Hydro One GMD Preparedness Plan for Cycle 24. Presented at: EPRI/NERC Geomagnetic Disturbance Analysis Workshop April , Atlanta, GA

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1 Hydr One GMD Preparedness Plan fr Cycle 24 Presented at: EPRI/NERC Gemagnetic Disturbance Analysis Wrkshp April , Atlanta, GA L. Marti Hydr One Netwrks Inc. 483 Bay St. Trnt, Ontari Canada M5G 2P5 Abstract This dcument describes the preparedness plan that Hydr One is implementing t manage the effects f Gemagnetic Disturbances. This effrt has built n mre than 25 years f in-huse experience as well as cperative effrts with the Gemagnetic Labratry f NRCAN and the University f Western Ontari. The plan calls fr an expanded GIC mnitring netwrk, sftware tls t assess the distributin f GIC and its effects n majr pwer equipment in the Hydr One 230 kv and 500 kv netwrks in real time, and ff-line analysis tls that integrate lad flw analysis with GIC simulatins. All these tls and greater visibility int the effects f any given strm will cnverge int perating measures t prtect Hydr One s assets, and ultimately in crdinatin with the IESO, the security and reliability f supply in the Prvince f Ontari. Keywrds: GIC, Transfrmer Saturatin, Slar strms, GMD 1 Intrductin Ontari Hydr and its successr transmissin cmpany Hydr One have been active in the area f assessment f the impact f Gemagnetic Disturbances (GMD) n the high vltage transmissin netwrk since the mid 80 s. The degree f engagement has increased ver the years, frm the installatin f a few Gemagnetically Induced Current (GIC) mnitrs in the early 90 s, the installatin f 12 new GIC mnitring statins in 2005 [1], t the cmprehensive preparedness plan presently being develped fr sunspt cycle 24. Alng the way Hydr One has maintained a cperative relatinship with the gephysicists at Gemagnetic Labratry f Natural Resurces Canada [2], and has carried ut research wrk with the University f Western Ontari [3-5]. The preparedness plan fr sunspt cycle 24, is fcused n the prtectin f majr high vltage assets such as transfrmers, shunt capacitr banks, and Static var Cmpensatrs (SVCs), but it has a substantial research cmpnent aimed at mdel tuning and validatin with actual measurements. 2 Effects f GIC n High Vltage Transmissin Netwrks During nrmal steady-state peratin, practically all the magnetic flux f a transfrmer is cntained within its laminated steel cre. Electrically, this is equivalent t saying that the magnetizing characteristic f a transfrmer represented by the nnlinear shunt branch X mag f the simplified representatin f Figure 1 is in the linear, high inductance regin (see Figure 2 (a)). The flw f quasi-dc currents such as GIC in a transfrmer winding can intrduce dc flux in the cre, which Page 1 f 11

2 effectively shifts the flux-current perating pint. In this case, the transfrmer is perating in the lw inductance (L air-cre ) saturated regin fr part f the 60 Hz cycle, where flux is nt cntained in the cre and can flw thrugh structural parts such as the transfrmer tank (see Figure 2 (b)). This is nrmally called half-cycle saturatin. The shift in the perating pint depends n the amunt f dc current in the winding and n the cre design. Fr the same amunt f dc current in the winding, a bank f single-phase units see a larger shift in perating pint that a three-phase, three-limb cre-type unit. Xsc/2 1:1 Xsc/2 Xmag V Fig. 1: Simplified representatin f a single-phase transfrmer λ λ λ L air-cre λ λ knee L m L air-cre λ knee L λ λ' d I I I I (a) (b) Fig. 2: Flux-current characteristic f a transfrmer. (a) Nrmal peratin. (b) dc-biased r half-cycle saturatin λ rms λ + λ dc L air-cre λ knee λ 20 Lm Leff 33 λ' d Idc I I rms 47 (a) (b) Fig. 3: (a) RMS flux vs. RMS current. (b) Magnetizing currents fr increasing values f dc flux bias. The main effects f half-cycle saturatin are: Very distrted magnetizing currents (generatin f even and dd current harmnics). Increased harmnics in the HV netwrk can cause generatr verheating, increased shunt capacitr bank harmnic currents, ptential imprper peratin f prtective relays. Page 2 f 11

