Working Group PC Guide for Fault Current Limiter Testing Sponsored by IEEE Switchgear ADSCOM Fall Switchgear Committee Meeting San Diego, CA

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1 Wrking Grup PC Guide fr Fault Current Limiter Testing Spnsred by IEEE Switchgear ADSCOM Fall Switchgear Cmmittee Meeting San Dieg, CA Octber 3, 2012 Minutes Mischa Steurer called the meeting f the Wrking Grup t rder at 8:10 AM EDT with 15 members and guests present. Intrductins f the attendees were made. The agenda was apprved. The minutes f ur September 13, 2012 meeting were apprved. Three cnference calls have been held since the April 30, 2012 Switchgear meeting. (6/25/2012, 8/20/2012 and 9/13/2012) A SharePint website is being used fr ur Wrking Grup. The draft Guide dcument, CIGRE Reprts and ther pertinent IEEE and IEC Standards have been placed n the SharePint fr WG use. Cntact Paul Bishp pcbishp@bishpgrup.net t request user name / passwrd fr the SharePint site. Yu can access the website at Click n view next t Advanced Electrical Pwer Systems Click OK n pp-up (Digital Certificate) Enter user name and passwrd Navigate t FCL Testing Task Frce Dcuments under Shared Dcuments can be checked ut fr editing. New dcuments can be upladed but must be checked in fr thers t view A cpy f the latest draft f dcument IEEE PC Draft Guide fr Fault Current Limiter (FCL) Testing has been made available t the grup n the share pint site. Writing assignments are nted therein. Please send an t steurer@caps.fsu.edu if yu wuld like t vlunteer t draft a particular sectin. New material shuld be added by sending changes t Tim Chicchi at Chicchi@caps.fsu.edu. Please accept all changes and then track changes in rder t make new material easily identifiable. Chairman s Reprt: The next face t face meetings f ur WG will be held n May 2-3 in Galvestn, TX in cnjunctin with the IEEE Spring PES Switchgear Cmmittee meetings. Registratin infrmatin is available at: An editrial grup was frmed t cmplete the final draft f the Guide fr ballting by the end f Members include: Ram Adapa, Jachim Bck, Andreas Brandt, Gil Carmna, Tim Chicchi, Francisc DeLaRsa, Jerry Earl, Paul Leufkens, Franc Mricni, Christian Schacherer, Gerald Schnenberg, Judith Schramm and Jim van de Ligt. Please send an t Mischa Steurer if yu are interested in serving n this grup. 1

