Basics of earthing

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Basics of earthing

  1. 1. E54530 ASIF EQBALASIF EQBAL Electrical & Electronics EngineerElectrical & Electronics Engineer BASICS OF EARTHINGBASICS OF EARTHING
  2. 2. ContentsContents 1.1. TERMINOLOGIESTERMINOLOGIES 2.2. DISADVANTAGES OF UNEARTHED SYSTEMDISADVANTAGES OF UNEARTHED SYSTEM 3.3. TYPES OF EARTHINGTYPES OF EARTHING 4.4. BASIC PRINCIPLEBASIC PRINCIPLE & METHODS OF SYSTEM EARTHING& METHODS OF SYSTEM EARTHING 5.5. SCHEME ADOPTED IN PROCESS PLANT FORSCHEME ADOPTED IN PROCESS PLANT FOR SYSTEM EARTHINGSYSTEM EARTHING 6.6. EARTHING CONDUCTORS SCHEDULE FOREARTHING CONDUCTORS SCHEDULE FOR SUBSTATIONS OF PROCESS PLANTSUBSTATIONS OF PROCESS PLANT 7.7. RECOMMENDED PRACTICES AS PER IEC 60364RECOMMENDED PRACTICES AS PER IEC 60364 AND IS 3043AND IS 3043
  3. 3. 33 TerminologiesTerminologies 1.1. CLASS I EQUIPMENTCLASS I EQUIPMENT 2.2. CLASS II EQUIPMENTCLASS II EQUIPMENT 3.3. EARTH ELECTRODEEARTH ELECTRODE 4.4. EARTH ELECTRODE RESISTANCEEARTH ELECTRODE RESISTANCE 5.5. EARTH FAULT LOOP IMPEDANCEEARTH FAULT LOOP IMPEDANCE 6.6. EARTH LEAKAGE CURRENTEARTH LEAKAGE CURRENT 7.7. PROTECTIVE CONDUCTORPROTECTIVE CONDUCTOR 8.8. NEUTRAL CONDUCTORNEUTRAL CONDUCTOR 9.9. PEN CONDUCTORPEN CONDUCTOR 10.10. RESIDUAL CURRENT DEVICERESIDUAL CURRENT DEVICE 11.11. RESIDUAL OPERATING CURRENTRESIDUAL OPERATING CURRENT 12.12. TOUCH VOLTAGETOUCH VOLTAGE 13.13. STEP VOLTAGESTEP VOLTAGE 14.14. EARTH GRIDEARTH GRID 15.15. EARTH MATEARTH MAT
  4. 4. 44 Disadvantages of Unearthed SystemDisadvantages of Unearthed System 1.1. Unearthed system experience repeatedUnearthed system experience repeated arcing grounds.arcing grounds. 2.2. Insulation failure occurs during single phaseInsulation failure occurs during single phase to ground faults.to ground faults. 3.3. Earth fault protection for unearthed systemEarth fault protection for unearthed system is difficult.is difficult. 4.4. Voltage due to lightning surges do not findVoltage due to lightning surges do not find path to earth.path to earth.
  5. 5. 55 Types of EarthingTypes of Earthing 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 EARTHINSTATIC AND LIGHTNING PROTECTION EARTHING
  6. 6. 66 Equipment EarthingEquipment Earthing TheThe connection between non current carrying metallic partsconnection between non current carrying metallic parts in electrical installation to earth is equipment or bodyin electrical installation to earth is equipment or body earthing.The basic objectives are:-earthing.The basic objectives 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 systemAvoidance of thermal distress & preservation of system performance.performance.
  7. 7. 77 Reference or Signal EarthingReference or Signal Earthing The connection of floating point in the circuit to earth is called referenceThe connection of floating point in the circuit to earth is called reference or signal earthing. It is performed to achieve both a suitable level ofor signal earthing. It is performed to achieve both a suitable level of protection for personnel and equipment,& to provide suitable electricprotection for personnel and equipment,& to provide suitable electric noise immunity for signal ground references in generating stations.noise immunity for signal ground references in generating stations. 1.1. Mainly used in electronic, communication & data processing equipmentMainly used in electronic, communication & data processing equipment in electrical installation building.in electrical installation building. 2.2. Earthing of chassis of instruments, computer room ensures freedomEarthing of chassis of instruments, computer room ensures freedom from electromagnetic disturbances on operation of isolator,thyristors infrom electromagnetic disturbances on operation of isolator,thyristors in main power circuits.main power circuits. 3.3. It is of three type Single point earthing, Multiple point earthing & floatingIt is of three type Single point earthing, Multiple point earthing & floating earth.earth.
