E54530

ASIF EQBALASIF EQBALElectrical & Electronics EngineerElectrical & Electronics Engineer

BASICS OF EARTHINGBASICS OF EARTHING

ContentsContents

1.1. TERMINOLOGIESTERMINOLOGIES

2.2. DISADVANTAGES OF UNEARTHED SYSTEMDISADVANTAGES OF UNEARTHED SYSTEM

3.3. TYPES OF EARTHINGTYPES OF EARTHING

4.4. BASIC PRINCIPLE BASIC PRINCIPLE & METHODS OF SYSTEM EARTHING& METHODS OF SYSTEM EARTHING

5.5. SCHEME ADOPTED IN PROCESS PLANT FOR SYSTEM SCHEME ADOPTED IN PROCESS PLANT FOR SYSTEM EARTHINGEARTHING

6.6. EARTHING CONDUCTORS SCHEDULE FOR SUBSTATIONS EARTHING CONDUCTORS SCHEDULE FOR SUBSTATIONS OF PROCESS PLANTOF PROCESS PLANT

7.7. RECOMMENDED PRACTICES AS PER IEC 60364 AND IS RECOMMENDED PRACTICES AS PER IEC 60364 AND IS 30433043

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TerminologiesTerminologies

1.1. CLASS I EQUIPMENTCLASS I EQUIPMENT2.2. CLASS II EQUIPMENTCLASS II EQUIPMENT3.3. EARTH ELECTRODEEARTH ELECTRODE4.4. EARTH ELECTRODE RESISTANCEEARTH ELECTRODE RESISTANCE5.5. EARTH FAULT LOOP IMPEDANCEEARTH FAULT LOOP IMPEDANCE6.6. EARTH LEAKAGE CURRENTEARTH LEAKAGE CURRENT7.7. PROTECTIVE CONDUCTORPROTECTIVE CONDUCTOR8.8. NEUTRAL CONDUCTORNEUTRAL CONDUCTOR9.9. PEN CONDUCTORPEN CONDUCTOR10.10. RESIDUAL CURRENT DEVICERESIDUAL CURRENT DEVICE11.11. RESIDUAL OPERATING CURRENTRESIDUAL OPERATING CURRENT12.12. TOUCH VOLTAGETOUCH VOLTAGE13.13. STEP VOLTAGESTEP VOLTAGE14.14. EARTH GRIDEARTH GRID15.15. EARTH MATEARTH MAT

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Disadvantages of Unearthed Disadvantages of Unearthed SystemSystem

1.1. Unearthed system experience Unearthed system experience repeated arcing grounds.repeated arcing grounds.

2.2. Insulation failure occurs during single Insulation failure occurs during single phase to ground faults.phase to ground faults.

3.3. Earth fault protection for unearthed Earth fault protection for unearthed system is difficult.system is difficult.

4.4. Voltage due to lightning surges do not Voltage due to lightning surges do not find path to earth.find path to earth.

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Types of Types of EarthingEarthing

1.1. SYSTEM EARTHINGSYSTEM EARTHING

2.2. EQUIPMENT EARTHINGEQUIPMENT EARTHING

3.3. REFERENCE OR SIGNAL EARTHINGREFERENCE OR SIGNAL EARTHING

4.4. STATIC AND LIGHTNING PROTECTION STATIC AND LIGHTNING PROTECTION EARTHINGEARTHING

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Equipment EarthingEquipment Earthing

The The connection between non current carrying connection between non current carrying metallic parts in electrical installation to earth is metallic parts in electrical installation to earth is equipment or body earthing.The basic objectives equipment or body earthing.The basic objectives are:-are:-

1.1. Freedom from Electric shock.Freedom from Electric shock.

2.2. To provide adequate current carrying capability.To provide adequate current carrying capability.

3.3. Avoidance of thermal distress & preservation of Avoidance of thermal distress & preservation of system performance.system performance.

