Activities In Cigré In The Field Of Surge Arresters - An .
SC A3 High Voltage EquipmentWG A3.17 / WG A3.25October 16th 2012, San Diego, USActivities in Cigré in the Field of Surge Arresters- an overview Bernhard Richter (Switzerland)1
A3.17Evaluation of stresses of Surge Arresters and appropriatetest proceduresFirst meeting:October 2003 in Darmstadt / GermanyLast meeting:August 2008 in Paris / France(in total 11 meetings)20 members (15/5) representing 13 countriesA3.25MO varistors and surge arresters for emerging systemconditionsFirst meeting:August 2009 in Stellenbosch /South AfricaNext meeting:March 2013 in Beatenberg / Switzerland22 members (18/4) representing 10 countries2
Technical Brochure(to be published in 2012/2013)Content1. Stresses on Surge Arresters2. Surge Arresters3. Energy handling capability of MO surge arresters3
1. Stresses on Surge Arresters- Stresses from three phase systems- Stresses from HVDC networks- Stresses in traction systems- Stresses from lightning- Stresses from ambiance4
Stresses from the power system network- temporary overvoltages with power frequency (TOV) mainly a problem in medium voltage systems- voltage increase due to load rejection- switching overvoltagesVoltage stresses generated in the system can be calculated if thesystem parameters and characteristics of the circuit breakers etc.are known (mostly worst case scenarios).5
Example: TOV in a MV system with isolated star pointSymmetric loadEarth fault in phase L36
HVDC networksThe voltage waveforms in HVDC networksrequire other dimensioning rules for thecontinuous voltage and some specific testson the MO arresters (e.g. the acceleratedageing procedure).7
Lightning stresses- lightning categories- summer and winter lightningLightning overvoltages and the energy content of a surge depend on thelightning current only and are pure statistically.But only a fraction of the lightning current will stress the MO arrester,depending on the system voltage and line configuration.8
Lightning categories (acc. ativedownwardsupwards9
Annual number of days with thunderstormsSource: Martyn D., Climates of the World, Elsevier, Amsterdam, 199210
Probability of lightning currentsStatistical evaluation of lightningmeasurements all over the world.Described is the probability ofoccurrence above the lightningcurrents‘ peak value.11
Winter lightningJapan as well as Norway and some other countries experience rather oftenthunderstorms during winter. Typical weather conditions to create the winterthunderstorms are strong winds from the west which bring rather warm airfrom the ocean to the mountains of the main land.Example of a positive lightning current in a winter lightning at Fukui in Japan inFebruary 1983. Winter lightning flashes have typically one discharge only, butwith a very high charge lowered to earth.12
In low voltage (LV) and medium voltage (MV) power systems (0,23 kV Us 52 kV)distribution lines are generally of lower height and less exposed to direct flashes thantransmission lines. Most of the occurring overvoltages are due to induced voltagescoming from lightning to or in surrounding structures.High voltage (HV) systems in the range of 52 kV Us 245 kV consist both ofdistribution and transmission lines which pass through rural areas. Direct strokes,back flashovers and induced voltages will statistically result in a higher stress for theinstalled arresters than in other voltage systems.Transmission lines in extra high voltage (EHV) with 245 kV Us 800 kV and ultrahigh voltage (UHV) systems above 800 kV have steel towers with shield wires andare in spite of their height above ground well protected against direct lightning strokesto the phase wires. Only shielding failures and back flashovers will cause a criticalsurge in the phase wire.13
Stresses from ambianceAmbient stresses can be very different in the different regions of the world.Very cold climates with ice and snow load have to be considered as well asclimates with high temperature and high relative humidity.Mechanical stresses like seismic loads influence strongly the structure andmaterials used for the design of the MO arresters.Vibrations as well as static loads have to be considered and appropriate testprocedures have been developed accordingly.Observations of biological growth on the surface of polymer insulation havebeen made worldwide. Three types of organic growth have been identified:Algae, Fungi and Lichen. Despite all the reports of biological growth on theinsulation in some areas of the world there are no known failures of MOarresters caused by it.14
Chugoku13170205332Kansai951714[25-80] [80-250] [250-400]Sismic intensity scale[Acceleration (Gal)]Chugoku5813Kyushu4100Seismic records in the past 75years from 1921 to 1995 in JapanSeismic test of GISarrester, horizontalinstallation15
