EARTHING…. …….. REVISITED A Project Report by :- A. A. PHADKE COURSE No. DIT-2, IRIEEN, NASIK 1. 0 Earthing :- Earthing or earthing system is the total of all means and measures by which part of an electrical circuit, accessible conductive parts of electrical equipment (exposed conductive parts) or conductive parts in the vicinity of an electrical installation (extraneous conductive parts) are connected to general conductive mass of the earth, whose electric potential at any point is conventionally taken as zero. . 0 Requirements of earthing :- Requirements of a good earthing system are :- a) Protection of buildings and installations against lightning. b) Safety of human/animal life by limiting touch and step voltages to safe values. c) Electro Magnetic Compatibility (EMC) i. e. limitation of electromagnetic disturbances to equipments and systems. d) Correct operation of the electricity supply network and to ensure proper line voltage and good power quality with reduced harmonics. 3. Evolution of earthing :- In France in 1923 a Standard for electrical installations made earthing of frames a compulsory requirement, for casings of fixed and moving motors which may be touched in uninsulated area, in installations with a voltage greater than 150V and for fixed and portable electrical household appliances with a power rating greater than 4 kW. In 1927, a Decree stipulated the earthing of the transformer neutral in public distribution in France compulsory for Voltages above 150 V AC. Thus the first earthing system came into existence in the form of the unearthed neutral.
The Permanent Insulation Monitor (PIM), with three lamps (in three-phase) was used up to 1955. The Lamp-Monitors continued till 1962, when alongside the Standard, the Decree of the 14. 11. 62 legalised the unearthed and the earthed neutrals. The development of Residual Current Device (RCD) or Short Circuit Protection Device (SCPD) or Earth Leakage Circuit Breaker (ELCB) and Lightning Arresters, revolutionized the earthing & protection. 4. 0 Standards on earthing :- Following are some useful Standards to be referred :- * IS:3043 – 1987 Reaffirmed 2006: Indian Standard Code of Practice for Earthing. * IEEE Std. 42-1991: IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems * IEEE Std. 80-2000 IEEE Guide for Safety in AC Substation Grounding. * Indian Electricity Rules : 1956 & National Electric Code by BIS : SP : 1985 5. 0 Effects of earth fault :- As shown in following diagrams :- a) Supply is earthed, but metal-casing of equipment is un-earthed, causing probability of electrical shock to a person, touching it, in case of internal fault causing live wire coming in contact with the enclosure. b) In this second instance, casing is earthed, allowing fuse to blow, making it safe. ) In this third instance, location of fault within casing, goes undetected, but is safe. So, following factors govern the protection by means of earth fault current :- i) Rating of fuse or breaker. ii) Impedance of earth loop circuit of return path. iii) Impedance of the fault itself, e. g. arc having high impedance. iv) Location of earth-fault on supply-side or neutral-side of load. v) Continuity of earth wire between casing and equipment & system earth. 6. 0 Types of earthing :- There are basically six types of earthing as described below : 1. equipment grounds, 2. tatic grounds, 3. systems grounds, 4. maintenance grounds, 5. electronic grounds and 6. lightning grounds. Each of the above is explained below :- 7. 1 Equipment Grounds :- An equipment ground is the physical connection to earth of non-current carrying metal parts. This type of grounding is done so that all metal parts of equipment that personnel can come into contact with, are always at or near zero (0) volts with respect to ground. All metal parts must be interconnected and grounded by a conductor in such away so as to ensure a path of lowest impedance for flow of ground fault current.