2 The editrial grup will cntinue t meet by web / cnference calls in preparatin fr a ne and a half day meeting targeted fr the week f February 4 th, 2013 at Gergia Tech / NEETRAC in Atlanta t review the final draft and reslve any issues. The next cnference call fr the editrial grup will be held n Mnday, 10/29/2012 frm 10:30AM 12:30PM EST. Paul Leufkens will crdinate a Panel Sessin n FCLs at the 2013 IEEE PES General Meeting in Vancuver. Sectin 3.1 FCL definitin mdified: a device which limits the prspective peak and/r RMS fault current in an alternating current pwer system t the specified value by prviding cnditin-based increase in resistive and/r reactive impedance between nrmal cnducting mde and current limiting mde. The FCL may cnsist f discrete functinally integrated, spatially separated equipment. Adpted as new Definitin Mischa Steurer will investigate the pssibility f cmbining Sectin 6.12 Circuit Breaker Operatin and 6.13 Prtective Devices. Presentatins: Francisc DeLaRsa made a presentatin frm his sub-grup (attached) n the impact f a lightning surge current thrugh an FCL when the FCL is in CL mde r in the transitin between C mde and CL mde. Their cnclusin was the prbability f a lightning strike t the substatin was very lw and damage t FCL equipment due t shielding failures was extremely lw. Francisc DeLaRsa, Jim van de Ligt and Mischa Steurer will draft text fr t acknwledge the issue and pint t C requirements t perfrm lightning surge tests thrugh series reactrs t stress turn t turn insulatin. Chapter 6.11 Recvery - Judith Schramm - The definitins fr recvery in the current draft f the dcument were cmpletely reviewed and cmpletely re-wrked. New definitins fr recvery and partial recvery were develped. - Recvery is defined as the prcess f resetting t C mde after a fault current event. - Partial recvery is defined as the prcess f regaining rated current limiting capability after a fault current event withut resetting t C mde but with rated r reduced cntinuus current capability. - Recvery time is the time frm the clearing f a fault current event t the mment when the FCL regains cntinuus current and fault current limitatin capabilities. - Rated recvery time is the time frm the clearing f a maximum rated fault current event t the mment when the FCL regains rated cntinuus current and maximum rated fault current limitatin capabilities. - Partial recvery time is the time frm the clearing f a fault current event t the mment when the FCL regains rated fault current limitatin capabilities. - Rated partial recvery time is the time frm the clearing f a maximum rated fault current event t the mment when the FCL regains rated fault current limitatin capabilities. The Carried Over Actin Item list was reviewed and updated: - OPEN Judith Schramm will review literature t recmmend vltage waveshapes fr liquid N 2 based insulatin systems. After discussin, it was decided t write a paragraph summarizing the issue fr the Guide with a list f references. - OPEN Chapter 6.14 EMC Andreas Brandt - Prvided material fr review in latest draft f the Guide. - OPEN (N Change) Chapter 6.13 Prtective Devices Jim van de Ligt - OPEN (N Change) Jim van de Ligt vlunteered t investigate fuse standards IEEE regarding rated minimum breaking current (test duty 3). 2

3 - OPEN (N Change) Chapter 6.17 Plarity Jerry Earl - OPEN (N Change) Chapter 6.18 Visual Inspectin Paul Leufkens Prvided material fr review. Text still needs t be develped fr the Guide. - OPEN (N Change) Sectin 7 Prductin Tests Jim van de Ligt - OPEN (N Change) Sectin 8 Field Tests Gil Carmna vlunteered t take ver this sectin Sectin Chairs: First pririty Pwer Frequency Vltage Withstand (Jim van de Ligt) Lightning Impulse Vltage (Francisc De La Rsa) Partial Discharge (Francisc De La Rsa) Cntinuus Current (Tim Chicchi) Shrt-time Withstand Current (Andreas Brandt) Current Limiting (F. Mrcni, P. De, T. Shah) Recvery (Judith Schramm) EMC (Andreas Brandt) Secnd pririty Switching Impulse Vltage (Janne Hu, Jim van de Ligt) Chpped-Wave Vltage Impulse (Tim Chicchi) Cntrl Circuit Vltage Withstand (Jim van de Ligt) Harmnic Distrtin (Francisc De La Rsa) Prtective Device (Jim van de Ligt) Audible (Gil Carmna) Vibratin (Andreas Brandt) Plarity (Jerry Earl) Visual Inspectin (Paul Leufkens) FCL Technlgy -- Specific Tests (Tim Chicchi) - Sectin 7 - Prductin (Rutine) Tests (Jim van de Ligt) - Sectin 8 Field Tests (Gil Carmna) Mischa Steurer adjurned the meeting at 5:10 PM EDT. Submitted by: Frank Lambert Apprved by: Mischa Steurer 3

