Direct Lightning Stroke Shielding Of Substations
Understanding DirectDirectUnderstandingLightning StrokeStroke ShieldingShieldingLightningof SubstationsSubstationsofP.K. Sen, Ph.D., P.E.ProfessorDivision of EngineeringColo. School of MinesGolden, Colorado(303) 384-2020psen@mines.eduPSERC SeminarGolden, ColoradoNovember 6, 2001 2002 Colorado School of Mines
Understanding DirectLightning Stroke Shieldingof SubstationsPresentation Outline:! Lightning Stroke Fundamentals! Surge Protection and Surge!!!!ArrestersDesign ParametersDesign ProblemDesign MethodsConclusions
Main ReferenceEEIEdSt89.9-1699
Lightning StrokeFundamentals (1)Several Theories have beenadvanced regarding the:!Formation of charge centers!!Charge separation within acloudUltimate development oflightning strokesTypes of Lightning Strokes:!Strokes within clouds!!!Strokes between adjacentcloudsStrokes to tall structuresStrokes terminating on theground
Lightning StrokeFundamentals (2)Stroke Development:(Two-Step Process)1. Ionization (Coronabreakdown) of the airsurrounding the chargecenter and the developmentof “Stepped Leaders.”2. Development of a lightningstroke called “ReturnStroke.” The totaldischarge of current from athundercloud is called a“Lightning Flash.”
Lightning StrokePhenomenaCharge Distribution at Various Stages of Lightning DischargeRef: IEEE Std. 998-1996 (Figure 2-2)
Lightning StrokeFundamentals (3)Three Issues:1.Usually the stroke consists ofnegative charge flowing fromcloud to earth.2.More than half of all lightningflashes consist of multiple(subsequent) strokes.3.Leaders of subsequent strokesare called Dart Leader.
Effects of Direct Strokeon SubstationAssumptions: No Shielding and NoSurge Protective Devices."Possible Insulation Flashover(depends primarily on the strokecurrent magnitude)"Damage (and possible failure) toMajor Substation Equipment"Substation Outage"CostUse ofof DirectDirect StrokeStroke ShieldingShielding andandUseSurge ArrestersArresters toto MinimizeMinimizeSurgethe PossibilityPossibility ofof DamageDamage ofof EquipmentEquipmenttheand Outage.Outage.and
Surge Protection andSurge Arresters (1)8 x 20 µsCrestValue1.2 x 50 µsT1 : Rise TimeT2 : Time to Half valueStandard CurrentCurrent andand VoltageVoltageStandardWaveshapes toto DefineDefineWaveshapesLightning forfor LaboratoryLaboratory TestsTestsLightning
Surge Protection andSurge Arresters (2)"Standard Lightning Voltage Test Wave:1.2 x 50 µsec"Standard Lightning Current Test Wave:8 x 20 µsec"BIL (Basic Impulse Insulation Level):A specified insulation level expressed(in kV) as the crest value of a standardlightning impulse."CFO (Critical Flashover Voltage): Voltage(negative) impulse for a disruptivedischarge around or over the surface ofan insulator. BIL is determinedstatistically from the CFO tests."Arrester Classes (Defined by Tests):###Distribution (Standard & Heavy Duty)IntermediateStation
Surge Protection andSurge Arresters (3)Metal Oxide Varistors (MOVs)Important Characteristics:"Maximum Continuous OperatingVoltage (MCOV)"Temporary Over Voltage (TOV)"Lightning Discharge Voltage (IR)"Protective Level: Maximum Crest Valueof voltage that appears across itsterminals under specified conditions."Volt-Time Characteristics
Surge Protection andSurge Arresters (4)Protective Margins:Three Protective Margins (PMs) arenormally calculated.PM(1) [(CWW/FOW) – 1)] x 100%PM(2) [(BIL/LPL) – 1)] x 100%PM(3) [(BSL/SPL) – 1)] x 100%Where:CWW: Chopped Wave WithstandFOW: Front-of-WaveBIL: Basic Lightning Impulse Insulation LevelLPL: Lightning Impulse Classifying Current(Also Called IR: Lightning Discharge Voltage)BSL: Basic Switching Impulse Insulation LevelSPL: Switching Impulse Protective Level
Surge Protection andSurge Arresters (5)PM(1)PM(2)PM(3)Insulation CoordinationRef:Ref: IEEEIEEEStd.Std.C62.22-1991C62.22-1991
Surge Protection andSurge Arresters (6)Lead Length Voltage:" For standard lightning surge current testwaves (8 x 20 µs) the value is approx.1.6 kV/ft." For actual lightning current this value isbetween 6-10 kV/ft.di(t)v(t) LdtL 0.4 µΗ/ft.
