PowerWorld Simulator GIC

Transcription

1 Tom Overbye PowerWorld Client Conference February 23, South First Street Champaign, Illinois (217)

2 Geomagnetic Disturbances (GMDs) Overview GMDs have the potential to severely disrupt operations of the electric grid by inducing quasi-dc geomagnetically induced currents (GICs) in the high voltage grid Until recently power engineers had few tools to help them assess the impact of GMDs on their system First integrated tool introduced by PowerWorld GMD assessment tools are now moving into the realm of power system planning and operations engineers Calculations are now implemented in power flow and transient stability GIC impact is certainly still an area of research, but tools are here Presentation presents PowerWorld implementation 2

3 GMD Background Solar corona mass ejections (CMEs) can cause changes in the earth s magnetic field (i.e., db/dt). These changes in turn produce a non-uniform electric field at the surface Changes in the magnetic flux are usually expressed in nt/minute; from a 60 Hz perspective they produce an almost dc electric field 1989 North America storm produced a change of 500 nt/minute, while a stronger storms, such as the ones in 1859 and 1921, could produce more than 5000 nt/minute variation Storm footprint can be continental in scale (much of USA) Image source: J. Kappenman, A Perfect Storm of Planetary Proportions, IEEE Spectrum, Feb 2012, page 29 3

4 July 2012 GMD Near Miss According to a July 2014 NASA press release, in July of 2012 there was a solar CME that barely missed the earth If it had hit the earth it would likely have caused the largest GMD that we have seen in the last 150 years There is still lots of uncertainly about how large a storm is reasonable to consider in electric utility planning Image Source: science.nasa.gov/science-news/science-at-nasa/2014/23jul_superstorm/ 4

5 Solar Cycles Sunspots follow an 11 year cycle, and have been observed for hundreds of years We're in solar cycle 24 (first numbered cycle was in 1755); minimum was in 2009, maximum in 2014/2015 Images from NASA 5

6 But Large CMEs Are Not Well Correlated with Sunspot Maximums The large 1921 storm occurred four years after the 1917 maximum 6

7 There would be a day or so warning but without specifics on the actual magnitude or location It could strike quickly (they move at millions of miles per hour) with rises times of less than a minute, rapidly covering a good chunk of the continent Early warning satellites at Lagrange points, 1 million miles out Reactive power loadings on hundreds of transformers could sky rocket, causing heating issues and potential large-scale voltage collapses Power system software like state estimation could fail Control room personnel would be overwhelmed The storm could last for days with varying intensity Waiting until it occurs to prepare might not be a good idea Impact of a Large GMD From an Operations Perspective 7

8 FERC and NERC Actions May 2013: FERC Order 779 issued to NERC to develop Operations Standards and Planning Standards November 2013: NERC files EOP-010-1, Geomagnetic Disturbance Operations Ongoing: NERC TPL Transmission System Planned Performance During Geomagnetic Disturbances May 20, 2014: Technical Conference Several requirements, including study of Benchmark GMD Event every 5 years NERC proposed a non-uniform field magnitude model that FERC has partially accepted (FERC has been seeking industry comments) FERC workshop next week (March 1, 2016) 8

9 Geomagnetically Induced Currents (GICs GMDs cause slowly varying electric fields Along length of a high voltage transmission line, electric fields can be modeled as a dc voltage source superimposed on the lines These voltage sources produce quasi-dc geomagnetically induced currents (GICs) that are superimposed on the ac (60 Hz) flows 9

10 Transformer Impacts of GICs The superimposed dc GICs can push transformers into saturation for part of the ac cycle This can cause large harmonics; in the positive sequence (e.g., power flow and transient stability) these harmonics can be represented by increased reactive power losses in the transformer Harmonics Images: Craig Stiegemeier and Ed Schweitzer, JASON Presentations, June

11 Overview of GMD Assessment The two key concerns from a big storm are 1) large-scale blackout due to voltage collapse, 2) permanent transformer damage due to overheating Image Source: 11

