be avoided when choosing a site for earthing systems?

<p>Dry sand, gravel, chalk, limestone, granite, very stony ground, and areas with virgin rock close to the surface should be avoided.</p> Signup and view all the answers

Why is a water-logged situation not essential for earthing systems unless the soil is sand or gravel?

<p>Because above 15 to 20 percent moisture content, additional moisture does not significantly improve the earthing effectiveness.</p> Signup and view all the answers

How does the shape of an electrode affect its resistance?

<p>The resistance is lower for shapes like pipes, rods, or strips compared to plates due to the current density decreasing rapidly with distance from the electrode.</p> Signup and view all the answers

What is the formula for calculating the electrode to earth resistance of a plate electrode?

<p>The formula is $R = \frac{\rho}{2\pi L} \left[\ln(8L/T) + \ln(L/h) - 2 + (2h/L) - (h/L)^{2}\right]$.</p> Signup and view all the answers

What influence does the length (L) of a plate electrode have on its resistance?

<p>The length (L) has a major influence on reducing the electrode to earth resistance.</p> Signup and view all the answers

What factors are less influential on the resistance of a plate electrode compared to its length?

<p>The thickness (T) of the electrode has a minor influence compared to the length.</p> Signup and view all the answers

What advantages do strip or conductor electrodes have in specific ground conditions?

<p>They are beneficial where high resistivity soil lies beneath shallow layers of low resistivity.</p> Signup and view all the answers

Why did electrical engineers shift from using large area earthing plates to electrode grids in substations?

<p>They realized that large area plates did not effectively solve the problem of high 'electrode to earth' resistance.</p> Signup and view all the answers

What are the maximum mesh sizes for the Class I LPS as per BS EN/IEC 62305?

<p>5X5 meters.</p> Signup and view all the answers

What condition must be met for the mesh method to be suitable for protecting plain surfaces?

<p>Air termination conductors must be at roof edges and no metal installations can protrude above the system.</p> Signup and view all the answers

What spacing is required between vertical air rods as recommended in the standards?

<p>Not more than 10 meters apart.</p> Signup and view all the answers

How far apart should strike plates be placed over roof areas according to the guidelines?

<p>Not more than 5 meters apart.</p> Signup and view all the answers

Why are edges and corners of roofs considered particularly vulnerable to lightning damage?

<p>They are most susceptible to strikes, necessitating additional protection measures.</p> Signup and view all the answers

What role do fortuitous metalworks play in the current lightning protection standards?

<p>They can be utilized as part of the air termination system.</p> Signup and view all the answers

What major type of systems did the IEC 62305 standards evaluate regarding their validity?

<p>Non-conventional air termination systems.</p> Signup and view all the answers

What is the effect of a roof pitch of more than 1 in 10 on air termination conductors?

<p>It requires conductors to be positioned along the roof edges and ridges for optimal protection.</p> Signup and view all the answers

What are the primary physical effects of lightning on signal and telecom installations?

<p>Lightning can cause physical damage, electrical surges, and malfunctions in S&amp;T installations.</p> Signup and view all the answers

Explain the concept of Lightning Protection Zones (LPZ).

<p>LPZs are designated areas that define the levels of lightning protection and the corresponding risks within those areas.</p> Signup and view all the answers

What is the significance of the IEC 62305 standard in surge protection?

<p>The IEC 62305 standard provides comprehensive guidelines for lightning protection systems and risk management.</p> Signup and view all the answers

What key characteristics define a good earthing system?

<p>A good earthing system should have low resistance, effective current dissipation, and proper grounding techniques.</p> Signup and view all the answers

Describe the role of the earth termination system in lightning protection.

<p>The earth termination system safely conducts lightning currents into the ground, minimizing damage to structures.</p> Signup and view all the answers

How does soil resistivity influence the design of earthing systems?

<p>Low soil resistivity allows for better current flow, which is critical for the effectiveness of earthing systems.</p> Signup and view all the answers

What are the implications of having high earth resistance in an earthing system?