Typical items (equipment) to be grounded are; electrical motor frames, outlet boxes, breaker panels, metal conduit, support structures, cable tray, to name a few. 7. 2 Static Grounds :- A static ground is a connection made between a piece of equipment and the earth for the purpose of draining off static electricity charges before a flash-over potential is reached. This type of grounding system is utilized in dry materials handling, flammable liquid pumps and delivery equipment, plastic piping, and explosive storage facilities. 7. System Grounds :- A system ground refers to the point in an electrical circuit that is connected to earth. This connection point is typically at the electrical neutral. The sole purpose of the system ground is to protect the equipment. This type of ground also provides a low impedance path for fault currents improving ground fault coordination. This ensures longer insulation life of motors, transformers and other system components. Following four types of System Grounds exist :- a) Ungrounded System b) Solidly Grounded System c) Low Resistance Grounded System ) High Resistance Grounded System These are explained as following:- * Ungrounded System: The ungrounded system is one that has no intentional connection between the neutral or any phase and ground. An ungrounded system is grounded through the concept of capacitive coupling. The neutral potential of an ungrounded system, with balanced loading will be close to ground potential due to the capacitance between each phase conductor and ground. This system has:- * Low ground fault current. * Very high voltages to ground potential on unfaulted phases. Sustained faults due to restriking leading to system Insulation failure. Ground fault is shown on Phase “A”, with voltages & currents:- During earth fault on “A” phase, increase in charging currents & line vol. is explained in the following diagram :- * Solidly Grounded System: The solidly grounded system is one that has the neutral connected to ground without any intentional impedance. In contrast to the ungrounded system, the solidly grounded system will result in a large magnitude of current to flow (Aids in coordination), but has no increase in voltage on unfaulted phases. Low initial cost to install and implement, but stray currents then become a possible consequence. * Common in low voltage distribution systems, such as overhead lines. * Not the preferred grounding scheme for industrial or commercial facilities due to high magnitude fault currents. * Low Resistance Grounded System: The low resistance grounded system is one that has the neutral connected to ground through a small resistance that limits the fault current. The size of the grounding resistor is selected so as to detect and clear the faulted circuit. The resistor can limit ground currents to a desired level based on coordination requirement or relay limitations. * Limits transient overvoltages during ground faults. * Low resistance grounding is not recommended for low voltage systems due to the limited ground fault current. This reduced fault current can be insufficient to positively operate fuses and/or series trip units. * Ground fault current typically in the 100 – 600 Amp range. * High Resistance Grounded System:
The high resistance grounded system is one that has the neutral connected to ground through a resistive impedance whose resistance is selected to allow a ground fault current through the resistor equal to or slightly more that the capacitive charging current of the system. * The resistor can limit ground currents to a desired level based on coordination requirement or relay limitations. * Limits transient overvoltages during ground faults. * Physically large resistor banks. * Very low ground fault current, typically under 10 Amps. Maintenance grounds: This type ground is utilized for safe work practices, and is a temporary ground. * Electronic and computer grounds: Grounding for electronic equipment is a special case in which the equipment ground and the system ground are combined and applied in unity. Electronic equipment grounding systems must not only provide a means of stabilizing input voltage levels, but also act as the zero (0) voltage reference point. Grounding systems for the modern electronics installation must be able to provide effective grounding and bonding functions well into the high frequency megahertz range. Lightning protection grounds: Lightning protection grounding requirements are dependent upon the structure, equipment to be protected, and the level of lightning protection required or desired. 7. 0 Types of supply and earthing systems :- It is represented by symbols TT, TN etc. , consisting of 2 to 4 letters, having the basis for its meaning as follows :- The first letter (T or I) indicates the type of supply earthing. T-(Terre or Direct) indicates that one or more points of the Supply are directly earthed (for example, the earthed neutral at the transformer).
I-(Isolation) indicates either that the supply system is not earthed at all, or that the earthing includes a deliberately inserted impedance. The second letter (T or N) indicates the earthing arrangement in the installation. T – All exposed conductive metalwork is connected directly to earth. N – (Networked) all exposed conductive metalwork is connected directly to an earthed supply conductor Network provided by the Electricity Supply Company. The third and fourth letters (S or C or both) indicate the arrangement of the earthed supply conductor system.
S – (Separate)-neutral and earth conductor systems are quite separate. C – (Combined)-neutral and earth are combined into a single conductor. Following main types of the systems are prevalent :- a) TN system – It has one or more points of the source of energy directly earthed, and the exposed and extraneous conductive parts of the installation are connected by means of protective conductors to the earthed point(s) of the source, that is, there is a metallic path for earth fault currents to flow from the installation to the earthed point(s) of the source.
