central networks earthing manual e6

All equipments and structures are required to be earthed by two separate and distinct connections with earth. All these earthing points should be interconnected with the substation earth mat. An effective substation earthing system typically consists of earth rods, connecting cables from the buried earthing grid to metallic parts of structures and equipment, connections to earthed system neutrals, and the earth surface insulating covering material. Current flowing into the earthing grid from lightning arrester operation, impulse or switching surge flashover of insulators, and line to ground fault current from the bus or connected transmission lines all cause potential differences between earthed points in the substation. The earthing is broadly divided into 1. Neutral earthing The neutral earthing is essential requiring for transformer, generator, star point loads, circuits, star points of CT and PT(secondary).The purpose of the neutral earthing is to hold neutral at grounding potential, prevent arcing ground on OH lines, discharge of voltage surges, path for out of balance current and simple earth fault protection. All rights reserved. HNIN NU WAI, KYAW SAN LWIN 2. Equipment earthing (safety earthing) B. Advantages for Earth Grid Equipment earthing needs for electronic equipments used In the substation earth grids, the basic ideas and concepts in the substation such as metallic non-current carrying parts.Enclosing more area also reduces the switches, current transformer, surge arrestor, capacitor bank resistance of the earthing grid.Earth rods must also substations, the following data are necessary and important to be installed at major equipments.Ground conductor must be potential rise and maintain the safe value of the substation adequate for fault current (considering corrosion). Layout diagram of Myauk Pyin Substation IV. This figure describes that the more the depths of burial grid conductor are plenty, the less the mesh voltage decreases.

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Discover everything Scribd has to offer, including books and audiobooks from major publishers. Start Free Trial Cancel anytime. Report this Document Download Now Save Save EON E1 Earthing Manual Scope For Later 0 ratings 0% found this document useful (0 votes) 832 views 27 pages EON E1 Earthing Manual Scope Uploaded by barosull Description: Full description Save Save EON E1 Earthing Manual Scope For Later 0% 0% found this document useful, Mark this document as useful 0% 0% found this document not useful, Mark this document as not useful Embed Share Print Download Now Jump to Page You are on page 1 of 27 Search inside document Browse Books Site Directory Site Language: English Change Language English Change Language. A good substation earthing is considered three basic conditions: personal safety, protective device operation and noise control. The calculated results show the amount of decreasing values. Substation earthing is divided into four separated grids such as primary earthing, two transformer earthing and secondary earthing. The advantage of the separated earthing grids is to reduce the installing equipments and to protect human and equipments. The results are showed by using MATLAB figures. Keywords: Earthing Designs, Substation Earthing Resistance, Grid Potential Rise, Mesh Voltage, Step Voltage And MATLAB Figures. I. INTRODUCTION Earthing is essential for the outdoor AC substation designs and the installed equipments in the substation. It is also provided and saved for personnel and the animals. Earth grid designs depend on the soil resistivity, the number of earth rods, the earth rod spacing and the depth of burial grid conductor in order to reduce the substation earthing resistance, Grid Potential Rise, mesh voltage and step voltage. This paper considers and calculates the safe design values on the base of the earth rod spacing and the depth of burial grid conductor.

9m depth 1m depth 0 6 7 Earth rod spacing in m 8 6 7 Earth rod spacing in m 8 Step Voltage in V 150 100 50 0 VI. CONCLUSION This paper aims to show the design and analysis of 230 kV substation earthing grid (Myauk Pyin) in Myanmar and to display the different result figures by changing and rising the depths of burial grid conductor (0.6m, 0.7m, 0.8m, 0.9m, 1m) and the earth rod spacing (6m, 7m, 8m). After changing the depths as well as spacing values and calculating these data, the values of substation earthing resistance, grid potential rise, mesh voltage and step voltage in the substation grids are decreasing slightly. VII. ACKNOWLEDGMENT The author is deeply gratitude to Dr. Myint Thein, Rector, Mandalay Technological University, for his guidance and advice. The author wishes to express grateful thanks to her chairman Dr. Khin Thu Zar Soe, Associate Professor and Head Department of Electrical Power Engineering, Mandalay Technological University, supervisor U Kyaw San Lwin, Lecturer, Department of Electrical Power Engineering, for his guidance and moral support provided during this research effort and to her all teachers from Electrical Power Department, Mandalay Technological University. International Journal of Scientific Engineering and Technology Research Volume.03, IssueNo.07, May-2014, Pages: 1245-1250 We are a non-profit group that run this service to share documents. We need your help to maintenance and improve this website. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Wiring practice by region or country The point of reference is the Earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the installation. Regulations for earthing systems vary considerably among countries, though most follow the recommendations of the International Electrotechnical Commission.