4 REVIEW OF LIGHTNING STROKES PASSING THROUGH FAULT CURRENT LIMITERS IN A POWER SUBSTATION Subject Investigate the impact f a lightning surge n a Fault Current Limiter (FCL) when lightning strikes n the surce side f the FCL during limiting stage. T illustrate this, Fig. 1 depicts a simplified diagram shwing a lightning strike hitting the surce side f a Slid State Fault Current Limiter (SSFCL) while it is limiting a fault current. The SSFCL used in the illustratin is just as an example since the questin addressed is fr the general FCL situatin. Shielding Failure Fig. 1. Lightning Strike hitting the Surce Side f a SSFCL The striking distance, fr practical purpses the attractive range, f a substatin shielding system dented here as r s, is a functin f the lightning current amplitude accrding t the electrgemetrical mdel in [1], and can be calculated as: r s = 8I (1) where r s is the striking distance in meters and I is the return strke current in ka. When the shielding system f a pwer substatin des nt intercept an appraching clud t grund lightning strike, this is knwn as a shielding failure. This ccurs nly if the striking distance leaves live wires and equipment expsed t appraching lightning strikes. Fig. 2 illustrates a dwnward lightning strike riginating n the left side f the verhead clud being safely intercepted by the substatin shielding wire system. Ntice that the strike distances frm the tw shielding wires, dented as r 1, verlap abve the live parts f the substatin, prviding an effective shielding. Shielding cables are earthed at several pints, s currents intercepted by them are securely cnducted t grund. Nevertheless, the secnd strike t the right hand side f the clud makes its way t the live cnductr inside the substatin fllwing a failure f the shielding system t intercept it. Ntice that the striking distance r 2 f the shielding system in this case is s small that it des nt extend enugh t verlap abve the live cnductrs and falls shrt f prviding an effective shielding. Lightning currents entering the live cnductrs in a substatin fllwing a shielding failure can pass thrugh any fault current limiter Page 1 f 5

5 if it happens t be in their way. Hwever, strke currents invlved in shielding failures are typically f small amplitude, as it will be shwn. Shielding systems are generally designed using the electrgemetrical mdel cncept described by eq. (1) t make sure that the prtective znes prvided by the shielding cables verlap as thse with radius r 1 in Fig. 2, fr currents larger than the critical current that can prduce insulatin flashver. Critical Strke Current Fig. 2. Illustratin f Substatin Shielding Failure Substatin equipment is designed t withstand impulse vltage surges, like thse prduced by switching and lightning vervltages. When lightning hits a phase cnductr, tw waves f current traveling in ppsite directins frm the pint f cntact are created in the cnductr. This means that the vervltage created by these traveling waves f current reaches peaks as high as half the strke current times the surge impedance f the cnductr. If this vervltage rises abve the insulatin withstand f the line cnductrs acrss the air, a phase-t-phase flashver develps. If the basic impulse insulatin level (BIL) f the equipment is exceeded, a phase-t-grund insulatin flashver ccurs. The lightning surge current that will prduce insulatin flashver acrss equipment insulatin, let us call it critical current can be, accrding t [2], expressed as fllws: where: Is = BIL(1.1) = (2.2)BIL Zs 2 Zs (2) Is is the peak amplitude f the lightning current abve which insulatin flashver ccurs in ka. BIL is the basic lightning impulse level f the insulatin in kv. Zs is the surge impedance f the cnductr thrugh which lightning current passes in Ohms. 1.1 is a factr that accunts fr the reductin f strke current when hitting a cnductr instead f zer impedance earth. Page 2 f 5

6 Fr a distributin class system with BIL in the range f 110 kv and a typical surge impedance f 300 hms, the peak lightning critical current Is, calculated frm (1), is 0.7 ka. A 138 kv line, with a BIL f 650 kv, wuld see a critical lightning current f 4.8 ka. Lightning currents belw r equal t thse calculated using eq. (2) will penetrate the substatin shielding system but will nt prduce insulatin flashver. Any Fault Current Limiter in the substatin can be expsed t thse currents. Larger lightning currents which can ptentially be mre harmful t equipment will be intercepted by the shielding system. Prbability fr Lightning Current Peak Amplitude Reference [3] prvides an equatin t calculate the prbability fr a lighting strke t exceed a given value. This can be expressed as fllws: where P(I) = 1 1+ I (3) P(I) is the prbability that the peak current in any strke will exceed I I is the specified crest current f the strke in ka Frm eq. (3) it is evident that the prbability fr lightning currents larger than 4.8 ka, thse that wuld nt penetrate the shielding system in a 138 kv substatin prvided it is prperly designed, is arund 98%. This can als be expressed as a 2% prbability fr lightning currents belw 4.8 ka that wuld reach the substatin bus. In ther wrds, the prbability fr lightning currents passing thrugh fault current limiters installed n r acrss substatin busses as a result f shielding failures fr systems with BIL 650 kv and belw, is 2% r smaller. Ntice that nly half f the lightning current, 2.4 ka in this illustratin, wuld pass thrugh a fault current limiter since the ther half wuld travel in the ppsite directin in the struck cnductr. Grund Flash Density The next questin is hw many lightning grund flashes are likely t strike a particular substatin. This depends n the lightning activity f the specific area, which is usually expressed in terms f grund flash density (GFD). This can be btained frm available GFD maps r estimated frm iskeraunic levels available frm mst Natinal Weather Service ffices arund the wrld using the fllwing relatinship described in [3]: where: GFD = 0.12 T (4) GFD = number f flashes t earth per square kilmeter per year, and T = average annual iskeraunic level (number f thunderstrm days per year) The expected number f lightning grund flashes terminating in a pwer substatin per year can then be estimated as: Page 3 f 5

