This is the submitted version of a paper presented at IEEE PowerTech Conference Eindhoven.

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1 hp:// Preprin This is he submied version of a paper presened a IEEE PowerTech Conference Eindhoven. Ciaion for he original published paper: Singh, R S., Hooshyar, H., Vanfrei, L. (2015) Laboraory Tes Se-up for he Assessmen of PMU Time Synchronizaion Requiremens. In: IEEE conference proceedings hp://dx.doi.org/ /ptc N.B. When ciing his work, cie he original published paper. Permanen link o his version: hp://urn.kb.se/resolve?urn=urn:nbn:se:kh:diva

2 Laboraory Tes Se-up for he Assessmen of PMU Correc ime= Time Synchronizaion Requiremens Ravi Shankar Singh Aalo Universiy Espoo, Finland Hossein Hooshyar KTH Royal Insiue of Technology Sockholm, Sweden Luigi Vanfrei KTH Royal Insiue of Technology Sockholm, Sweden Sane SF, Oslo Oslo, Norway Absrac This paper presens he consrucion of a Hardwarein-he-loop laboraory es se-up designed o assess he ime synchronizaion requiremens of Phasor Measuremen Unis (PMUs). The es se-up also allows o invesigae he effecs of signal phase shifs caused by curren and volage ransformers, errors in iming source and he impac of hese errors when deermining ime synchronizaion compliance of PMUs. The paper also describes he srucure of an IRIG-B ime-sync realime implemenaion, which allowed real-ime hardware-in-heloop simulaion by providing a PMU wih a high-accuracy iming source. Xm Signal X in Time Domain Same Signal X in Time Domain Xm 1 1 Index Terms Phasor Measuremen Uni (PMU), Real-Time Simulaion, Hardware-in-he-Loop (HIL), IRIG-B. A. Moivaion I. INTRODUCTION Phasor Measuremen Unis (PMUs) are nowadays being used o generae ime synchronized phasor measuremens used in wide-area monioring, conrol and proecion sysems for he modern power grid [1]. Logged synchrophasor records also help in even reconsrucion afer disurbances or failures ake place in he grid. This helps in deailed examinaion of he evens leading up o a disurbance [2]. To obain reliable phasor esimaes from a PMU, he insrumen should be supplied wih a high-accuracy iming source. The iming source should accuraely synchronize he PMU s clock wih he Coordinaed Universal Time (UTC) which serves as a common reference for all PMUs in he grid [3]. As shown in Fig. 1, inaccuracies in PMU iming will degrade PMU phasor esimaes. In he figure, a signal X is coninuously sampled by wo PMUs o obain phasor esimaes. If he iming of PMU2 is offse by seconds and he esimaed phasors of boh he PMUs are ploed in phasor domain, hen boh phasors will differ by a cerain amoun of phase error. This phase error will presen iself in he phasor esimae of he PMU whose iming was incorrec. A iming error of 5ms can cause an error of ±90 in he esimaed phasor a a sysem frequency of 50Hz. The error in esimaed phasor by PMU can be quanified in erms of he Toal Vecor This work is suppored by he FP7 IDE4L projec funded by he European Commission, he STandUp for Energy Collaboraion Iniiaive and by Sane SF, he Norwegian TSO). Represenaion in Phasor Domain X= Xm 2 Represenaion in Phasor Domain X=( Xm 2 )e j ( degrees phase error) Fig. 1: Imporance of ime in correc phasor esimaion Error (TVE). The TVE is an expression of he difference beween he heoreical value and he PMU s esimae of he signal a he same ime [4]. So PMU iming errors will affec he TVE direcly. As saed in he IEEE Sandard C for Synchrophasors Measuremens for Power Sysems, he iming source should be accurae enough o keep he TVE wihin 1% [4]. B. Previous Work Previous works have focused on assessing he TVE compliance crieria of PMUs under seady-sae condiions [5]. However, hese ess were performed using sand-alone relay es kis. These es kis supply curren and volage signals direcly o he PMUs. In pracical applicaions of commercial PMUs, hese signals are fed o he PMUs via insrumen channel consising of curren and volage ransformers (CTs and VTs). This insrumen channel inroduces raio and phase errors in he volage and curren signals before feeding hem o he PMUs [6]. The errors will affec he final TVE of he PMU. As shown before, PMU iming accuracy will direcly affec he phase errors of he PMU. As he oal TVE should be less han 1%, he share of TVE due o iming source inaccuracy need o decrease in he presence of errors caused by he insrumenaion channel. This requires he reassessmen

