1Abstract — Test results obtained during fault currentinterruption tests with an air-core reactor are compared to testresu...
2it incorporated an equivalent series reactor instead of theMFCL. The inductance of the series reactor used in the testwas...
3Fig.3 – Fault Current (I), Line to Neutral Voltage (V-N) and Source Voltage(U) with Air Core Reactor in circuit.Fig. 4 – ...
4Fig. 9 shows the PSCAD three-phase representation of thetest circuit with the MFCL used to corroborate the voltage andcur...
5Fig. 13 – PSCAD®-Calculated waveforms for Phase C with CLRC. TRV CalculationsAs described by eq. (2) the TRV is the diffe...
6VI. REFERENCES[1] Schmitt, H., Amon, J. Braun,D., Damstra, G., Hartung, K-H, Jager, J.,Kida, J, Kunde, K., Le, Q., Martin...
7VII. BIOGRAPHIESFranco Moriconi leads Zenergy’s Engineeringeffort in the development of a commercialSuperconducting Fault...
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Transient Recovery Voltage Test Results of a 25 MVA Saturable-Core Fault Current Limiter

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Test results obtained during fault current interruption tests with an air-core reactor are compared to test results obtained using a saturating-core inductive HTS Fault Current Limiter in the same circuit under the same circumstances. These test results are further compared with analytical simulations developed using the PSCAD® software suite. The simulations exhibit good agreement with the test results and confirm that compared to an equivalent air-core reactor, the HTS FCL results in lower amplitude and significantly lower rate of rise of the Transient Recovery Voltage.

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Transient Recovery Voltage Test Results of a 25 MVA Saturable-Core Fault Current Limiter

  1. 1. 1Abstract — Test results obtained during fault currentinterruption tests with an air-core reactor are compared to testresults obtained using a saturating-core inductive HTS FaultCurrent Limiter in the same circuit under the samecircumstances.These test results are further compared with analyticalsimulations developed using the PSCAD® software suite. Thesimulations exhibit good agreement with the test results andconfirm that compared to an equivalent air-core reactor, theHTS FCL results in lower amplitude and significantly lower rateof rise of the Transient Recovery Voltage.Index Terms — transient recovery voltage, rate of rise oftransient recovery voltage, fault current limiter, HTS FCL,saturating-core FCL, inductive FCL, air-core reactor.I. INTRODUCTIONince 2006, Zenergy Power has been developing a type ofinductive magnetic fault current limiter (MFCL) forelectric power grid applications. For efficiency, theZenergy MFCL currently relies on a high-temperaturesuperconductor (HTS) DC magnet to bias a magnetic core,though any source of DC magnetic flux could be employed.The DC-flux-saturated magnetic core, when coupled with asurrounding AC coil, acts as a variable inductor in an electriccircuit. The inductance of the HTS MFCL changes instantly inreal-time in response to the current in the electrical circuitbeing protected. The inductance varies from a low steady-state value, which oscillates slightly as the DC magnetic biaslevel oscillates with changing AC current in the deeplysaturated portion of the magnetic core material B-H curveduring normal operating conditions, to a high value during afault condition, which is sufficient to limit the fault current tothe desired maximum value. A number of superconductingfault current limiter concepts have been extensively reportedupon to date [1-5]. Likewise, the development and evolutionof Zenergy’s MFCL has been extensively documented in thisand other papers [6-10, 15]. A remarkable agreement betweenmeasurements