7 where: Ns = GFD (A) (5) Ns the expected number f lightning flashes in n a pwer substatin A is the substatin area in square meters. Illustratin n Ptential Number f Lightning Events n the Surce Side f Fault Current Limiters that can Ptentially Pass Thrugh FCL s in a Substatin An extreme case regarding lightning incidence in the USA is Central and Suth Flrida, with GFD levels f arund 14 flashes/km 2 /year [4]. A typical distributin substatin ccupies arund 1 acre r mre [5]. The estimated number f flashes expected t strike a 1 acre ( m 2 ) area in a lcatin with GFD f 14 estimated frm eq. (5) is: Ns = GFD (A) 14 ( ) = = flashes/year Frm the reasning abve, nly arund 2%, f these flashes wuld penetrate the substatin shielding system, hit the bus bars and ptentially pass thrugh a Fault Current Limiter. These wuld be lwamplitude-current flashes belw 4.8 ka. Thus the expected number f flashes in the 1-acre area in this example wuld reduce t Ns (2/100) = , r ne flash every 888 years! This can be cnsidered incnsequential. This prbability shuld be reassessed fr substatins f different dimensins, being even smaller fr areas f mderate r lw lightning activity. The idea in this assignment was t assess the need fr recmmending a FCL surge current test t reprduce the event f a lightning surge n the surce side f the FCL right at the time when the FCL is in the limiting stage, i.e. limiting a dwnstream fault. The analysis presented here des nt cnsider the prbabilistic nature f the fault event. Hwever, merely cnsidering the amplitudes f lightning current surges that can penetrate a shielding system and ptentially pass thrugh fault current limiters in substatins with perating vltages 138 kv and belw, it appears that they wuld be f little significance. This statement shuld be cnfirmed by every FCL manufacturer, thugh. Cnclusin Cnsidering the amplitudes f lightning current surges that can penetrate a shielding system and ptentially pass thrugh fault current limiters in substatins with perating vltages 138 kv and belw, it appears that they wuld be f little significance t require a separate lightning surge current test n the FCL. This statement shuld yet need t be cnfirmed by every FCL manufacturer. Page 4 f 5

8 References [1] ] IEEE Wrking Grup, Estimating lightning perfrmance f transmissin lines II Updates t analytic mdels, IEEE Transactins n Pwer Delivery, vl. 8, N. 3, pp , July [2] Gilman D. W. and Whitehead, E. R., The Mechanism f Lightning Flashver n High Vltage and Extra-High Vltage Transmissin Lines, Electra, n. 27, pp , Mar [3] IEEE Std (R2002), IEEE Guide fr Direct Lightning Strke Shielding f Substatins, Reaffirmed 1 August [4] F. De La Rsa, Pwer Systems, Chapter 6.3.1, CRC Press, Edited by Lenard Grigsby, 2007 [5] H. L. Willis, Walter G. Sctt, Distributed Pwer Generatin: Planning and Evaluatin, Chapter 1, page 18, Marcel Dekker, 2000 Page 5 f 5