3 of iming requiremens for PMUs. Noe ha he es se-up menioned above did no include CTs and VTs and hence will only be suiable for he ideal case where i is assumed ha he PMU is geing error free inpu signals. C. Conribuions This paper proposes a mehod and presens a real-ime, Hardware-in-he-Loop (HIL) es se-up o assess PMU iming requiremens. I also shows ha he iming requiremen in erms of accuracy for commercial PMUs should be sricer han he 31.8µs limi se in he IEEE Sandard C The paper is organized as follows. Secion II presens he ess carried ou in previous works using sand-alone relay es kis. Secion III discusses he concep of he proposed es and hen discusses he se-up for real-ime HIL es o access he PMU iming requiremens in a laboraory. Some resuls in brief are presened in secion IV and conclusions are drawn in secion V. II. STAND-ALONE PMU TEST This secion briefly oulines he sand-alone es se-up o es he seady-sae compliance of PMUs. To esimae phasors reliably, a PMU requires wo inpus, power sysem signals (V & I) and a high accuracy iming source. To es he performance of a PMU in he laboraory, sources o generae boh inpus are required. In his sand-alone es, sandard volage and curren signals are injeced ino he PMUs using sand-alone relay es kis such as Freja 300 [7]. A highaccuracy ime signal is supplied using a Global Posiioning Sysem (GPS)-assised subsaion clock (Arbier 1094b [8]). Phasor esimaes generaed by he PMUs are sen o Phasor Daa Concenraor (PDC). The se-up is shown in Fig. 2. The measured values of he signals are compared o he original signal and he TVE and phase error is calculaed from he logged PMU daa. This phase error in he PMU phasor esimae is caused by he PMU s signal processing uni (which includes Analog o Digial converers and sep down ransformers) [2]. This es se-up does no include he insrumenaion channel, and herefore, he PMU esimae is no affeced by any kind of exernal phase errors caused by CTs and VTs. I is known ha phase angle error for VTs is in he range of ±4 and for CTs in he range of ±2. In high accuracy insrumen ransformers, he phase angle varies beween ±0.1 [9]. The oupu volage from he VTs lags he original volage signal and he curren oupu form he CTs leads he original curren signal as shown in Fig. 3. These phase shifs will affec he accuracy of phasor esimaes generaed by a PMU, hus direcly affecing he TVE also. A 1% TVE corresponds o a phase angle error of 0.573, provided no oher errors are presen. This ranslaes o 31.8µs in ime a a power sysem frequency of 50Hz (or 26µs a 60Hz). The presence of phase errors in inpu signals reduces he margin for ime source inaccuracies o be less han he 31.8µs limi specified in IEEE C [4]. The nex secion presens a mehod and HIL es se-up o sudy and FrejaA300 WindowsAGUI y y FrejaA300 RelayATesAKi PhasorADaaAConcenraor EherneASwich ThreeAPhaseAVolageAgACurren PMUAUnderATes Fig. 2: PMU es using sand-alone relay es ki Time Domain Time Domain CT Oupu Curren CT Inpu Curren VT Oupu Volage VT Inpu Volage GPSAAnenna SubsaionAClock Phasor Domain Phasor Domain Fig. 3: Phase shif in curren and volage signals due o CTs and VTs assess he ime synchronizaion requiremens of PMUs in a conrolled laboraory environmen. III. TEST SET-UP FOR ASSESSMENT OF PMU TIME SYCNHRONIZATION REQUIREMENTS This mehod assesses he iming requiremens of PMUs when he required accuracy of he iming source is of concern. For a fair assessmen, i is necessary o es he PMU in an environmen emulaing he on-field implemenaion of a PMU. On field, he PMU is supplied wih signals via an insrumenaion channel. Also, o see he effec of varying iming errors on he TVE and hence esimae he accepable accuracy limis of he iming source, a conrollable PMU iming soluion is required. This iming soluion mus be able o supply ime wih varying accuracy as required. In he case of above menioned sand-alone es, here is no insrumenaion channel and also he ime clock supplying he ime o PMU is assised by GPS and hence is unconrollable. The es se-