3 Increased transfrmer winding and structural ht spt heating because the flux is nt cntained within the cre all the time Reductin f the effective magnetizing reactance f the transfrmer frm L m t L eff, as illustrated in Figure 3. This is equivalent t adding a relatively small inductance acrss the terminals f the transfrmer, frcing the vltage acrss its terminals dwn, and causing what in pwer system terms is called drain r lss f reactive pwer. These effects are summarized in Figure 4. GIC currents in HV lines Transfrmer saturatin Reactive pwer lss Harmnics Transfrmer ht spt heating Capacitr bank tripping P&C incrrect peratin Generatr tripping Fig. 4: Effects f GIC n the pwer system The relatinship between GIC, reactive pwer lss and vltage can be illustrated by measurements made with Hydr One s GIC detectin netwrk during Cycle 23. The event in questin was relatively mild frm the pint f view f the effects n the Ontari system and tk place n July 26, Figure 5 shws the transfrmer neutral currents recrded in ne f the mnitring statins. Of significance is the 17 A per phase (50 A neutral) peak fllwed by lwer magnitude scillatins fr apprximately 12 hurs. Figure 6 shws the slar activity between June and August 2004 with data frm NOOA (Natinal Oceanic and Atmspheric Administratin). The planetary A index rse sharply t 155 and 190 n July 26 and July 27, respectively. Page 3 f 11

4 Spike at 22:44 July 26, 2004 ESSA GIC 30 A :24 19:12 0:00 4:48 9:36 14: Time. Fig. 5: July GMD event. Measured neutral GIC Fig.6: Slar activity recrded by NOAA/SEC (Time is GMT) Page 4 f 11

5 The effect f the GIC peak was reflected in bth the 230 kv and 500 kv netwrks. Figures 7 and 8 shw the recrded vltage drp f mre than 1% in sme 500 kv and 230 kv buses. Althugh the vltage drp was bserved thrughut the netwrk, its magnitude was nt unifrm thrugh every bus kv CWD HNM Bruce :52 21:21 21:50 22:19 22:48 23:16 23:45 0:14 Time Fig.7: 500kV buses vltage respnses t the GIC peak kv ESSA CLV 21:21 21:36 21:50 22:04 22:19 22:33 22:48 23:02 23:16 23:31 23:45 0:00 Time Fig.8: 230kV buses vltage respnse t the GIC peak 3 Hydr One s GMD preparedness plans Hydr One s apprach t the management f GMD effects has been an evlutinary prcess ver a number f years. The primary fcus has always been increasing the visibility f GIC in the netwrk t allw mre infrmed peratinal decisins and utage management. Page 5 f 11

6 Kenra Pinard Lakehead Wawa Hamner Ott Hlden Hawthrne Lngwd Orangevill Bruce Essa St. Lawrence Lennx Darlingtn Leslie, Leaside Belleville Middleprt Preparatin fr cycle 24 includes: Fig. 9: Hydr One GIC mnitring statins Review f prtective relaying. This review is carried ut every sunspt cycle t assess the impact f changes in relaying technlgy and prtectin philsphy. This cycle s review cncluded that the replacement f electrmechanical relays with IEDs has practically eliminated the impact f GIC n reliability and security f the prtectin schemes used in Hydr One. Increase the size f the GIC detectin netwrk t18 mnitring statins (see Figure 9). Cmplement GIC measurements with real-time applicatins t calculate GIC in every part f the 230 kv and 500 kv netwrk frm magnetic field measurements. These applicatins als estimate harmnic generatin, reactive pwer lss, and ht-spt heating fr all HV transfrmers with a grund cnnectin. Estimate in real time the GIC flwing thrugh the windings f the transfrmer directly frm SCADA measurements f reactive pwer lss Estimate in real time GIC flwing thrugh selected transfrmer frm the harmnic currents measured with mdern relays (IEDs) Measure in real time the rate f change f disslved gasses in selected transfrmers t establish crrelatins with the estimated ht spt heating. Page 6 f 11

