Sobretensiones y Coordinacione de Aislamiento

Overvoltage Protection and Insulation Coordination in Power Systems

Prof. Dr.-Ing. Volker Hinrichsen Dipl.-Ing. Simona Feier-IovaTechnische Universitt Darmstadt High Voltage Laboratories Siemens

Fachgebiet Hochspannungstechnik

Overvoltage Protection and Insulation Coordination / Chapter 1

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What is Insulation Coordination?Definition Definition in in IEC IEC 60071-1 60071-1

Definition Definition in in IEEE IEEE 1313.1 1313.1



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Fundamentals of Insulation Coordination5

Possible voltages without arresters Magnitude of (over-)voltage / p.u.4

Withstand voltage of equipment3

2

1

Voltages limited by arresters0Lightning overvoltages (Microseconds) Switching overvoltages (Milliseconds) Temporary overvoltages Highest voltage of equipment (Seconds) (Continuously)

Time duration of (over-)voltage



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What is Insulation Coordination?Procedure of insulation coordination [THI-01]Three Three elements elements are are involved involved in in the the insulation insulation coordination coordination discipline, discipline, namely: namely: the the study study of of the the "stresses" "stresses",, both both electrical electrical and and environmental, environmental, acting acting on on the the equipment equipment insulation. insulation. This This is is usually usually performed performed by by calculations calculations or or field field measurements; measurements; the the study study of of the the "strength" "strength" (dielectric (dielectric withstand withstand characteristics) characteristics) of of the the insulation insulation (both (both new new and and aged) aged) when when submitted submitted to to such such stresses, stresses, taking taking into into account, account, when when applicable, applicable, the the effect effect of of the the environmental environmental stresses stresses (pollution, (pollution, rain, rain, snow, snow, ice, ice, atmospheric atmospheric conditions conditions at at large large altidudes), altidudes), including including the the study study of of the the "test "test and and measurement measurement techniques" techniques" which which are are employed employed to to assess assess such such strength. strength. The The strength strength is is determined determined by by calculations, calculations, based based on on suitable suitable discharge discharge models, models, and/or and/or by by laboratory/factory laboratory/factory tests, tests, on-site on-site tests tests and and in-service in-service measurements measurements (diagnostics); (diagnostics); the the assessment assessment of of the the insulation insulation performance performance (usually (usually expressed expressed in in terms terms of of risk risk of of failure) failure) in in the the considered considered situation situation of of stresses stresses and and strength, strength, including including the the selection selection and and application application of of "protective "protective devices devices and and techniques", techniques", to to establish establish the the final final insulation insulation design design fulfilling fulfilling the the specified specified requirements. requirements. This This may may be be based based on on "deterministic" "deterministic" or or "statistical" "statistical" approach. approach.Fachgebiet Hochspannungstechnik


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Literature (1)[BAL-04-1] G. Balzer Power Systems, Part 2 Chapter 4: Insulation coordination Script TU Darmstadt, 2004 G. Balzer Elektrische Energieversorgung, Teil 2 Kapitel 4: Isolationskoordination Skript der TU Darmstadt, 2004 CIGRE W.G. 13-02 Switching overvoltages in EHV and UHV systems with special reference to closing and reclosing transmission lines ELECTRA 30 (1973) pp. 70-122 CIGRE WG 33.02 Phase-to-phase Insulation Co-ordination: Part 1: Switching overvoltages in three-phase systems ELECTRA 64 (1979) pp. 138-158 CIGRE WG 33.03 Phase-to-phase Insulation Co-ordination Part 2: Switching impulse strength of phase-to-phase external insulation ELECTRA 64 1979, pp. 158-181

[BAL-04-2]

[CIG-73]

[CIG-79-1]

[CIG-79-2]



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Literature (2)[CIG-79-3] CIGRE WG 33.06 Phase-to-phase Insulation Co-ordination Part 3: Design and testing of phase-to-phase insulation ELECTRA 64 1979, pp. 182-210 CIGRE TF 33-03.03 Phase-to-phase Insulation Co-ordination Part 4: The influence of non-standard conditions on the switching impulse strength of phase-to-phase insulation ELECTRA 64 1979, pp. 211-230 CIGRE WG 33.01 Guide to procedures for estimating the lightning performance of transmission lines, CIGRE technical brochure No. 63, 1991 buch_020.pdf CIGRE WG 33-07 Guidelines for the evaluation of the dielectric strength of external insulation, CIGRE technical brochure No. 72, 1992 buch_019.pdf H. Dorsch berspannungen und Isolationsbemessung bei Drehstrom-Hochspannungsanlagen Siemens AG, Erlangen, 1981 (ISBN 3-8009-1325-9)

[CIG-79-4]

[CIG-91]

[CIG-92]

[DOR-81]



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Literature (3)[ERI-88] A.J. Eriksson, K.-H. Weck Simplified procedures for determining representative substation impinging lightning overvoltages, CIGRE report 33-16, 1988 ETG-Fachbericht 49 ETG-Tage '93: Isolationskoordination in Hoch- und Mittelspannungsanlagen vde-Verlag GmbH Berlin, Offenbach (ISBN 0341-3934) FGH Technischer Bericht 1-240 Isolationskoordination auf der Grundlage der neuen DIN/VDE-Bestimmung 0111 FGH, Mannheim, Juli 1978 A. R. Hileman Insulation Coordination for Power Systems Marcel Dekker, Inc., New York, Basel, 1999 V. Hinrichsen Metalloxidableiter: Grundlagen Siemens AG Berlin, 1. Auflage 2000 AbleiterBuch.pdf V. Hinrichsen Metalloxidableiter: Grundlagen Siemens AG Berlin, Edition 1, 2001 ArresterBook.pdf

[ETG-93]

[FGH-78]

[HIL-99]

[HIN-00]

[HIN-01]



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Literature (4)[HIN-03] V. Hinrichsen Latest Designs and Service Experience with Station-Class Polymer Housed Surge Arresters World Conference on Insulators, Arresters & Bushings Marbella (Mlaga), Spain, November 16-19, 2003, Proceedings pp. 85-96 pub_048.pdf V. Hinrichsen Latest Testing Requirements and Emerging Standards for Transmission Line Arresters World Conference on Insulators, Arresters & Bushings Hong Kong, November 27-30, 2005 inmr_2005_paper.pdf I. Kishizima, K. Matsumoto, Y. Watanabe, New facilities for phase switching impulse tests and some test results, IEEE PAS TO3 No. 6, June 1984 pp. 1211-1216. D. Knig, Y. N. Rao Teilentladungen in Betriebsmitteln der Energietechnik vde-Verlag, Berlin, Offenburg, 1993, ISBN 3-8007-1764-6 D. Knig, Y. N. Rao Partial discharges in Power Apparatus vde-Verlag, Berlin, Offenburg, 1993, ISBN 3-8007-1760-3

[KIN-05]

[KIS-84] [KOE-93-1]

[KOE-93-2]



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Literature (5)[PAR-68] L. Paris, R. Cortina Switching and lightning impulse discharge characteristics of large air gaps and long insulation strings, IEEE Trans on PAS, vol 87, No. 4, April 1968, p. 947-957 R. Rudolph, B. Richter Dimensioning, testing and application of metal oxide surge arresters in medium voltage networks 3rd Edition, 1999, ABB Switzerland, 26 pages (also available in German) application_guide_medium_voltage_networks.pdf R. Rudolph, B. Richter Bemessung, Prfung und Einsatz von Metalloxid-Ableitern in Mittelspannungsnetzen ABB Schweiz AG, Wettingen (CH), 3. Auflage 1999 Anwendungsrichtlinien_Mittelspannung.pdf L. Thione Insulation coordination in electrical power systems theory and application Tutorial, ALPI, Milan, 2001 (www.alpiass.com) buch_018.pdf

[RUD-99-1]

[RUD-99-2]

[THI-01]