TN systems are further sub-divided into TN-C, TN-S & TN-C-S, which shall be explained later. b) TT system – has one or more points of the source of energy directly earthed and the exposed and extraneous conductive parts of the installation connected to a local earth electrode or electrodes are electrically independent of the source earth(s). c) IT system – has the source either unearthed or earthed through high impedance and the exposed conductive parts of the installation are connected to electrically independent earth electrodes. Above systems are explained in Indian context as below:- ) Indian TN-S System :- 415 V Three Phase Domestic / Commercial Supply having 3-phase and 1-phase loads with this system is shown below. All exposed parts of the installation are connected to PE via main earthing terminal of the installation. An independent earth electrode within Consumer’s premises is necessary. Advantages are Low earth-fault loop impedance, high earth fault current, rapid operation of earth fault relay. Disadvantage is high cost. ii) Indian TN-C System :- Neutral and protective functions are combined in a single conductor (PEN) throughout the system.
All exposed conductive parts of installation are connected to the PEN conductor, as shown below. For 3-phase consumer, local earth electrode has to be provided in addition. Features of this System are – Low earth fault loop impedance, Neutral Voltage is tied to near zero, current-operated protective devices not desirable, due to triplen harmonic currents. iii) Indian TN-C-S System :- Here the supply is TN-C and the arrangements in the installation is TN-S, as shown below. This system is also known as Protective Multiple Earthing with PEN conductor also known as Combined Neutral Earth (CNE).
The supply system’s PEN conductor is earthed at several points and an earth electrode may be necessary at or near consumer’s installation. All exposed parts of an installation are connected to PEN conductor via main earthing terminal and neutral terminal, as these terminals, in this System are being linked together. iv) TT System :- As shown below, 415 V three phase industrial supply having three-phase and single-phase loads. All exposed conductive parts of installation are connected to an earth electrode, which is electrically independent of the source earth.
Single phase TT systems are not present in India. v) IT System :- As shown below, all exposed parts of an installation are connected to an earth electrode. The Source is either connected to earth through deliberately introduced earthing impedance, or is kept isolated from earth. 8. 0 Electro Magnetic Compatibility (EMC) :- Electromagnetic interference is increasingly becoming a major problem with more and more use of phase-controlled electronic circuits and high frequency wireless networks. EMC describes the ability of any electrical or electronic system, machine, appliance etc. o operate without malfunction in a disturbing electromagnetic environment while not itself disturbing the operation of other components of the system. This disturbance is particularly likely in a TN-C-type installation. Due to the combination of the neutral (N) conductor and the protective earth (PE) conductor into a PEN conductor, and the consequent connections to other conducting parts of the building, the currents may reach every region of the building and magnetic fields may cause EMI effects almost everywhere.
However, the TN-S system is EMC friendly. To immunise electrical installations against electromagnetic fields, careful design and installation of shielding measures have to be carried out, as per Standards, to get CC marking. 9. 0 SOME COMMON MYTHS & FACTS ABOUT EARTHING :- 9. 1 Myth: ‘Grounding’ implies connection of current carrying parts to ground, like transformer or generator neutral and ‘Earthing’ implies connection of non-current carrying parts to ground, like metallic enclosures. Fact: As per IS 3043-1987, vide Cl. 0. , the terms ‘earthing’ and ‘grounding’ are synonymous. Perhaps the different nomenclature is due to the usual conflicting usage of English language between the Americans & the British. While the British termed it as ‘earthing’, the Americans termed it as ‘grounding’. IEC & IS Standards refer as ‘earthing’, whereas IEEE & ANSI Standards refer it as ‘grounding’. 9. 2 Myth: Natural earth serves as a return path for fault current. Fact: It is surprised to note that natural earth is a very poor conductor of electric current.
The typical resistivity of the general mass of earth is about 100 Ohm-m, compared to Copper, which has 1. 7 x 10-8 Ohm-m and that of GI which is 1 x 10-7 Ohm-m. Definitely, natural earth is much more resistive than Copper or GI. Even the Indian Standard (IS 3043-1987) recognizes this fact. It mentions in its clause 0. 3 that ‘the earth now rarely serves as a part of the return circuit, but is being used mainly for fixing the voltage of the system neutrals’. That is why the recent practice is to use a metallic conductor, as the return path for the fault current.
This conductor is termed as the ‘PEN’ conductor (in TN-C systems) or the ‘PE’ conductor (in TN-S systems). 9. 3 Myth: Copper Earth Electrodes are better than GI/Steel Earth Electrodes. Fact: The material resistivity is not considered anywhere in the formulae for calculation of electrode’s earth resistance. Any material of given dimensions would offer the same resistance to earth. Of course, the material-type matters, while sizing the earthing conductor for designing short time withstand earth current ratings. 9. 4 Myth: Plate Earthing is better than Pipe Earthing.