Effects of Direct Strokeon SubstationAssumptions:Provide both Shielding andSurge Arresters.1.Minimize the possibility of directlightning strike to bus and/or majorequipment in the substation andhence, the outage and possible failureof major electrical equipment.2.Shielding may allow some smallerstrokes to strike the buswork andequipment. Even though these strokesmay not cause flashover, they maydamage internal insulation systems oftransformers, etc., unless they haveproper surge arresters mounted attheir terminals.
Effects of Direct Strokeon SubstationAssumptions:Provide both Shielding andSurge Arresters (contd.).3. Surge arresters will provide coordinatedprotection from lightning and switchingsurges for the internal insulation ofpower transformers, etc.4. Arresters cannot effectively absorb verylarge stroke currents (arresters may fail,or discharge voltage become too high).5. Arresters may not protect all of thebuswork from lightning flashover, due todistance effect.6. Lightning shielding can reliably interceptthe large strokes, and can generallyprotect buswork from lightningflashover.
Design Parameters! Ground Flash Density (GFD)! Stroke Current! Strike Distance
Design ParametersGround Flash Density (GFD)Ground Flash Density (GFD) : The average number oflightning strokes per unit area per unit time (year) at aparticular location.Approximate Relationships:Nk 0.12 TdNm 0.31 TdorNk 0.054 Th1.1Nm 0.14 Th1.1Where,Nk No. of Flashes in Earth per sq. kmNm No. of Flashes in Earth per sq. mileTd Average Annual “keraunic level”(thunderstorm-days)Th Average Annual “keraunic level”(thunderstorm-hours)
Mean AnnualGround Flash Density (GFD)GFD D 66Flashes/kmFlashes/km22/year/yearGFD
Mean AnnualGround Flash DensityDenver, ColoradoThunderstorm-days (Td) 42Thunderstorm-hours (Th) 70(GFD) Nk(GFD) Nk 0.12 Td 0.12 x 50 6 0.054 Th1.1 5.8From the Graph, (GFD)Nk 6/km2/year(Compare to the value of 2 on NW corner ofColorado and a Value of 18 in CentralFlorida)
Stroke Current Magnitudeand DistributionP(I) Probability that the peakcurrent in any stroke will exceed II Specified crest current of thestroke (kA)Probability of Stroke Current Exceeding Abscissa forStrokes to Flat GroundMedian Value of I:31 kA for OHGW, Conductors, Masts & Structures24 kA, Flat groundStroke Current Range Probability for Strokes to Flat groundRef. IEEE Std. 998-1996
Design ParametersStrike DistanceSm 8 (k) I 0.65(m)Sf 26.25 (k) I 0.65 (ft)I 0.041 Sm1.54(kA)orWhere,WhereSm Strike Distance in (meters)Sf Strike Distance in (ft)I Return Stroke Current in (kA)k Constant (Introduced in Revised Model) 1, for strokes to wires or ground plane 1.2, for strokes to a lightingmastStrike Distance is the length of the final jump(last step) of the stepped leader as its potentialexceeds the breakdown resistance of this lastgap; found to be related to the amplitude of thefirst return stroke.
Strike Distance vs. StrokeCurrentRef: IEEE Std. 998-1996
Design Problem! Probabilistic nature of lightning! Lack of data due to infrequencyof lightning strokes in substations! Complexity & economics involvedin analyzing a system in detail! No known practical method ofproviding 100% shielding! Lower Voltage (69 kV and Below)Facilities:Simplified Rules of Thumb! EHV (345 kV and Above) Facilities:Sophisticated (EGM) Study
Design ProblemFour-Step Approach:! Evaluate the importance & valueof the facility being protected andprobable consequences of a directlightning strike (Risk Assessment).! Investigate the severity & frequencyof thunderstorms in the area of thesubstation facility and the exposureof the substation.! Select an appropriate designmethod (shielding and SA’s).! Evaluate the effectiveness and costof the design.