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Literature (6)[WEC-07] K.-H. Weck Standardization of insulation withstand levels for UHV systems in IEC TC 28 Insulation co-ordination IEC/CIGRE UHV Symposium Beijing 18-21 July 2007, report 5-4 5-4_KHWeck.pdf

Overview on CIGRE publications (very interesting!): Cigr Catalogue of Publications 01/07/2005 CATALOGUE_PUBLICATIONS_2005.pdf



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Standards (1)IEC 60071-1, Edition 8.0 (2006-01) Insulation co-ordination Part 1: Definitions, principles and rules IEC 60071-2, Third Edition (1996-12) Insulation co-ordination Part 2: Application guide IEC/TR 60071-4, First Edition (2004-06)

Insulation co-ordination - Part 4: Computational guide to insulation co-ordination and modelling of electrical networksIEC 60099-4, Ed. 2.1, 2006-07 Surge arresters Part 4: Metal-oxide surge arresters without gaps for a.c. systems IEC 60099-5, Ed. 1.1, 2000-03 Surge arresters Part 5: Selection and application recommendations DIN EN 60071-1, 1996-07 Isolationskoordination - Teil 1: Begriffe, Grundstze und Anforderungen (IEC 60071-1:1993); Deutsche Fassung EN 60071-1:1995 DIN EN 60071-2, 1997-09 Isolationskoordination - Teil 2: Anwendungsrichtlinie (IEC 60071-2:1996); Deutsche Fassung EN 60071-2:1997 IEEE 1313.1-1996 IEEE Standard for Insulation CoordinationDefinitions, Principles, and RulesFachgebiet Hochspannungstechnik


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Standards (2)IEEE 1313.2-1999 IEEE Guide for the Application of Insulation Coordination IEEE C62.11-2005 IEEE Standard for Metal-Oxide Surge Arresters for AC Power Circuits (> 1 kV) IEEE C62.22-1997 IEEE Guide for the Application of Metal-Oxide Surge Arresters for Alternating-Current Systems



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Organization1 2 3 4 5 6 7 8 9 18.10.2007 25.10.2007 01.11.2007 08.11.2007 15.11.2007 22.11.2007 29.11.2007 06.12.2007 13.12.2007 20.12.2007 27.12.2007 03.01.2008 10 11 12 13 10.01.2008 17.01.2008 24.01.2008 31.01.2008 Lecture 1 Lecture 2 Lecture 3 cancelled Lecture 4 Lecture 5 Lecture 6 Lecture 7 Lecture 8 Lecture 9 Christmas holidays Christmas holidays Lecture 10 Lecture 11 Lecture 12 Lecture 13 Insulation coordination Calculation Examples Test procedures; condition monitoring (life time aspects, partial discharges, non-conventional approaches) Traveling waves Overvoltage protection incl. protective distance Dielectric strength (incl. gap factors, pollution, rain, parallel insulation, aging) Insulation coordination Voltage stresses in power systems Introduction



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OrganizationExamination ExaminationExclusively oral

Exercises ExercisesNone; but calculation examples in the lecture

Script ScriptSlides will be available for download www.hst.tu-darmstadt.de User: studentiso PW: isows0708



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Insulation Coordination - Principles

System

System voltages

Overvoltage protection devices Environment

Equipment

stress versus strength

Dielectric strengthOvervoltage Protection and Insulation Coordination / Chapter 1 - 15 -


Insulation Coordination - Principles Voltages of the system Nominal voltage Un rounded value for characterizing the system 10 kV - 20 kV - 110 kV - 220 kV - 380 kV System voltage voltage at which the system is being operated around the nominal value, but not constant Highest system voltage Us highest operating voltage between phases under normal conditions 12 kV - 24 kV - 123 kV - 245 kV - 420 kV (IEC 60038)

Voltages of equipment Highest voltage for equipment Um highest voltage between phases for which the insulation is designed 12 kV - 24 kV - 123 kV - 245 kV - 420 kV (IEC 60071-1)Fachgebiet Hochspannungstechnik


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Insulation Coordination - Principles Overvoltages voltages exceeding the peak value of the highest system voltage various amplitudes and shapes depending on system configuration (grid size, degree of meshing, etc.) origin of overvoltage (failure, switching, lightning strike etc.)

Dielectric strength of insulation verified by type test in the laboratory with the help of standardized test voltages (shape, amplitude) specified test setups specified environmental conditions

Insulation coordination Determination of interdependence between voltages and overvoltages of the system and necessary test voltages for the equipment in the laboratory



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Insulation Coordination - PrinciplesEquipment in the system Equipment in the laboratory

Variety Variety of of amplitudes amplitudes and and shapes shapes of of overvoltages overvoltages

Standardized Standardized amplitudes amplitudes and and shapes shapes of of test test voltages voltages

Variety Variety of of operating operating conditions conditions and and age age

Standardized Standardized setups setups and and conditions conditions

Variety Variety of of environmental environmental conditions conditions

Standardized Standardized environmental environmental conditions conditions



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Insulation Coordination - Principlesbb 1

Insulation phase - groundstressed by voltages between one phase and ground

bb 2

1 2 3 1

Insulation phase - phasestressed by voltages between two phases

2

busbar disconnectors line

Longitudinal insulationstressed by voltages between same phases of two different systems

3Fachgebiet Hochspannungstechnik


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Insulation Coordination according to IEC 60071-1 (and 60071-2)



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...39 ...39 pages pages in in sum sum

Procedure Procedure for for insulation insulation coordination coordination = = 10 10 pages! pages!



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...125 ...125 pages pages in in sum sum



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Procedure for Insulation Coordination - GeneralThe procedure for insulation coordination consists of the selection of a set of standard withstand voltages which characterize the insulation of the equipment.

Range I

Range II



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Procedure for Insulation Coordination - GeneralBasic difference between ranges I and II

Range Range II IIwithstand voltage

gap spacing 3 m

Minimum Minimum of of withstand withstand voltage voltage for for switching switching overvoltage overvoltage

Range Range II[FGH-78]

Withstand Withstand voltage voltage continuously gap spacing 0.5 m continuously decreasing decreasing with with time time duration duration of of stress stress

peak

time duration of stressFachgebiet Hochspannungstechnik


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Procedure for Insulation Coordination in Four StepsDetermination of the representative overvoltages Urp The representative overvoltages are derived from real service conditions, but have just standardized shapes. They are determined in amplitude, shape and duration by system analysis, taking into account overvoltage limiting devices.

[IEC 60071-1]Fachgebiet Hochspannungstechnik


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Procedure for Insulation Coordination in Four StepsDetermination of the coordination withstand voltages Ucw The coordination withstand voltages are the lowest values of withstand voltages of each overvoltage class, for which the expected low failure rate of the equipment is not exceeded over its full lifetime. Derived from the representative overvoltages Urp by the coordination factor Kc.

Typical for Germany: 0.1% per year 1 failure in 1000 years

[IEC 60071-1]



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Procedure for Insulation Coordination in Four StepsDeterministic Deterministic approach approach Assumed Assumed maximum maximum of of representative representative overvoltage overvoltage Statistical Statistical approach approach

Statistical Statistical distribution distribution of of representative representative overvoltages overvoltages Determination Determination of of failure failure probability probability of of insulation insulation

Multiplication Multiplication by by coordination coordination factor factor based based on on operating operating experience experience

Calculation Calculation of of failure failure risk risk depending depending on on assumed assumed coordination coordination withstand withstand voltage voltage

Coordination Coordination withstand withstand voltage voltage (0% value) Statistical (10% value) Assumed Statistical U Ucw Assumed conventional conventional U Ucw cw (0% value) cw (10% value)Fachgebiet Hochspannungstechnik


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Procedure for Insulation Coordination in Four StepsDetermination of the required withstand voltages Urw The required withstand voltages are determined by converting the coordination withstand voltages to appropriate standard test conditions. Usually different from the coordination withstand voltages. Derived from the coordination withstand voltages Ucw by the safety factor Ks and the atmospheric correction factor Kt or the altitude correction factor Ka.