Ambient stress: high humidityThe world’s climatic zones. The most humid climates in equatorialand tropical climate zones are indicated by colors.Source: Martyn D., Climates of the World, Elsevier, Amsterdam, 199216
Leakage Current ( A)Internal leakage currents of MO arresters (for MV system with Uc 24 kV) according to their internal structure during a “humiditychamber test” at 18 kV DC.1009080706050403020100Group IGroup IIGroup III0100200300400500600700800Testing Time (days)Group Ihousing molded directly onto the arrester body, no end capsGroup II housing manufactured separately and pressed onto the arrester body, end capsGroup III as group II, but a considerable gas volume in the arrester due to the design17
Change of leakage current due to diffusion and recovery300Type AXLeakage current (nA)250Type BTypeY200150100500020406080100120140Testing time (days)18
Ambient stress: pollution of the arrester housingMO columnGas32ConductivelayerSolid1Risk of externalflashover (seeIEC 60507)Risk of partialheating of the activeparts (see Annex Fof IEC 60099-4)Uaxial, intRisk of "internal"partial discharges,degradation of theMO resistors anddeterioration of thesupporting structureU radialPossible voltage distributions of anarrester unit under polluted conditionPossible risks due to pollution19
Ambient stress: biological growth (examples)20
Ambient stresses: animal attack21
2. Surge Arresters- Function and relevant parameters- MO-Varistors: state of the art and actual trends- Design of surge arresters- Special designs of surge arresters- SF6 gas insulated MO surge arresters- Integrated arrester systems22
Function and design of MO arrestersMO arresters have basically two parts:- the active part stack of MO resistors electrical characteristic- the housing, providing insulation and mechanical support23
Insulation co-ordinationMain criteria for selecting MO surge arresters:Protection level Upl and maximum continuous operating voltage UcEnergy capability W and highest temporary overvoltage UTOVEconomic and safety margin aspects24
Log-log plot of thenormalized E-Jcharacteristic of atypical MO resistorA Pre-breakdown regionB Breakdown regionC Upturn region1 DC voltage characteristic2 AC voltage characteristic3 Residual voltage characteristicE Field strengthJ Current densityUG Continuous operating voltage (DC)UB Breakdown (or switching) voltageUv Continuous operating voltage (50 Hz)Up Residual voltage at InResistivityNon-linearity exponent (U)25
Electron microscope image of the MO structureSchematic view of the structureFracture surface,2000 times enlargedA: ZnO-crystalB: triple point, phase Bi2O3C: mono atomic layer of O- and Bi-atomsD: electrical active grain boundary(voltage controlled “switch”)26
Band diagram scheme of the hole induced breakdown mechanism27
Long term performance of MO resistors1.41.21.2power loss ratio P / Popower loss ratio P / Po10.80.6stable0.4unstable10.80.6stable varistor in air or N2unstable varistor in airunstable varistor in N20.40.20.2000100200300400500time 0time [h]Power loss ratio vs. time for stable and unstable MO resistors duringaccelerated ageing tests at 115 C and slightly elevated AC operating voltage.left: AC stress onlyright: influence of the surrounding medium28
MO Surge Arrester Design – Polymer HousedDue to their simple internal structure, MO arresters were amongst thefirst apparatuses in electrical power systems equipped with polymerhousings: Mid 1980s – first polymer housed distribution arresters End 1980s – first polymer housed high-voltage arrestersIn the meantime, three basic design principles have emerged: "tube" design "wrapped" design "cage" design29
History of surge arresters for medium voltage systemsGapped designs18981972MO surge arresters without gaps19851991Example ABB30
MO Surge Arrester Design – Porcelain HousedO-ringPressure relief ventSulfur cement bondingPressure relief diaphragmMO columnCompression springSupporting rod (FRP)Fixing plate (FRP)Porcelain housingAluminum flangeInsulating baseExample: Siemens31
Polymer Housed – "Tube" DesignPorcelain housedExamples: SiemensPolymer housed32
Polymer Housed – "Cage" DesignLoops ( bondage)RodsExample: SiemensExample: ABBExample: ABB33
Progress in arrester designHV arresters station class forUs 145 kVLeft: SiC arrester with gaps andporcelain housing (about 40 years ago)Right: completely molded MO arresterwithout gapsBoth arresters have the same ratings.Example ABB34
HV substation 245 kVHV: Uc 174 kVMV: Uc 44 kVTertiary winding:Uc 18 kVExample ABB, Switzerland35
High-voltage arrester integrated in a 420-kVcenter break disconnector (Siemens/RWE)36
Polymer housed arresters serving as post insulators:EnBW/Germany (left), Powerlink /Australia (right)37
3. Energy handling capability ofMO surge arresters- The different aspects of “energy handlingcapability”- State of the knowledge about energy handling of MOarresters- Energy handling capability in international arresterstandards38