Fact: To examine this, let us consider a Copper plate electrode of size 1. 2m x 1. 2m x 3. 15mm thick. Assuming a soil resistivity of 100 Ohm-m, the resistance of this electrode to earth will be: 36. 27 Ohms. Now, consider a GI Pipe Electrode of 50 mm Diameter and 3 m Long. Assuming a soil resistivity of 100 Ohmm, the resistance of this electrode to earth will be: 29. 09 Ohms. As can be seen from the above calculation the GI Pipe electrode offers a much lesser resistance than even a copper plate electrode. IS 3043 too acknowledges this fact vide Cl. 9. 1. , wherein it states that ‘a pipe, rod or strip has a much lower resistance than a plate of equal surface area’. 9. 5 Myth: More water, less resistance; It is observed that in some installations, to bring down the earth resistance value, buckets & buckets of water is poured into the earth pit. Fact: Moisture content is one of the controlling factors of earth resistivity upto a limit. As can be seen from the graph below, above 20 % of moisture content, the resistivity is very little affected by addition of water. Below 20 %, the resistivity increases abruptly with the decrease in moisture content.
If the moisture content is already above 20 %, there is no point in adding barrels of water into the earth pit, except perhaps wasting it. Also, it should be noted that If the water is relatively pure, it will have a very high resistivity and unless it contains sufficient natural elements to form a conducting electrolyte, just the abundance of water will not provide the soil with good conductivity. 9. 6 Myth: More salt, less resistance; it was also observed in some installations that the earth pit is filled to the brim with salt and charcoal to reduce earth-resistance.
Fact: To reduce soil resistivity, it is necessary to dissolve in the moisture of soil, some substance, which is highly conductive in its water solution form. The most commonly used substances are salt & charcoal in suitable proportion. It must be noted that the additive substance would reduce the resistivity of the soil, only when it is dissolved in the moisture in the soil. Dry additives do not serve any purpose at all. There is noticeable effect of salt on soil resistivity, only when it is added upto a maximum of 5% only, as shown below. 9. 7 Myth: Deeper the earth pit and longer the earth pipe/rod, lesser will be the resistance.
Fact: The resistance to earth of a pipe or rod electrode, diminishes rapidly within the first few feet of driving, but less so at depths greater than 2 to 3m in soil of uniform resistivity. As can be seen from the graph on next page, after about 4m of depth, there is no appreciable change in resistance to earth of the electrode. When a number of rods or pipes are connected in parallel, the resistance is practically proportional to the reciprocal of the number employed, provided each electrode is situated outside the resistance area of any other electrode.
The ideal separation distance would be the sum of the depths of the two electrodes. 10. 0 DISCARD CONVENTIONAL PIT TYPE EARTHING AND SWITCH OVER TO CHEMICAL PIPE TYPE MODERN EARTHING! The conventional copper pit type earthing is out of date, because:- 1. The water level is going down to the extent of 20-50 mtr. 2. The commonly used substances in pit type earthing were Sodium Chloride known as common salt, soft coke & charcoal. The common salt (sodium chloride) is a hygroscopic substance & it gets dissolved in water & losses its hygroscopic properties when it becomes water itself. 3.
The salt is known to be a corrosive electrolyte which decays the pipe and the conductor used for earthing. Due to decay, one does not get the consistent ohmic values, throughout its life. 4. The soft coke & charcoal tend to become ash due to heavy heat generated by heavy electric fault currents generated in the system especially at higher voltages at above 1. 1kv. 5. The heat generated is proportional to I2Rt (Time in seconds) e. g. for the fault current of 10,000amps in the system with an earth resistance of 2 ohms and as permitted by IS in 0. 01 seconds, heat is given as under. H=I2Rt, H=10,000×10, 000x2x0. 1=20, 00,000 calories =1053 °C This much heat is generated in one fault. Assuming 6 faults in a year, and in a period of four years -24 faults occur , each fault generating 1053 °C. 6. Each fault of this magnitude will turn the soft coke/ charcoal into ash gradually in a period of 3-4 years. The earth system will deteriorate and gives larger value of ohmic resistance thereby endangering the entire installation and consequently people & property. 7. If the ohmic values goes up from 2 to 3 ohms because of faulty earth systems, heat generated will be 30,00,000 calories (i. e. 1600 °C ).