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Reference or Signal EarthingReference or Signal Earthing

The connection of floating point in the circuit to earth is called The connection of floating point in the circuit to earth is called reference or signal earthing. It is performed to achieve both a reference or signal earthing. It is performed to achieve both a suitable level of protection for personnel and equipment,& to suitable level of protection for personnel and equipment,& to provide suitable electric noise immunity for signal ground provide suitable electric noise immunity for signal ground references in generating stations.references in generating stations.

1.1. Mainly used in electronic, communication & data processing Mainly used in electronic, communication & data processing equipment in electrical installation building.equipment in electrical installation building.

2.2. Earthing of chassis of instruments, computer room ensures Earthing of chassis of instruments, computer room ensures freedom from electromagnetic disturbances on operation of freedom from electromagnetic disturbances on operation of isolator,thyristors in main power circuits.isolator,thyristors in main power circuits.

3.3. It is of three type Single point earthing, Multiple point earthing It is of three type Single point earthing, Multiple point earthing & floating earth.& floating earth.

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Basic Principles & Methods of Basic Principles & Methods of System EarthingSystem Earthing

1.1. The potential of neutral is held at The potential of neutral is held at earth potential due to earthing.earth potential due to earthing.

2.2. The fault current lags behind the The fault current lags behind the voltage of unhealthy line by 90 voltage of unhealthy line by 90 degree due to predominantly degree due to predominantly inductive nature of circuit.inductive nature of circuit.

3.3. The current through neutral in The current through neutral in this case is in phase opposition to this case is in phase opposition to capacitive ground current.capacitive ground current.

4.4. By neutralisation of capacitive By neutralisation of capacitive ground currents arcing grounds ground currents arcing grounds is eliminated.is eliminated.

RYBN

PE

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Basic Principles & Basic Principles & Methods of System Methods of System Earthing(Earthing(contcont…….)…….)

1.1. For a ground fault in line B the For a ground fault in line B the vectorial sum of current measured vectorial sum of current measured by CBCT non zero.by CBCT non zero.

2.2. In case of small unbalance this sum In case of small unbalance this sum is non zero and there will be flow is non zero and there will be flow current through neutral.current through neutral.

3.3. So the current flowing through So the current flowing through neutral has to be distinguished for neutral has to be distinguished for being due to ground fault or due to being due to ground fault or due to small unbalances.small unbalances.

4.4. To make this differentiation we To make this differentiation we employ a protective earth employ a protective earth conductor (PE) .conductor (PE) .

5.5. The path of fault current gets The path of fault current gets essentially completed through this essentially completed through this conductor providing low impedance.conductor providing low impedance.

R

BN

PE

Y

F

1010

Basic Principles & Methods of Basic Principles & Methods of System Earthing(System Earthing(contcont…….)…….)

1.1. So measuring the current through So measuring the current through PE which is equal to fault current PE which is equal to fault current is the principle of System is the principle of System earthing.earthing.

2.2. Any other normal current Any other normal current especially the neutral current especially the neutral current under small unbalances must not under small unbalances must not flow through PE in order to avoid flow through PE in order to avoid nuisance tripping.nuisance tripping.

3.3. Two ways to measure the current Two ways to measure the current through PE is by Residual current through PE is by Residual current sensing & by source ground sensing & by source ground return sensing. return sensing.

R

N

PE

YB

1111

Methods OF System EarthingMethods OF System Earthing1.1. Non-effective earthing with resistance or reactance.Non-effective earthing with resistance or reactance.2.2. Effective earthing or solid earthing.Effective earthing or solid earthing.3.3. Resonant earthing.Resonant earthing.

There is no rule or theory as regards which earthing should There is no rule or theory as regards which earthing should be used resistance or reactance. If resistance is used fault current is limited be used resistance or reactance. If resistance is used fault current is limited and system reactance provides the necessary phase opposition between and system reactance provides the necessary phase opposition between capacitive ground current & fault current. Circuits where high charging currents capacitive ground current & fault current. Circuits where high charging currents are involved such as transmission lines, underground cables Reactance are involved such as transmission lines, underground cables Reactance earthing is preferred. earthing is preferred.