4 widh modulaed oupu volage (V) up discussed in he paper ess he PMUs in presence of an emulaed insrumenaion channel and using a user conrollable ime source. To emulae he insrumenaion channel, Megger amplifiers SMRT1 were placed in beween he curren and volage signals generaion source and he PMU under es. The phase angle accuracy of he amplifier s oupu curren and volage signals could be up o ±0.25 a 50Hz [10]. This accuracy range was found suiable as a subsiue o emulae high accuracy insrumen ransformers whose phase angle accuracy varies beween ±0.1. To be able o conrol he PMU iming signal, i was decided o simulae he ime signal in real-ime and hen feed i o he PMU. Basic conrol blocks from SIMULINK s library can be used o vary he accuracy of he ime signal supplied. An Iner- Range Insrumenaion Group Code B (IRIG-B) ime signal was chosen as he high accuracy PMU iming source [11]. I disribues ime o PMUs wih an accuracy of ±500ns [12] and can be simulaed and conrolled using SIMULINK. The PMU under es also requires balanced hree-phase volage and curren signals as inpus. Boh signals required for he es, i.e. IRIG-B iming signal and he hree-phase volage and curren (V and I) signals, can be simulaed in SIMULINK. These signals can be sen in real-ime as inpus o he PMU. The srucure of IRIG-B ime code which was simulaed in real-ime for PMU ime synchronizaion is briefly discussed below. A. IRIG Overview IRIG-B is a serial ime code developed by he Telecommunicaion Group of IRIG. IRIG has six differen encoding formas labelled A, B, D, E, G and H, ou of which IRIG-B is mos commonly used o disribue ime o Inelligen Elecronic Devices (IEDs) [11]. IRIG-B can be disribued in wo ways, one as a DC Level Shifed (DCLS) pulse widh coded signal (unmodulaed) or as an ampliude modulaed signal based on a sine wave carrier wih a frequency of 1kHz [13]. GPS based clocks can generae IRIG-B coded iming signals which can be disribued o many IEDs in single subsaion. Unmodulaed DCLS IRIG-B can achieve accuracies in he range of ±500ns., which is beer han he accuracy of ±10µs achievable by is ampliude modulaed counerpar [12]. This makes he DC shifed, unmodulaed form of IRIG- B, he mos suiable forma for ime disribuion in PMU applicaions. B. Unmodulaed DCLS IRIG-B Unmodulaed DCLS IRIG-B is disribued in frames. Each frame is one second long and has a pulse rae (or a bi rae) of 100 pulses per second (pps). The on-ime for each bi refers o he leading edge of he pulse. Each bi has an index coun idenificaion number. The Index coun inerval is he ime inerval beween he leading edges of wo consecuive pulses. Each bi has an index inerval of 10ms. [13]. The index coun ranges from 0 o 99 and hen rolls over o 0 for he nex second. Each frame uses five ypes of pulses: logic zero, logic one, posiion markers P 0 -P 9, a reference bi P r and index markers. Reference bi P r indicaes sar of a new frame. Posiion idenifiers from P 0 hrough P 9 are placed every en bis. Index markers occur beween decimal digis in each sub-word o provide visual separaion. The widh of hese pulses are pulse widh coded where he widh of logic zero is se o be 20% of he index inerval (2ms), he widh of logic one is 50% of he index inerval (5ms). Posiion markers and he reference bi are 80% of he index inerval (8ms) and index marker bis are 20% of he index inerval (2ms). Every new one-second ime frame is idenified by wo consecuive 8ms pulses, P 0 and P r. The srucure of an IRIG-B frame is presened below: <synch>ss:mm:hh:ddd<conrol><binary Seconds> where: SS The second of he minue [00 o 59 (60 during leap seconds)] in Binary Coded Decimal (BCD) MM The minue of he hour (00 o 59) in BCD HH The hour of day (00 o 23) in BCD DDD Conrol Binary Seconds The day of year (001 o 366) in BCD Informaions like leap second, dayligh saving, qualiy informaion and a pariy bi included in a block of 27 bis Second of he day in 17 bis To be able o use IRIG-B as a conrollable iming source for PMUs under es, MATLAB code was wrien o generae pulse widh modulaed IRIG-B signals in he DCLS forma specified above. The code was embedded in a SIMULINK model as a MATLAB funcion. The code includes an opion o se he iniial ime from which ime sars rolling. Oher conrol parameers like dayligh saving, leap seconds and ime qualiy can also be se and changed. The parameers giving iniial ime of he IRIG-B ime block can be se as shown in Fig ime (seconds) Fig. 4: IRIG-B pulses simulaed in SIMULINK C. Real-Time Hardware-in-he-loop se-up For his es se-up, real-ime volage and curren signals and real-ime and conrollable IRIG-B iming signals were required as inpus o he PMUs under es. All hese signals use he same ime reference. These signals were obained by execuing he IRIG-B and balanced hree phase curren and volage signals SIMULINK blocks on he Opal-RT s emegasim real-