So, it concludes that the pit type earthing is inefficient , not reliable & causes serious damage to life & property in a period of 3-4 years . 8. It is therefore observed that separate watering arrangement is required to be made for maintaining moisture in conventional earthing, through a separate water-pipe dug along the earthing system. 9. Instead of water producing the moisture in the earth pit, the additional quantity of water collected in with a natural rain fall will wash away the charcoal & the soft coke from its main position, thereby it will further deteriorate the functioning of the earth system. 1. 0 Modern Maintenance Free Chemical Pipe Type Earthing :- It is a new type of earthing system which is available readymade, standardized, and is scientifically developed. Its benefits are :- 1. Maintenance Free: No need to pour water or salt at regular interval. 2. Consistency: Maintains stable and consistent earth resistance value around the year. 3. More Surface Area: The conductive compound creates a conductive zone, which provides the increased surface area for peak current dissipation and also get stable reference point. 4. Low earth resistance: Highly conductive.
Carries high peak current. 5. No corrosion, Eco Friendly, and longer life. 6. Easy Installation and requires less volume of pit. 7. As per IS: 3043- 1987. Now technical details of modern maintenance free earthing shall be discussed below. 12. 0 TECHNICAL DETAILS OF MAINTENANCE FREE EARTHING 12. 1. Earthing Electrode:- Two ‘B’ class mild steel pipes, one inside the other, are used hot dip Galvanized. Empty space inside the electrodes is filled with CRYSTALLINE CONDUCTIVE MIXTURE (CCM) and then sealed. This Conductor rich CCM contains metal alloys and natural compounds.
It is highly conductive, anticorrosive, and does not disintegrate or collapse when Outer electrode becomes inactive. Pipe in pipe technology concept involves two mild steel pipes one inserted inside the other. Both the pipes are subjected to Hot dip galvanization of 250-300 microns for inner shell and 80-100 microns for outer shell. This is done to strengthen the flow/dissipation of fault/ static current, thus providing maximum safety. The empty space in the sealed pipes is filled with a specially developed Crystalline Conductive Mixture (CCM) or Gel.
The space surrounding the pipe-electrode in pit is filled with special ground-enhancing Back Fill Compound (BFC), which retains moisture & conductivity, without maintenance, for 15 to 20 years. Concentric Pipe Earthing Electrodes Crystalline Conductive Mixture (CCM) is a combination of metal alloys such as copper & aluminum powder, conductive carbon and bonding material etc. mixed in different proportions. Conductive mixture contents shall be 70% Carbon powder & 30% metal powder preferably pure copper or aluminum material along with the required quantity of bonding materials.
Granule size of the carbon & metal powder shall be 100 mesh. The mixture is forced (Pressurized) inside the earth electrode in empty space of inner pipe & in empty space between the inner & outer pipe of the earth electrode, in paste or gel form and after solidification of the same, the bottom & top end caps are provided and sealed. The metal alloys help in conducting the current and conductive carbon has an excellent anticorrosive property. The bonding material helps in keeping all the above materials bonded together and gives it the required strength.
The top end of the inner pipe is pressed to have flat surface at the top end for connecting bus bar connection plate. Necessary precaution shall be taken as to have no air gap inside the pipe while pressing. The crystalline conductive mixture which is machine pressed in the pipes should not disintegrate or collapse when the outer pipe corrodes. Resistivity of the material shall be less than 0. 2 ohm meter. The Concentric Pipe Electrode filled with CCM is then inserted in a small ground-pit of dia 1 foot and depth 10 feet, and about 50 to 60 kg. f ground-enhancing back-fill material is filled in pit surrounding the pipe. This earth enhancement material (Back fill compound) is a superior conductive material, retaining moisture for a long time, and thus improves earth’s conductivity. 2. Back Fill Compound:- Empty space around the electrode in pit, is filled with a compound which contains eco-friendly hygroscopic materials. It maintains moisture and enhances conductivity around the electrode. It does not mix with or leach in to the soil. It absorbs moisture 13 times its dry volume. There is no need to recharge pit, except in sandy areas.