Generally one neutral ground is provided at each voltage level. Between Generally one neutral ground is provided at each voltage level. Between

generator voltage level and distribution voltage levels. One ground is provided generator voltage level and distribution voltage levels. One ground is provided at each voltage level. The earth is provided at source end & not load end.at each voltage level. The earth is provided at source end & not load end.

To avoid circulating current only one generator neutral is earthed at a time if To avoid circulating current only one generator neutral is earthed at a time if several generators are operating in parallel. several generators are operating in parallel.

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Scheme Adopted in Process Scheme Adopted in Process plants for System Earthingplants for System Earthing

SYSTEMSYSTEM VOLTAGEVOLTAGE NEUTRAL NEUTRAL EARTHINGEARTHING

MAIN RECEIVING SUBSTATIONMAIN RECEIVING SUBSTATION 220kV,3 phase,3 wire220kV,3 phase,3 wire Solidly earthedSolidly earthed

MAIN POWER GENERATORSMAIN POWER GENERATORS 11-19kV,3 phase,3 wire11-19kV,3 phase,3 wire High resistance earthedHigh resistance earthed

MAIN POWER DISTRIBUTION MAIN POWER DISTRIBUTION 33kV,3 phase,3 wire33kV,3 phase,3 wire Solidly earthedSolidly earthed

SECONDARY POWER SECONDARY POWER DISTRIBUTIONDISTRIBUTION

11kV,3 phase, 3 wire11kV,3 phase, 3 wire

6.6kV,3 phase,3 wire6.6kV,3 phase,3 wireLow resistance earthedLow resistance earthed

EMERGENCY POWER EMERGENCY POWER GENERATIONGENERATION

6.6kV,3 phase,3 wire6.6kV,3 phase,3 wire

415V,3 phase,3 wire415V,3 phase,3 wireLow resistance earthedLow resistance earthed

Solidly earthedSolidly earthed

LV POWER DISTRIBUTIONLV POWER DISTRIBUTION 415V,3 phase,4 wire415V,3 phase,4 wire Solidly earthedSolidly earthed

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Earthing Conductors Earthing Conductors Schedule Schedule

EQUIPMENTEQUIPMENT BODY EARTH BODY EARTH CONNECTIONCONNECTION

INSTRUMENT/INSTRUMENT/CLEAN EARTHCLEAN EARTH

Transformer Transformer 33/6.6kV33/6.6kV

75X10mm, at 4 75X10mm, at 4 placesplaces

Not RequiredNot Required

Neutral Point To Neutral Point To NERNER

Single Core XLPE Single Core XLPE cable of relevant cable of relevant sizesize

Not RequiredNot Required

NER to Earth PitNER to Earth Pit 75X10mm,with 2 75X10mm,with 2 pit connectionspit connections

Not RequiredNot Required

Marshalling BoxMarshalling Box 75X10mm (2 75X10mm (2 No's)No's)

Not RequiredNot Required

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Earthing Conductors ScheduleEarthing Conductors ScheduleEQIPMENTEQIPMENT BODY EARTH BODY EARTH

CONNECTIONCONNECTIONINSTRUMENT/INSTRUMENT/CLEAN EARTHCLEAN EARTH

Transformer 6.6/0.433kVTransformer 6.6/0.433kV 75X10mm,at 4 places75X10mm,at 4 places Not requiredNot required

NeutralNeutral 75X10mm,with 2 pit 75X10mm,with 2 pit connectionsconnections

Not requiredNot required

Bus-DuctBus-Duct 1cX70 sq mm1cX70 sq mm Not requiredNot required

Trip Push button, Welding Trip Push button, Welding Socket, HVAC Duct,Socket, HVAC Duct,

1cX35 sq mm1cX35 sq mm Not requiredNot required

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Earthing Conductors ScheduleEarthing Conductors Schedule

EQUIPMENTEQUIPMENT BODY EARTH BODY EARTH CONNECTIONCONNECTION

INSTRUMENT/ INSTRUMENT/ CLEAN EARTHCLEAN EARTH

6.6kV Switchgear 6.6kV Switchgear PCC,MCC,Battery PCC,MCC,Battery charger,VFD,main charger,VFD,main earth grid & riser earth grid & riser conductorconductor

75X10mm75X10mm 1cX16 mm sq only 1cX16 mm sq only for PCC,MCC VFDfor PCC,MCC VFD

Fiber optic panel, Fiber optic panel, HVAC control panel HVAC control panel DBs Space heater DBs Space heater panel.panel.