12 GMD Enhanced Power Analysis Software By integrating GIC calculations directly within power flow and transient stability engineers can see the impact of GICs on their systems, and consider mitigation options GIC calculations use many of the existing model parameters such as line resistance. Some non-standard values are also needed; either provided or estimated Substation grounding resistance transformer grounding configuration transformer coil resistance whether auto-transformer whether three-winding transformer, generator step-up transformer parameters 12

13 Geographic Information GMD-induced DC voltages depend on the storm strength and orientation and the latitude and longitude of the lines The electric field is integrated along the transmission line path The geo-coordinates of the terminal buses are sufficient for uniform field modeling Hence buses must be mapped to substations, and substations to their geo-coordinates Substation/geographic data can be supplied by PowerWorld for FERC 715 planning models Buses mapped to subs, latitude and longitude for substations 13

14 Mapping Transformer GICs to Transformer Reactive Power Losses Transformer specific, and can vary widely depending upon the core type Single phase, shell, 3-legged, 5-legged Most significant with single phase designs Ideally information supplied by the transformer owner Currently support default values, a user specified linear mapping, or a piecewise linear mapping For large system studies default data is used when nothing else is available. Scaling value changes with core type Still debate in the industry with respect to the magnitude of damage GICs would cause in transformers (from slight aging to permanently destroyed) 14

15 Four Bus PowerWorld Example 150 volts I GIC,3Phase = = Ω ( ) amps or amps/phase Substation A with R=0.2 ohm Neutral = 18.7 Volts Bus 3 Substation B with R=0.2 ohm Neutral = Volts Bus 1 Bus 2 Bus 4 DC = 18.7 Volts DC = 28.1 Volts DC =-28.1 Volts DC =-18.7 Volts pu pu 765 kv Line pu pu 3 ohms Per Phase GIC/Phase = 31.2 Amps High Side = 0.3 ohms/ Phase GIC Input = Volts High Side of 0.3 ohms/ Phase GIC Losses = 52.6 Mvar GIC Losses = 52.5 Mvar slack The line and transformer resistance and current values are per phase so the total current is three times this value. Substation grounding values are total resistance. Brown arrows show GIC flow. 15

16 Specifying the Transformer Loss Values in Per Unit Previously K was specified as Mvars/amps Q loss = V pu KI GIC K is the loss factor, depends on core type, phases, etc. Q loss is in Mvars, I GIC is in Amps Since Q loss varies with V, this required an assumed nominal voltage (usually 500 kv) with the actual nominal voltage of each transformer used to scale the K values Q loss = V pu K V base,highkv 500 I GIC Disadvantages: Arbitrary assumed kv needed, K in Mvars/Amp cannot well model default piece-wise linear relationships that may exist for the three-leg transformers 16

17 Specifying Transformer Losses Scalars in Per Unit Current Approach: Representing the K values in per unit Using a base derived using the transformer s high side voltage Peak (or "crest") value Current base using the peak value used since this is a dc Sbase current base Ibase, highkv, peak = V 3 base, highkv Convert to per unit by dividing Q loss by S base,3ph V VpuK Q old loss = 500 S V I base base, highkv base, highkv 1000I 2 base, highkv, peak GIC K Q = V ( ) I = V ( K ) I = V K I K = 1.633K old loss, pu pu eff,pu pu old eff,pu pu new eff,pu new old 17

18 Specifying Transformer Losses Scalars in Per Unit Example: 345/138 kv transformer with I GIC = 100 amps and K = 1.5; use S base of 100 MVA Ibase, highkv, peak = = A I pu = = Q = = Q = Mvar loss, pu loss PowerWorld cases all use the new approach now 18

19 Four Bus Example: Input Data Next several slides demonstrate how GICs and their impacts can be calculated in an integrated fashion Earlier four bus system with an assumed electric field Substation coordinates need to be given to get line length In example Sub A is at 40N, 87W, Sub B is at 40N, 89W Line length is km (106.2 mile) 19

20 Four-Bus Inputs: Substations Key inputs are the grounding resistance and geo-location (latitude and longitude) 20 Latitude and longitude Grounding resistance = 0.2 Ω 20

21 Four-Bus Inputs: Transformers 21 Key inputs Coil resistance (DC ohms) Grounding configuration Autotransformer? (Yes/No) Core Type Most essential parameters; these determine the basic topology of the GIC network 21