<p>High earth resistance can lead to inadequate dissipation of fault currents, increasing the risk of electric shock or equipment damage.</p> Signup and view all the answers

What factors should be considered when selecting surge protective devices (SPDs)?

<p>Considerations include protection level, voltage ratings, and environmental conditions where the SPDs will be installed.</p> Signup and view all the answers

Why is the concept of 'equivalent earth resistance' important in grounding systems?

<p>Equivalent earth resistance measures the effectiveness of the grounding system in dissipating fault currents safely.</p> Signup and view all the answers

How can moisture content in soil affect its resistivity, and what is its optimal range?

<p>Increased moisture content typically lowers soil resistivity; an optimal range is generally between 10-20%.</p> Signup and view all the answers

How does the Type A arrangement facilitate lightning dissipation compared to Type B?

<p>The Type A arrangement connects horizontal or vertical earth electrodes directly to each down conductor, providing localized dissipation, while Type B uses a periphery ring for a broader, integrated grounding strategy.</p> Signup and view all the answers

What limitations arise from having 20% of the Type B earth electrode not in soil contact?

<p>The limitation is that it reduces the overall effectiveness of the grounding system, as not being in soil contact can lead to higher resistance and less efficient current dissipation.</p> Signup and view all the answers

Explain the importance of the integrated earth termination system recommended by BS EN/IEC 62305.

<p>An integrated system minimizes the risk of dangerous sparking and ensures effective protection for lightning, power, and telecommunication systems by maintaining a common grounding point.</p> Signup and view all the answers

How do foundation earth electrodes enhance the function of earthing systems?

<p>They augment the earthing capability by incorporating electrodes directly into the concrete foundation, thus ensuring stability and continuity in grounding.</p> Signup and view all the answers

What measures can be taken to achieve the separation distance necessary for external lightning protection systems?

<p>Measures include strategically placing lightning conductors away from structural metal parts to avoid any bridging of electrical currents during a discharge.</p> Signup and view all the answers

Discuss the impact of internal LPS design on spark prevention after a lightning event.

<p>Internal LPS design is critical for preventing dangerous sparking by mitigating the flow of lightning current through conductive internal components.</p> Signup and view all the answers

Why is the material property of Earth enhancement critical in sustaining the effectiveness of earthing systems?

<p>The material must maintain stability and not leach, which ensures that its resistivity levels remain consistent over time without requiring regular maintenance.</p> Signup and view all the answers

How does the interaction of moisture content within soil affect the performance of earthing systems?

<p>If the moisture content drops below 20%, soil resistivity increases, reducing the efficiency of grounding, while normal moisture levels promote adequate electrical conductivity.</p> Signup and view all the answers

What is the impact on soil resistivity when moisture content decreases below 20 percent?

<p>Soil resistivity increases very abruptly with decreases in moisture content below 20 percent.</p> Signup and view all the answers

How does temperature influence soil resistivity at low temperatures?

<p>At low temperatures, particularly below 0°C, soil resistivity increases significantly due to the freezing of water in the soil.</p> Signup and view all the answers

What types of soil are most preferred for locating earth pits?

<p>Wet marshy ground is the most preferred, followed by clay or loamy soil.</p> Signup and view all the answers

What is the significance of maintaining moisture content within 10 to 35 percent in soil?

<p>This range allows for optimal conductivity, ensuring that soil resistivity remains stable enough for effective earth connections.</p> Signup and view all the answers

What happens to the resistivity of soil at temperatures around 20°C?

<p>The resistivity changes by approximately 9 percent per degree Celsius at this temperature.</p> Signup and view all the answers

Why should earth electrodes be installed well below the frost line in colder climates?

<p>This prevents significant variations in resistance caused by freezing temperatures and ensures consistent grounding.</p> Signup and view all the answers

What are the consequences of not driving earth electrodes below the frost depth?

<p>There will be a substantial variation in resistance throughout different seasons, affecting grounding effectiveness.</p> Signup and view all the answers

How does the presence of frozen soil affect the length of an electrode in contact with normal resistivity soil?

