Oct. 28, 2024
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Let us identify the various factors, considered for an efficient earthing system and the right earthing material. The main factors that need prime consideration while selecting an earthing electrode are:
From all the points listed above, soil resistivity is a crucial factor in deciding the earthing system design and requirements. IS provides the soil resistivity values and the soil corrosion level that affects the electrodes used for earthing.
In substations, all equipment, their metallic parts and all other metallic objects like fences etc are connected to the earthing grid, this grid has horizontal and vertical electrodes which are connected using cross clamps or are exothermically welded. The earthing material used in substations is very critical as the fault clearance time is expected to be at a minimum always, for this the earthing resistance offered by the material should be the lowest. IEEE 80 and IS give details for calculating the earth resistance and how the designing of the earthing system for a substation should be performed.
In India, we see that GI electrodes are generally used in telecommunication towers, LT and HT lines, substations etc. It is one of the most commonly used earthing materials with good conductivity. Some of the features of GI earthing material are listed below:
Lifetime: The maximum life of galvanised iron flat is approximately 6-8 years, after which the earth grid made of GI will have to be replaced.
Corrosion resistance: Corrosion of galvanised coating in marine areas is around 6-8 microns per year and once it is placed in corrosive soil it will get aggravated further depending on the soil properties. The galvanised coating undergoes corrosion in presence of acidic soil, and soils containing certain chemicals.
Installation: Installation of GI electrodes is prone to human error, because manual welding, nut bolting, and cold galvanising have to be performed, if any one of these procedures is faulty, it can result in a flashover and this can cause the GI grid to corrode.
Cost: GI is comparatively cheap and easily available in the market.
The main reason why Galvanised Iron or Steel is used instead of pure copper in countries like India is due to the high cost of copper. Copper tapes can cost 10 times the cost of GI strips. Copper theft is also another challenge in using pure copper as the earthing electrode. The use of pure copper for earthing can be difficult in rocky areas as it does not have enough strength and can result in breakage while burying. Damage to the conductor can lead to poor conduction and thus reduce the efficiency of the earthing system.
The copper flats (also known as copper-bonded steel tapes) are a combination of mild steel and copper bonding. They can be used for the earthing grids in substation earthing for increased conductivity. The combination of steel and copper contributes to the high tensile strength and remarkable conductivity. The process of electrolysis forms a strong bonding between the metals and thus the copper does not break or slip over the surface. Copper being the surface material increases the conductivity and corrosion resistance of the flats.
The properties of copper flats comply with IEC -2 and undergo the resistivity test. Thus, they are recommended in almost every soil condition due to their high mechanical strength and conductivity. These copper flats are generally used in substations instead of rods or pipes as they provide a greater cross-sectional area for quicker conduction of fault current.
They have higher corrosion resistance and thus the lifetime is also more compared to normally used GI and steel tapes. They have a lifetime of almost 30 years which makes them more advantageous.
When it comes to the cost of copper flats, we can see that the initial investment seems a bit high compared to the present GI tapes, but it has higher corrosion resistance which reduces overall maintenance making it cost-effective in the long term.
From the above-mentioned features, we can see that copper flats are more beneficial when compared to galvanised iron or steel. Here are some basic aspects where copper flats have proven to be better than GI.
Durability: Copper bonded steel flats have a higher lifespan, which is almost thrice more than GI.
Corrosion resistance: The copper bonded steel flats have a higher corrosion resistance due to the copper bonding and so can be used in all types of soils.
Electrical and mechanical performance: Copper is the highest conducting material compared to all the currently used earthing materials. Hence, they have high conductivity and great mechanical strength. The installation of copper bonded steel flats is simple and has lesser steps involved, so there is a lesser possibility of human errors.
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Axis has been designing and manufacturing high conductivity copper flats, especially for substation facilities. The process of electroplating copper over mild steel increases the overall conductivity. The thickness of the outer copper bonding layer depends on the electrolysis time; the common coating thickness is 250 microns.
Our flats are manufactured in mainly two sizes 50*6mm & 75*12mm and obtain a maximum length of 6 meters. Axis flats are mainly used for substations, power plants, railways and other high-voltage applications as they provide quick and efficient earthing. The electrolytic effect holds the copper bonded coating tightly to the steel core without slipping or breaking.