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Procedure for Insulation Coordination in Four StepsInfluences covered by the safety factor Ks Differences in equipment assembly Dispersion in product quality Quality of installation Aging of the installation during expected lifetime Other unknown influences



- 35 -

Procedure for Insulation Coordination in Four StepsDetermination of the required withstand voltages Urw The required withstand voltages are determined by converting the coordination withstand voltages to appropriate standard test conditions. Usually different from the coordination withstand voltages. Derived from the coordination withstand voltages Ucw by the safety factor Ks and/or the altitude correction factor Ka.



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Procedure for Insulation Coordination in Four StepsSelection of the rated and of the standard insulation level (set of standard rated withstand voltages Uw) Most economical set of standard withstand voltages Uw of the insulation to prove that all the required withstand voltages are met. For each range (I or II) a combination of only two withstand voltages defined: Range I: standard lightning impulse withstand voltage standard short-duration power-frequency withstand voltage Range II: standard switching impulse withstand voltage standard lightning impulse withstand voltage For range I, only phase-to-earth standard withstand voltages are defined, which have to cover phase-to-earth, phase-to-phase and longitudinal insulation.



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Procedure for Insulation Coordination in Four StepsDefinitions



- 38 -

Procedure for Insulation Coordination in Four StepsExamples for... non-self-restoring insulation (power transformers, instrument transformers*))*) mixed insulation

... self-restoring insulation (disconnectors, insulators)



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Procedure for Insulation Coordination in Four StepsList of standard short-duration power-frequency withstand voltages (r.m.s. values in kV)

10 70 275 480

20 95 325 510

28 140 360 570

38 185 395 630

50 230 460

List of standard impulse withstand voltages (peak values in kV)

20 325

40 450

60 550

75 650

95 750

125 850

145 950

170

250

1050 1175

1300 1425 1550 1675 1800 1950 2100 2250 2400[IEC 60071-1]Fachgebiet Hochspannungstechnik


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Procedure for Insulation Coordination in Four StepsRange I: Um = 1 kV up to and including Um = 245 kV The standard voltage values are all the same for phase-to-earth-, phase-to-phase-, longitudinal insulation!



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Procedure for Insulation Coordination in Four StepsRange II: Um above 245 kV Different standard voltage values for phase-to-earth-, phase-to-phase-, longitudinal insulation!



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Procedure for Insulation Coordination in Four Steps Outcome of insulation coordination For three types of insulation phase to ground phase to phase longitudinal and for 4 values each of required withstand voltages Urw required continuous operating voltage required short-duration power-frequency withstand voltage required switching impulse withstand voltage required lightning impulse withstand voltage

twelve voltages

Standardization of tests for equipment Reduction of these 12 values to a necessary minimum number of withstand voltages Uw of the insulation Determination of necessary withstand voltages from tables for two ranges of highest voltage for equipmentFachgebiet Hochspannungstechnik


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Procedure for Insulation Coordination in Four Steps - SummaryFlow chart acc. to IEC 60071-1 (Figure 1)

continued next slideFachgebiet Hochspannungstechnik

[IEC 60071-1] - 44 -


Procedure for Insulation Coordination in Four Steps - SummaryFlow chart acc. to IEC 60071-1 (Figure 1) (continued)



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Voltage Stress in Power Systems - ClassificationIEC 60071-1



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Voltage Stress in Power Systems - ClassificationClassification Classification of real stress"Continuous (power-frequency) voltage"

Power-frequency voltage, considered having constant r.m.s. value, continuously applied to any pair of terminals of an insulation configuration f = 50 Hz or 60 Hz T1 3 600 s Any power-frequency voltage lasting for 1 h or more is considered a continuous voltage! Conversion into

Standard Standard voltage voltage

"Standard power-frequency voltage"

A sinusoidal voltage with frequency of 50 Hz or 60 Hz T1 to be specified by the apparatus committees T1 up to 2 years!



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Voltage Stress in Power Systems - ClassificationClassification Classification of real stress"Temporary overvoltage"

Power-frequency overvoltage of relatively long duration. The overvoltage may be damped or undamped. In some cases its frequency may be several times smaller or higher than power frequency. 10 Hz < f < 500 Hz 3 600 s T1 0.02 s Highest values by following main reasons: phase-to-earth earth faults and load rejection phase-to-phase load rejection longitudinal phase opposition during synchronization of two grids Conversion intoExample [THI-01]


"Standard short-duration power-frequency voltage"

A sinusoidal voltage with frequency between 48 Hz and 62 Hz T1 = 60 sFachgebiet Hochspannungstechnik


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Voltage Stress in Power Systems - ClassificationClassification Classification of real stress"Transient overvoltage"

Short-duration overvoltage of few milliseconds or less, oscillatory or non-oscillatory, usually highly damped. May be followed by temporary overvoltages. In this case, both events are considered as separate events. "Slow-front overvoltage" Transient overvoltage, usually unidirectional 5000 s Tp > 20 s T2 20 ms Main reasons: line faults, switching Conversion into

Standard Standard voltage voltageAn impulse voltage of Tp = 250 s T2 = 2 500 sFachgebiet Hochspannungstechnik

"Standard switching impulse"

Example [THI-01]


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Short-duration overvoltage of few milliseconds or less, oscillatory or non-oscillatory, usually highly damped. May be followed by temporary overvoltages. In this case, both events are considered as separate events. "Fast-front overvoltage" Transient overvoltage, usually unidirectional 20 s T1 > 0.1 s T2 300 s Main reasons: lightning strokes, switching Conversion into

Standard Standard voltage voltageAn impulse voltage of T1 = 1.2 s T2 = 50 sFachgebiet Hochspannungstechnik

"Standard lightning impulse"

Example [THI-01] Overvoltage Protection and Insulation Coordination / Chapter 2 -5-


Short-duration overvoltage of few milliseconds or less, oscillatory or non-oscillatory, usually highly damped. May be followed by temporary overvoltages. In this case, both events are considered as separate events. "Very-fast-front overvoltage" Transient overvoltage, usually unidirectional Tf < 100 ns (Tt 3 ms) basic oscillation (1st harmonics) 30 kHz < f < 300 kHz superimposed oscillations 300 kHz < f < 100 MHz Main reasons: switching of disconnectors in GIS Conversion into

Standard Standard voltage voltageFachgebiet Hochspannungstechnik

not standardizedExample [THI-01]


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Voltage Stress in Power Systems - ClassificationClassification Classification of real stress"Combined (temporary, slow-front, fast-front, very-fast-front) overvoltage"

Consisting of two voltage components simultaneously applied between each of the two phase terminals of a phase-to-phase (or longitudinal) insulation and earth. It is classified by the component of the higher peak value. Conversion into


"Standard combined switching impulse"

Combined impulse voltage having two components of equal peak value and opposite polarity. The positive component is a standard switching impulse and the negative one is a switching impulse whose times to peak and half value should not be less than those of the positive impulse. Both impulses should reach their peak values at the same instant. The peak value of the combined voltage is, therefore, the sum of the peak values of the components.