50X6mm50X6mm Only for Fiber optic Only for Fiber optic panel & HVAC control panel & HVAC control panelpanel

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Recommended practices for Recommended practices for system Earthingsystem Earthing

Power system earthing arrangements are distinguished Power system earthing arrangements are distinguished as follows:as follows:

The first letter denotes the connection between earth and The first letter denotes the connection between earth and power supply equipment (generator or transformer). The power supply equipment (generator or transformer). The second letter denotes the relationship of the exposed second letter denotes the relationship of the exposed conductive parts of the installation to earth i.e. conductive parts of the installation to earth i.e. connection between earth and electrical device being connection between earth and electrical device being supplied.supplied.

1.1. T-direct connection of one or more points to earth. T-direct connection of one or more points to earth. (French:terre).(French:terre).

2.2. N-direct electrical connection of the exposed conductive N-direct electrical connection of the exposed conductive parts to the earthed points of the source of energy, parts to the earthed points of the source of energy, which for AC,is usually the neutral pointwhich for AC,is usually the neutral point

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Recommended practices for Recommended practices for system Earthingsystem Earthing

Further classification of TN system of earthingFurther classification of TN system of earthing

For low voltage systems the designation 'TN' is further For low voltage systems the designation 'TN' is further subdivided depending on the arrangement of neutral and subdivided depending on the arrangement of neutral and protective conductors, the arrangement being denoted by a protective conductors, the arrangement being denoted by a further letter or letters:further letter or letters:

SS == neutral and protective functions provided by separate neutral and protective functions provided by separate conductors (N and PE).conductors (N and PE).

CC == neutral and protective functions combined in a single neutral and protective functions combined in a single conductor (PEN).conductor (PEN).

Earthing system IEC 60364Earthing system IEC 60364TT systemTT system

1.1. The Neutral point of The Neutral point of LV transformer is directly LV transformer is directly connected to an earth connected to an earth electrodeelectrode

2.2. The exposed conductive The exposed conductive parts of the installation are parts of the installation are connected to an electrically connected to an electrically

separate earth electrodeseparate earth electrode

3.3. The protective earth The protective earth connection of the consumer is connection of the consumer is provided by a local provided by a local connection to earth, connection to earth, independent of any earth independent of any earth connection at the generator connection at the generator or supply end.or supply end.

Rn RuPE

E56888

RYBN

Earthing system IEC 60364Earthing system IEC 60364 TN systemTN system

1.1. The star point of the LVThe star point of the LVtransformer is directlytransformer is directlyconnected to an earthconnected to an earthelectrode (source earth)electrode (source earth)

2.2. The exposed conductiveThe exposed conductiveparts of the installation areparts of the installation areconnected by the PE to theconnected by the PE to thesame earth electrode (The same earth electrode (The

body of the electrical device body of the electrical device is connected with earth via is connected with earth via this earth connection at the this earth connection at the transformer).transformer).

E56890

RYBNPE

Earthing system IEC 60364Earthing system IEC 60364 TN-S systemTN-S system

The PE and NeutralThe PE and Neutral

conductor are separate (Theyconductor are separate (They are connectedare connected

together only near the power source. ).together only near the power source. ).

RYBNPE

E56890

Earthing system IEC 60364Earthing system IEC 60364 TN-C systemTN-C system

The PE and Neutral conductor are common The PE and Neutral conductor are common = the PEN= the PEN

(A combined PEN conductor fulfils the functions (A combined PEN conductor fulfils the functions

of both a PE and an N conductorof both a PE and an N conductor). ).