7 Integrate the GIC applicatin with standard lad flw sftware t evaluate system cntingencies and mitigating measures fr any GMD event. Set a training envirnment with the strm playback ptin f the real time applicatins. The plan als calls fr the tuning and validatin f the new applicatins. This means a staged apprach t final g-live cntingent, f curse n measurements and analysis frm a cuple f mderate GMD events. 4 Incremental innvatin Fr the mst part, the analytical basis f the new applicatins is well knwn and mature, albeit applied in real time and n a relatively large scale. The real-time GIC calculatin applicatin is based n the engine develped by NRCAN, and it has been used fr a number f years [7]. It has been adapted fr the cntrl rm envirnment t handle dynamic netwrk changes and asynchrnus data input frm SCADA and magnetmeter readings. Sme f the highlights are: The size f the netwrk is defined by the transfrmers cnnected t the 230 kv and 500 kv netwrks that have a path t grund. On average, this subset f the Hydr One netwrk has 500 transfrmers, 820 circuit segments, 30 shunt capacitr banks, 5 SVCs, and tw seriescmpensatin capacitrs. The mdel includes ne transfrmer statin past intercnnectin pints with Manitba, Quebec and the U.S. Cmputatinal cycle is under 50 ms n an rdinary desktp cmputer. Access t sixty secnds f magnetic field data is under 400 ms, therefre it can handle a 1 secnd magnetic field data rate in real time. Overall latency due t system data acquisitin and utput strage is between 1 t 2 minutes. Sixty secnds f magnetic field data are acquired every minute Sme f the mdest innvatins built int the applicatins are summarized belw: Three-way cmparisn f measured GIC in selected transfrmers: frm direct neutral GIC measurements, frm measured reactive pwer lss, and frm GIC calculated frm magnetic field measurements. Assessment f transfrmer vulnerability n the basis f winding and structural ht spt heating due t half-cycle saturatin. This assessment is based n either measured (see Figure 10) r calculated thermal respnse f a transfrmer and it takes int accunt magnitude and duratin f GIC (see Figure 11). These temperatures are cmpared t either suggested ht spt limits and IEEE C57.91, r t mre cnservative limits estimated n the basis f transfrmer age, gas cntent, misture, and maintenance histry. Page 7 f 11

8 Fig. 10: Thermal respnse f metallic ht spts in a single-phase 500/16.5 kv 400 MVA transfrmer. Temperature Fig. 11: Incremental temperature rise f the tie plate f a single-phase 500/16.5 kv 400 MVA transfrmer under a pre-recrded GMD event. Blue trace is the estimated temperature and the red trace is the abslute value f the GIC in the winding. The intent f the study-mde versin f the GIC simulatr (QSAT) is t assess the effects f reactive pwer lss n system vltages. The time frame fr the effects f reactive pwer lss is tens f secnds, as ppsed t tens f minutes fr the effect f half-cycle saturatin heating. Therefre, the phase angle f the electric field can be assumed t vary mdestly. Page 8 f 11

9 Maximum GIC in different parts f the system generally ccurs fr different rientatins f the electric field. We have subdivided the pssible number f electric field rientatin t six znes (fur f which are illustrated in Figure 12). N N Zne 3 W Zne 1 E W E S N Zne 4 S N W E W Zne 6 E S S Fig. 12: Off-line study-mde electrical filed znes. In an ff-line system study, an electrical field strength between 1-10 V/km is selected and the distributin f GIC and estimated reactive pwer lss is calculate fr each f the six znes (average ver 5 increments) and passed as cnstant Q surces t the lad flw prgram. If vltages calculated with the lad flw prgram are very different frm the vltages assumed in QSAT, the new vltages are passed back t QSAT t estimate the crrected reactive pwer lss. Mre than 1 iteratin is seldm necessary. QSAT als prduces an estimate f transfrmer stress based n thermal functins by using a prerecrded strm such as the ne shwn in Figure 10, scaled t the V/km assumed in the simulatin. This prvides an indicatin f whether transfrmer vulnerability r vltage issues are the limiting factr in a given simulatin. 5 GIC mitigatin Fr the mst part, the effects f GIC n the pwer system have been understd fr decades. Their impact n pwer system equipment and peratin are mre than academic speculatin. Hwever, utilities usually react t ptential GIC cnsequences accrding t past perating experience and Page 9 f 11