  8. 8. 88 Basic Principles & Methods ofBasic Principles & Methods of System EarthingSystem Earthing 1.1. The potential of neutral is held atThe potential of neutral is held at earth potential due to earthing.earth potential due to earthing. 2.2. The fault current lags behind theThe fault current lags behind the voltage of unhealthy line by 90 degreevoltage of unhealthy line by 90 degree due to predominantly inductive naturedue to predominantly inductive nature of circuit.of circuit. 3.3. The current through neutral in thisThe current through neutral in this case is in phase opposition tocase is in phase opposition to capacitive ground current.capacitive ground current. 4.4. By neutralisation of capacitive groundBy neutralisation of capacitive ground currents arcing grounds is eliminated.currents arcing grounds is eliminated. R Y B N PE
  9. 9. 99 Basic Principles & Methods ofBasic Principles & Methods of System Earthing(System Earthing(contcont…….)…….) 1.1. For a ground fault in line B the vectorialFor a ground fault in line B the vectorial sum of current measured by CBCT nonsum of current measured by CBCT non zero.zero. 2.2. In case of small unbalance this sum isIn case of small unbalance this sum is non zero and there will be flow currentnon zero and there will be flow current through neutral.through neutral. 3.3. So the current flowing through neutralSo the current flowing through neutral has to be distinguished for being due tohas to be distinguished for being due to ground fault or due to smallground fault or due to small unbalances.unbalances. 4.4. To make this differentiation we employTo make this differentiation we employ a protective earth conductor (PE) .a protective earth conductor (PE) . 5.5. The path of fault current getsThe path of fault current gets essentially completed through thisessentially completed through this conductor providing low impedance.conductor providing low impedance. R B N PE Y F
  10. 10. 1010 Basic Principles & Methods ofBasic Principles & Methods of System Earthing(System Earthing(contcont…….)…….) 1.1. So measuring the current through PESo measuring the current through PE which is equal to fault current is thewhich is equal to fault current is the principle of System earthing.principle of System earthing. 2.2. Any other normal current especiallyAny other normal current especially the neutral current under smallthe neutral current under small unbalances must not flow through PEunbalances must not flow through PE in order to avoid nuisance tripping.in order to avoid nuisance tripping. 3.3. Two ways to measure the currentTwo ways to measure the current through PE is by Residual currentthrough PE is by Residual current sensing & by source ground returnsensing & by source ground return sensing.sensing. R N PE Y B
  11. 11. 1111 Methods OF System EarthingMethods OF System Earthing 1.1. 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 be usedThere is no rule or theory as regards which earthing should be used resistance or reactance. If resistance is used fault current is limited and system reactanceresistance or reactance. If resistance is used fault current is limited and system reactance provides the necessary phase opposition between capacitive ground current & faultprovides the necessary phase opposition between capacitive ground current & fault current. Circuits where high charging currents are involved such as transmission lines,current. Circuits where high charging currents are involved such as transmission lines, underground cables Reactance earthing is preferred.underground cables Reactance earthing is preferred. Generally one neutral ground is provided at each voltage level. Between generator voltageGenerally one neutral ground is provided at each voltage level. Between generator voltage level and distribution voltage levels. One ground is provided at each voltage level. Thelevel and distribution voltage levels. One ground is provided at each voltage level. The earth is provided at source end & not load end.earth is provided at source end & not load end. To avoid circulating current only one generator neutral is earthed at a time if severalTo avoid circulating current only one generator neutral is earthed at a time if several generators are operating in parallel.generators are operating in parallel.