E56892

RYBPEN

2222

Earthing system IEC 60364Earthing system IEC 60364 TN-C–S SystemTN-C–S System

Part of the system uses a combined PEN Part of the system uses a combined PEN

conductor, which is at some point split up into conductor, which is at some point split up into

separate PE and N lines. separate PE and N lines.

The combined PEN conductor typically occurs The combined PEN conductor typically occurs

between the substation and the entry point into the between the substation and the entry point into the building, whereas within the building separate PE building, whereas within the building separate PE and N conductors are used. and N conductors are used.

(This system is also known as protective multiple (This system is also known as protective multiple earthing (PME), because of the practice of earthing (PME), because of the practice of connecting the combined neutral-and-earth connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce conductor to real earth at many locations, to reduce the risk of broken neutrals .the risk of broken neutrals .

This system is also designated as multiple earthed This system is also designated as multiple earthed neutral (MENneutral (MEN) ) particularly in Australia.particularly in Australia.

E56892

RYBNPE

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TN system examplesTN system examples For HV Systems supplied from an overhead line, the earthing For HV Systems supplied from an overhead line, the earthing

system shall be of the TN configuration from the point of supply. system shall be of the TN configuration from the point of supply. Refer Figure for explanatory schematic.Refer Figure for explanatory schematic.

SOURCE OVERHEAD LINE POINT OF SUPPLY

L1L2L3

PE

EXPOSED CONDUCTIVE PARTS ARE CONNECTED TO PE

CONSUMER EQUIPMENT

SOURCE EARTH

INSTALLATION EARTH

Figure : TN System for installation supplied from Overhead LineFigure : TN System for installation supplied from Overhead Line

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TN system examplesTN system examples TN-S System is adopted for LV System Earthing. TN-S System is adopted for LV System Earthing.

Refer following Fig. for an explanatory Refer following Fig. for an explanatory schematic of a TN-S system.schematic of a TN-S system.

SOURCE

L1L2L3NPE

EXPOSED CONDUCTIVE

PARTS ARE CONNECTED TO PE

CONSUMER EQUIPMENT

CONSUMER EQUIPMENT

SOURCE EARTH

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The Protective Conductor (PE) The Protective Conductor (PE) systemsystem

1.1. An electrically continuous system which provides aAn electrically continuous system which provides a permanent direct return permanent direct return path for fault currents between exposed conductive parts (e.g. the metallic path for fault currents between exposed conductive parts (e.g. the metallic enclosure of electrical equipment) and the neutral of the source of supply. enclosure of electrical equipment) and the neutral of the source of supply. In conjunction with protective devices, the PE system controls magnitude In conjunction with protective devices, the PE system controls magnitude and duration of touch voltages to safe levels.and duration of touch voltages to safe levels.

2.2. In permanent LV systems PE's and protective devices shall ensure automatic In permanent LV systems PE's and protective devices shall ensure automatic disconnection of an earth fault from the source of supply within one second disconnection of an earth fault from the source of supply within one second For personnel safety and to ensure proper operation of the protection relays For personnel safety and to ensure proper operation of the protection relays the impedance of the return path shall be as low as possible, hence the PE the impedance of the return path shall be as low as possible, hence the PE should be integrated in the power cable.should be integrated in the power cable.

3.3. Common examples of PE's are Cable armouring, cable screens, neutral Common examples of PE's are Cable armouring, cable screens, neutral point connections, earth bars etc. Where no suitable cable armour or screen point connections, earth bars etc. Where no suitable cable armour or screen is available either the power cable shall have an additional PE conductor or is available either the power cable shall have an additional PE conductor or a separate PE conductor shall be installed parallel to the power cable a separate PE conductor shall be installed parallel to the power cable (yellow/green PVC sheath).(yellow/green PVC sheath).