<p>Frozen upper soil increases resistivity and effectively shortens the active length of the electrode.</p> Signup and view all the answers

What is the effect of increasing the distance between two earth electrodes on their resistance?

<p>Increasing the distance reduces the total earth resistance due to decreased mutual influence.</p> Signup and view all the answers

Why must the water pipe system in the Dead Earth method be metallic and extensive?

<p>It must be metallic to ensure low resistance and extensive to minimize resistance impact on measurement.</p> Signup and view all the answers

Explain the concept of the sphere of influence and its importance in earthing systems.

<p>The sphere of influence is the volume around the earth electrode where electrical charges spread, impacting resistance measurements.</p> Signup and view all the answers

What must be avoided when placing multiple earth pits to ensure effective earthing?

<p>Earth pits should not be placed within the sphere of influence of each other.</p> Signup and view all the answers

How does resistance in the Dead Earth method differ when using non-metallic pipes?

<p>Using non-metallic pipes would increase resistance, leading to inaccurate measurement.</p> Signup and view all the answers

What is the minimum separation distance recommended between two earth electrodes?

<p>The separation distance should be at least twice the length of the electrode.</p> Signup and view all the answers

What precautions should be taken regarding the earth electrode's distance from the water pipe system in the Dead Earth method?

<p>The earth electrode must be far enough away to avoid being influenced by the water pipe's resistance.</p> Signup and view all the answers

Describe how the concept of shells influences earth resistance measurements.

<p>The closest shell to the electrode has the highest resistance and affects the measurements significantly.</p> Signup and view all the answers

What is the maximum current density at the surface of an earth electrode to prevent failure under normal system operation?

<p>40 A/m²</p> Signup and view all the answers

How does the duration of the earth fault (t) affect the maximum permissible current density according to the formula provided?

<p>The maximum permissible current density is inversely proportional to the duration of the earth fault.</p> Signup and view all the answers

What happens to soil resistance when moisture is driven away from the soil-electrode interface?

<p>The resistance increases, potentially becoming infinite with enough temperature rise.</p> Signup and view all the answers

According to the provided research, what is the relationship between specific loading and time to failure during short-time overload?

<p>Time to failure is inversely proportional to the square of the current density (i²).</p> Signup and view all the answers

What is the formula for maximum permissible current density (i) in relation to soil resistivity (ρ) and fault duration (t)?

<p>i = 7.57 x 10³ / √(ρ t) A/m²</p> Signup and view all the answers

What general effect does sustained current loading have on the resistance of soils with a negative temperature coefficient?

<p>It generally leads to an initial decrease in electrode resistance.</p> Signup and view all the answers

In regards to earth electrodes, what critical condition of operation is affected by soil moisture content?

<p>Long-time overloading conditions are significantly affected by soil moisture.</p> Signup and view all the answers

What characteristic of soil helps prevent failure of earth electrodes during long-duration loading?

<p>The initial decrease in electrode resistance due to soil properties.</p> Signup and view all the answers

Flashcards

Electrode to Earth Resistance

The electrical resistance between an electrode and the earth.

Soil Resistivity

A measure of how much a soil resists the flow of electricity.

Plate Electrode Resistance

Resistance of a plate-shaped electrode to earth, influenced mainly by its length and depth.

Electrode Separation

The distance between multiple electrodes.

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Grounding Electrode

An electrode used to establish a connection to the earth.

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Maintenance-free earthing

System design for earth that needs little or no maintenance.

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Methods to Reduce Earth Resistance

Various approaches to lower the electrical resistance of an earthing system.

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Soil Types and Resistivity

Different soil types have varying resistances to electricity flow.

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Type A earthing

Horizontal or vertical electrodes connected to down conductors outside a structure. Each down conductor has an attached electrode (rod).

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Type B earthing

A ring electrode around a structure, in contact with soil for at least 80% of its length.

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Foundation earthing

Type B earthing system installed within the concrete foundation.

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External LPS separation

Electrical insulation between external lightning protection system (LPS) and building metal parts to prevent internal sparking.