  12. 12. 1212 Scheme Adopted in Process plants forScheme Adopted in Process plants for System EarthingSystem Earthing SYSTEMSYSTEM VOLTAGEVOLTAGE NEUTRALNEUTRAL 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 DISTRIBUTIONMAIN POWER DISTRIBUTION 33kV,3 phase,3 wire33kV,3 phase,3 wire Solidly earthedSolidly earthed SECONDARY POWERSECONDARY POWER DISTRIBUTIONDISTRIBUTION 11kV,3 phase, 3 wire11kV,3 phase, 3 wire 6.6kV,3 phase,3 wire6.6kV,3 phase,3 wire Low resistance earthedLow resistance earthed EMERGENCY POWEREMERGENCY POWER GENERATIONGENERATION 6.6kV,3 phase,3 wire6.6kV,3 phase,3 wire 415V,3 phase,3 wire415V,3 phase,3 wire Low resistance earthedLow resistance earthed Solidly earthedSolidly earthed LV POWER DISTRIBUTIONLV POWER DISTRIBUTION 415V,3 phase,4 wire415V,3 phase,4 wire Solidly earthedSolidly earthed
  13. 13. 1313 Earthing ConductorsEarthing Conductors ScheduleSchedule EQUIPMENTEQUIPMENT BODY EARTHBODY EARTH CONNECTIONCONNECTION INSTRUMENT/CLEAINSTRUMENT/CLEA N EARTHN EARTH TransformerTransformer 33/6.6kV33/6.6kV 75X10mm, at 475X10mm, at 4 placesplaces Not RequiredNot Required Neutral Point ToNeutral Point To NERNER Single Core XLPESingle Core XLPE cable of relevantcable of relevant sizesize Not RequiredNot Required NER to Earth PitNER to Earth Pit 75X10mm,with 2 pit75X10mm,with 2 pit connectionsconnections Not RequiredNot Required Marshalling BoxMarshalling Box 75X10mm (2 No's)75X10mm (2 No's) Not RequiredNot Required
  14. 14. 1414 Earthing Conductors ScheduleEarthing Conductors Schedule EQIPMENTEQIPMENT BODY EARTHBODY EARTH CONNECTIONCONNECTION INSTRUMENT/CLEAINSTRUMENT/CLEA N EARTHN EARTH Transformer 6.6/0.433kVTransformer 6.6/0.433kV 75X10mm,at 4 places75X10mm,at 4 places Not requiredNot required NeutralNeutral 75X10mm,with 2 pit75X10mm,with 2 pit connectionsconnections Not requiredNot required Bus-DuctBus-Duct 1cX70 sq mm1cX70 sq mm Not requiredNot required Trip Push button, WeldingTrip Push button, Welding Socket, HVAC Duct,Socket, HVAC Duct, 1cX35 sq mm1cX35 sq mm Not requiredNot required
  15. 15. 1515 Earthing Conductors ScheduleEarthing Conductors Schedule EQUIPMENTEQUIPMENT BODY EARTHBODY EARTH CONNECTIONCONNECTION INSTRUMENT/INSTRUMENT/ CLEAN EARTHCLEAN EARTH 6.6kV Switchgear6.6kV Switchgear PCC,MCC,BatteryPCC,MCC,Battery charger,VFD,main earthcharger,VFD,main earth grid & riser conductorgrid & riser conductor 75X10mm75X10mm 1cX16 mm sq only for1cX16 mm sq only for PCC,MCC VFDPCC,MCC VFD Fiber optic panel, HVACFiber optic panel, HVAC control panel DBscontrol panel DBs Space heater panel.Space heater panel. 50X6mm50X6mm Only for Fiber opticOnly for Fiber optic panel & HVAC controlpanel & HVAC control panelpanel
  16. 16. 1616 Recommended practices for systemRecommended practices for system EarthingEarthing Power system earthing arrangements are distinguished as follows:Power system earthing arrangements are distinguished as follows: The first letter denotes the connection between earth and powerThe first letter denotes the connection between earth and power supply equipment (generator or transformer). The second lettersupply equipment (generator or transformer). The second letter denotes the relationship of the exposed conductive parts of thedenotes the relationship of the exposed conductive parts of the installation to earth i.e. connection between earth and electricalinstallation to earth i.e. connection between earth and electrical device being supplied.device being supplied. 1.1. T-direct connection of one or more points to earth. (French:terre).T-direct connection of one or more points to earth. (French:terre). 2.2. N-direct electrical connection of the exposed conductive parts toN-direct electrical connection of the exposed conductive parts to the earthed points of the source of energy, which for AC,isthe earthed points of the source of energy, which for AC,is usually the neutral pointusually the neutral point
  17. 17. 1717 Recommended practices for systemRecommended practices for system EarthingEarthing Further classification of TN system of earthingFurther classification of TN system of earthing For low voltage systems the designation 'TN' is further subdividedFor low voltage systems the designation 'TN' is further subdivided depending on the arrangement of neutral and protective conductors, thedepending on the arrangement of neutral and protective conductors, the arrangement being denoted by a further letter or letters:arrangement being denoted by a further letter or letters: SS == neutral and protective functions provided by separate conductors (Nneutral and protective functions provided by separate conductors (N and PE).and PE). CC == neutral and protective functions combined in a single conductorneutral and protective functions combined in a single conductor (PEN).(PEN).
