earthing system
DESCRIPTION
A brief idea about the earthing system used in our home as well as in industries for safety pupose.TRANSCRIPT
Earthing/Grounding Earthing/Grounding
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What is Earthing?What is Earthing?
Earthing an equipment means connecting that equipment to general mass of earth by means of an electrical conductor.
What is ground?
A conducting connection, whether intentional or accidental, between an electrical circuit or equipment
and the earth, or to some conducting body that serves in place of earth*
Ground is a connection to Earth made either intentionally or accidentally
Earth / Ground BasicsEarth / Ground Basics
Why ground?
By dissipating stray energy from:
Electrical faults (fuses, breakers etc.)Lightning strikesRadio FrequencyStatic discharges
To protect people and equipment
Earth / Ground BasicsEarth / Ground Basics
Grounding in BroadcastingGrounding in Broadcasting
Four different types of ground system in broadcasting --Grounding for lightening protection.Grounding for power distribution safety.Grounding all station equipment together.Grounding for maximum efficiency.
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Main objectives of Earthing Main objectives of Earthing
To provide an alternative path for the fault current to flow.
To ensure that all exposed conductive parts do not reach a dangerous potential.
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Earth Resistance Earth Resistance
Effectiveness of the Earthing connection made by embedding a suitable electrode in earth.
Measured in ohms.
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Earth Resistance contd…Earth Resistance contd…
Earth resistance consists of Resistance of metal electrode.Contact resistance between electrode and soil.Resistance of soil surrounding the electrode.
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Earth Resistance contd…Earth Resistance contd…
To increase the effectiveness of earth, the resultant earth resistance should be reduced .
Efforts should be made to reduce the resistance contributed by each of above three components.
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Earth Resistance contd…Earth Resistance contd…
The qualities of a good Earthing system are:
Must be of low electrical resistance. Must be of good corrosion resistance. Must be able to dissipate high fault current repeatedly.
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Earth Electrodes Earth Electrodes Earth electrodes can
be of following shapes:
Driven Rods or pipes.Horizontal Wires.Four Pointed Stars.Buried Radial Wires.Spheres made of metal.Conductive Plates• Round Vertical Plates.• Square Vertical Plates.
Types of Grounding Systems
Ground rod
Many different types available Choice depends on local conditions
and required function
Simplest form is a single stake
Mostly used for:Lightning protectionStand alone structuresBack-up for utility ground
Types of Grounding Systems
Ground rod group
ground rod group
typically for lightning protection on larger structures or protection around potential hotspots such as substations.
Types of Grounding Systems
Ground plate
For areas where there is rock (or other poor conducting material) fairly close to the surface ground plates are preferred as they are more effective
Types of Grounding Systems
Ground mesh
A ground mesh consists of network of bars connected together, this system is often used at larger sites such as electrical substations.
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Effect of Soil Properties on Earthing
Effect of Soil Properties on Earthing
Soils arranged in ascending order with regard to their electrical resistance:
Wet marshy lands.Clay, loamy soil.Clay & loam mixed with varying proportion of gravel & sand.Damp & wet sands.Dry sand.Gravel & Stones – Note: A location, which has water flowing over it is not
preferred, because flowing water normally washes away all conducting salts.
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Effect of Soil Properties on Earthing contd…
Effect of Soil Properties on Earthing contd…
While it is not possible to change the fundamental nature /properties of soil at a given location, but local variations of soil conditions do occur even in a small area.
Preference should be given to a location that is likely to give minimum electrical resistance.
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Effect of Soil Properties on Earthing contd…
Effect of Soil Properties on Earthing contd…
When the soil available is of high electrical resistance, then its resistance can be lowered by treatment.
The treatment is limited to the area in the neighbourhood of earth electrode.
Pure water is a bad conductor, but the addition of salts improves the conductivity to a large extent.
The presence of small quantity of salt reduces the soil resistance by eighty percent.
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Treatment of soilTreatment of soil Earth electrode should be
buried in soil at least 3 meters into the ground with charcoal and cokepowder mixed with chemical salts like sodium chloride or magnesium chloride put around the electrode. A typical method is to place the chemical in a circular trench around but not touching the electrode.