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Temporary Overvoltages Earth FaultsReasons for temporary overvoltages: earth faults load rejection resonance phenomena In case of earth faults the overvoltage amplitudes depend on neutral earthing fault location. Important Important parameter: parameter: Earth Earth fault fault factor factor k k

IEC 60071-1

... in other "words": k =Fachgebiet Hochspannungstechnik

U LE Ub / 3

ULE ... phase-to-earth voltage of sound phase during fault Ub ... phase-to-phase voltage at same location before fault-8-


Temporary Overvoltages Earth FaultsThe earth fault factor depends on the ratio of the complex impedances Z1 and Z0 of the positive and zero sequence systems (German: "Mitsystem", "Nullsystem"). In case of neglecting the resistances (possible in high-voltage systems) it depends on the ratio of the reactances X0 and X1:1 + X 0 / X1 + ( X 0 / X1 ) k = 3 2 + X 0 / X12

solidly earthed neutral

resonant earthed not for neutral, practical use! isolated neutral

resonant earthed neutral, isolated neutral

a ratio of X0/X1 = -2 must be avoided!

according to [BAL-04]Fachgebiet Hochspannungstechnik


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Temporary Overvoltages Earth FaultsTreatment of neutral in Germany (VDEW, 1998):treatment of neutral isolated resonant earthed solidly earthed 10 kV 8.6% 77.8% 13.6% 20 kV < 0.1% 92.8% 2.2% 110 kV 0.0% 80.9% 19.1% 380 kV 0.0% 0.7% 99.3%according to [BAL-04]

Pictures: VATech

Earthing reactor (Petersen coil): fixed or switchable typeFachgebiet Hochspannungstechnik

Earthing reactor (Petersen coil): variable core type

Caused Caused by by several several recent recent blackouts blackouts it it has has been been considered considered internationally internationally to to increasingly increasingly operate operate sub-transmission sub-transmission systems 170 kV) in the resonant systems ( (U Us s 170 kV) in the resonant earthed earthed mode mode in in order order to to increase increase reliability reliability of of power power supply. supply. [Information [Information from from a a Cigr Cigr meeting meeting in in Frankfurt, Frankfurt, October October 2005] 2005]- 10 -


Temporary Overvoltages Earth FaultsDrive

Lead screw (the core is actually in 100% position) core movement

Fixed part of the core

Active part of a high-voltage reactor with variable coreFachgebiet Hochspannungstechnik


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Temporary Overvoltages Earth FaultsEarth fault in case of isolated neutral system:

according to [BAL-04]Fachgebiet Hochspannungstechnik


- 12 -


faultFachgebiet Hochspannungstechnik

according to [BAL-04] - 13 -



fault clearing

k = 2 due to capacitances of zero sequence system, charged to a direct voltageaccording to [BAL-04]Fachgebiet Hochspannungstechnik


- 14 -

Temporary Overvoltages Earth FaultsIntermitting earth fault in case of isolated neutral system: new fault after initial fault clearing

voltage of faulty phaseFachgebiet Hochspannungstechnik



Temporary Overvoltages Earth FaultsIntermitting earth fault in case of isolated neutral system: new fault after initial fault clearing

voltage of sound phaseFachgebiet Hochspannungstechnik



Temporary Overvoltages Earth FaultsIntermitting earth fault in case of isolated neutral system:

voltage of the zero sequence systemFachgebiet Hochspannungstechnik



Temporary Overvoltages Earth Faultsk 3 ... 2

k 1.4

1.4 < k 0 for x 0

M ... Median = 0.5 probability not to be mixed up with the mean or average value! .... log standard deviation

Calculation of the mean or average value: = M e Calculation of the standard deviation:Fachgebiet Hochspannungstechnik

22

= M e e 12-6-

2

2


Direct Lightning Strikes to OHL Berger's DataLightning research station of Prof. Berger in a radio transmission station on top of Monte San Salvatore (912 m; Lake of Lugano, Switzerland) Installed 1942 on behalf of SEV Lightning studies up to 1970 Bergers Data



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Direct Lightning Strikes to OHL Berger's Datat10/30 t30/90 I10

I tm = F Sm = tm II Sm

I30

The The strike strike current's current's front front typically typically has has a a concave concave shape. shape.

I90 I100

Difference Median Mean value: Mean value of first strike's final crest current

I F = M I F e

IF 22

= 31.1 e

0.484 2 2

= 35 kA



-8-

Direct Lightning Strikes to OHL Berger's DataExtract of the table values of primary importance , mean value1.54 s 4.46 s 29 kA/s 91.5 stm = IF Sm

=Me2

2

, mean value35 kA 14.2 kA

Sm S30/90 Sm S30/90Fachgebiet Hochspannungstechnik

29 kA/s 8.7 kA/s 57.4 kA/s 32.1 kA/s-9-


Direct Lightning Strikes to OHL CIGR ModelCIGR and IEEE strike current probability curves, first strike, negative downward flash [CIG-91]P(I < IF)

CIGR curve:

The The CIGR CIGR distribution distribution is is based based on on the the latest latest data data available available and and better better represents represents the the actual actual data. data. CIGR CIGR curve curve should should preferably preferably be be used! used!Note: M = 61.1 kA for IF < 20 kA does not mean that this current really occurs. It is just a parameter that characterizes the curve, which is actually valid only in the range < 20 kA, however!Fachgebiet Hochspannungstechnik

IF, median = 33.3 kA IF, median = 61.1 kA


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Direct Lightning Strikes to OHL Berger's DataDerived parameters of conditional lognormal distributions, derived from Berger's data



- 11 -

Direct Lightning Strikes to OHL CIGR ModelAverage wave shape of the first and subsequent negative strike currents as developed by CIGR [CIG-91]



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Direct Lightning Strikes to OHL CIGR ModelModels of lightning strike acc. to IEC 60071-4

Double Double ramp ramp shape shape easy easy to to use use

CIGR CIGR concave concave shape, shape, parameters parameters from from [CIG-91] [CIG-91] higher higher accuracy accuracy



- 13 -

Direct Lightning Strikes to OHL strike Multiplicityno subsequent strikes, highest reported current peak values and charges cloud-to-cloud flash

> >90% 90%

downward flash

Seldom!

negative cloud-to-ground from exposed points such as aerials, tv towers

positive cloud-to-ground

upward flash

negative ground-to-cloudFachgebiet Hochspannungstechnik

positive ground-to-cloud Overvoltage Protection and Insulation Coordination / Chapter 4 - 14 -

Direct Lightning Strikes to OHL strike MultiplicityOnly 45% of negative downward flashes consist of one strike per flash. In all other cases: multiple strikes in time intervals of 10 ms to 100 ms (see HVT II, Chapter 11). Subsequent strikes have higher front steepness lower amplitude up to 54 follow strikes reported often: dc component (in ca. 50% of all cases)scale of dc component

11 current impulses of 7 kA up to 63 kA peak value

dc component



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Direct Lightning Strikes to OHL strike MultiplicityNumber of strikes per flash, negative downward flash 1)

Probability of 4 strikes or more

= =Probability of 8 strikes or more

based on 6000 flash records from different regions of the world median of the distribution: 2 1) R. B. Anderson, A. J. Eriksson mean or average value: 3

Lightning Parameters for Engineering Application ELECTRA 69, Mar. 1980, pp. 65-102



- 16 -

Direct Lightning Strikes to OHL Lightning ActivityKeraunic levels worldwide TD = 20 ... 80 TD = 80 ... 180 TD = number of thunderstorm days per year

Middle = 10 ... 25 D MiddleEurope: Europe:T T D = 10 ... 25 in D = inequator equatorregions: regions:T T =100 100... ...180 180D

Lightning ground flash density Ng = number of lightning ground flashes per km2 and year1.25 Empirical relation: Ng = 0.04 Td

Ng in (km2a)-11)

reported by Eriksson1) from observations in South Africa generally accepted both by CIGR and IEEEFachgebiet Hochspannungstechnik

A. J. Eriksson The Incidence of Lightning Strikes to Transmission Lines IEEE Trans. on Power Delivery, Jul. 1987, pp. 859-870


- 17 -

Direct Lightning Strikes to OHL Geometric ModelBasic idea (see also HVT II, Chapter 11)For a specific current I, calculate the striking distance rg and rc. Draw a line parallel to the ground at a distance rg from the ground. With compasses centered at the tower top, draw an arc of radius rc until it intersects the parallel lines drawn in 2, above.

Any Any strike strike that that arrives arrives between between A A and and B B will will terminate terminate on on the the ground ground wire, wire, and and any any strike strike that that arrives arrives to to the the left left of of A A or or to to the the right right of of B B will will terminate terminate to to ground. ground.