Design Methods(Commonly Used)1. Empirical (Classical)Designa. Fixed Anglesb. Empirical Curves2. Electro-GeometricModel (EGM)a. Whitehead’s EGMb. Revised EGMc. Rolling Sphere
Fixed Angles Method (1)(Examples)ProtectedobjectsobjectsProtectedFixed Angles for Shielding Wires
Fixed Angles Method (2)(Examples)ProtectedobjectsobjectsProtectedFixed Angles for Masts
Fixed Angle Methods (3)(Examples)Shielding Substation with Masts Using FixedAngle Method (Ref: IEEE 998, Fig. B.2-3)
Fixed Angles Method (4)(Summary)1.Commonly used value of the angle“alpha (α)” is 45o.2.Both 30o and 45o are widely used forangle “beta (β)”.3.Notes:"""""Independent of Voltage, BIL, SurgeImpedance, Stroke Current Magnitude,GFD, Insulation Flashover Voltage, etc.Simple design technique and easy toapply.Commonly used in REA DistributionSubstation design.Has been in use since 1940’s.For 69 kV and below produces verygood results.
Empirical Curve Method (1)Developed in 1940’s (Experimental):Assumptions:1.All lighting strokes propagatevertically downward.2.The station is in a flat terrain.3.Thunderstorm cloud base is at1000 ft. above ground.4.Earth resistivity is low.
Empirical Curve Method (2)Assumptions (contd.):5.Based on “Scale Model” Tests.6.Independent of Voltage Level.7.Depends on the geometricrelationship between the shield(or mast), the equipment, andthe ground.8.Independent of Insulation Level,Surge Impedance, StrokeCurrent Magnitude, and theProbability of LightningOccurrence.9.Designed for different shieldingfailure rates. A failure rate of0.1% is commonly used.
Empirical Curve Methods (3)(Examples)Single Mast Protecting Single ObjectDerived from the Original Curvespublished by Westinghouse Researchers
Empirical Curve Methods (4)(Examples)Single Shield Wire Protecting HorizontalConductorsDerived from the Original Curvespublished by Westinghouse Researchers
Empirical Curve Methods (5)Summary :1.Developed Experimentally in 1940’s.2.Limited Applications Capabilities.3.Modified Curves Developed in the IEEEStd. 998-1996.4.Not Very User Friendly, TimeConsuming and Used by Very Few.5.Not Recommended Design Practice forEHV Substations.
Electrogeometric Method (1)1.2.3.Whitehead’s EGM ModelRevised EGM ModelRolling Sphere MethodAssumptions:a.B.The stroke is assumed to arrivein a vertical direction.The differing strike distance(value of “k”) to masts, wires,and the ground plane are takeninto considerations.
Electrogeometric Method (2)(Recommended EHV Transmission Substationand Switching Station)Allowable Stroke Current:BIL x 1.1 2.2 (BIL)Is ZsZs2( )Or0.94 x CFO x 1.1 2.068 (CFO)Is ZsZs2( )Where,Is Allowable Stroke Current in kABIL Basic Lightning Impulse Levelin kVCFO Negative Polarity Critical FlashoverVoltage of the Insulation in kVZs Surge Impedance of the Bus Systemin Ohms
Electrogeometric Method (3)(EHV Transmission Substationand Switching Station)Procedure:1. Calculate Bus Surge Impedance Zs fromthe Geometry. For two heights, use thehigher level heights.2. Determine the Value of CFO (or BIL). Forhigher altitude use correction factor forBIL.3. Calculate the Value of Is.4. Calculate the Value of the StrikingDistance (or Radius of the Rolling Sphere)5. Use Two or more Striking Distance Valuesbased on BIL Voltage Levels in aSubstation with two different voltages.