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Internal LPS

Lightning protection system within a structure to prevent internal sparking after a lightning strike.

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Integrated earthing system

Combining lightning, power, and telecommunication grounding into one system.

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Down Conductor

A conductor used to direct lightning currents to ground.

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Earthing electrode

A conductive object placed in contact with the ground to provide a low-resistance path to the earth.

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Lightning Protection and Equipment

Lightning protection of structures needs to be coupled with surge protection for electrical/electronic systems within them.

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Surge Protection Devices (SPDs)

Enhanced SPDs are cost-effective devices for protecting critical systems during lightning events (LEMP).

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Earthing System Objective

Earthing systems ensure non-current carrying parts of electrical systems have zero potential to prevent electrocution.

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Earthing Safety

Earthing protects personnel by providing a path for fault currents to ground.

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Fault Current Return Path

Earthing provides a pathway for fault currents in electrical systems.

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EMI/RFI Protection

Earthing protects equipment from electromagnetic (EMI) and radio frequency interference (RFI).

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Equipment Protection (Earthing)

Earthing protects equipment by reducing/limiting voltages due to interference from EMI/RFI.

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RDSO Specifications

RDSO specifications outline the standards for the earthing systems for signal and telecommunication (S&T) installations.

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Soil Moisture Effect

Soil resistivity is greatly affected by moisture content. Above 20% moisture, resistivity changes little; below 20%, resistivity increases significantly with less moisture.

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Moisture Threshold

A moisture content of approximately 20% in soil where soil resistance changes little compared to changes in lower moisture levels.

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Frost Line Depth

Installation depth for earth electrodes; crucial to prevent ground freezing and soil resistance fluctuations due to temperature.

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Soil Temperature

Temperature significantly impacts soil resistivity, especially around and below freezing point (0°C).

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Temperature Coefficient

How much a soil's resistivity changes with a 1-degree Celsius temperature change. Below freezing point, it's much higher.

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Wet Marshy Ground

Preferred location for installing earth electrodes due to its low resistivity.

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Optimum Soil

Clay, loamy, arable land, or a mix of clay and loam with a small amount of sand are good choices for earth electrode locations.

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Soil Selection

For proper grounding, select sites with damp or wet conditions, clay and loam mixed with limited sand, gravel, or stones, or marshlands.

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Earthing Electrode Shape

The shape of an electrode affects its resistance; long, thin shapes (e.g., pipes, rods) have lower resistance than broad shapes (e.g., plates).

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Plate Electrode Resistance

Resistance of a flat electrode (plate) to earth is primarily determined by its length and depth, but also affected by its thickness, calculated using a specific formula.

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Soil Moisture (Earthing)

Soil's moisture content directly impacts earthing efficiency. While more moisture generally reduces resistance, excessive moisture can be detrimental.

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Avoidance of Well-Drained Sites

For optimal earthing, avoid natural, well-drained soil sites, including those near surface rock or those with constantly flowing water.

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Current Density and Electrodes

Optimal earthing design focuses on minimizing the highest concentration of current flow directly near the electrode to reduce overall resistance.

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Electrode Resistance (Effect of Shape)

The majority of the potential drop in a soil-electrode system happens close to the electrode.

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Soil Types and Earthing

Different soil types have varying electrical resistivity, influencing the design choice for earthing systems.

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Electrode-Grids for Substations

Using multiple electrodes in a grid pattern resolves issues with high resistance in some sites, which large standalone electrodes could not manage.

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Earth Enhancement Material

A superior conductive material used to improve earthing effectiveness in poor conductivity areas.

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Conductivity Improvement

Enhancing the ability of the earth to conduct electricity.

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Graphite and Portland Cement

Main components of earth enhancement material.

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Resistivity (Earth Enhancement)

Measure of how much the material resists electricity flow (less than 0.2 ohm-meters).

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Non-corrosive Material

Earth enhancement material does not corrode.

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Backfill Material

Suitable material to fill around the electrode for improved contact.