- 18 -

Direct Lightning Strikes to OHL Geometric ModelBasic idea (see also HVT II, Chapter 11)

N (G ) I = 2 N g LDgN(G)|I ... number of strikes to ground wire for current I L ... length of line

N (G ) = 2 N g L

3 kA

f (I )d I Dg

f(I) ... probability that current I occurs 3 kA = lowest observed lightning flash current amplitude D'g may be expressed in terms of striking distances and tower height:

= r ( rg h ) = rc cos Dg2 c 2Fachgebiet Hochspannungstechnik


- 19 -

Direct Lightning Strikes to OHL Geometric ModelPractical approach (by empirical observations) (Eriksson)

N (G ) =N'(G) ... Ng ... b h

N g ( b + 28 h 0.6 ) 10

(assuming an approximate median current of 35 kA)

number of strikes to the line in (100 km a)-1 ground flash density in (km2 a)-1 distance of outer conductors in m average ground wire height (htower 2/3sag) in m

N'(G)

TD = 35 d

b TD = 20 d

[BAL-04]

hFachgebiet Hochspannungstechnik

Note: Note: in in case case of of good good shielding shielding most most of of these these strikes strikes will will hit hit the the shield shield wire wire!!- 20 -


Direct Lightning Strikes to OHL Geometric ModelStriking distance b Basic dependence: r = A I many different factors A, b published:

Adopted by CIGR Working Group

rc = 7.1 Ifor references, see [HIL-99]Fachgebiet Hochspannungstechnik

0.75

[I] = kA, [rc] = m = striking distance to an OHL conductor or ground wireOvervoltage Protection and Insulation Coordination / Chapter 4 - 21 -

Direct Lightning Strikes to OHL Shielding FailureShielding effect of ground wire Shielding failure rate:

SFR I = 2 N g LDc = 2Ng LIm

3 kA

Dc f ( I ) d I

L ... length of line

= shielding angle

Im is the maximum current at and above which no strikes will terminate on the phase conductor see next slide

strikes strikes between between A A and and B B phase phase conductor conductor strikes strikes between between B B and and C C ground ground wire wire strikes strikes beyond beyond A A ground groundFachgebiet Hochspannungstechnik


- 22 -

Direct Lightning Strikes to OHL Shielding FailureShielding effect of ground wire Point where all three striking distances rc,GW , r c,PhC, rg meet c,GW c,PhC g each other. =0 Dc c = 0 will hit Currents Currents I I I Im m will hit ground ground wire wire or or ground ground



- 23 -

Direct Lightning Strikes to OHL Shielding FailureSituation for I = Im

c

x

c a = 180 - 90 x = 180 - - 90 = 180 - 180 + + 90 - 90 =



- 24 -

Direct Lightning Strikes to OHL Shielding FailureSituation for I = Imsin = rgm h+ y 2 c2 2 rcm 4

c2 r 42 cm

As

2 rcm

c 42

sin =

rgm

h+ y 2

rcm

c

Simplification:

rgm rcm = rm

sin

rm

h+ y 2 rm

h+ y 2 rm 1 sin Fachgebiet Hochspannungstechnik


- 25 -

Direct Lightning Strikes to OHL Shielding AngleSituation for I = Imh+ y 2 rm 1 sin With0.75 rm = 7.1 I m

(see slide 20)

h+ y 0.75 2 rm 7.1 I m 1 sin

h+ y 2 Im 7.1 (1 sin )

1 0.75

Examples: h = 60 m, y = 45 m, = 30 Im 36.3 kA h = 30 m, y = 25 m, = 15 Im 9.1 kA

The The higher the structure structure and the larger larger the the shielding shielding angle angle, the higher is is the the maximum maximum current current of of a a direct direct lightning lightning strike strike to to the the OHL OHL conductor. conductor.Fachgebiet Hochspannungstechnik


- 26 -

Direct Lightning Strikes to OHL Shielding AngleSituation for I = Imh = 60 m, y = 45 m

h = 45 m, y = 35 m h = 30 m, y = 25 m

[BAL-04]

deg



- 27 -

Direct Lightning Strikes to OHL Shielding AngleChoice of ImiiBlitz stroke

u i

u ii = istroke /2 Blitz/2 u= i u =Z Zi

Strom-and und voltage Spannungswellen nach Blitzeinschlag in ein Leiterseil Current surges after lightning stroke into a line conductor

If flashovers of the insulators shall be avoided, following requirement has to be fulfilled:

Im t0

t = t0

Apparent increase of radius from non-corona conductor radius r to corona conductor radius Rc Increase of conductor capacitance (whereas inductance remains unchanged)

L L Zc = Decrease of surge impedance for surge front: Z 0 = C C + C Decrease of velocity for parts of surge voltage u > Ui: v0 =Fachgebiet Hochspannungstechnik

1 vc = LC - 31 -

1 L(C + C )


Direct Lightning Strikes to OHL Corona DampingEffect of corona Steepness of the surge depending on traveling distance:

SA =

1 1 K C0 A + S0

S ... KC0 ... ... S0 ...

steepness of surge after traveling distance in kV/s corona damping constant in s/(kVm) traveling distance in m initial steepness of surge in kV/s

Distribution

5 x 10-6

[IEC 60071-2], [BAL-04]



- 32 -

Direct Lightning Strikes to OHL Corona Damping

[BAL-04]

(for S0 )



- 33 -

Direct Lightning Strikes to OHL Corona DampingMeasured overvoltage surges on a single-line conductorca. 2200 kV/s Voltage

ca. 370 kV/s

TimeFachgebiet Hochspannungstechnik


- 34 -

Back FlashoverSee HVT II, Chapter 11 and [BAL-04]

iB = 2iE + iMuM = iMRMShield wire

R tower surge impedance M ... R M ... tower surge impedance uinsul. = uM - uL At unfavorable phase relation:

Line conductor

uinsul. = uM + |uL| If uinsul. > ud, LI Problem: Problem: extreme extreme d du u/d /dtt-values! -values! For tower footing resistances < 10 : Flashovers at IB > 190 kA



- 35 -

Protection by Surge Arresters and Representative Overvoltage Due to separation effects, surge arresters have a limited protection distance. The larger the distance between arrester and the equipment to be protected and the higher the steepness, the higher the fast front overvoltage at its terminals. Representative overvoltage when surge arresters are applied (simplified equation):

U rp = U pl + 2 ST U rp = 2U pl (!)

for U pl 2 ST for U pl < 2 ST

S ... T ...

steepness of surge in kV/s travel time along distance L in s

T=

L c0

L ... distances a1 + a2 + a3 + a4 in m next slide c0 ... velocity of light: 300 m/sNote: depends exclusively on steepness and distance arrester equipment, Note: U Urp rp depends exclusively on steepness and distance arrester equipment, but but not not on on the the overvoltage overvoltage amplitude amplitude!!Example: Um = 420 kV Upl = 825 kV; S = 1000 kV/s; L = 30 m

U rp = U pl + 2 ST = 825 kV + 2 1000 kV/s Fachgebiet Hochspannungstechnik

30 m = 1025 kV 300 m/s- 36 -


Protection by Surge Arresters and Representative Overvoltage



- 37 -

Protection by Surge Arresters and Representative OvervoltageConsiderations on steepness S Impact of number of connected linesS ... KC0 ... ... S0 ... steepness of surge after traveling distance in kV/s corona damping constant in s/(kVm) traveling distance in m initial steepness of surge in kV/s

SA =

1 1 K C0 A + S0

1 K C0 A

(for S0 )

Steepness is reduced inversely proportional to number n of connected lines:

1 SA = n K C0 A

(Explanation see next slide)



- 38 -

Protection by Surge Arresters and Representative OvervoltageConsiderations on steepness S Impact of number of connected linesZ Z n 1

n n= = 1: 1:

2U0

Z=

UTr

UTr = 2U0

Z Z =Z Z= n 1

n n= = 2: 2:

2U0

UTr

UTr Z 1 U = Tr = 2U0 2U0 2Z 2

Z Z Z = Z= n 1 2

n n= = 3: 3:

2U0

UTr

UTr Z 1 = UTr = 2U0 2U0 3Z 3

and when the voltage amplitude is reduced, the steepness is reduced proportionally.Fachgebiet Hochspannungstechnik


- 39 -

Protection by Surge Arresters and Representative OvervoltageConsiderations on steepness S Impact of number of connected linesS ... KC0 ... ... n ... steepness of surge after traveling distance in kV/s corona damping constant in s/(kVm) traveling distance in m number of connected lines

1 SA = n K C0 A

Practical observations on the relevant traveling distance : 1) Shielding failures do not occur in the first span adjacent to the substation.Reason: shielding is intentionally improved by lower shielding angles or double ground wires.