and analytical simulation of fault currentlimitation was described in [6] where a comprehensivedescription of the work conducted on the development, testingand application of a compact saturable core HTS fault currentlimiter was presented.During the extended field demonstration of the firstZenergy MFCL to operate in the commercial electrical grid,Zenergy and system host, Southern California Edison (SCE)became aware of a number of important considerations,including the potential for the MFCL to experience resonance________________________________________________Franco Moriconi(franco.moriconi@zenergypower.com) and Francisco De LaRosa (francisco.delarosa@zenergypower.com) are with Zenergy Power, Inc.,Burlingame, CA, USAin the protected circuit under some conditions [8], along withissues raised by projection engineers concerned with theimpact of the MFCL on relay settings and circuit-breakerperformance parameters. In particular, questions were raisedregarding the time rate of change of the limited fault current atinterruption and the effects of the MFCL on transient recoveryvoltage (TRV) and the rate of rise of recovery voltage(RRRV). The burden on a circuit-breaker is a function of themagnitude of the interrupted current and the TRV [11].The use of conventional series reactors can reduce thecurrent interruption rating of a circuit breaker. However, theycan increase the RRRV and the peak TRV value to above thatwhen the series reactor is absent [11-13]. A larger RRRVreduces the interrupting capability of the circuit breaker andthe beneficial effects of fault current limiting. Even thoughfault current limiting devices impose the same interruptingburden on the circuit breaker regardless of the side of thebreaker on which they are installed, analysis suggests that theyare best placed on the downstream side of the circuit breakerto reduce the source side voltage [14]. Dependence of RRRVwith distance to the fault for a series reactor with very smallparallel capacitance has been reported to be minimal [11].In 2010, Zenergy received its first commercial contract for asaturable-core MFCL – an 11kV device to be installed in a33/11kV primary substation operated by CE Electric in NorthLincolnshire, UK. The 1,250 amp continuous-rated MFCLwill be installed on the low-side of one of the 33/11kVtransformers and the incoming circuit-breaker on the existing11kV switchboard [9]. CE Electric and their integrationcontractor, Applied Superconductor Ltd (ASL), raised similarissues regarding MFCL transient effects on protectionengineering. Zenergy recognized that this project, which wasscheduled to undergo full-power and full-voltage type andacceptance testing, afforded the opportunity to directlymeasure the MFCL transient effects on current interruption.This paper compares actual TRV and RRRV measured valuesfrom fault current testing of a circuit with a saturable-coreHTS FCL and a series reactor providing equivalent faultcurrent reduction. In a earlier paper, an analytical method ofevaluating the transient recovery voltage of a series currentlimiting reactor (CLR) was derived and verified using EMTP-RV®, and PSCAD® simulations were conducted for a 1.188mH, 2 mH and 3 mH series reactors [16]. The simulationresults also compare favourably to the real-world test results.II. TEST CIRCUIT AND RESULTSFig. 1 illustrates the three-phase line diagram of the testcircuit used with the 11kV, 1,250-amp MFCL. The testingwas conducted at KEMA’s Powertest’s laboratories inChalfont, PA, USA in February 2011. The correspondingcircuit with the series reactor was exactly the same except thatF. Moriconi, Member, IEEE, and F. De La Rosa, Senior Member, IEEETransient Recovery Voltage Test Results of a 25MVA Saturable-Core Fault Current LimiterS978-1-4673-1935-5/12/$31.00 ©2012 IEEE