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Sieved Excavated Soil

Soil with large stones removed for improved backfill.

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Acceptable Backfill Materials

Suitable backfill materials, such as sieved soil, are non-corrosive.

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Surge Protection Devices (SPDs)

Devices used to protect electrical equipment from surges, like lightning.

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Earthing System Objective

To ensure non-current carrying system parts have zero potential, preventing electrocution.

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Soil Resistivity

Measure of a soil's resistance to electrical current flow.

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Earth Electrode

A conductive object placed in contact with earth to provide a low-resistance path to ground.

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Lightning Protection Zones

Areas categorized based on the risk of being struck by lightning.

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Surge Protection Standard (IEC 62305)

International standard for surge protection devices and systems.

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Earth Resistance

The measure of how hard it is for current to flow from an electrode to the earth.

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Pipe Electrode

A long cylindrical metal pipe used to lower soil resistance, often buried deeply.

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RDSO Specifications

Guidelines for signal and telecommunication (S&T) earthing systems.

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Surge Protection Measures (SPMs)

Techniques and devices used to protect electrical/electronic systems from voltage surges.

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Mesh Method

A lightning protection method using a mesh of conductors on the roof. Specific mesh sizes correlate to different lightning protection classes.

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Air termination mesh size (LPS Class)

Different mesh sizes (5x5m, 10x10m, 15x15m, 20x20m) relate to varying protection classes (I-IV) of lightning protection systems (LPS).

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Roof edges and corners

Most vulnerable parts of roofs to lightning strikes, especially flat roofs. Perimeter conductors are best placed here.

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Pitch > 1 in 10

Roof slope requirement of more than 5.7 degrees (1 in 10) for correct air termination system placement.

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Non-conventional air termination

Alternative lightning protection systems for which the validity of claims is uncertain and not accepted by current lightning protection standards.

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Air Rods/Strike Plates

Air termination devices (vertical rods or flat strike plates) strategically placed above the roof to channel lightning strikes to down conductors.

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Maximum Rod Spacing

Air termination rods should be no more than 10 meters apart and strike plates should be spaced at maximum 5 meters apart.

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BS EN/IEC 62305

International standard for surge protection, replacing BS 6651.

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Type A Earthing

Horizontal or vertical electrodes connected to down conductors outside a structure. Each down conductor has an attached electrode (rod).

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Type B Earthing

A ring electrode around a structure, in contact with soil for at least 80% of its length.

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Foundation Earthing

Type B earthing system installed within the concrete foundation of a structure.

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External LPS Separation

Electrical insulation between the external lightning protection system and the building's metal parts.

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Internal LPS

Lightning protection system within a structure to prevent internal sparking after a lightning strike.

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Integrated Earthing System

Combining lightning, power, and telecommunication grounding into one system.

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Surge Protection Standard (IEC 62305)

International standard for surge protection devices and systems.

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Earth Resistance

The measure of how hard it is for current to flow from an electrode to the earth.

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Soil Moisture Effect

Soil resistivity is significantly affected by moisture content. Above 20%, resistivity changes little; below 20%, resistivity increases with decreasing moisture.

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Frost Line Depth

The depth at which earth electrodes should be installed to prevent ground freezing and associated soil resistance fluctuations.

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Soil Temperature Effect

Soil temperature affects resistivity, especially near and below freezing point. It has a negligible effect above freezing.

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Moisture Threshold

The approximate moisture content (around 20%) in soil where soil resistivity changes are minimal compared to drier conditions.

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Wet Marshy Ground

Preferred location for installing earth electrodes due to its generally low resistivity.

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Optimum Soil Type

Clay, loamy soil, arable land, and certain combinations of clay, loam and sand offer suitable conditions for earth electrodes.

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Soil Resistivity

A measure of how much a soil resists the flow of electrical current.

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Earth Electrode Placement

Selecting an appropriate site for earth electrodes depends on soil type and moisture content.

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Current Density (Earth Electrode)

The amount of current flowing per unit area at the surface of an earth electrode.