2) Back flashovers do not occur at the first tower(s) adjacent to the substation.Reason: low footing impedance due to connection to substation earthing.

The . The minimum minimum value value of of is is one one span span length length L Lsp sp.

1 Srp = n K C0 ( Lsp + Lt )

Srp ... representative steepness of surge in kV/s Lsp ... span length in m overhead line length with the adopted return rate; in m Lt ...

Lt =Fachgebiet Hochspannungstechnik

adopted return rate 1/a shielding failure rate + back flashover rate 1/a m- 40 -


Protection by Surge Arresters and Representative OvervoltageU rp = U pl + 2 STS ... T ...

steepness of surge in kV/s travel time along distance L in s

(from slide 35)

1 U rp = U pl + 2 T n K C0 ( Lsp + Lt )Introduction of a factor A describing the lightning performance of the OHL:

A=

2 K C0 c0

compare with slide 31, e.g.:K C0 = 0.6 106 s kV m



- 41 -

Protection by Surge Arresters and Representative OvervoltageA c0 A L U rp = U pl + T = U pl + n ( Lsp + Lt ) n ( Lsp + Lt )L ... distances a1 + a2 + a3 + a4 in m

Assumed maximum value (worst case) by assuming the return rate equal to zero, i.e. Lt = 0:

A L U rp = U pl + n Lsp(To be used for convenience if the result gives satisfyingly low Urp) Note: Note: n n should should reasonably reasonably be be set set to to n n= =1 1 (if (if only only one one line line is is connected) connected) or or n n= =2 2 (if (if two two or or more more lines lines are are connected). connected). Assuming Assuming n n> >2 2 could could yield yield too too optimistic optimistic results results that that are are not not valid valid in in a a real real failure failure scenario scenario (e.g. (e.g. possible possible loss loss of of lines). lines).Fachgebiet Hochspannungstechnik


- 42 -

Protection by Surge Arresters and Representative OvervoltageExample: Um = 420 kV Upl = 825 kV; A = 11000 kV (quadruple bundle); L = 30 m; Lsp = 400 m; 2 lines connected; shielding failure rate (typ. for Germany; one OHGW): 2.5 per 100 km and year = 2.510-5 (am)-1 adopted failure rate: 110-3 a-1 LIWV = 1425 kV; 15% safety factor allowed umax = 1211 kV

a) using the "worst case" equation:

U rp = U pl +

A L 11000 kV 30 m = 825 kV + = 1238 kV n Lsp 2 400 m

4Note Note again: again: No No effect effect of of the the lightning lightning overvoltage overvoltage amplitude amplitude!! !!

b) using the "realistic" equation:

1 103 Lt = = 40 m 5 2.5 10 A L 11000 kV 30 m U rp = U pl + = 825 kV + = 1200 kV n Lsp + Lt 2 (400+40) mFachgebiet Hochspannungstechnik

5- 43 -


Protection by Surge Arresters and Representative OvervoltageExample: Um = 420 kV Upl = 825 kV; A = 11000 kV (quadruple bundle); L = 30 m; Lsp = 400 m; lines connected shielding failure rate (typ. for Germany; one OHGW): 2.5 per 100 km and year = 2.510-5 (am)-1 adopted failure rate: 110-3 a-1 LIWV = 1425 kV; 15% safety factor allowed umax = 1211 kV

Effect of double OHGW in span field adjacent to substation: shielding failure rate reduced by factor of 10, i.e. to 2.510-6 (am)-1

1 103 Lt = = 400 m 6 2.5 10 A L 11000 kV 30 m U rp = U pl + = 825 kV + = 1031 kV n Lsp + Lt 2 (400+400) mNote: Note: these these equations equations yield yield the the representative representative overvoltages, overvoltages, which which are are not not implicitly implicitly the the real real overvoltages overvoltages (see (see next next two two slides)! slides)!



- 44 -

Protection by Surge Arresters and Representative OvervoltageMaking use of breakdown voltage-time-characteristic of the insulation2000

3.0 MV/s 1.5 MV/s1800 1600 1400

1.0 MV/s 0.7 MV/s 0.5 MV/s 0.3 MV/s

V-t-curves of 245 kV AIS and GIS equipment (LIWV = 1050 kV) The V-t-curve of GIS is flatter due to more homogeneous field distribution.

1200 U [kV] 1000 800 600 400 200 0 0 0,5 1 1,5 2 2,5 t [s] 3 3,5 4

V-t SF6Ste epn ess o

f ov erv o

V-t airltag e

4,5

5



- 45 -

Protection by Surge Arresters and Representative OvervoltageMaking use of breakdown voltage-time-characteristic of the insulation1000

1800 Amplitude in kV

Example: Um = 300 kV LIWV = 950 kV Upl = 550 kVThe real overvoltage at the equipment's terminals, limited by the surge arrester, has oscillations due to traveling wave effects. Case 1: the representative overvoltage Urp is the real overvoltage as there is no time dependance of the V-t-curve. Case 2: the representative overvoltage Urp is lower than the real overvoltage, e.g. 650 kV. (The first voltage peak will not cause a dielectric breakdown.)

2600

400

200

0 0 5 Time in s 10 15



- 46 -

Very-Fast-Front Overvoltages VFFO originate from disconnector operations or faults within GIS due to the fast breakdown of the gas gap and the nearly undamped surge propagation within the GIS. Amplitudes are rapidly damped and front times increased when leaving the GIS through the bushing. VFFO are usually not a concern or a dimensioning parameter for the hv insulation. Therefore no standardized test has yet been defined (and is not under consideration, either). Mainly an EMI problem, as external electric fields may appear between the metal enclosure and ground problem for secondary control circuits. Countermeasures: usual means of EMC.VFFO measured in a GIS [ETG-93] (LScircuit breaker; TRdisconnector, operated; Dbushing; OHLoverhead lineFachgebiet Hochspannungstechnik

OHL


- 47 -

Very-Fast-Front OvervoltagesOccurrence of VFFO depends on type of disconnector:SF6 disconnecor, type A SF6 disconnector, type B



- 48 -

Very-Fast-Front Overvoltages7 p.u. 65

fast-front overvoltage

43 2 10

slow-front overvoltage

VFTO very-fast-front-overvoltage

temporary overvoltage

cont. service voltage-7

DC-voltage 10 0 10 2 10 4 10 6

10

10

-6

10 -4

10 -2

secondFachgebiet Hochspannungstechnik


- 49 -

Traveling WavesEach electromagnetic wave (in the free space/on a line) has a certain velocity of propagation. Changes of voltage and current result in traveling waves on the line. Dependence on time and location Example: lightning overvoltage on an OHLDependence on time at a certain location Dependence on location at a certain time instant

u0 1 s 2 s 3 s

u0 300 m 600 m 900 m 1200 m

tFachgebiet Hochspannungstechnik

x-1-


Traveling WavesTraveling waves to be taken into account whenever the change in voltage or current takes place in a time duration of the same order of magnitude as the propagation time electrically long line Velocity of propagation in air: v = c0 = 300 m/s Time for traveling along one span of a HV-OHL (300 m): 1 s Time for traveling along an OHL of 300 km length: 1 ms Spatial length of a lightning overvoltage surge (100 s): 30 km Spatial length of the front of a lightning overvoltage surge (1s): 300 m Spatial length of a switching overvoltage surge (5 ms): 1500 km Spatial length of the front of switching overvolage surge (250 s): 75 km Spatial length of one half-period of 50-Hz voltage (10 ms): 3000 km