However, the values of the mesh voltage increase because of the wide spacing for the earth rods. The above figure8 shows the results of the substation earthing resistance and the grid potential rise varying with the different depths of burial grid conductor and the earth rod spacing. The more the values of the depths of burial grid conductor and the earth rod spacing increase, the less the substation earthing resistance and the grid potential rise decrease gradually. The values of the substation earthing resistance are maximum comparing with the primary side and the secondary side. Similarity, the more the depth of burial grid conductor and the earth rod spacing are wide, the less the resistance and GPR are decreasing. 6m space 7m space 8m space Step Voltage in V 20 Mesh Voltage in V 25 200 150 100 6m space 7m space 50 8m space 15 0 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 Depth of burial grid conductor in m 0.95 1 1.05 10 5 0 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 Depth of burial grid conductor in m 0.95 1 1.05 Step Voltage in V 80 60 40 6m space 7m space 20 8m space Figure9. Various results for Step voltage according to the depths of burial grid conductor (Primary side). 0 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 Depth of burial grid conductor in m 0.95 1 1.05 Figure11. Comparison with the values of Mesh voltage The values of the step voltage are steadily decreasing and Step voltage due to the depths of burial grid because the depths of burial grid conductor and the earth rod conductor (Transformer).The values step voltage are decreasing due to increase the earth rod of the step voltage are inversely proportional to that of the spacing and the depth of burial grid conductor. The mesh mesh voltage.The above figure12 shows the decreasing values for the substation earthing resistance and the grid potential rise by changing the earth rod spacing and the depth of burial grid conductor. Mesh Voltage in V 200 150 0.6m depth 100 0.7m depth 0.8m depth 50 0.

For these reasons, most countries have now mandated dedicated protective earth connections that are now almost universal.Where the earthing system does not provide a low-impedance metallic conductor between equipment enclosures and supply return (such as in a TT separately earthed system), fault currents are smaller, and will not necessarily operate the overcurrent protection device. In such case a residual current detector is installed to detect the current leaking to ground and interrupt the circuit.The body of the electrical device is connected with earth via this earth connection at the transformer.The conductor that connects to the star point in a three-phase system, or that carries the return current in a single-phase system, is called neutral ( N ). Three variants of TN systems are distinguished:The combined PEN conductor typically occurs between the substation and the entry point into the building, and earth and neutral are separated in the service head.The PEN must be suitably reinforced against failure, as an open circuit PEN can impress full phase voltage on any exposed metal connected to the system earth downstream of the break. The alternative is to provide a local earth and convert to TT. The main attraction of a TN network is the low impedance earth path allows easy automatic disconnection (ADS) on a high current circuit in the case of a line-to-PE short circuit as the same breaker or fuse will operate for either L-N or L-PE faults, and an RCD is not needed to detect earth faults.There is no 'earth wire' between the two. The fault loop impedance is higher, and unless the electrode impedance is very low indeed, a TT installation should always have an RCD (GFCI) as its first isolator.TT has always been preferable for special applications like telecommunication sites that benefit from the interference-free earthing. Also, TT networks do not pose any serious risks in the case of a broken neutral.

Regulations may identify special cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants.Tall structures may have lightning rods as part of a system to protect them from lightning strikes. Telegraph lines may use the Earth as one conductor of a circuit, saving the cost of installation of a return wire over a long circuit. Radio antennas may require particular grounding for operation, as well as to control static electricity and provide lightning protection.System grounding works by sending any built up static discharge to the ground through a heavy grounding electrode conductor and then into an earthing electrode.Fault currents are mainly caused by insulation failure of a conductor and subsequent contact with a conductive surface. This type of grounding is not a grounding connection, technically speaking. The over-current protective devices sense this as a short-circuit condition and open the circuit, safely clearing the fault.The earthing system, in combination with protective devices such as fuses and residual current devices, must ultimately ensure that a person does not come into contact with a metallic object whose potential relative to the person's potential exceeds a safe threshold, typically set at about 50 V.In the United States and Canada, 120 V power outlets installed before the mid-1960s generally did not include a ground (earth) pin. In the developing world, local wiring practice may not provide a connection to an earthing pin of an outlet. This was not permitted for plug-in equipment as the neutral and energized conductor could easily be accidentally exchanged, creating a severe hazard. If the neutral was interrupted, the equipment enclosure would no longer be connected to ground. Normal imbalances in a split phase distribution system could create objectionable neutral to ground voltages. Recent editions of the NEC no longer permit this practice.