22 Four-Bus Inputs: Transformers Manually Enter Coil Resistance Yes, User Set : user enters High Side Ohms per Phase and Medium Side Ohms per Phase No, Auto Default : values estimated XF Config High and XF Config Med: most common options are Gwye and Delta Is Autotransformer: Yes, No, or Unknown Core Type 22

23 Other Considerations Specifying a minimum voltage level to include in the analysis allows electric fields to be ignored on transmission lines below a cutoff kv GIC losses can be ignored on an area basis GIC input voltages can be ignored on an area basis 23

24 GIC Modeling Inputs Template MS Excel spreadsheet for data collection Does not require use of PowerWorld Simulator Contains transformer and substation GIC model inputs and allowable values in PowerWorld Simulator 24

25 Reactor Models Grounded shunt reactors can provide a GIC current path, similar to transformers Simulator GIC does not currently include reactors in the GIC circuit model, but it is possible to include a dummy transformer with an open-circuit secondary winding to approximate the affect for GIC modeling 25

26 Reactor Models Dummy Transformer as GIC Reactor Model: Delta Connected Secondary, Autotransformer = NO W ar Mvar Giant R 26

27 GMD Event Modeling After model inputs are assembled, the next step is to describe a GMD event Modern methods model GIC as DC voltage sources in transmission lines With pertinent parameters, GIC computation is a straightforward linear calculation 27

28 Other Considerations 28 Specifying a minimum voltage level to include in the analysis allows electric fields to be ignored on transmission lines below a cutoff kv GIC losses can be ignored on an area basis GIC input voltages can be ignored on an area basis 28

29 Scaled Electric Field Modeling GICs are dependent upon the assumed electric field NERC approach is to use a scaled uniform direction electric field Field/voltage input is Electric-Field Magnitude (V/mile or V/km) Storm Direction (0 to 360 degrees) 29 All directions are a linear combination of the north and east directions α and β scaling factors (covered later) 29

30 Four Bus Case Eastward Field Below values show results with uniform 0.88 V/km eastward field With uniform field, voltage is path independent 0.88 V/km km = 150 V Ibase, highkv, peak (100 MVA Base) = = A QLoss,pu, GIC = = Mvar Substation A with R=0.2 ohm Substation B with R=0.2 ohm Neutral = 18.7 Volts Neutral = Volts Bus 3 Bus 1 Bus 2 Bus 4 DC = 18.7 Volts DC = 28.1 Volts DC =-28.1 Volts DC =-18.7 Volts pu pu 765 kv Line pu pu 3 ohms Per Phase GIC/Phase = 31.2 Amps High Side = 0.3 ohms/ Phase GIC Input = Volts High Side of 0.3 ohms/ Phase Losses GIC = 52.6 Mvar GIC Losses = 52.5 Mvar slack Values would be zero for a N-S field for this case 30

31 42 Bus Example System: No Electric Field 31

32 42 Bus Example System: 5 V/km Northward Electric Field 32

33 42 Bus Example System: 5 V/km Eastward Electric Field 33

34 Determining the Worst Direction For a uniform direction field, the worst direction can now be determined analytically This can be done for individual transformers, areas and the system as a whole This allows easy "worst case" analysis 34

35 Default WECC Example with Uniform Electric Field: 5 V/km Eastward Transmission Atlas Results: Mvar Losses: 21,408 Highest Losses: 21,847 Highest Dir.: 65 deg Lowest Losses: 17,619 Lowest Dir.: 156 deg But highest/lowest directions vary for areas (28 deg for BC Hydro) 35

36 NERC Proposed Benchmark GMD Event (TPL-007) Peak GMD electric field magnitude corresponding to reference value of 8 V/km at 60 degrees north geomagnetic latitude and for the reference Quebec earth model Apply scaling factors for local geomagnetic latitude and earth resistivity E = 8 α β (V/km) α = e (0.115 L) Geomagnetic latitude scalar β is an earth resistivity scalar that ranges from 0.21 to 1.17 in the US and Canada 36