-2-

Traveling WavesImpact on measurement of changes in sub-microsecond range Example: fast voltage change voltage breakdown/flashover

Velocity of propagation in air: v = c0 = 300 m/s Velocity of propagation in a measuring cable: v = 150 m/s Spatial length of voltage ramp (-du/dt) t = 100 ns in the test circuit (air) along the cable 30 m 15 m t = 10 ns 3m 1,5 m



-3-

Traveling WavesOccurrence of traveling waves / Making use of traveling wave effects energization of a unloaded line propagation of lightning overvoltages on lines propagation of very fast transients in GIS separation effects / protective zone of surge arresters generating and measuring of LI voltages generating rectangular current impulses (energy tests on surge arresters) fault location on cables fault location on light wave guides / optical fibers location of partial discharges in GIS



-4-

Traveling Waves - Laws of PropagationGeneral electrical equivalent circuit of a line element

R ... Resistance L ... Inductance G ... Parallel conductance C ... Capacitance



-5-

Traveling Waves - Laws of PropagationElectrical equivalent circuit of a loss-less line element

u i u (u + d x ) = L ' d x x t i u i (i + d x ) = C ' dx x tFachgebiet Hochspannungstechnik

u i = L ' x t

i u = C ' x t-6-


Traveling Waves - Laws of Propagationu i Partial derivative with respect to x: = L ' x t 2u 2i = L ' 2 x t x

i u Partial derivative with respect to t: = C ' x t

2i 2u = C ' 2 t x t

2u 2u = L ' C ' 2 2 x t



-7-

Traveling Waves - Laws of Propagationu i = L ' Partial derivative with respect to t: x t 2u 2i = L ' 2 xt t

i u Partial derivative with respect to x: = C ' x t

2i 2u = C ' 2 x xt

2i 2i = L ' C ' 2 2 x t



-8-

Traveling Waves - Laws of Propagation 2u 2u = L ' C ' 2 2 x t 2i 2i = L ' C ' 2 2 x t

General wave equations of the loss-less line General solution acc. to dAlembert (1717-1783):

u ( x, t ) = f1 ( x vt ) + f 2 ( x + vt ) = uv + uruv ur

v=

1 L 'C '

Velocity of propagation

1 1 i ( x, t ) = f1 ( x vt ) f 2 ( x + vt ) = iv + ir Z ZivFachgebiet Hochspannungstechnik

L' C' Surge impedance Z=

irOvervoltage Protection and Insulation Coordination / Chapter 5 -9-

Traveling Waves - Laws of Propagationu ( x, t ) = f1 ( x vt ) + f 2 ( x + vt ) = uv + uruv ur

i ( x, t ) =

1 1 f1 ( x vt ) f 2 ( x + vt ) = iv + ir Z Ziv ir

Both voltage and current are composed of a forward and a backward wave. A positive forward voltage wave is linked to a positive forward current wave:

uv iv

x

A positive backward voltage wave is linked to negative backward current wave:

ur ir

x



- 10 -

Traveling Waves - Laws of Propagation

Wanderwellenausbreitung beimrelease pltzlichen Abflieen einer freigewordenen Influenzladung auf einer Traveling waves after sudden of influenced charges on an OHL - left: development with time of fields Freileitung; linke Bildhlfte: zeitliche Entwicklung der Felder; rechte Bildhlfte: auf deris Leitung right: traveling waves on the line (Note: ur and ir have the same traveling direction, but Wanderwellen the measured current negative.)Fachgebiet Hochspannungstechnik


- 11 -

Traveling Waves - Laws of PropagationVelocity of propagation r d r

d L ' = 0 r ln r

C'=

0 r ln d r1 = L 'C '

Velocity of propagationwith 0 = 1.25610-6 Vs/Am 0 = 8.85410-12 As/Vm c0 300 m/sFachgebiet Hochspannungstechnik

v=

1

0 0

1

r r

= c0

1

r r

Permeability of vacuum Permittivity of vacuum Velocity of light- 12 -


Traveling Waves - Laws of PropagationVelocity of propagation Velocity of propagationwith 0 = 1.25610-6 Vs/Am 0 = 8.85410-12 As/Vm c0 300 m/s

v=

1 = L 'C '

1

0 0

1

r r

= c0

1

r r

Permeability of vacuum Permittivity of vacuum Velocity of light

As r = 1:

v = c0

1

r

exclusively dependent on dielectrics!

Air: r = 1.0006 1 Cable: r = 2.5 ... 4

vair = c0 = 300 m/s vcable = 190 m/s ... 150 m/s



- 13 -

Traveling Waves - Laws of PropagationSurge impedance r d r

d L ' = 0 r ln r

C'=

0 r ln d r

Surge impedance

1 L' Z= = C'

0 r d ln r 0 r

depends on dielectrics! depends on geometry! does not depend on location!Permeability of vacuum Permittivity of vacuum- 14 -

with 0 = 1.25610-6 Vs/Am 0 = 8.85410-12 As/VmFachgebiet Hochspannungstechnik


Traveling Waves - Laws of PropagationSurge impedanceZ = 1

0 r d ln r 0 rPermeability of vacuum Permittivity of vacuum

with 0 = 1.25610-6 Vs/Am 0 = 8.85410-12 As/Vm

Figures: OHL 420 kV, quadruple bundle: OHL 123 kV, single conductor: GIS, GIL: polymeric (XLPE) hv-cable: polymeric (XLPE) mv-cable: measuring (coaxial) cable (RG-58): transformer winding:Fachgebiet Hochspannungstechnik

Z 250 Z 400 Z 60 Z 40 Z < 40 Z 50 Z 102 ... 104 - 15 -


Traveling Waves - Reflection and Refractionuv iv Leitung line 1 1 Z1

line 2 2 Leitung Z2

uv = Z1iv uv and iv suffer changes at the location of discontinuity Refraction Reflection(forward waves proceed at increased or reduced amplitudes) (waves travel back from the location of discontinuity)



- 16 -

Traveling Waves - Reflection and Refractionu1v , i 1v i1line 1 1 Leitung

i2

u1 = u2 i1 = i2Leitung line 2 2 Z2

u1

Z1

u2

u1 = u1v + u1r i1 = i1v + i1r

= =

u2 = u2v + u2r = u2v i2 = i2v + i2r = i2v

u1v + u1r = u2v i1v + i1r = i2v



- 17 -


i2


u1

Z1

u2

u1 = u1v + u1r i1 = i1v + i1r2.

= =

u2 = u2v + u2r = u2v i2 = i2v + i2r = i2v

u1v + u1r = u2v i1v + i1r = i2v

1.

u1v u1r u 2 v = Z1 Z1 Z2

u1v u1r =

Z1 u2v Z2

u2v 2 Z2 = = bu u1v Z1 + Z 2Fachgebiet Hochspannungstechnik


- 18 -

Traveling Waves - Reflection and Refractionu2v 2 Z2 = = bu u1v Z1 + Z 2

voltage voltage refraction refraction factor factor



- 19 -

Traveling Waves - Reflection and Refractioni2 v = u2v b Z = u1v u = i1v bu 1 Z2 Z2 Z2 u2v 2 Z2 = = bu u1v Z1 + Z 2

i2 v Z 2 Z1 = bu 1 = = bi i1v Z 2 Z1 + Z 2



- 20 -



i2 v 2 Z1 = = bi i1v Z 1 + Z 2

current current refraction refraction factor factor



- 21 -


i2


u1

Z1

u2

u1 = u1v + u1r i1 = i1v + i1r

u2 = u2v + u2r = u2v i2 = i2v + i2r = i2v

u1v + u1r = u2v i1v + i1r = i2v



- 22 -

Traveling Waves - Reflection and Refractionu1r = u 2 v u1v = bu u1v u1v = u1v (bu 1) = u1v ruru = u1r Z Z1 = bu 1 = 2 u1v Z 2 + Z1u1v + u1r = u2v