effec of iming errors on he phase errors of he measured signals and consequenly on he overall TVE of he esimaed phasor was sudied and ploed on he graphs. IV.

7 shows he phase angle errors for volage signals fed o a commercial PMU.

Therefore, i can be assered ha he errors due o he insrumenaion channel and errors in he iming source should be considered while examining he iming requiremens for commercial PMUs. Fig.

The simulaor can produce analog oupus up o ±16V. As he commercial PMUs required IRIG-B ime code pulse of 5.5V ampliude, he analog IRIG-B pulses were generaed in real-ime wih ampliude of 5.

The raed volage and curren inpus of he commercial PMUs were higher han he signals generaed by he real-ime simulaor, i.e. ±16V.

In his se-up, he Megger amplifiers emulaed on-field CTs and VTs as hey similarly inroduce phase angle shifs in he volage and curren signals.

5 effec of iming errors on he phase errors of he measured signals and consequenly on he overall TVE of he esimaed phasor was sudied and ploed on he graphs. IV. RESULTS Afer analysing he recorded phasor daa, i was realized ha he phase error due o he insrumenaion channel can cause a major rise in he final TVE. Fig. 7 shows he phase angle errors for volage signals fed o a commercial PMU. I is observed ha in presence of insrumenaion channel errors he ime error of 10µs caused he volage phase angle errors cross he mark which breaches he 1% TVE limi. Therefore, i can be assered ha he errors due o he insrumenaion channel and errors in he iming source should be considered while examining he iming requiremens for commercial PMUs. Fig. 5: Iniial parameers for IRIG-B generaor block in SIMULINK ime simulaor plaform [14]. Analog pulses of IRIG-B and analog volage and curren signals were obained from he simulaors analog oupu erminals. The simulaor can produce analog oupus up o ±16V. As he commercial PMUs required IRIG-B ime code pulse of 5.5V ampliude, he analog IRIG-B pulses were generaed in real-ime wih ampliude of 5.5V and were direcly sen o he PMU IRIG-B inpu. This synchronized he PMUs o he ime specified by he user as he iniial parameers. The raed volage and curren inpus of he commercial PMUs were higher han he signals generaed by he real-ime simulaor, i.e. ±16V. Thus, he hree phase volage and curren signals generaed by he simulaor were amplified using he Megger SMRT1 amplifiers and hen were fed o he volage and curren inpus of he PMU. In his se-up, he Megger amplifiers emulaed on-field CTs and VTs as hey similarly inroduce phase angle shifs in he volage and curren signals. The whole channel from he real-ime simulaor s oupu o he PMU s curren and volage inpus including he amplifiers and he connecion cables represens he insrumenaion channel. The complee model-o-daa analysis work-flow for his es is shown in Fig. 6 The green lines in he figure indicae ransfer of daa over Eherne. The insrumen channel is shown using he red arrows. The PMU makes phasor esimaes of he signals received. The iming signals can be manipulaed by he user during he es. Basic blocks like Transmission Delay from SIMULINK s library can be used o delay he ime signals for a few microseconds o a few milliseconds. In he experimen, he ime errors were varied in he seps of 10µs. Coninuously generaed synchrophasor esimaes by he PMU for differen iming errors were sen o he Phasor Daa Concenraor (PDC) and sored. This logged daa was analysed using MATLAB. The ConorlDofDIRIG-BDDD imingdaccuracy ---- Real-TimeDAnalogDCurrenDandDVolageDSignals MeggerDAmplifier AnalysisDofDPMUDDaa ConrolDSignals AmplifiedDVDandDDID PMU SimulaionDofDreal-imeDIRIG-B,D CurrenDandDVolageDSignalsDin Real-TimeDSimulaorD Real-Time IRIG-BDPulsesD PhasorDDaaDConcenraor Fig. 6: Real-Time, Hardware-in-he-loop se-up o deermine iming accuracy requiremens

