SABO EARTHING SOLUTION

Transcription

1 SABO SABO EARTHING SOLUTION The installation and maintenance of an effective low resistance earthing system is essential due to the following- - Efficiently dissipate heavy fault currents and electrical surges, both in magnitude and duration, to protect equipment being damaged so as to minimize down time, service interruption and replacement cost. - Provide a stable reference for electrical and RF circuits at the installation to minimize noise during normal operation. - Protection of personnel who work within the area from dangerous electric shock caused due to step potential or touch potential. Characteristics of good Earthing system - Excellent electrical conductivity - Low resistance and electrical impedance - Conductors of sufficient dimensions capable of withstanding high fault currents with no evidence of fusing or mechanical deterioration. - Lower earth resistance ensures that energy is dissipated into the ground in the safest possible manner. - Lower the earth circuit impedance, the more likely that high frequency lightning impulses will flow through the ground electrode path, in preference to any other path. - High corrosion resistance - The choice of the material for grounding conductors, electrodes and connections is vital as most of the grounding system will be buried in the earth mass for many years. Hence, highly galvanised electrodes should be used to avoid corrosion. - Mechanically robust and reliable. Location for Earth - Low lying areas close to the building or equipment are good for locating Earth Electrodes. - The location can be close to any existing water bodies or water points but not naturally welldrained. - Dry sand, lime stone, granite and any stony ground should be avoided. - Earthing electrode should not be installed on high bank or made-up soil. Acceptable Earth Resistance value The acceptable Earth Resistance at electrode terminal shall not be more than 5 Ohm. Components of Earthing & Bonding system The components of Earthing & Bonding system are- Earth electrode, Earth enhancement material, Earth pit, Equi-potential earth busbar, connecting cable & tape/strip and all other associated accessories. Design of Earthing & Bonding system GI Electrode (SABO-Electrode) 1. Highly galvanised pipe is used for electrode 2. Highly conductive & non corrosive mixture is poured inside the electrode so that inner strip or pipe will never corrode and provide lowest possible resistance. 3. Made of G.I. 4. ISI marked pipe.

2 SABO 5. Weight of 40mm dia electrode SABO-MFE-40-3 is > 17.0 Kg, 50mm dia electrode SABO-MFE is> 23.0Kg and 80mm dia electrode is > 45Kg. Earth Enhancement material : (30Kg per electrode ) SABO-EREC Earth enhancement material (NABL lab tested) is a superior conductive material that improves earthing effectiveness, especially in areas of poor conductivity (rocky ground, areas of moisture variation, sandy soils etc.). It improves conductivity of the earth electrode and ground contact area. It shall have following characteristics: - shall have high conductivity, improves earth s absorbing power and humidity retention capability. - shall be non-corrosive in nature having low water solubility but highly hygroscopic. - shall be suitable for installation in dry form or in a slurry form. - shall not depend on the continuous presence of water to maintain its conductivity. - shall be permanent & maintenance free and in its set form, maintains constant earth resistance with time. - shall be thermally stable between C to C ambient temperatures. - shall not dissolve, decompose or leach out with time. - shall not require periodic charging treatment nor replacement and maintenance. - shall be suitable for any kind of electrode and all kinds of soils of different resistivity. - shall not pollute the soil or local water table and meets environmental friendly requirements for landfill. - shall not be explosive. - shall not cause burns, irritation to eye, skin etc. Backfill material The excavated soil is suitable as a backfill but should be sieved to remove any large stones, plastic or debris and placed around the electrode taking care to ensure that it is well compacted. Material like sand, salt, coke breeze, cinders and ash shall not be used because of its acidic and corrosive nature. Earth Pit Construction of unit earth pit - A hole of > 100mm dia shall be augured /dug to a depth of about 3.0 meters. - Sieved soil should be poured inside the hole for about 100mm and earth enhancing material thoroughly mixed with 6 times of water should be poured (around 5 litres in the pit). Now the earth electrode shall be placed into this hole. - Remaining earth enhancement material mixed with 6 times of water shall be filled into the augured/dug hole in slurry form and allowed to set. After the material gets set, the diameter of the composite structure (earth electrode + earth enhancement material) shall be of minimum 100mm dia covering entire length of the hole for SABO-MFE-40-3 and SABO-MFE-50-3 and 150mm dia.. - Top of the pit should be covered with normal sieved soil for about 50mm. - A GI strip of 25mmX6mm in case of SABO-MFE-40-3 and 32x6 in case of SABO-MFE-50-3 and 50x6 mm in case of shall b used for interconnections to the earth pits or to the MEBB (Main equipotential bus bar). All the joints between the GI strips or between the GI strip and earth electrode or GI strip to MEBB should be done by welding or Stainless steel nuts and bolts. - Earth pit shall be located as near to the MEBB in the equipment room as possible. - MEBB should be of size 450*50*6 and should be mounted on the wall and insulators are provided so that it should not touch the wall.