Electrogeometric Method (4)(Examples)Principle of Rolling Sphere
Electrogeometric Method (5)(Examples)Shield Mast Protection for Stroke Current Is
Electrogeometric Method (6)(Examples)Multiple Shield Mast Protection for Stroke Current Is
Electrogeometric Method (7)(Examples)Protection by Shield Wires and Masts
Electrogeometric Method (8)(Distribution Substation – Below 115 kV) Shield spacing becomes quite close (byEGM method) at voltages 69 kV an below. For Voltage 69 kV and below, Select aminimum Stroke Current of 2 kA (also 3kA has been recommended). According the data available 99.8% of allstroke currents exceed 2 kA. Lowerpossibility of flashover and lowerconsequences. Usually surge arrester willprotect the transformer from anyinsulation damage. For, a 69 kV Design,BIL 350 kV, Zs 360 ΩStroke Current (Is) 2.1 kA For, a 12.47 kV Design,BIL 110 kV, Zs 360 ΩStroke Current (Is) 0.67 kA Striking (Radius) Distance:##Rsc 41 ft (for 2 kA, k 1)Rsc 54 ft (for 3 kA, k 1)
Electrogeometric Method(Applied to Building)Single Mast Zone ofProtectionOverhead Ground WiresRef: NFPA 780, 1995
Electrogeometric Method (9)(Summary)! Originally, developed in the 1960’s for EHV (345kV) Transmission Line Design and later Modified toinclude EHV Substation and Switching StationDesign.! Major Difference (Fixed Angle and EmpiricalMethods) : Shielding design is based on the BIL(CFO), Surge Impedance, Lightning currentprobability distribution, lightning strikepropagation, etc.! The EGM method is based on more scientificresearch and well documented theoreticalfoundation.! The basic EGM concept also has been modified andsuccessfully adopted to protect building, powerplant and other tall structures.! This method is recommended for large EHVsubstations and switching Stations in an area withhigh GFD values. Also very effectively used in 230kV switchyard design.! Direct stroke shielding complemented byappropriately selected surge arrester provides thenecessary protection.
Lightning Eliminating Devices(Active Lightning Terminals)References1. IEEE Std. 998-1996, Section 6, pp. 42-43.2. A.M. Mousa, The Applicability of LightningElimination Devices to Substations andPower Lines, IEEE Trans. on PowerDelivery, Vol. 13, No. 4, October 1998, pp.1120-1127.3. D. W. Zipse, Lightning Protection Systems:Advantages and Disadvantages, IEEETrans. On Industry Applications, Vol. 30,No. 5, Sept/Oct. 1994, pp. 1351-1361.4. Many Others.
Lightning Eliminating Devices(Summary)1.Ref [1]:“There has not been sufficient scientific investigation todemonstrate that the above devices are effective, and thesesystems are proprietary, detailed design information is notavailable It is left to the design engineer to determine thevalidity of the claimed performance for such systems. Itshould be noted that IEEE does not recommend or endorsecommercial offerings.”2.Ref [2]:“Natural downward lightning flashes cannot be prevented.”“The induced upward flashes which occur on structures havingheights (altitude of the peak) of 300 m or more can beprevented by modifying the needle-like shape of the structure.Some charge dissipater designs inadvertently accomplish thisand hence appear to “eliminate “ lightning. Such an effect haslittle or nothing to do with the existence of multiple points onthose devices.”“Charge dissipaters will have no effect, whether intended orinadvertent, on the frequency of lightning strikes to talltowers where the altitude of the site is such that the effectiveheight of the tower is less than about 300 m.“Charge dissipaters will have no effect whatsoever on thefrequency of lightning strikes to substations and transmissiontowers since such systems do not experience upward flashes.”
Lightning Eliminating Devices(Summary)3. Ref [3]“NFPA has subdivided Standard 78 into twostandards and has renumbered it. NFPA 780,entitled, “The Lightning protection Code,” andNFPA 781, “Lightning Protection Systems usingEarly Streamer Emission Air terminal,” are thenew numbers and titles. NFPA 781 is underdevelopment and consideration.”“As stated above, there is little factual dataavailable to substantiate the claims being madefor the system. Many installations have beenmade. The owners have not inspected thesystems for direct strikes, nor have any systemsbeen instrumented. The lack of viable andrepeatable testing, when compared to the NASAand FAA studies and the multitude of experts inthe lightning field who claim the system fails tofunction as advertised, casts doubt on theeffectiveness of the multipoint discharge systemto prevent lightning strikes.”