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Maximum Current Density for Normal Operation

40 A/m² for long-duration, normal system operation, preventing electrode failure (due to excessive heat).

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Short-Time Overload Formula

i = 7.57 x 10³ / √(ρt), where 'i' is current density (A/m²), 'ρ' soil resistivity (Ω.m), and 't' duration (s).

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Soil Resistivity (ρ)

A measure of how resistant the soil is to the flow of electric current.

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Time to Failure (Short-Time Overload)

Inversely proportional to the square of the current density (i²).

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Long Duration Loading

Earth electrode loading during normal system operation.

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Earth Electrode Failure

Failure of the earth electrode due to extensive temperature increase at the electrode surface during overloading.

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Temperature Coefficient (Soil)

A measure of how much the resistance of the soil changes when the soil temperature changes.

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Sphere of Influence

The area surrounding an earth electrode where electrical charges spread.

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Two Electrode Method

Measuring earth resistance by using two electrodes, often with a water pipe as one.

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Dead Earth Method

The simplest method for measuring earth resistance using a water pipe as one terminal.

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Electrode Separation

Distance between earth electrodes; must be at least twice the length of the electrode for accurate measurements.

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Water Pipe Requirements

Water pipe system, used in dead earth method for measuring earth resistance, must be extensive and metallic without any insulating material.

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Sphere of Influence (Electrode Placement )

Electrodes should be placed outside the sphere of influence of each other to prevent interference in the earth resistance measurement.

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Minimizing Earth Resistance

Reducing earth resistance (measured during installation or testing) can be achieved through strategic placement and connection of multiple earth electrodes.

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Two Terminal Method Precautions

For accurate two-terminal method measurements, the water pipe should be extensive, metallic and far enough outside the influence of the measured electrode.

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Study Notes

TC 5 EARTHING AND SURGE PROTECTION DEVICES

  • Material presented in these IRISET notes is for guidance only. It does not override or alter any of the provisions contained in manuals or railway board directives.
  • The document is from the Indian Railway Institute of Signal Engineering and Telecommunications, Secunderabad, February 2020.

Surges and Their Effects on S&T Installations

  • Signal and Telecommunication systems function continuously for safe and smooth train operations on Indian Railways.
  • These systems use sophisticated devices like ICs, Microprocessors, and Microcontrollers that are susceptible to transient surge voltage and currents.
  • Surge protection is required to ensure uninterrupted service and avoid costly equipment replacement damage.
  • Surges are transient phenomena involving potential and current buildups that exceed normal operating values, potentially damaging equipment.
  • Causes of surges include: lightning discharges, switching inductive loads (transformers, relays, motors), welding, tripping of fuses/circuit breakers, power supply malfunctions, and short circuits.
  • Results of surges include: service interruption and equipment replacement costs.
  • Lightning takes place due to charge accumulation in clouds during thunderstorms.
  • Tropical thunderstorms (heat storms) are caused by warm air rising, creating cloud cells.
  • Temperate thunderstorms (frontal storms) involve frontal waves pushing up warm air.
  • Lightning involves a stepped leader (from cloud to ground), which makes a zigzag path of negative charge, resulting in a return stroke (ground to cloud).
  • Physical effects of lightning include: air heating, pressure shock waves, high current flow, and high voltage differentials, requiring surge protection.
  • Surge current is characterized by surge amplitude, time to reach maximum value, and time to reach half-maximum value.

Fundamentals of Earthing

  • Earthing is not about good conductivity but the ideal equipotential surface of earth.
  • Earth is a poor conductor but required for equipotential surface.
  • Earth's resistivity varies with material (e.g., copper, GI, wet/moist/dry soil, bedrock).
  • Factors influencing earth resistance include electrode material properties, geometry, and soil resistivity.
  • Pipe Electrode: Resistance is given by R = (ρ / 2πL) [In {(8L / D) - 1}]
  • Plate Electrode: Resistance is given by: R = ρ/2πL [In(8L/T) + In(L/h)-2+(2h/L)-(h/L)²], where L, h, and T represent length, depth, and thickness
  • Methods of reducing earth resistance include: adding salt, charcoal, and sand mixture to the pit; introducing earth enhancement material; using larger electrodes; burying electrodes deeper; and using parallel electrodes with sufficient spacing.
  • Soil resistivity varies by soil type, and values are given in a table.
  • Ring earth systems use equipotential bonding of electrodes (external and internal rings) to ensure safety and a low effective earth resistance.