  2. 2. 2it incorporated an equivalent series reactor instead of theMFCL. The inductance of the series reactor used in the testwas that which produced the same fault current limitation asthe MFCL, and was calculated as follows:,1The source resistance is neglected in (1), as it is assumedthat .In Equation (1), Vs is the source line-to-ground voltage, ωthe angular velocity = 2πf, and , is the fault current of thenetwork when a fault current limiter is installed to limit thecurrent by a specific percentage of its prospective value.The relevant parameters of this application are as follows:Rs=0.0163 ΩVs=11.3 kVXs=1.0577 ΩLs = 0.0032 Hf=50 HzXs/Rs≈60Prospective symmetric fault current = 6.2 kALimited prospective fault current , = 4.63 kA (25%reduction).LCLR=0.001285 H, from eq. (1). A 1.2 mH reactor was used inthe test.A bolted three phase fault is set up by closing the MakingSwitch MS under Master Breaker MB closed and by openingthe Auxiliary Breaker AUX a few cycles later, the voltage onboth sides of this breaker are measured to determine theTransient Recovery Voltage as illustrated in Fig. 1. This wasseparately done with the MFCL or the series reactor in thecircuit. The objective was to demonstrate that the TRV andthe RRRV in the upstream breaker would be less pronouncedwith the MFCL in the circuit than it would with the seriesreactor, as our preliminary simulations had revealed.Fig. 1 – TRV Circuit Setup with the FCL in the CircuitFig. 2 is a representative sample of the fault currentwaveforms recorded during the test from its start throughinterruption a few cycles (119 ms) thereafter, when the currentis interrupted to measure TRV across the AUX breaker.Notice that during the fault, the voltage across the AUXbreaker or L-N voltage depicted in the three waveforms onthe center is zero, and that the voltage recovers its normalvalue at the time of fault interruption. The three bottomwaveforms illustrate the source voltage waveform showing adip at the initiation and throughout the duration of the fault.Fig. 3 shows the corresponding L-N and source voltagewaveforms for the case with the series current limiting reactorin the circuit..Fig. 2 – Fault Current (I), Line to Neutral Voltage (V-N) and Source Voltage(U) with MFCL in circuit.The voltage waveforms shown in Fig. 4 and Fig. 5, labeledas TRV waveforms, represent the difference between the timevarying voltage signals measured at both sides of theAuxiliary Breaker AUX in Fig. 1, here described as voltagesVs and Vl on the source and load side of the breaker,respectively:2Measurements were performed with a 1 MHz samplingrate, yielding a digital sample per microsecond.Fig. 6 depicts around 10 ms of high resolution TRVwaveforms presented on the same scale for convenience toquickly compare the cases with the MFCL and with the CLRin the circuit. Notice the larger peak of the waveform withCLR.-10010Ia[kA]-10010Ib[kA]0 0.05 0.1 0.15 0.2 0.25-10010Time [sec]Ic[kA]-10010Va-N[kV]-10010Vb-N[kV]0 0.05 0.1 0.15 0.2 0.25-10010Time [sec]Vc-N[kV]-10010Ua[kV]-10010Ub[kV]0 0.05 0.1 0.15 0.2 0.25-10010Time [sec]Uc[kV]
  3. 3. 3Fig.3 – Fault Current (I), Line to Neutral Voltage (V-N) and Source Voltage(U) with Air Core Reactor in circuit.Fig. 4 – TRV Waveforms for MFCLFig. 5 – TRV Waveforms for Air Core ReactorFig.6 – Comparative TRV Waveforms for MFCL and Series Air-CoreReactor. B phase only.III. PSCAD® SIMULATIONSSimulations were conducted in PSCAD® to determine thefault current and transient recovery voltage. Both, a single-phase and a full three phase representations of the test circuitwere created to produce fault current waveforms up to thetime when fault current reaches the symmetric level and highresolution runs to produce the microstructure of the TRV,respectively. Output waveforms were separately produced forcases with the MFCL and the CLR.A. Case 1: MFCLFig. 