Earthing System

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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