Back Fill Compound (BFC) may contain conductive cement (20%), graphite carbon powder (50%), hydrous aluminum silicate (10%), sodium montmorillonite (20%) etc. It shall be placed around earth electrode in the earth pit to improve the conductivity of earth electrode & ground contact area. The material is supplied in sealed moisture proof bags. It is easily compacted and when water is added, BFC absorbs it fifteen times its dry volume. BFC consistently holds its own shape and adheres to any surface it touches. These capabilities resolve the issues of compatibility of soil/rod contact that are crucial to an Earthing system.
There is no need to recharge the pit in normal soils. BFC is not soluble in water. It retains its moisture property up to the life of the electrode which is more than 20 years. BFC maintains moisture within the sphere of influence of the electrode, thus resulting in lower earth resistance. Back Fill Compound (BFC) has the following characteristics :- i) It should have low resistivity preferably below 0. 2 ohm-meter. (Resistivity shall be tested by making a 20cm cube of the material & checking the resistance across the opposite faces of the cube). i) It shall not depend on the continuous presence of water to maintain its conductivity. iii) It should be a little alkaline in nature with a pH value between 7 & 9. iv) It should have better hygroscopic properties to absorb moisture. It should absorb & release the moisture in the dry weather condition and help in maintaining the moisture around the earth electrode. v) It should have capacity to retain more than 10% moisture at 105? C. vi) This material is nontoxic, nonreactive, nonexplosive & noncorrosive. vii) Material is in granular form of size 0. 1mm to 3mm and absorbs water to the extent of @ 51%.
Specific gravity of BFC material shall be between 2. 5 to 2. 7. viii) Material shall be thermally stable between temperature range of -10? C to 60? C. ix) Material shall not decompose or leach out with time. x) It shall not pollute the soil or local water table & shall meet environmental friendly requirement for landfill. xi) It should expand & swell considerably & remove entrapped air to create strong connection between earth electrode & soil. xii) It should diffuse in to the soil pores & create conductive roots enlarging conductive zone of the earth pit. CHEMICALS USED IN BFC – BENTONITE :-
Bentonite is naturally occuring hydrated Aluminium Silicate. The most important use of Bentonite is based on its natural swelling property. One can surely say that bentonite is most economic natural thickener available to industries. It has ability to absorb water several (15) times its weight and gives thickstropic fluid. Chemically Bentonite is HYDRATED ALUMINIUM SILICATE. Chemical Formula : Al2O34SiO2H2O Physical Properties : Sp. Gravity: 2. 4 Bulk density: 0. 6 PH of 10% Aqueous solution:8 to 8. 8 Chemical Composition : Silica : 54. 26, Aluminium: 18. 34, Ferric Oxide: 10. 91, TiO2: 01. 25 13. Comparison between Conventional & Modern Earthing :- a) Why install chemical earthing: The following points shall conclude that pit type earthing is out of date and it is being replaced by chemical pipe earthing due to reasons given below :- 1. The sealed pipe for the chemical earthing is generally 2 mtr or 3mtr in length and the earth bore need not be more than the 250 to 300mm dia with maximum depth of 3mtr. 2. The moisture is maintained at a small depth of 3mtr by using ground enhancement material, commonly known as GBFC (Grounding Back Fill Compound), which retains moisture around sealed electrode-pipe. . The efficacy of the chemical earthing to maintain the moisture, which is essential for low ohmic values of earthing resistance, is due to the use of special hygroscopic chemical like aluminum silicate or Bentonite etc. which absorbs the moisture but doesn’t get dissolved in water. 4. The heat generated due to electric faults developing at 1060 °C and above, is resisted by CCM (Crystalline Conducive Material) filled in sealed electrode pipe, which can withstand temperatures upto 2500°C. . The CCM is filled in the pipe of appropriate dimension of 50mm or 80mm dia and is sealed at both ends. It incorporates the earth conductor of GI strip of suitable size of 30x6mm or 40x6mm, welded or bolted or welded on top, depending upon the individual design. 6. The electrode pipes, being a good conductor, increases the fault current capacity of the system, but when filled with CCM, it behaves like almost a solid conducting pipe, multiplying the current capacity. 7.