Surge Protection Standard IEC 62305

  • IEC 62305 is a comprehensive lightning protection standard for structures and connected equipment, considering risk assessment.
  • It defines lightning protection zones to determine appropriate protection for different equipment types.
  • Damage and losses due to lightning include: injury to people, physical damage (fire or explosion), and failure of internal systems.
  • Lightning Protection Levels (LPL) establish protection levels for equipment based on lightning current parameters.
  • External Lightning Protection Zones (LPZs) address direct lightning strikes and proximity.
  • Internal Lightning Protection Zones (LPZs) address reduced lightning current and switching surges.
  • Coordinated surge protective devices (SPDs) are important for safeguarding equipment from surge currents.
  • Non-conventional air termination systems and external LPS components and their design and positioning are important design considerations.
  • Natural components like metal reinforcements in structures are important as well.
  • Earth Termination Systems should be designed to conduct high current safely to earth.
  • Type A, Type B, and Foundation Earthing are types of earth termination systems.
  • Isolation distance between structural metal and external lightning protection systems is vital.
  • Equipotential bonding of metallic parts is required to avoid sparking.

RDSO Specifications for Earthing Systems for Signal and Telecom Installations

  • RDSO specifications for earthing systems for signal and telecom installations are presented in this chapter.
  • RDSO specs are based on the Indian Standard (IS 3043-1987).
  • The main objective of earthing systems is to ensure zero potential for non-current carrying parts to avoid electric shock.
  • Earthing systems serve as a return path for fault currents, protect equipment from high voltages, eliminate EMI/RFI and provide a path for quick protective device operation.
  • System earthing and equipment earthing are important aspects.
  • The purpose and definition of bonding conductors, earth, earth electrode, and earthing conductors are provided.

Code of Practice for Earthing and Bonding System for S&T Installations

  • This document covers earthing and bonding for signalling equipments, especially those with solid-state components, prone to surge damage.
  • It refers to standards like IS 3043, ANSI/UL 467, IEEE 80, IEEE 837, and IEC 62305.
  • Key characteristics for good earthing systems include excellent conductivity, high corrosion resistance, and mechanical robustness.
  • Acceptable earth resistance values are defined.
  • Component details, including earth electrodes, earth enhancement materials, earth pits, equipotential earth busbars, and connecting cables, are specified.
  • Construction methods for loop-earth using multiple pits, and measurement and calculation methods for resistance values are also addressed.

Surge Protection Devices for Telecommunication Equipments

  • Specification details for telecommunication equipment surge protection devices and general specifications (e.g., IEC, ITU).
  • SPDs need to meet safety and performance requirements (like temperature range, bandwidth, and immunity)
  • Various SPD classes (e.g., A, B, C, and D) are mentioned, which specify protection requirements based on the location and equipment type: Class-A, Class-B, Class-C, and Class-D protection devices.
  • A range of SPDs are outlined (Gas Discharge Tubes (GDTs), Metal Oxide Varistors (MOVs), and silicon avalanche diodes, etc), along with their characteristics.
  • Electrical parameters of several types of SPDs are given.
  • Different data protection devices mentioned for protection devices (Class-A, Class-B, Class-C, Class-D) are suitable for usage with different cables like Co-axial and Ethernet LAN.

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TC 5 Earthing and Surge Protection Devices PDF

Description

Test your knowledge on the characteristics of Type A and Type B earthing arrangements, the role of foundation electrodes, and the importance of separation distances in lightning protection systems. This quiz also addresses the recommendations of BS EN/IEC 62305 regarding earth termination and the functions of surge protective devices.

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