3 Construction of loop Earth by providing multiple earth pits SABO - At certain locations, it may not be possible to achieve earth resistance of 2ohm / as desired with one earth electrode /pit due to higher soil resistivity. In such cases, provision of loop earth consisting of more than one earth pit shall be done. The number of pits required shall be decided based on the resistance achieved for the earth pits already installed. The procedure mentioned above for one earth pit shall be repeated for other earth pits. However, for rocky soils, it is recommended to make 4 earth pits. - The distance between two successive earth electrodes shall be min. 3mtrs. and max. upto twice the length of the earth electrode i.e. 6 mtrs. approx. - These earth pits shall then be inter linked using min. 32X5 mm. GI strip to form a loop and connected by suitable galvanized or SS nuts and bolts. - The interconnecting tape shall be buried at depth not less than 500mm below the ground level. This interconnecting tape shall also be covered with earth enhancing compound. In such cases, 10Kg. earth enhancing compound is required for each interconnection of electrodes, i.e, for every 3m. 10Kg earth enhancing compound is required. Measurement of Earth resistance The earth resistance shall be measured at the Main Equi-potential Earth Busbar (MEEB) or at the electrode itself with all the earth pits interconnected using Fall of Potential method as per para 37 of IS: Inspection Chamber - A 300X300X300 mm concrete chamber with smooth cement plaster finish shall be provided on the top of the pit. A concrete lid, painted black, approx. 50 mm. thick with pulling hooks, shall be provided to cover the earth pit. In case of remote sites, the pit of bricks of suitable size / as per the availability of material, can be prepared and the cover of C.I./other material should be provided. Earth pit is necessary. - Care shall be taken regarding level of the floor surrounding the earth so that the electrode terminal is not too deep in the masonry or projecting out of it. Note: It is avoided to construct earth pit in the road side so that it may not destroy or the place exposed to drainage to avoid chemical reaction of drain water. Which model should be used - For all LT (low voltage) body earth SABO-MFE-40-3 should be used - For all MV/HT body earth SABO-MFE-50-3 should be used - For all neutral earthing should be used - SABO-EREC 30Kg should be used for all types of earth pits - In rocky soils, it is recommend to use 4 earth pits so that round the year there will be almost no fluctuation in the earth resistance achieved.

4 SELECTION OF EARTH SYSTEM SABO SN Neutral earthing 1. House hold earth/3ka 2. Commercial premises Office buildings/ 5kA 3 Transformers, substation earthing, LT line equipment/ 15kA 4 Transformers, substation earthing, HT line equipment/ 40kA 5 Extra high current applications etc./ 50kA 6 PRS, UTS, RTUs,FOIS, COIS, ATMs and data processing centre etc./5ka IR Value Soil Type/ Resistivity Required 8 ohm Normal Soil/ upto 50 ohmmtr Sandy Soil/ between 50 to ohm Normal Soil/ upto 50 ohmmtr 1-2 ohm Normal Soil/ upto 50 ohmmtr less than Normal Soil/ upto 50 ohmmtr 1 ohm less than Normal Soil/ upto 50 ohmmtr 1 ohm less than Normal Soil/ upto 50 ohmmtr 0.5 ohm Earth System Single Electrode SABO-MFE-40-3 / SABO-MFE-50-3 Single Electrode Two Electrodes Single Electrode 3/ Note: For body earthing and lightning arrester earthing, earth resistance required for anything at any type of soil is less than 10 Ohm.

5 TYPE OF SOILS Soil can be classified in to various types, though based on the size of the particles it contains: SABO Normal soil Black cotton soil, vegetable soil, garden soil, loamy garden, soil shallow black, soil medium black soil,deep black soil and marshy soil etc having low soil resistivity value ( up to 50 ohm meter) Sandy soil This type has the big particles and the size of the particles does determine the degree of aeration and drainage that the soil allows. It is granular and consists of rock and mineral particles that are very small. Therefore the texture is gritty and sandy soil is formed by the disintegration and weathering of rocks such as limestone, granite, quartz and shale, thus resulting in over-drainage. It warms very fast in the spring season. Coastal area, silt soil, red sandy soil, sandy clay and coastal alluvium etc having soil resistivity up to 2000 ohm-meter are considered as sandy soil. Rocky soil The area containing rocks, pebbles, uneven hard surface laterite soil, lime stone, sand stone, gravel, granite and chalk etc having soil resistivity more than 2000 ohm-meter is considered as rocky soil. This type of soil does not absorb moisture and are extremely poor conductor.

6 SABO SABO EARTHING SOLUTION CROSS SECTIONAL DIAGRAM 300X300X300 CONRETE CHAMBER WITH HOOKS MEBB 450*50*6 GROUND LEVEL NORMAL SIEVED SOIL 50MM 0.5M 25*6 GI STRIP SABO-EREC EARTH PIT 3000MM X 100MM NORMAL SIEVED SOIL 50MM (NOT TO SCALE)