7 illustrates the PSCAD® representation of the circuitwith the MFCL in it. The non-linearity of the FCL is describedin [16]. Notice that the fault is represented by the groundconnection attached to the load side of the FCL.Fig. 7 – PSCAD® TRV Test Circuit With Saturable-Core HTS FCLIn this simulation the MFCL was confirmed to provide a25% reduction in fault current as depicted in Fig. 8. Thesymmetrical current was reduced from 6.2 kA rms to 4.63 kArms.Fig. 8 – Fault Current Reduction with a Saturable-Core MFCL-10010Ia[kA]-10010Ib[kA]0 0.05 0.1 0.15 0.2 0.25-10010Time [sec]Ic[kA]-10010Va-N[kV]-10010Vb-N[kV]0 0.05 0.1 0.15 0.2 0.25-10010Time [sec]Vc-N[kV]-20020TRVa[kV]-20020TRVb[kV]0 0.05 0.1 0.15 0.2-20020Time [sec]TRVc[kV]-20020TRVa[kV]-20020TRVb[kV]0 0.05 0.1 0.15 0.2-20020Time [sec]TRVc[kV]0.02 0.022 0.024 0.026 0.028 0.03-20-15-10-50TRVb-phase[kV]FCLReactor
  4. 4. 4Fig. 9 shows the PSCAD three-phase representation of thetest circuit with the MFCL used to corroborate the voltage andcurrent signals in the different nodes of the circuit. Fig. 10depicts, in descending order, the C-phase calculated faultcurrent and L-N and source voltage waveforms in the samesequence that was presented for the measured current in Fig.2. Notice that the waveform asymmetry in the fault current isevident in the measured and calculated waveforms of Fig. 2and Fig. 10. This is because the presented simulation timewindow corresponds to the initial part of the waveform whenthe DC component of the current is still decaying.Fig. 9 – PSCAD three-phase representation of the test circuit with a Saturable-Core MFCLB. Case 1: 1.2mH Series ReactorFig. 11 depicts the PSCAD® model for the TRV test circuitwith the series reactor in the circuit. The series reactorinductance required to deliver the same reduction in faultcurrent as the MFCL, as it was described in II above usingeq.(1), is around 1.2 mH. This was confirmed through thePSCAD® simulation shown in Fig. 12. Notice the overlappingof the two curves showing an air core reactor limited currentcomparable to that provided by the FCL. Here again, the faultis represented by the ground connection on the load side of theseries reactor.Fig. 10 – PSCAD Calculated waveforms for Phase C with FCLFig. 11 – PSCAD® Model for 1.2 mH Series ReactorFig. 12 – Instantaneous and RMS Fault Current Profiles for TRV Circuit witha 1.2 mH Series ReactorIdentically as presented for the case with the MFCL, Fig 13depicts in descending order, the C-phase calculated faultcurrent and L-N and source voltage waveforms in the samesequence that was presented for the measured current in Fig. 3in the case when the CLR is in the circuit. Likewise, themeasured and calculated waveform asymmetries are evidentcomparing Fig. 3 and Fig. 13, respectively.0.0032[H]BRK40.0032[H]0.0032[H]BRK5BRK6E2a_FCLEa_FCLLvara bIa_w_FCLBRK40.0163[ohm]Ea_MB_w_FCL0.012[uF]8.5E-3[uF]Ia_FCLE1a_FCLIb_FCLIc_FCLE2b_FCLEb_FCLLvara bIb_w_FCLBRK50.0163[ohm]Eb_BRK_w_FCL0.012[uF]8.5E-3[uF]E1b_FCLE2c_FCLEc_FCLLvara bIc_w_FCLBRK60.0163[ohm]Ec_BRK_w_FCL0.012[uF]8.5E-3[uF]E1c_FCLCustInd2.FBRK8BRK8TimedBreakerLogicClosed@t0TimedBreakerLogicOpen@t0TimedBreakerLogicOpen@t0TimedBreakerLogicOpen@t0Eb_MB_w_FCLBRK11Ec_MB_w_FCLBRK12BRK11TimedBreakerLogicClosed@t0BRK12TimedBreakerLogicClosed@t0Ea_BRK_w_FCL1.0[ohm]Main:Graphs0.000 0.050 0.100 0.150 0.200 0.250-15.0-7.50.07.515.0(kA)Ic_FCL-15.0-7.50.07.515.0(kV)Ec_MB_w_FCL-15.0-7.50.07.515.0(kV)Vcn_FCL