37 Default WECC Example with Scaled Electric Field: 5 V/km Eastward Transmission Atlas Results (greatly reduced) Mvar Losses: 4303 Highest Losses: 4638 Highest Dir.: 57 deg Lowest Losses: 3751 Lowest Dir.: 145 deg 37

38 GMDs, GDVs and Sparklines ALBERTA B.C.HYDRO NORTHWEST FORTISBC IDAHO MONTANA WAPA U.M GMD results can be easily visualized using GDVs. This display uses sparklines to show the angular variation in the area GMD losses SIERRA 7.37 PACE WAPA R.M PG AND E PSCOLORADO NEVADA 38

39 Sierra Wauna Da y t o n Grays Harbor Energy Facility Covant a Sunset Longview O liv e W a y St. Marys Murryhil Por t Of W Monitor L e x in g t o n ashingt on St. Johns Alcoa River Road Cushm an Chehalis Paul Centralia Switching Station Swif t BlueLake Gr esham Troutdale H a p p y V a le y M ayf ield Fairmount South Bremerton Nor t heast Fr eder ickson ( PSPL) G le n o m Cowlitz Fals S im p s o n a Massachusetts White River ( PSPL) Berrydale Covington Sammamish Novelt y T h e D a le s P h Big Eddy J ohn Day Ph Cascade B ig lo w C a n y o n W in d Rock Cr eek Union Gap Pamona Heights W hit e Cr eek W ind Pr oj ect Kittitas Valey Wind Power Project A n d r e w Y o r k Out look RockyReach Douglas Wind Ridge Boar dm Sulphur an ( PGE) Colum bia W anapum P r ie s t R a p id s Horse Heaven Coyot e Spr ings M idway White Bluf f s Hermiston Power Project Cold Spr ings Bent on Lar son Sand Dunes P E C He a d wo r k s Franklin I c e Ha r bo r S t a t e lin e W in d P r o j e c t - W a s h in g t o n Lower Monumental Little Goose Ph Kettle Fals L o n g L a k e Shawnee Bel Beacon ( Spokane) U p r iv e r D a m N.Lewist on I. E. P a p e r Lo 12. GDV of Substation Neutral GICs Port Angeles East Omak Snohomish Bothell Sno-king Monroe Addy Kitsap Eastpine Chief Joseph Wells (DOPD) Grand Coulee Maple Talbot Valley O' Brien Tillamook Clatsop Aberdeen Satsop Beaver Allston Keeler Shelton J.D. Ross Olympia Napavine Mossyrock Tacoma Southwest Cowlitz Bonneville Vantage McNary Ashe A two color contour is used to show currents coming out of the ground (red) and into the ground Lower Granite Central Ferry (green) Ha Sacajawea Carlton Sherwood Pearl Carver Mcloughlin Slatt Chemawa Salem Bethel (PGE)

40 Power Flow Convergence Integrated GIC modeling can certainly impact power flow convergence since the GIC induced reactive power losses simultaneously adds potentially lots of vars Several techniques can help prevent divergence Just calculating the GICs without solving the power flow Not calculating GMD voltages for equivalent lines Gradually increasing the electric fields to avoid adding too much reactive power at one time Only calculating the GIC transformer reactive power losses for specified areas vars do not tend to travel far Freezing the transformer taps and switched shunt Solving in transient stability for an increasing GMD 40

41 GMD Calculations in Transient Stability GMD calculations are fully integrated into transient stability as well Input is a time-varying electric field Values are calculated and report then as time-varying We are working on extending this to EMP analysis 20.0 Mvar 319 MW 785 Mvar 312 MW 743 Mvar Substation Substation 3 Total GIC Losses Mvar 758 MW Mvar 6 Substation MW 318 Mvar 630 MW 1153 Mvar 630 MW 1153 Mvar 88% MW 59 Mvar 234 MW 88 Mvar 29 Substation Mvar 210 MW MW 54 Mvar MW 16 Mvar Mvar 176 MW 73 Mvar MW 29 Mvar Substation Mvar Substation MW 892 Mvar Mvar 47 MW 20.0 Mvar MW 254 MW 584 Mvar 584 Mvar Substation 1 31 MW 12 Mvar MW 127 Mvar 41

42 Questions? 42