Therefore, main equipotential bonding conductors must be sized with this in mind; use of TN-C-S is inadvisable in situations such as petrol stations, where there is a combination of much buried metalwork and explosive gases. This is of particular importance with some types of telecommunication and measurement equipment. The neutral must be connected to earth only on the supply side of the customer's disconnecting switch. For an LV customer, it is a TN-C system from the transformer in the street to the premises, (the neutral is earthed multiple times along this segment), and a TN-S system inside the installation, from the Main Switchboard downwards. Looked at as a whole, it is a TN-C-S system. Rules are different when it comes to larger companies. Earthing is to be done with two separate connections. The grounding system must also have a minimum of two or more earth pits (electrodes) to better ensure proper grounding.Neutral is double grounded at each distribution transformer. Neutral and earth conductors run separately on overhead distribution lines. Separate conductors for overhead lines and armoring of cables are used for earth connection. After this, separate earth and neutral cores are used in all the internal wiring. This is no longer recommended practice. To mitigate the two-fault issues with IT systems, the isolation transformers should supply only a small number of loads each and should be protected with an insulation monitoring device (generally used only by medical, railway or military IT systems, because of cost). TT supplies to individual properties are also seen in mostly TN-C-S systems where an individual property is considered unsuitable for TN-C-S supply. This MEN Link is removable for installation testing purposes, but is connected during normal service by either a locking system (locknuts for instance) or two or more screws. In the MEN system, the integrity of the Neutral is paramount.

In Australia, new installations must also bond the foundation concrete re-enforcing under wet areas to the Protective Earth conductor (AS3000), typically increasing the size of the earthing (i.e. reducing resistance), and providing an equipotential plane in areas such as bathrooms. In older installations, it is not uncommon to find only the water pipe bond, and it is allowed to remain as such, but the additional earth electrode must be installed if any upgrade work is done.You can help by adding to it. ( October 2013 ) Only the magnitude of phase-to-ground short circuits, which are the most common, is significantly affected with the choice of earthing system, as the current path is mostly closed through the earth.In India it is restricted for 50 A for open cast mines according to Central Electricity Authority Regulations, CEAR, 2010, rule 100.As a result, ground fault currents have no path to be closed and thus have negligible magnitudes.On its resistance depends on the efficiency of the removal of unwanted currents to zero potential (ground). The resistance of a geological material depends on several components: the presence of metal ores, the temperature of the geological layer, the presence of archeological or structural features, the presence of dissolved salts, and contaminants (Porosity and permeability). There are several basic methods for measuring soil resistance. The measurement is performed with two, three or four electrodes. The measurement methods are: pole-pole,dipole-dipole, pole-dipole, Wenner method, and the Schlumberger method.Retrieved 30 March 2018. International Electrotechnical Commission, Geneva. IEE Wiring Matters, Autumn 2005. By using this site, you agree to the Terms of Use and Privacy Policy.

In addition, in locations where power is distributed overhead, earth conductors are not at risk of becoming live should any overhead distribution conductor be fractured by, say, a fallen tree or branch.But as residual current devices mitigate this disadvantage, the TT earthing system has become much more attractive providing that all AC power circuits are RCD-protected. In some countries (such as the UK) TT is recommended for situations where a low impedance equipotential zone is impractical to maintain by bonding, where there is significant outdoor wiring, such as supplies to mobile homes and some agricultural settings, or where a high fault current could pose other dangers, such as at fuel depots or marinas.This can impose added requirements on variable frequency drives and switched-mode power supplies which often have substantial filters passing high frequency noise to the ground conductor.The neutral is grounded (earthed) at each consumer service point thereby effectively bringing the neutral potential difference to zero along the whole length of LV lines.Instead of a solid connection of neutral to earth, a neutral grounding resistor ( NGR ) is used to limit the current to ground to less than 750 mA. Due to the fault current restriction it is safer for gassy mines. By comparison, in a solidly earthed system, earth fault current can be as much as the available short-circuit current.Residual-current devices (RCDs, RCCBs or GFCIs) are used for this purpose. Previously, an earth leakage circuit breaker is used.Such a connection (a buried metal structure) is required to provide protective earth in IT and TT systems. However, to mitigate the risk of broken neutrals, special cable types and many connections to earth are needed. With TT systems, the earth fault loop impedance can be too high to do this, or too high to do it within the required time, so an RCD (formerly ELCB) is usually employed.