The CCM resists cracking, warping, shrinking, or distortion even when temperature exceed 2500 °C due to severe repeated electric faults which may happen in operations over the years. 8. The GI pipe used are adequately galvanized (80-100 microns) as per IS -3043. 9. Zinc oxide will be formed during the use of the earth system. Zinc oxide has following advantages over the conventional earthing which uses the copper plate or copper conductors:- a) Zinc oxide so formed is insoluble in water. ) Zinc oxide has a unique Dielectric strength that exhibits semiconducting & piezoelectric dual properties. (Unlike in copper where the copper oxide is a bad conductor of electricity & becomes powdered Red Oxide (Copper Oxide) under high fault current that generate high temperatures) c) ZnO finds application in Varistors which are used to prevent voltage surges in the electronic devices like mobile phone. d) ZnO is not combustible & is used as a fire extinguishing material. b) Why watering is required for New Earth bore?
When the pipe-earthing / chemical-earthing / maintenance-free earthing /Gel earthing is done, the initial watering of the bore is necessary for the following reasons:- a. Unlike pit earthing where the salt (Nacl) & coal is used with copper plate, the pit is dug very deep approximately 40ft to 70 ft. depending on soil conditions where the dampness/moisture is achieved at various levels of depth. b. In case of the modern type of earthing which is free from future maintenance , the watering of the bore prior to installation is necessary for the following reasons:- . The depth of the bore is either 2m/3m (6ft/10ft) which is much less than the normal depth required in pit earthing, so not reaching upto underground water-table. 2. The diameter of the bore is also limited to 250/300mm against the pit earthing which is almost in meters causing faster drying-up of moisture. 3. Unlike salt which is used in pit earthing which dissolves in water and salt itself becomes water in the course of time, thereby loosing the conductivity in surrounding of the pit.
Salt itself reacts with copper & makes copper chloride & other corrosive chemicals which corrode the copper plates, whereas modern chemical earthing uses non-corrosive hygroscopic material. 4. The GBFC (Ground Back Fill Compound) used in chemical earthing absorbs the water upto 13 to 15 times its weight & dosen’t dissolve in water, therefore it retains its moisture property upto the lifetime of the electrode which is more than 25 years as it contains soil friendly materials. 5.
Since there is no need to recharge the pit as the GBFC remains moist through out the life, therefore it is desirable and absolutely necessary to keep watering the bore for first three to four days continuously before installing the electrode and filling pit with GBFC so that the GBFC will have moist bore available with enough water soaked in the bore due to continuous watering before installation. 6. After the installation, no watering is necessary for future maintenance in whatever soil or weather condition it has been installed in either indoor or outdoor installation. 7.
The earthing is quite successful in the normal climatic condition where the average rain fall in a year may not exceed 250mm. This will give enough moisture to the soil. 8. This earthing is being recommended by most of the consultants in desert areas where there is scanty rain-fall and where the water level to achieve the normal dampness is very-very deep. 9. Since we are able to achieve required dampness in a depth of 2 to 3meters with continuous watering of the bore & adequate quantity of the GBFC filled at the time of earthing which remains moist for the rest of life, it maintains the good ohmic values of earth resistance. 0. To conclude, the old copper pit type earthing is out of date & maintenance free earthing is easy to install, occupies less space & economical in the long run. c) Subject: – Location of Earthing? 1. OLD TRADITIONAL SYSTEM:- I) The conventional pit type copper plate Earthing with large Quantity of Charcoal & Salt was requiring large area of about 4’x3’or 6’x4’ & depth used to be 20’ to 60’ (7 to 20 mtr) depending on the soil condition. II) This much area was conveniently available in the factories/office premises in earlier days when the space was not a constraint.
III)The distance between the earth pit & the point of application used to be about 50-100mtrs & therefore to maintain the low resistance of the earthing wire from the earth pit to the machinery the copper wire of 8/10 swg was used. IV) The copper wire was theft-prone for professional wire cutters who used to cut the wire at the first opportunity there by disconnecting the earthing system & causing an electrical danger to the system. 2. PRESENT DAY MODERN SYSTEM:- I) The space is become expensive & in short supply.