The advanced technology used in manufacturing Axis Copper Bonded Steel Flats results in an electrically and mechanically robust earthing solution that complies with National and International standards.
When it comes to selecting a ground rod, engineers must avoid a one-size-fits-all approach. Different factors&#;material, soil resistivity, location, facility type, size, among others&#;play into the overall efficiency and service life of both the ground rod and overall grounding system. Below we provide key considerations for ground material selection and then compare the most common types.
Once the soil and environmental conditions have been assessed, materials should be compared according to their individual performance in the following areas, and their compatibility with your unique situation.
Corrosion Resistance: Perhaps most influential to the service life of the ground rod, assess materials based on their inherent corrosion resistance to your soil conditions. Depending on salt, sulfate content or pH, different materials will work best.
Cost: The upfront cost of one ground rod material should not be compared directly to another material. Rather, the lifecycle value of two materials should be compared. If one rod is $20 and another costs $30 but the cheaper rod will only last one-quarter as long as the other, the more expensive rod is the more cost-effective choice.
Ease of Driving into the Earth: This relates to the material&#;s strength and the soil&#;s hardness. If a ground rod is bent or broken when driven into the ground, it may be more likely to corrode. Also, a damaged ground rod will less reliably provide the most direct path for electrical currents to travel and dissipate.
Copper Theft: Some have called copper theft an &#;epidemic&#; at different times, and ground rods are not exempt. Depending on your proximity to a population and local theft rates, consider the potential cost of replacing stolen copper ground rods and the immediate system inefficiency it would cause. Typically theft is related to conductors and other above-grade materials, but ground rods are not completely exempt.
Conductivity: As a ground electrode, a ground rod&#;s purpose is to provide a physical connection to the earth and provide the most direct path for a current to dissipate. Though conductivity differences are typically minimal between the most common materials, certain conductivity levels are required in specific regions and are important for providing that path to ground.
Copper-bonded and galvanized ground rods are the two most common types of ground rods throughout most of the world. In certain situations, stainless steel or solid copper ground rods may be installed to meet unique environmental conditions. What is commonly overlooked, however, is the life expectancy of the grounding electrode system compared to the life expectancy of the facility.
Copper-bonded steel ground rods are manufactured through a continuous electro-plating process of copper over a steel core, resulting in a permanent molecular bond between the two materials. This should not be confused with copper-clad steel, as that method is no longer employed for ground rods due to a less reliable bond.
Stainless steel is not a naturally occurring metal like copper, but it is an alloy of iron with at least 10.5% chromium and varying amounts of carbon, silicon, manganese and sometimes other materials. A stainless steel ground rod is created with a layer of oxide to help prevent corrosion.
Solid copper ground rods are very corrosion resistant (except when faced with salts) and are also very conductive. However, you will rarely see solid copper outside of the Middle East or similar environments because copper is a ductile, soft metal that often bends when driven into soil other than sand.
Another issue with solid copper is that it is extremely expensive when compared to alternatives. Also, copper theft can be a huge problem for solid copper, making it costly to replace these ground rods.
Zinc-coated steel ground rods are on the opposite side of the cost scale from solid copper ground rods. These are the cheapest of common ground rod materials, offering limited reliability in the long term.
The problem, according to the NEGRP corrosion study mentioned previously, is that galvanized rods with 3.9 mils of zinc should only be expected to last for 10 to 15 years reliably (compared to 40 or more years for copper-bonded rods). Salts, in particular, are likely to corrode the zinc coating.
Because a lightning protection system is one that installers would prefer to &#;install and forget,&#; only 10 or 15 years of performance is poor. Constant replacement, including material and labor costs, can cause long-term issues and costs for galvanized ground rod users.
Ready to take the next step? To make the best decision possible when selecting ground rods for your application, make sure you read our post about
The 2 Most Important Factors to Weigh When Selecting Ground Rod Material
Download the nVent ERICO Grounding, Bonding and nVent ERICO Cadweld Solutions Guide for an overview of facility electrical protection and where grounding fits in.
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