10 available resurces. Sme utilities chse t "ride thrugh" GMD events, while sme g t cstly measures such as cnnecting series capacitrs n their majr lines r transfrmer neutrals t blck dc currents [5]. In Hydr One, the experience with adverse GIC effects has been relatively mild. T-date, Hydr One has fllwed NERC/NPCC guidelines fr severe GMD events, which amunt t adpting a "safe system psture", as well as a number f perating/utage management instructins based n studies frm earlier cycles. As the new applicatins and systems are tuned and validated, with real event data, a mve twards a mre surgical respnse will likely take place. Nevertheless, enugh cnservatism has been built in the new applicatins s that they are used tday t assess all wrstcase scenaris ntwithstanding the severity f strm. The pssibility f using GIC reductin/blcking hardware slutins has als been investigated as part f the preparedness activities. EMTP studies were carried ut t assess the applicability f resistrbased and capacitr-based transfrmer neutral devices in tw different statins t address very specific issues. In ne study, a resistr-based device was cnsidered as a ptential ptin t address asymmetrical fault current issues, and the re-distributin f GIC was investigated. In this case, the main issue frm a GIC pint f view, was the ptimal placement f the devices (number and lcatin) under different perating cnditins and cntingencies. The study cncluded that there was very little rm fr ptimizatin under all perating cnditins and that the devices wuld have t be installed in practically every transfrmer in the statin. The fcus f the study f capacitr-based neutral devices was the ptential fr linear resnance. Althugh the study was by n means exhaustive, it shwed that resnance wuld have been an issue in the study system if the bypass mechanism f the GIC blcker were t fail during a line-t-grund fault. The study system fcused n a relatively small twtransfrmer statin, s the re-distributin f GIC within the statin was nt an issue. Hydr One is nt suggesting that there are nt instances where the installatin f phase r neutral GIC blcking wuld be a gd slutin in sme specific circumstances. Studies t date, hwever, strngly suggest that careful system studies are needed fr every ptential applicatin f a GIC blcking device. 6 Cnclusins In preparatin fr sunspt cycle 24, Hydr One is putting in place a number f cst-effective GMD management measures aimed at having well-planned and well-infrmed perating strategies and decisins, as well as unparalleled visibility f GIC and its effects in the system. Plans fr cycle 25 based n lessns learned in this cycle are already being discussed. They include imprvements such as the implementatin f GIC calculatin algrithms based n nn-unifrm electric fields, integratin f ht-spt and dynamic transfrmer rating algrithms, integratin f GIC mdels f neighburing utilities, and the expansin f the mdeled netwrk belw 230 kv, t name a few. References [1] L. Marti, Chun Li, "Real-Time GIC Mnitring in the Ontari HV Netwrk". Nrth American Transmissin and Distributin Cnference (NATD), Trnt, May 2005 Page 10 f 11

11 [2] D.H. Bteler, L. Trichtchenk, R. Pirjla, J. Parmelee, S. Suksaly, A. Fss, L. Marti, "Real time simulatin f gemagnetically induced currents", Canadian Cnference n Electrical and Cmputer Engineering, IEEE Canada, Ottawa May 2006 [3] Luis Marti, Jn Berge, and Rajiv K. Varma, "Determinatin f Gemagnetically Induced Current Flw in a Transfrmer frm Reactive Pwer Absrptin", IEEE Transactins n Pwer Delivery [4] J. Berge, L. Marti, R. K. Varma. "Mdelling and Mitigatin f Gemagnetically Induced Currents n a Realistic Pwer System Netwrk", Prc. f 2011 Electrical Pwer and Energy Cnference, Winnipeg, Manitba, Canada, Octber 2011 [5] J. Berge, R. K. Varma, L. Marti. "Labratry Validatin f the Relatinship Between Gemagnetically Induced Current (GIC) and Transfrmer Absrbed Reactive Pwer", Prc. f 2011 Electrical Pwer and Energy Cnference, Winnipeg, Manitba, Canada, Octber 2011 [6] P.R. Price, "Gemagnetically Induced Current Effects n Transfrmers," Pwer Engineering Review, IEEE, vl.22, n.6, Octber [7] D. H. Bteler. Gemagnetically Induced Currents: Present Knwledge and Future Research. IEEE Trans. Pwer Delivery, vl.9, n.1, Jan. 1994, pp [8] Lenard Blduc, Michel Granger, GreGire Pare, etc. Develpment f a DC Current-Blcking Device fr Transfrmer Neutrals, IEEE Trans. Pwer Delivery, v.20, n.1, Jan. 2005, pp Page 11 f 11