II) The conventional pit type earthing is very cumbersome, laborious & occupies more space in term of sq. mtr & it is being replaced with chemical pipe earthings. III) The advantages of pipe earthing are:- a) It needs a bore of only 250-300mm dia & the depth of only 2 to 3 mtr. b) It is a neat & clean installation and doesn’t spoil the look of the office c) It is conveniently covered up with a location-flag. d) The pipe earthing is a compact unit & can be installed very near to the equipment, i. e. hardly 2-5 mtr away from the equipment. ) The closeness of the earthing has a advantage of providing very low resistance value to the system obtained due to less length of the wire. f) The G. I. strip of cross section area of 10x3mm or more are used for connecting the pipe electrode to the equipment. g) G. I. wire is not favorite of wire cutters so there are no chances of disconnection of wire cutting or theft. h) The copper wire of 8/10 swg which was used earlier were subjected to more mechanical damages because of very low cross section area & the round wire is more subjected to more cross sectional damage than the ectangular strip of 10×3 mm or above. CONCLUSION:- In view of above, provision of earthing electrodes close to the point of application or equipment is more desirable for electrical & electronics equipments, which demand low value of ohmic resistance through out the year under all working condition i. e. extreme dry to extreme cold or wet climates. d) Why Neutral Earthing /Grounding 1 All Neutral should have Zero Potential Difference. 2. Why Neutral Voltage is Noticed Now a Days. Reasons for Neutral voltage. A. More use of electronic equipment /UPS/computers /CFL lamps/Speed drives etc.
These non-linear devices operate at different cut off voltages in the sine wave cycle and hence the sine wave is distorted resulting in higher “triplen harmonic” current in the Neutral and causes its heating-up, it also results in the damage of PCB cards and other sensitive components in the electronic circuit/equipments. B) The Industrial loads are in general Not Balanced Loads and therefore the line voltages are spill over to Neutral, which results into stray currents thereby damaging the electronic equipments/ PCB cards. Why Neutral Grounding ?
A. To maintain the ZERO PD between the Neutral and earth by grounding the Spill over voltages. It is therefore very necessary to immediately connect Neutral to the Earth by Solid Permanent contact so that there is no possibility of loose connection /disconnection at any stage OF OPERATION to prevent any electrical mishaps. Method of testing the New Earth Electrode A) Connect the New Electrode to the Neutral of Supply Line by very Good secure Connection Either Bolted or soldered. B) Connect the Volt meter as shown in the Picture below.
C) When the Neutral is properly grounded and the earthing is Successful the voltmeter should give Nearly ZERO voltage between Earth and Neutral. D) Electricity finds always easier path to flow therefore the spill over voltage in the neutral will go to the newly installed earth electrode. In case earthing is not successful or has the higher ohmic value of resistance or loose contact/ disconnection in the earthing circuit, the voltmeter will show the undesirable voltage. In case the earthing is ok and correctly done the voltmeter will show almost Zero Volts.
CONCLUSION:- The industry, project managers & the electrical consultants find it very convincing to use & specify the chemical pipe earthing which is convenient to install, no maintenance what so ever with a long life of over 15 years. 14. 0 CORE FEATURES OF CHEMICAL EARTHNG :- * Ultra low resistance grounding electrode. * Easy to install and takes less space. * Makes maximum safety from electrical system faults. * Maintenance free system, no need to dispense water/salt recurrently. * Maintains dependable & unfailing earth resistance. * Limits the system-to-ground or system-to-frame voltage to values safe for personnel. Offers a relatively firm & secure system with a minimum of transient over voltages. * Authorize any system fault to ground to be quickly isolated. * Protection against static electricity from friction. * Prevents static charge & stray current accidents. * Endow with good grounds for electric process control and communication circuits. * Conductive compound constructs a conductive zone and offers much increased area for peak current dissipation * Low earth resistance. Highly conductive. * Transmits high peak current repeatedly. * Endlessly sustains almost the identical earth resistance value egardless of soil & climate conditions. * Multi-directional dissipation of current. * Stabilizes circuit potential with respect to ground and limits overall potential rise. * Eco Friendly, safe, reliable and anti corrosive. * Longer life. * Straight forward & trouble free mounting. Thus, it is recommended that, modern maintenance-free type of chemical gel type of earthing should be more and more encouraged, in preference to conventional large pit type earthing. ———————————————————————————————————————