  5. 5. 5Fig. 13 – PSCAD®-Calculated waveforms for Phase C with CLRC. TRV CalculationsAs described by eq. (2) the TRV is the difference of thesource and load side voltages of the AUX Breaker. Fig. 14depicts the measured TRV waveforms across the AUXbreaker with the MFCL in the circuit, and Fig. 15 shows thecorresponding PSCAD calculated waveforms with the air-corereactor CLR in the circuit, as the breaker opens at the zero-crossing of the current to interrupt the fault.Fig. 14 – Measured TRV waveforms for the MFCL and the 1.2 mH CLRcasesFig, 15– PSCAD®-Calculated TRV waveforms for the MFCL and the 1.2mH CLR casesIV. RELEVANT FIDNINGSComparing Figs. 14 and 15, the measured and calculatedwaveforms show a close agreement both in the amplitudes andin the oscillation frequency. The parameters of the connectingcables were ignored and this may be responsible for the microstructural differences in the waveforms. However, bothmeasured and calculated waveforms reveal a first oscillationwith a peak of around 5 kV in the CLR TRV waveform. Thisfirst swinging is associated with an initial measured RRRV of2100 kV/µs, compared with around 863 kV/µs for the MFCLfor the same range of voltage involved in that first oscillation.As previously noticed, both measured and calculated resultsreveal a higher peak for the TRV as compared with the MFCLarrangement.V. CONCLUSIONSSaturable-core MFCL devices are a potential alternative tothe application of series reactors. The use of series reactorsmight stress the interruption duty of the circuit-breaker byintroducing a fast transient oscillation in the TRV. This is dueto the combination of both low capacitance and highinductance in the device.Analytical studies conducted with PSCAD® and laterconfirmed with full-power testing laboratory measurementssuggest that the employment of equivalent saturable-coreMFCL would have a significantly lower impact on the TRV ofthe upstream circuit-breaker compared to the use of anequivalent series reactor. This should make it possible forMFCL devices to be installed in the electrical grid withouthaving to apply TRV mitigation methods such as addingexternal capacitors.Main:Graphs0.000 0.050 0.100 0.150 0.200 0.250-15.0-7.50.07.515.0(kA)Ic_CLR-15.0-7.50.07.515.0(kV)Ec_MB_w_CLR-15.0-7.50.07.515.0(kV)Vcn_CLR
  6. 6. 6VI. REFERENCES[1] Schmitt, H., Amon, J. Braun,D., Damstra, G., Hartung, K-H, Jager, J.,Kida, J, Kunde, K., Le, Q., Martini, L., Steurer, M., Umbricht, Ch,Waymel, X, and Neumann, C., “Fault Current Limiters – Applications,Principles and Experience”, CIGRE WG A3.16, CIGRE SC A3&B3Joint Colloquium in Tokyo, 2005[2] CIGRE Working Group, “Guideline of the impacts of Fault CurrentLimiting Devices on Protection Systems”. CIGRE publishing, VolA3.16, February 2008. Standard FCL and Cigre[3] CIGRE Working Group, “Fault Current Limiters in Electrical mediumand high voltage systems”. CIGRE publishing, Vol A3.10, December2003.[4] Noe. M, Eckroad. S, Adapa. R, “Progress on the R&D of Fault CurrentLimiters for Utility Applications,” in Conf. Rec. 2008 IEEE Int. ConfPower and Energy Society General Meeting pp.1-2.[5] Orpe, S. and Nirmal-Kummar, C.Nair, “State of Art of Fault CurrentLimiters and their Impact on Overcurrent Protection”, EEA ApexNorthern Summit 08, November 2008, Power Systems Research Group,The University of Auckland[6] Moriconi, F., De La Rosa, F, Singh, A.,, Chen, B., Levitskaya, M.,Nelson, A., “An Innovative Compact Saturable-Core HTS Fault CurrentLimiter - Development, Testing and Application to Transmission ClassNetworks, in 2010 IEEE PES Conf. Proceedings, Minneapolis, MN, July25-29, 2010.[7] F. Moriconi, F. Darmann, R. Lombaerde, “Design, Test andDemonstration of Saturable-Core Reactor HTS Fault Current Limiter,”presented at the US DOE Superconductivity for Electric Systems PeerReview, August 5, 2009, Alexandria, Virginia[8] Clarke, C., Moriconi, F., Singh, A., Kamiab, A., Neal, R., Rodriguez, A.,De La Rosa, F., Koshnick, N., “Resonance of a Distribution Feeder witha Saturable Core Fault Current Limiter,” Proceedings of 2010 IEEE PESTransmission and Distribution Conference, April 19-22, New Orleans,LA, USA.