"Thermal" vs. "Impulse" EnergyUIf the arrester is permanently connected to powerfrequency voltage no use can be made fromsingle impulse energies that are higher than thethermal energy limit (else: thermal runaway!)Station arresters, distribution arrestersBut there are (more and more!) otherapplications, e.g. Externally GappedLine ArrestersEGLAHere, only impulse energy limits areof interest.39
Energy Handling CapabilityThermal:Loss of thermal stability40
Examples of MO resistors, mechanically failed bysingle impulse energy overload.Left: failed by thermo-mechanical cracking.Right: failed by flashover of the coating.41
OutlookWG A3.17 will publish the outcome of the WG in a TBMO Surge ArrestersPart 1– Stresses and Test Procedures –Follow Up working group A3.25 (Metal oxide varistors and surge arresters foremerging system conditions is working on- Further aspects of energy handling capability such as durability or combined stresses- UHV arresters- consequences of increasing field strength of MO resistors- consequences of axial temperature distribution in an MO arrester-The outcome of WG A3.25 will be published in an additional Technical Brochure (Part 2)42
Publications of the working group A3.17(or in the name of the working group)Integrated Surge Arrester SystemsCigré colloquium, Tokyo /Japan, September 2005, paper No. 201A critical review of the actual standard IEC 60099-4: Metal Oxidesurge arresters without gaps for a.c. systemsCigré colloquium , Rio de Janeiro, 2007, PS3-06Energy handling capability of High Voltage Metal-Oxide SurgeArresters: A Critical Review of International Arrester StandardsCigré colloquium, Rio de Janeiro, 2007, PS3-08MO-surge arresters for voltage systems above 550 kV- Experience and challenges for the future B. Richter (A3.17), M. de Nigris (A3.21), V. Hinrichsen (IEC TC 37 MT4)IEC/CIGRÉ UHV Symposium Beijing 2007, paper 2-5-143
Publications of the working group(or in the name of the working group)Energy handling capability of High Voltage Metal-Oxide SurgeArresters, Part 2: results of a research projectCigré 2008, ParisLong Term Performance of Polymer housed MO Surge ArrestersB. Richter et.al., Cigré 2004, Paris44
Tutorials given in the name of the working group A3.17Concapan XXIV/IEEECosta Rica, 10. November 2004Brazilian Cigré NC(contributions of several working group members)Rio de Janeiro, 6./7. April 2005SC A3/B3 meetingTokyo, Japan, September 2005SC A3/B3 meetingSomerset West, South Africa, 17.-21. August 2009CIREDPrague, 8.-11. June 2009SC A3 meeting (outcome of A3.17)Vienna 201145
Structure of A3.25 (intended TB to be published in 2013)EXECUTIVE SUMMERYForewordIntroduction1 History of Surge Arresters2 Energy handling capability of MO surge arresters3 Ageing of MO varistors4 High Field MO varistors5 Simulation5.1 Simulation of MO varistors5.2 Simulation of MO arresters5.3 Electro-thermal and temperature distribution46
Structure of A3.25 (intended TB to be published in 2013)6 Indirect means for determining insulation withstand7 MO surge arresters for UHV systems8 EGLAs and NGLAs9 Mitigation10 MonitoringConclusionReferencesAnnexes47
13 metersMO arresters for UHV systemsExamples SiemensExample ABB48
GIS arresters for 550 kV systems with MO resistors with «normal» fieldstrength (left) and high field MO resistors of 400 V/mm (middle) and600 V/mm (right), courtesy Toshiba.49
Possible executions of line arresters (description in principle)MO arrester in parallel to aninsulator in an overhead line.These so-called NGLAs (NonGapped Line Arresters) can beinstalled with or withoutdisconnectors.MO arrester with an externalspark gap in series parallelto an overhead line (EGLA Externally Gapped LineArrester)50
Technical Brochures from various working groups dealing withsurge arrestersTB 60METAL OXIDE ARRESTERS IN AC SYSTEMS1991TB 287PROTECTION OF MV AND LV NETWORKS AGAINST LIGHTNINGPART 1: COMMON TOPICS2006TB 441Protection of Medium Voltage and Low Voltage Networks against LightningPart 2: Lightning protection of Medium Voltage Networks2010TB XXProtection of Medium Voltage and Low Voltage Networks against LightningPart 3: Lightning Protection of Low-Voltage NetworksTo be published 2012/201351
Technical Brochures from various working groups dealing withsurge arrestersTB 440Use of Surge Arresters for Lightning Protection of Transmission Lines2010TB 362TECHNICAL REQUIREMENTS FOR SUBSTATION EQUIPMENTEXCEEDING 800 KV2008TB 456Background of Technical Specifications for Substation Equipmentexceeding 800 kV AC2011TB 455Aspects for the Application of Composite Insulators to High Voltage72 kV) Apparatus201152
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Lightning stresses - lightning categories - summer and winter lightning Lightning overvoltages and the energy content of a surge depend on the lightning current only and are pure statistically. But only a fraction of the lightning current wil
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