  18. 18. Earthing system IEC 60364Earthing system IEC 60364 TT systemTT system 1.1. The Neutral point ofThe Neutral point of LV transformer is directlyLV transformer is directly connected to an earthconnected to an earth electrodeelectrode 2.2. The exposed conductiveThe exposed conductive parts of the installation areparts of the installation are connected to an electricallyconnected to an electrically separate earth electrodeseparate earth electrode 3.3. The protective earth connection ofThe protective earth connection of the consumer is provided by athe consumer is provided by a local connection to earth,local connection to earth, independent of any earthindependent of any earth connection at the generator orconnection at the generator or supply end.supply end. Rn Ru PE E56888 R Y B N
  19. 19. Earthing system IEC 60364Earthing system IEC 60364 TN systemTN system 1.1. The star point of the LVThe star point of the LV transformer is directlytransformer is directly connected to an earthconnected to an earth electrode (source earth)electrode (source earth) 2.2. The exposed conductiveThe exposed conductive parts of the installation areparts of the installation are connected by the PE to theconnected by the PE to the same earth electrode (Thesame earth electrode (The body of the electrical device isbody of the electrical device is connected with earth via this earthconnected with earth via this earth connection at the transformer).connection at the transformer). E56890 R Y B N PE
  20. 20. 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. ). R Y B N PE E56890
  21. 21. Earthing system IEC 60364Earthing system IEC 60364 TN-C systemTN-C system The PE and Neutral conductor are commonThe 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 R Y B PEN
  22. 22. 2222 Earthing system IEC 60364Earthing system IEC 60364 TN-C–S SystemTN-C–S System Part of the system uses a combined PENPart of the system uses a combined PEN conductor, which is at some point split up intoconductor, which is at some point split up into separate PE and N lines.separate PE and N lines. The combined PEN conductor typically occursThe combined PEN conductor typically occurs between the substation and the entry point into the building,between the substation and the entry point into the building, whereas within the building separate PE and N conductorswhereas within the building separate PE and N conductors are used.are used. (This system is also known as protective multiple earthing(This system is also known as protective multiple earthing (PME), because of the practice of connecting the combined(PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations,neutral-and-earth conductor to real earth at many locations, to reduce the risk of broken neutrals .to reduce the risk of broken neutrals . This system is also designated as multiple earthed neutralThis system is also designated as multiple earthed neutral (MEN(MEN)) particularly in Australia.particularly in Australia. E56892 R Y B N PE
  23. 23. 2323 TN system examplesTN system examples  For HV Systems supplied from an overhead line, the earthing system shallFor HV Systems supplied from an overhead line, the earthing system shall be of the TN configuration from the point of supply. Refer Figure forbe of the TN configuration from the point of supply. Refer Figure for explanatory schematic.explanatory schematic. SOURCE OVERHEAD LINE POINT OF SUPPLY L1 L2 L3 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
  24. 24. 2424 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 schematic of aRefer following Fig. for an explanatory schematic of a TN-S system.TN-S system. SOURCE L1 L2 L3 N PE EXPOSED CONDUCTIVE PARTS ARE CONNECTED TO PE CONSUMER EQUIPMENT CONSUMER EQUIPMENT SOURCE EARTH
  25. 25. 2525 The Protective Conductor (PE) systemThe Protective Conductor (PE) system 1.1. An electrically continuous system which provides aAn electrically continuous system which provides a permanent direct return path forpermanent direct return path for fault currents between exposed conductive parts (e.g. the metallic enclosure offault currents between exposed conductive parts (e.g. the metallic enclosure of electrical equipment) and the neutral of the source of supply. In conjunction withelectrical equipment) and the neutral of the source of supply. In conjunction with protective devices, the PE system controls magnitude and duration of touch voltages toprotective devices, the PE system controls magnitude and duration of touch voltages to safe levels.safe levels. 2.2. In permanent LV systems PE's and protective devices shall ensure automaticIn permanent LV systems PE's and protective devices shall ensure automatic disconnection of an earth fault from the source of supply within one second Fordisconnection of an earth fault from the source of supply within one second For personnel safety and to ensure proper operation of the protection relays the impedancepersonnel 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 should be integrated in theof the return path shall be as low as possible, hence the PE should be integrated in the power cable.power cable. 3.3. Common examples of PE's are Cable armouring, cable screens, neutral pointCommon examples of PE's are Cable armouring, cable screens, neutral point connections, earth bars etc. Where no suitable cable armour or screen is availableconnections, earth bars etc. Where no suitable cable armour or screen is available either the power cable shall have an additional PE conductor or a separate PEeither the power cable shall have an additional PE conductor or a separate PE conductor shall be installed parallel to the power cable (yellow/green PVC sheath).conductor shall be installed parallel to the power cable (yellow/green PVC sheath).