u2v = bu u1v



- 23 -



i2 v 2 Z1 = = bi i1v Z 1 + Z 2u1r Z 2 Z1 ru = = bu 1 = u1v Z 2 + Z1


voltage voltage reflection reflection factor factor



- 24 -


i2


u1

Z1

u2

u1 = u1v + u1r i1 = i1v + i1r

u2 = u2v + u2r = u2v i2 = i2v + i2r = i2v

u1v + u1r = u2v i1v + i1r = i2v



- 25 -

Traveling Waves - Reflection and Refractioni1r = i2v i1v = bi i1v i1v = i1v (bi 1) = i1v rii1r Z Z2 = bi 1 = 1 i1v Z1 + Z 2i1v + i1r = i2v

ri =

i2 v = bi i1v



- 26 -



i2 v 2 Z1 = = bi i1v Z 1 + Z 2u1r Z 2 Z1 ru = = bu 1 = u1v Z 2 + Z1


voltage voltage reflection reflection factor factor

ri =

i1r Z Z2 = bi 1 = 1 i1v Z1 + Z 2

current current reflection reflection factor factor



- 27 -

Traveling Waves - Reflection and Refraction at End of Lineu 1v, i1v

line 1 1 Leitung

i

R

u

Z1



- 28 -


line 1 1 Leitung

i

R

u

Z1

a) end = open circuit ru = 1 ri = 1 u1r = u1v

R u = 2u1v i=0

i1r = i1v

doubling of voltage at lines end, current = zero



- 29 -


line 1 1 Leitung

i

R

u

Z1

b) end = short-circuit ru = 1 ri = 1

u1r = u1v i1r = i1v

R=0 u=0 i = 2i1v

doubling of current at lines end, voltage = zero



- 30 -


line 1 1 Leitung

i

R

u

Z1

c) matched end ru = 0 ri = 0 u1r = 0 i1r = 0

R=Z u = u1v i = i1v

Neither refraction nor reflection



- 31 -

Traveling Waves - Reflection and Refraction at End of Lineopen circuit

short-circuit



- 32 -

Traveling Waves - Reflection and Refraction at End of Line

matched: R = Z

open circuit

short-circuit



- 33 -

Traveling Waves - Reflection and Refraction at End of LineTraveling wave equivalent electrical circuit

Z12uv

uik = 2uv/Z1 = 2iv

2u v

R

L

C

Z1

i2iv



- 34 -

Protective Distance of Surge Arresters Model CalculationOvervoltage surge of s = 800 kV/ s

Arrester u pl = 800 kV = const. ?= = 300 m x=0Fachgebiet Hochspannungstechnik

Transformer LIW = 1425 kV

x=- 35 -


Protective Distance of Surge Arresters Model Calculation2000 1600 1200 800 400 0 0 -400 -800 -1200 1600 kV 0 0,5 1 1,5 2 s 2,5 800

t t= =0 0 s s

1600 kV 1200

uArr (x = 0)

400

uTr (x = )

x=0

x=

1200

x = 0 kV x= = 0: 0: u uArr Arr = 0 kV

800

400

x = 0 kV x= = : : u uTr Tr = 0 kV0 0Fachgebiet Hochspannungstechnik

0,5

1

1,5 - 36 -

2 s

2,5



t t= = 0,5 0,5 s s

1600 kV 1200

uArr (x = 0)

u1v

400

uTr (x = )

x=0

x=

1200

x = u 1v = x= = 0: 0: u uArr = 400 400 kV kV Arr = u1v

800

400

x = u 1v = x= = : : u uTr =0 0 kV kV Tr = u1v0 0Fachgebiet Hochspannungstechnik

0,5

1

1,5 - 37 -

2 s

2,5



t t= =1 1 s s

1600 kV 1200

uArr (x = 0)

u1v400

uTr (x = )

x=0

x=

1200

x = u 1v = x= = 0: 0: u uArr = 800 800 kV kV Arr = u1v

800

400

x = u 1v = x= = : : u uTr =0 0 kV kV Tr = u1v0 0Fachgebiet Hochspannungstechnik

0,5

1

1,5 - 38 -

2 s

2,5


Protective Distance of Surge Arresters Model Calculation2000 1600 1200 800 400 0 -400 -800 -1200 1600 kV

t t= = 1,5 1,5 s s

1600 kV 1200

uArr (x = 0)

u1v u1r u2v

800

400

0 0 0,5 1 1,5 2 s 2,5

uTr (x = )Increase at double steepness!

x=0

x=

1200

(1200 (1200 400) 400) kV kV = = 800 800 kV kV400

x = u 1v + = x= = 0: 0: u uArr +u u2v Arr = u1v 2v =

800

(400 (400 + + 400) 400) kV kV = = 800 800 kV kVFachgebiet Hochspannungstechnik

x = u 1v + = x= = : : u uTr +u u1r Tr = u1v 1r =

0 0 0,5 1 1,5 - 39 2 s 2,5


Protective Distance of Surge Arresters Model Calculation2000 1600 1200 800 400 0 0 -400 -800 -1200

t t= =2 2 s s u1v

1600 kV 1200

uArr (x = 0)

800

u1r400

u2v

0 1600 kV

0,5

1

1,5

2 s

2,5

uTr (x = )

x=0

x=

1200

(1600 (1600 800) 800) kV kV = = 800 800 kV kV400

x = u 1v + = x= = 0: 0: u uArr +u u2v Arr = u1v 2v =

800

(800 (800 + + 800) 800) kV kV = = 1600 1600 kV kVFachgebiet Hochspannungstechnik

x = u 1v + = x= = : : u uTr +u u1r Tr = u1v 1r =

0 0 0,5 1 1,5 - 40 2 s 2,5


Protective Distance of Surge Arresters Model Calculation2000 1600 1200 800 400 0 -400 -800 -1200

t t= = 2,5 2,5 s s u1v u1r

1600 kV 1200

uArr (x = 0)

800

400

u3v

u2r u2v

0 0 1600 kV 0,5 1 1,5 2 s 2,5

uTr (x = )

x=0

x=

1200

(2000 (2000 + + 400 400 1200 1200 400) 400) kV kV = = 800 800 kV kV400

x = u 1v + + u 2v + = x= = 0: 0: u uArr +u u1r +u u3v Arr = u1v 1r + u2v 3v =

800

(1200 (1200 + + 1200 1200 400 400 400) 400) kV kV = = 1600 1600 kV kVFachgebiet Hochspannungstechnik

x = u 1v + + u 2v + = x= = : : u uTr +u u1r +u u2r Tr = u1v 1r + u2v 2r =

0 0 0,5 1 1,5 - 41 2 s 2,5


Protective Distance of Surge Arresters Model CalculationDue to traveling wave effects on the line the protection of the equipment by an arrester can be guaranteed only for short distances between arrester and equipment. Simplified estimation of the protective zone *): (LIWV / 1.15) - Upl 2sxs LIWV Upl s vtw*) For more detailed information see IEC 60099-5, IEC 60071-1 and IEC 60071-2

xs =

vtw

protective zone [m] standard rated lightning impulse withstand voltage [kV] LI protection level of the arrester [kV] front steepness of the overvoltage [kV/s] (in the range of 1000 kV/s) propagation speed of travelling wave: - 300 m/s (overhead line) (equals c0) - 200 m/s (cable)

Example 1: Distribution network, Um = 24 kV, insulated neutral, arrester of Ur = 30 kV: xs = (125 / 1.15) - 80 21000 300 = 4.3 m

Example 2: Transmission network, Um = 420 kV, effectively earthed, arrester of Ur = 336 kV: xs = (1425 / 1.15) - 823 21000 300 = 62.4 m



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Traveling Waves Bewley Diagram

2 3 4



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- 48 -

Traveling Waves Application Example: Oscillations1 2 line with surge impedance Z2 and propagation time 3

Ri

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