Earlier TT installations may lack this important safety feature, allowing the CPC (Circuit Protective Conductor or PE) and perhaps associated metallic parts within reach of persons (exposed-conductive-parts and extraneous-conductive-parts) to become energized for extended periods under fault conditions, which is a real danger. An insulation fault between either L or N and PE will trigger an RCD with high probability. In a TN-C system, they would also be very vulnerable to unwanted triggering from contact between earth conductors of circuits on different RCDs or with real ground, thus making their use impracticable. Also, RCDs usually isolate the neutral core. Since it is unsafe to do this in a TN-C system, RCDs on TN-C should be wired to only interrupt the line conductor. In an unbalanced multi-phase system, the potential of the earthing system will move towards that of the most loaded line conductor. There is also a risk if a cable is damaged, which can be mitigated by the use of concentric cable construction and multiple earth electrodes. Due to the (small) risks of the lost neutral raising 'earthed' metal work to a dangerous potential, coupled with the increased shock risk from proximity to good contact with true earth, the use of TN-C-S supplies is banned in the UK for caravan sites and shore supply to boats, and strongly discouraged for use on farms and outdoor building sites, and in such cases it is recommended to make all outdoor wiring TT with RCD and a separate earth electrode. However, a first insulation fault can effectively turn an IT system into a TN system, and then a second insulation fault can lead to dangerous body currents. Worse, in a multi-phase system, if one of the line conductors made contact with earth, it would cause the other phase cores to rise to the phase-phase voltage relative to earth rather than the phase-neutral voltage. IT systems also experience larger transient overvoltages than other systems.

Some links are removed, so that each (fused) distributor leaving a substation forms a branched open-ended radial system, as shown in Figure C4 This scheme exploits the principle of tapered radial distributors in which the distribution cable conductor size is reduced as the number of consumers downstream diminish with distance from the substation.This wiki is a collaborative platform, brought to you by Schneider Electric: our experts are continuously improving its content, as they were doing for the guide. Collaboration to this wiki is also open to all. It also explains why these techniques are the best practice. More specifically, this appendix describes the techniques for DC power and earth bonding for Cisco MGX switches. It identifies the earthing points, shows how they are to be earthed, and how the DC power connections are to be connected to the equipment. In general, a BN need not be connected to earth, but all BNs in this recommendation have an earth connection. It is the set of metallic components that are intentionally or unintentionally interconnected to form the principal BN in a building.Consequently, the mesh-BN augments the CBN. All IBNs in this document have a connection to earth via the SPC. Usually, the SPC is a copper bus-bar. If cable shields or coaxial outer conductors are to be connected to the SPC, the SPC could be a frame with a grid or sheet metal structure. This may, for example, be achieved by multiple interconnections between cabinet rows or by connecting all equipment frames to a metallic grid (bonding mat) that extends away from beneath the equipment. The bonding mat is, of course, insulated from the adjacent CBN. If necessary the bonding mat could include vertical extensions that result in an approximation to a Faraday-cage. The spacing of the grid depends upon the frequency range of the electromagnetic environment. This BN could be either a mesh-BN (resulting in a DC-C-MBN system) or an IBN (resulting in a DC-C-IBN system).

In this appendix, BN refers to common bonding networks (CBNs), mesh-BNs (MBNs), and isolated bonding networks (IBNs) collectively. The acronym BN implies that a connection to earth exists. Lightning and both AC and DC power faults are the energy sources that cause the greatest concern. Of less concern are quasi-steady-state sources such as AC power harmonics and function sources, such as clock signals from digital equipment. The people and equipment that can suffer adversely from these emitters are referred to as susceptors. The purpose of a BN is to reduce the magnitude of the transfer function to an acceptable level. Reducing the magnitude of the transfer function is achieved through the design of the BN; specifically, in the way that MBNs and IBNs are attached to the CBN. The practical aspects of this design are discussed below. A BN that can handle large currents can rapidly de-energize faulted power circuits. This method of grounding prevents transient currents caused by lightning or power surges from entering the system through the backplane, upsetting system performance and possibly damaging components. Digital systems today have such high speeds and large bandwidths that they now produce frequencies with harmful effects. Consequently, digital systems now require multipoint grounding. To mitigate these effects, you must bond and provide the lowest possible impedance to ground at the backplane. Therefore, isolation must be kept to multipoint ground the 48 VDC return to chassis and logical ground at the backplane level of the Cisco equipment. The bonding of meshed bonding networks and the digital high speeds dictate the eventual acceptance of this new philosophy on a universal basis. These standard grounding conductors have a very high impedance at frequencies greater than 10 MHz. This represents 2 ohms of reactance at a frequency of 30 MHz.