[9] D. Klaus, A. Wilson, A. Hobl, J. Bock, D. Jones, J. McWilliam, A.Creighton, L. Masur, F. Moriconi, “Fault Limiting Technologies inDistribution Networks,” Proceedings of the CIRED 21stInternationalConference on Electricity Distribution, 6-9 June, 2011, Frankfurt,Germany.[10] A. Nelson, F. Moriconi, F. DeLaRosa, D. Kirsten, L. Masur, “Saturated-Core Fault Current Limiter Field Experience at a DistributionSubstation,” Proceedings of the CIRED 21stInternational Conference onElectricity Distribution, 6-9 June, 2011, Frankfurt, Germany.[11] E. Calixte, et al., "Reduction of rating required for circuit breakers byemploying series-connected fault current limiters," Generation,Transmission and Distribution, IEE Proceedings-, vol. 151, pp. 36-42,2004.[12] D. F. Peelo, et al., "Mitigation of circuit breaker transient recoveryvoltages associated with current limiting reactors," Power Delivery,IEEE Transactions on, vol. 11, pp. 865-871, 1996.[13] T. A. Bellei, et al., "Current-limiting inductors used in capacitor bankapplications and their impact on fault current interruption," inTransmission and Distribution Conference and Exposition, 2001IEEE/PES, 2001, pp. 603-607 vol.1.[14] A. F. Alcidas, et al., "Evaluation of Position of a Fault Current Limiterwith Regard to the Circuit Breaker," in Power Symposium, 2006. NAPS2006. 38th North American, 2006, pp. 475-480.[15] Moriconi, F., Koshnick, N., De La Rosa, F., Singh, A., “Modeling andTest Validation of a 15kV 24MVASuperconducting Fault CurrentLimiter,” Proceedings of 2010 IEEE PES Transmission and DistributionConference, April 19-22, 2010, New Orleans, LA, USA.[16] Lopez-Roldan, J., Price, A. C., DeLaRosa, F., Moriconi, F., “Analysis ofthe Effect of a Saturable-Core HTS Fault Current Limiter on the CircuitBreaker Transient Recovery Voltage,” Proceedings of 2011 IEEE PESGeneral Meeting, July 24-28, Detroit, MI, USA.
  7. 7. 7VII. BIOGRAPHIESFranco Moriconi leads Zenergy’s Engineeringeffort in the development of a commercialSuperconducting Fault Current Limiter. Under histechnical leadership Zenergy Power installed andenergized a first-ever HTS FCL in the US electricgrid. In 1992, he joined ABB Corporate Researchto lead R&D work in the areas of numerical andFinite Elements methods, short-circuit strength andnoise reduction of power transformers, GasInsulated Switchgear technology, and high-speedelectrical motors and generators. He alsoparticipated in two IEC working groups, and was the Convener of the IECScientific Committee 17C on seismic qualification of GIS. Currently, he is anactive member of the IEEE Task Force on FCL Testing. Franco Moriconiearned a Bachelor of Science degree and a Master of Science degree inMechanical Engineering from UC Berkeley. He is the co-author of six patentsin the field of HV and MV electrical machines.Francisco De La Rosa joined Zenergy Power Inc.in April 2008 as Director of Electrical Engineering.Before joining Zenergy Power, Inc., Francisco heldvarious positions in R&D, consultancy and trainingin the electric power industry for around 30 years.Francisco holds a PhD degree in ElectricalEngineering from Uppsala University, Sweden anda MSc from ITESM in Monterrey, Mexico. He is aSenior Member of IEEE PES and a Member ofCIGRE. His main interests include the assessmentand integration of new technologies in the electric power system in utilitiesand industry. Francisco is the author of CRC’s Harmonics and Power Systemsbook and has coauthored in the CRC Power Systems, Electric PowerEngineering Handbook, 2ndEd. as well as in over 50 power quality relatedpapers in reviewed journals and in international technical conferenceproceedings.

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