  26. 26. 2626 The Equi potential bondingThe Equi potential bonding Conductor(EB) systemConductor(EB) system 1.1. An electricallyAn electrically continuouscontinuous system which directly or indirectly (via the earth grid)system which directly or indirectly (via the earth grid) interconnects exposed conductive parts (e.g., the metallic enclosure of electricalinterconnects exposed conductive parts (e.g., the metallic enclosure of electrical equipment) with extraneous conductive parts (of non-electrical equipment, e.g., aequipment) with extraneous conductive parts (of non-electrical equipment, e.g., a skid) and earth to ensure Equi potential between these parts and earth under normalskid) and earth to ensure Equi potential between these parts and earth under normal and electrical fault conditions. This system generally consists of a common earthand electrical fault conditions. This system generally consists of a common earth grid and EB conductors connecting exposed and extraneous parts to the earth grid.grid and EB conductors connecting exposed and extraneous parts to the earth grid. 2.2. Common examples of EBs are Earth grids in oil and gas facilities ,substations andCommon examples of EBs are Earth grids in oil and gas facilities ,substations and earth mats in switchyards with outdoor equipment.earth mats in switchyards with outdoor equipment. 3.3. The general rule is that, for reasons of reliability, the exposed and extraneousThe general rule is that, for reasons of reliability, the exposed and extraneous conductive parts of equipment shall be connected to the EB system by twoconductive parts of equipment shall be connected to the EB system by two separately routed earth conductors, marked green/yellow. These conductors shall beseparately routed earth conductors, marked green/yellow. These conductors shall be connected to the equipment at physically different points (e.g., diametricallyconnected to the equipment at physically different points (e.g., diametrically opposite).opposite). 4.4. The cross-section of conductors for the PE and EB systems shall in general beThe 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 to location,determined by the prospective fault level, which will vary from location to location, and the type of fault.and the type of fault.
  27. 27. 2727 PE and EB systemPE and EB system Although the PE-system and the EB-system have distinctlyAlthough the PE-system and the EB-system have distinctly different functions (namely fault clearing and Equipotential), these systemsdifferent functions (namely fault clearing and Equipotential), these systems are permanently interconnected. Thus, in addition to its function the EB-are permanently interconnected. Thus, in addition to its function the EB- system will affect earth loop impedance and fault clearing. Similarly, insystem will affect earth loop impedance and fault clearing. Similarly, in addition to its function, the PE-system will provide supplementaryaddition to its function, the PE-system will provide supplementary connections between exposed conductive parts and the earth grid, via theconnections between exposed conductive parts and the earth grid, via the neutral point of the source of supply.neutral point of the source of supply.
  28. 28. Earthing system IEC 60364Earthing system IEC 60364 IT systemIT system 1.1. The star point of the LVThe star point of the LV transformer is not connectedtransformer is not connected to an earth electrode (or it has only a highto an earth electrode (or it has only a high impedance connection).impedance connection). 2.2. The exposed conductive partsThe exposed conductive parts of the loads are connected byof the loads are connected by the PE conductor to a commonthe PE conductor to a common earth electrodeearth electrode 3.3. In such systems, an insulationIn such systems, an insulation monitoringmonitoring device is used to monitor the impedance.device is used to monitor the impedance. E56894 L1 L2 L3 N PE
  29. 29. Earthing System conclusionsEarthing System conclusions IEC 60364 Earthing TN-C TN-S TT IT System I fault High High Low Very low Protection SCPD SCPD RCD No problem of people Fire Forbidden Not Recommended Recommended Protection 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
  30. 30. ELECTROMAGANETICELECTROMAGANETIC COMPATIBILITYCOMPATIBILITY IEC 60364 Earthing TN-C TN-S TT IT System EM Forbidden Good Very good Very good disturbances PE and But be careful No problems No problems Neutral are avoiding PE even if Neutral even if Neutral together 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 PE and Neutral are in contact
  31. 31. 3131 Thank YouThank You

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