This high impedance would be a large change from earth reference if earth were several stories below the equipment installation. Therefore it is required that multipoint, meshed bonding networks be used to control these excitation currents. Because the design must anticipate the worst case scenario, concerns about RF damage are much greater. At 800 MHz only 10 inches of wire represents 500 ohms reactance. As frequency increases, the wave length becomes smaller, and the reactance of a fixed length of wire goes up. Using capacitors to achieve the necessary bonding becomes extremely difficult at these frequencies in addition to the added cost due to the isolation breakdown voltage requirements of 2.1 kilovolts, should the old philosophy be insisted upon. A consequence of applying these principles is that the number of conductors and interconnections in the CBN is increased until adequate shielding is achieved. Concerning the important issue of electric shock, the following implementation principles apply to mitigation of electric shock as well as to equipment malfunction: Multiple interconnections, resulting in a three-dimensional mesh, are especially desirable. Increasing the number of CBN conductors and their interconnections increases the CBN shielding capability and extends the upper frequency limit of this capability. In particular, the AC power entrance facilities, telecommunications cable entrance facilities, and the earthing conductor entry point should be close together. The main earthing terminal shall connect to the following: Multiple conductors between the CBN and the main earthing terminal are recommended. However, in the case of external surge sources, the currents in the CBN will tend to be greater in peripheral CBN conductors. This is especially true of lightning down-conductors. When this is unavoidable, metallic ducts that fully enclose the cables may be needed.

In general, the shielding effect of cable trays is especially useful, and metallic ducts or conduit that fully enclose the cables provide nearly perfect shielding. For cables extending between floors, maximum shielding is obtained by locating the cables near the center of the building. However, as stated above, cables enclosed in metallic ducts may be located anywhere. These protectors should be bonded with low impedance to the CBN. These jumpers shall comply with IEC requirements for safety. However, for EMC applications, the jumpers should have low impedance. Thus, most of the current driven by potential differences is carried by the highly conductive members of the CBN. Disconnection of one cable shield for inspection should minimally affect the current distribution in the CBN. Equipment interconnected by these circuits needs functional earthing. Most of this resistance is contributed by the earth electrodes. The performance provided by the earthing network via the main earthing terminal is generally sufficient for this signaling purpose. The purpose is to mitigate the damaging effects of electrostatic discharge or lightning. Therefore, the rack must connect to protective earth ground, and the equipment must be secured to the rack so as to ensure good bonding. In contrast, routers and other LAN equipment often use an isolated grounding scheme. The potential between any points in the ground system—whether or not the ground system is mixed—must not exceed 2 percent of the referenced voltage (2 percent of 48 V is 960 millivolts). This figure shows safety and earth grounds and the primary and redundant DC sources Battery A and Battery B. Individual ground conductors are labeled Z1, Z2, Z3, Z4, and Z5. The Z represents the impedance of the ground conductor between a chassis, for example, and a connection to the building's ground system. Each of these symbols indicates that a voltage drop may result (but must not exceed 2 percent of the referenced voltage).

See Table C-1 for a definition of each Z1-Z5. This ground creates low-impedance equalization between frames. This grounding scheme protects the signals on the backplane from corruption by transients that can result from lightning or electrostatic discharge. For more detailed information, refer to the recommendation itself. Also, the protective earth conductor must be large enough to carry all the current if the 48 VDC return fails. This latter requirement is for safety. Full fault redundancy is achieved by having equal size conductors for the protective earth ground and the 48 VDC return of the switch. For the resistance of 1000 feet of copper wire for each gauge of wire, see Table C-3. These references are for planning purposes and might be further subject to local laws and practices. It is recommended that you use 50-A or greater. You can find out more about our cookies usage policy and how to change your privacy settings or continue if you are happy to receive all cookies on our website. This figure helps NIE to design a new electricity connection to meet your needs. The postal address is: Connections Customer Liaison NIE Networks Unit 3 21 Old Channel Road Belfast ?BT3 9DE We will acknowledge receipt of your application and advise you from which of our three local depots your application will be handled. Above this capacity a three phase supply is required.You should be aware that a feasibility study does not reserve network capacity for a particular project, and we cannot guarantee that a connection will be available when making a formal application for connection. If you have finalised your requirements, obtained DOE Planning Approval and are ready to enter into a contract with us to provide your connection, we can give you a formal quotation. Click here to register for an Generation Connection application pack. We will then send you out a quote for the cost of your connection.