6 (a) Phase error in measured volage signals in sand-alone ess (b) Phase error in measured volage signals in presence of Insrumenaion Channel 10us ime error a =10s A B 20us ime error a =48s (c) Phase error in measured volage signals in presence of insrumenaion channel and varying ime error (leading ime) in seps of 10µs a poin A and B Fig. 7: Phase angle variaion in measured volage for a commercial PMU for differen es cases REFERENCES [1] B. Vandiver, A. Aposolov, F. Sein Hauser, Tesing of Phasor Measuremen Unis, in rd Annual Conference for Proecive Relay Engineers, pp. 1-5, Apr [2] B. Dickerson, Time in he Power Indusry:How and Why We Use I available online a:hp:// TimeInThePowerIndusry.pdf [3] IEEE Guide for Synchronizaion, Calibraion, Tesing, and Insallaion of Phasor Measuremen Unis (PMUs) for Power Sysem Proecion and Conrol, C , March [4] IEEE Sandard for Synchrophasor Measuremens for Power Sysems, C , Dec [5] M. S. Almas, J. Kiler and L. Vanfrei, Experiences wih seady-sae PMU compliance esing using sandard relay esing equipmen, in Proc. Elecric Power Qualiy and Supply Reliabiliy Conference (PQ), 2014, pp [6] Z. Wu, K. Thomas, R. Sun, V. A. Ceneno and A. G. Phadke, Threephase insrumen ransformer calibraion wih synchronized phasor measuremens, in Proc IEEE PES Innovaive Smar Grid Technologies (ISGT), pp [7] Megger, Freja Relay Tes Sysem, [Online]. Available: hp://www. megger.com/eu/producs/producdeails.php?id=861&descripion=. [8] Arbier, GPS Subsaion Clock Model 1094B, [Online]. Available: hp:// model-1094b-gps-saellie-precision-ime-clock.php [9] Z.Huang, e al, Performance evaluaion of phasor measuremen sysems, in Proc. Power and Energy Sociey General Meeing - Conversion and Delivery of Elecrical Energy in he 21s Cenury,2008, pp [10] Megger, SMRT1, Single Phase Relay Teser, [Online]. Available: hp: // [11] Jin-kai Huang, Liang Du and Qun-ying Liu, Applicaion of IRIG-B Code in Phase Measuremen Uni, in 2012 Asia-Pacific Power and Energy Engineering Conference (APPEEC), pp. 1-3, Mar [12] Jackie Peer, Eric Sagen, Shankar Achana and Veselin Skendzic, The Fuure of Time: Evolving requiremens for Precize Time Synchronizaion in he Elecric Power Indusry, Schweizer Engineering Laboraories, Inc., 2011, [Online]. available: hps:// DownloadAsse.aspx?id=9995 [13] IRIG Sandard ,IRIG Serial Time Code Formas, May [Online]. Available: hp:// [14] Opal-RT Technologies, OP5600 off-he-shelf Hardware-in-he-Loop (HIL) simulaor, [Online]. Available: hp://hp:// produc/op5600-hil-hardware-in-he-loop-compuer-and-io-sysem [15] R. S. Singh, H. Hooshyar and L. Vanfrei, Assessmen of Time Synchronizaion Requiremens for Phasor Measuremen Unis, unpublished, submied o IEEE PowerTech conference, V. CONCLUSION This paper has deailed he developmen and implemenaion of a real-ime es se-up o deermine he iming accuracy requiremens for PMUs. A generic hardware-in-he-loop seup was consruced using OPAL-RT s real-ime simulaion plaform and commercial PMU unis. A brief overview of IRIG-B as PMU s iming signals was also discussed. Tess were performed using a conrollable simulaion of a iming source o explore he effecs of iming errors on he Toal Vecor Error. Tes resuls performed on a commercial PMU were discussed and i was observed ha phase angle errors due o he insrumenaion channel and he iming source can significanly affec he final TVE of he PMU measuremen sysem. Hence he errors caused by he insrumenaion channels should be aken ino accoun while sandardizing he PMU iming requiremens. A deailed es resuls on wo differen commercial PMUs are discussed in a companion publicaion [15].

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