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Drawbacks of chemical treatment
Drawbacks of chemical treatment
The treatment is effective but not permanent.
The corrosion of the electrode is accelerated by the chemical treatment.
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Drawbacks contd…Drawbacks contd… To eliminate the corrosion of electrode to some extent
copper is used as the earth electrode since its resistance to corrosion is comparatively
large to that of the metal iron.
The salts commonly used for chemical treatment of soil areSodium Chloride/ Calcium Chloride Sodium NitrateMagnesium Sulphate/Copper Sulphate which make the soil conductive for a longer period.
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Other FactorsOther Factors
Temperature of the environment
Moisture Content of Soil
Mechanical Composition of soil
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Installation of electrodesInstallation of electrodes
Here, we may discuss the pipe and Plate Earthing only as the same are being used in most of our installations.
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Installation of pipe or rod electrodes
Installation of pipe or rod electrodes
Installation of rods or pipes is the most convenient & cheapest process.
In wet areas or where black soil is already there pipe or rods can be driven by hammering.
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Installation of Plate ElectrodesInstallation of Plate Electrodes
Plate electrodes invariably require excavation.
Hence the cost is higher.
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Points to be taken care of:Points to be taken care of: The joints, which will eventually be
embedded in earth, should be such that the joint resistance does not increase with passage of time.
The backfill used should not be acidic, so that corrosion of electrode does not take place.
If plate earths are used in pits in a row, alternate plates should be at 90 degrees to each other.
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Retaining Moisture & Regular Watering
Retaining Moisture & Regular Watering
Plantation can be done around Earth pits so as to ensure regular watering and increasing moisture content.
Drip Pipe lines/Sprinkler can be run in areas surrounding Earth pits for watering.
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Plantation around Earth Pits at LPTsPlantation around Earth Pits at LPTs
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Plantation around Earth Pits at LPTsPlantation around Earth Pits at LPTs
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Plantation around Earth Pits at LPTsPlantation around Earth Pits at LPTs
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Watering arrangements at DDK Indore
Watering arrangements at DDK Indore
Counterpoise-cont’dCounterpoise-cont’d
supports
antenna
radius = ¼
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Artificial Methods of reducing Earth Resistivity
Artificial Methods of reducing Earth Resistivity
Recalling drawbacks of adding chemicals:
Rapid corrosion of the electrodes.
Dilution of salts by rainwater or movement of water through the area –Hence, increase in resistivity of Earth.
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Probable SolutionsProbable Solutions Using deeper rods as electrodes. Using low resistivity backfill material. Some common backfill materials are:
Bentonite (Swells in volume in moist condition, increases surface area)
Marconite (Conductive concrete)
Gypsum (low solubility)
Others, like copper solution when mixed with other chemicals create gel
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An Earth Pit at LPT KhargoneAn Earth Pit at LPT Khargone Backfill Material:
Bed of Black soil in the bottomAlternate layers of 6” of Soil+Bentonite (4:1) and CharcoalJute Bag used for confining material (is not must)
Ground testing methodGround testing method
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Ground testing methodGround testing method
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Clamp-On Earth Loop Tester GEO 30Clamp-On Earth Loop Tester GEO 30
Feature Summary Ground loop resistance clamp measurement Low level measurement of ground leakage current Wide AC current measurement range up to 30A with one
instrument Rapid evaluation of continuity loop resistance by audible HI/LO
alarm Easy to use, convenient, Display-HOLD function Time saving memory function for saving measured values and
automatic recording Automatic self calibration ensures correct measurement every
timeCustomer Residential, Commercial, Industrial ElectriciansApplication Earth loop resistance testing for houses, commercial and
industrial buildings
Stakeless Ground Resistance Measurement
LEM GEO 30 - Ground Tester / Current Meter
The voltage UU developed by the clamp is injected into the circuit. This causes a current II which flows in this
measuring circuit. The second clamp measures this current II and the earth clamp displays the ground loop resistance
Rx+RnRx+Rn.
Current amplifier
Voltage generator
II
RxRn
U
Clamp-On Earth Loop Tester GEO 30
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