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The Equi potential bonding The Equi potential bonding Conductor(EB) systemConductor(EB) system

1.1. An electrically An electrically continuouscontinuous system which directly or indirectly (via the earth system which directly or indirectly (via the earth grid) interconnects exposed conductive parts (e.g., the metallic enclosure grid) interconnects exposed conductive parts (e.g., the metallic enclosure of electrical equipment) with extraneous conductive parts (of non-of electrical equipment) with extraneous conductive parts (of non-electrical equipment, e.g., a skid) and earth to ensure Equi potential electrical equipment, e.g., a skid) and earth to ensure Equi potential between these parts and earth under normal and electrical fault between these parts and earth under normal and electrical fault conditions. This system generally consists of a common earth grid and EB conditions. This system generally consists of a common earth grid and EB conductors connecting exposed and extraneous parts to the earth grid.conductors connecting exposed and extraneous parts to the earth grid.

2.2. Common examples of EBs are Earth grids in oil and gas Common examples of EBs are Earth grids in oil and gas facilities ,substations and earth mats in switchyards with outdoor facilities ,substations and earth mats in switchyards with outdoor equipment.equipment.

3.3. The general rule is that, for reasons of reliability, the exposed and The general rule is that, for reasons of reliability, the exposed and extraneous conductive parts of equipment shall be connected to the EB extraneous conductive parts of equipment shall be connected to the EB system by two separately routed earth conductors, marked green/yellow. system by two separately routed earth conductors, marked green/yellow. These conductors shall be connected to the equipment at physically These conductors shall be connected to the equipment at physically different points (e.g., diametrically opposite).different points (e.g., diametrically opposite).

4.4. The cross-section of conductors for the PE and EB systems shall in general The cross-section of conductors for the PE and EB systems shall in general be determined by the prospective fault level, which will vary from location be determined by the prospective fault level, which will vary from location to location, and the type of fault. to location, and the type of fault.

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PE and EB systemPE and EB system

Although the PE-system and the EB-system have Although the PE-system and the EB-system have distinctly different functions (namely fault clearing and distinctly different functions (namely fault clearing and Equipotential), these systems are permanently interconnected. Equipotential), these systems are permanently interconnected. Thus, in addition to its function the EB-system will affect earth Thus, in addition to its function the EB-system will affect earth loop impedance and fault clearing. Similarly, in addition to its loop impedance and fault clearing. Similarly, in addition to its function, the PE-system will provide supplementary connections function, the PE-system will provide supplementary connections between exposed conductive parts and the earth grid, via the between exposed conductive parts and the earth grid, via the neutral point of the source of supply.neutral point of the source of supply.

Earthing system IEC 60364Earthing system IEC 60364 IT systemIT system

1.1. The star point of the LVThe star point of the LVtransformer is not connectedtransformer is not connected

to an earth electrode (or it has only a to an earth electrode (or it has only a high impedance connection). high impedance connection).

2.2. The exposed conductive partsThe exposed conductive partsof the loads are connected byof the loads are connected bythe PE conductor to a commonthe PE conductor to a commonearth electrodeearth electrode

3.3. In such systems, an insulation In such systems, an insulation monitoring device is used to monitoring device is used to monitor the impedance.monitor the impedance.

E56894

L1L2L3NPE

Earthing System conclusionsEarthing System conclusionsIEC 60364

Earthing TN-C TN-S TT ITSystem

I fault High High Low Very low

Protection SCPD SCPD RCD No problemof people

Fire Forbidden Not Recommended RecommendedProtection recommended with RCD with RCD

Cost Most economical Expensive

economical than TN

TT and IT Systems naturally manage the Fire Risk by limiting the fault current

ELECTROMAGANETIC ELECTROMAGANETIC COMPATIBILITYCOMPATIBILITY

IEC 60364

Earthing TN-C TN-S TT ITSystem

EM Forbidden Good Very good Very gooddisturbances PE and But be careful No problems No problems

Neutral are avoiding PE even if Neutral even if Neutraltogether and Neutral to and PE are in and PE are in(PEN) be in contacts contacts contacts

l

There isn't any fault current in TT and IT System even if the PEand Neutral are in contact

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Thank YouThank You