Conclusions (1)1.Any design of Direct Lightning StrokeShielding depends on the probabilisticnature of lightning phenomena.2.There is no method available to provide100% shielding against direct lightningstroke of the substation equipment andbus structures.3.There are a number of other variablesnot addressed in the IEEE Std. 9981996 and not discussed in thispresentation, such as, effects ofaltitude on BIL, state (cleanliness) ofthe insulators, aging effect ofequipment on failure, temperaturevariations, and so on.4.Fixed angle method of design is quiteadequate for distribution substations.EGM method is more appropriate forlarge and important substations at 230kV and above voltage level.
Conclusions (2)5. The applicability of Lightning EliminatingDevices to substation direct lightningstroke shielding requires additional dataand research.6. Proper grounding system design is alsoan integral part of the total solution andshould be addressed during the design.7. In order to arrive at some practicalsolutions, many assumptions are made inthe different design techniques.8. Surge Arresters are added in strategiclocations in a substation to providecoordinated protection for all majorequipment.
of Substations Understanding Direct Lightning Stroke Shielding of Substations P.K. Sen, Ph.D., P.E. Professor Division of Engineering Colo. School of Mines Golden, Colorado (303) 384-2020 psen@mines.edu PSERC Seminar Golden, Colorado November 6, 2001 '2002 Colorado School of Mines
Make sure that the blank shielding wire (5) is not removed. Twist this blank wire with the shielding (4) as shown below. Figure 2.3 - Blank shielding wire and shielding braid Blank shielding wire Outer sheath (jacket) (1) Filling threads (2) Power elements (3) Copper wire shielding (4) Blank shielding wire (5) Shielding foil (6) Isolation .
Creating new Lightning Page using Lighting App Builder Salesforce Lightning pages can be created using Lightning App Builder. To create, navigate to Build Lightning Bolt Lightning App Builder New. Lightning App Builder - App page. In this step, select App page and click on next button as shown below. Lightning App Builder
RADIATION SHIELDING DESIGN 2010 2010 Shielding Construction Solutions 1 ACMP 2010 SAN ANTONIO, TEXAS – MAY 23, 2010 DANIEL G. HARRELL SHIELDING CONSTRUCTION SOLUTIONS, INC. . Graphic Image. DESIGN Shielding Material Data Shielding Design Sketch Specific Points Use & Occupancy Distance Obliquity Effective Thickness Unusual Conditions
Lightning stroke clustering into cloud-to-ground lightning ashes Author: Eloi Dalmasso Blanch Facultat de F sica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain. Abstract: Cloud-to-ground stroke data have been analysed for the years 2010-2012 for the Cata-lan region. These strokes have been grouped together into lightning
the cable's and lightning's parameters. Let us consider two cases; - The first one a study shows the direct strokes on telephone cables. - The second one represents direct lightning strokes on power system (tower and MV lines). A. Direct Lightning stroke on telephone cables If lightning surges appear in the telephone cable, we search .
2021 ANNUAL LIGHTNING REPORT V aisala 2022 Global lightning detection for more than 10 years. Vaisala's owned-and-operated . Global Lightning Dataset GLD. 360 is the only truly global lightning detection network and has been detecting lightning around the planet since 2009. It is the most advanced and accurate long-range lightning detection .
exercises focusing on strengthening particular parts of the body. Every stroke is unique. Every person’s needs are different. This new guide is a much needed and overdue tool box of practical and easily followed exercise regimes for those recovering from a stroke as well as the families and whānau who support them in theirFile Size: 1MBPage Count: 51Explore further10 Stroke Recovery Exercises For Your Whole Bodywww.rehabmart.comAfter Stroke: 3 Exercises for a Weak Leg. (Strengthening .www.youtube.comStroke Exercises.pdf - Stroke Exercises for Your Body .www.coursehero.com35 Fun Rehab Activities for Stroke Patients - Saebowww.saebo.comPost-Stroke Exercises for Left Arm and Shoulder SportsRecwww.sportsrec.comRecommended to you b
playing field within the internal market, even in exceptional economic circumstances. This White Paper intends to launch a broad discussion with Member States, other European institutions, all stakeholders, including industry, social partners, civil society organisations,
