Vulnerability Assessment and Planning

Transcription

1 Vulnerability Assessment and Planning Project (GMD Mitigation) Standard Drafting Team GMD Task Force In-person meeting March 18-19, 2014

2 Topics Application of the Benchmark GMD Event in System Impact Assessment Randy Horton, Southern Company Transformer Thermal Assessment Using the Benchmark GMD Event Time Series Data Luis Marti, Hydro One Overview of Draft Reliability Standard Frank Koza, PJM Interconnection 2

3 3

4 Purpose Provide an overview of the assessment process as envisioned by the Standard Drafting Team The GMD TF Planning Guide was used as technical reference in developing the draft standard Approved by the Planning Committee in December 2013 Approved Planning Guide available on the GMD TF page: e%20gmdtf%202013/gmd%20planning%20guide_approved.pdf 4

5 GMD Assessment and Planning Geomagnetic Field Geoelectric Field Potential Mitigation Measures B(t) Earth Conductivity Model E(t) dc System Model GIC(t) Transformer Model (Electrical) Transformer Model (Thermal) vars Power Flow Analysis Temp(t) Hot Spot Temp. Bus Voltages Line Loading & var Reserves Assessment Criteria Fail Pass Operating Procedures and Mitigation Measures (if needed) GMD Planning Guide highlights GMD-specific considerations and studies that may be outside the scope of the traditional planning process 5

6 Benchmark GMD Event Geomagnetic Field Geoelectric Field Potential Mitigation Measures B(t) Earth Conductivity Model E(t) dc System Model GIC(t) Transformer Model (Electrical) Transformer Model (Thermal) vars Power Flow Analysis Temp(t) Hot Spot Temp. Bus Voltages Line Loading & var Reserves Assessment Criteria Fail Pass Operating Procedures and Mitigation Measures (if needed) The Benchmark GMD Event defines the geoelectric field amplitude(s) used to compute GIC flows in the GMD Vulnerability Assessment Both peak geoelectric field amplitude and wave-shape are needed 6

7 Technical Considerations The Benchmark GMD Event defines the geoelectric field that the system will be subjected to, and is the starting point for GMD Vulnerability Assessment Special attention and engineering judgment is needed for: Ground conductivity model uncertainty Geographic location Systems that span more than one physiographic region 7

8 dc Model and GIC Study Geomagnetic Field Potential Mitigation Measures B(t) Earth Conductivity Model E(t) dc System Model GIC Transformer Model (Electrical) Transformer Model (Thermal) vars Power Flow Analysis Temp(t) Hot Spot Temp. Bus Voltages Line Loading & var Reserves Assessment Criteria Fail Pass Operating Procedures and Mitigation Measures (if needed) Planners will be required to develop a dc model for portions of the system that include a power transformer with a wyegrounded winding with terminal voltage greater than 200 kv. 8

9 dc Model The dc system model used for GIC calculations includes details not normally included in the ac model Equivalent substation ground grid resistance (including the effects of shield wires and/or grounded neutral conductors) Transformer connection information and dc winding resistance Geographical information (e.g. LAT/LON of each bus) dc resistance of transmission lines 9

10 Technical Considerations The dc model should represent projected System conditions which may include adjustments to System posture that occur at the onset of a GMD event Recalling maintenance outages, etc. Facilities should reflect those in the Near-Term Transmission Planning Horizon Estimated dc resistance values for some network elements may be necessary to fill in gaps of available data Because the orientation of the geoelectric field is constantly changing, the steady-state GIC analysis should consider various geoelectric field orientations (e.g deg. Increments). 10

11 Technical Resources for GIC Modeling Technical resources on the GMD TF Project page Disturbance-Task-Force-(GMDTF)-2013.aspx GIC Application Guide (PC approved December 2013) GMD Planning Guide (PC approved December 2013) 2012 GMD Report Technical resources are also available for free at Contact Rich Lordan (EPRI) at for additional information and listing of available information 11

12 Transformer Models Geomagnetic Field Geoelectric Field Potential Mitigation Measures B(t) Earth Conductivity Model E(t) dc System Model GIC(t) Transformer Model (Electrical) Transformer Model (Thermal) vars Power Flow Analysis Temp(t) Hot Spot Temp. Bus Voltages Line Loading & var Reserves Assessment Criteria Fail Pass Operating Procedures and Mitigation Measures (if needed) covered in detail later Planners will need to develop models for transformer Reactive Power absorption vs. effective GIC Lack of validated models remains a significant challenge for three-phase transformers Many commercially-available GIC software packages include default values for reactive power absorption (BE CAREFUL!) 12

13 Steady-State Analysis Geomagnetic Field Geoelectric Field Potential Mitigation Measures B(t) Earth Conductivity Model E(t) dc System Model GIC(t) Transformer Model (Electrical) Transformer Model (Thermal) vars Power Flow Analysis Temp(t) Hot Spot Temp. Bus Voltages Line Loading & var Reserves Assessment Criteria Fail Pass Operating Procedures and Mitigation Measures (if needed) A Steady-state power flow analysis is conducted that accounts for the additional reactive power absorption of transformers due to the flow of GIC in the system 13 System peak Load and Off-peak load should be examined Reactive Power compensation devices that may be impacted by GIC should be removed (e.g. capacitor banks or SVCs that may trip due to harmonics)

14 Technical Considerations Determining susceptibility of Reactive Compensation devices is difficult due to the lack of commercially available tools and knowledge necessary to perform large scale harmonics analysis taking into account the effects of GIC Determining the potential susceptibility of a device (e.g. possible damage to shunt capacitors due to harmonic current flow) or susceptibility to misoperation (tripping) is not possible without some type of harmonics study. One very crude approach (in the absence of system study) for determining susceptibility to misoperation is to assume that any shunt capacitor bank or SVC that uses electromechanical or static (solid-state) relays for protection will misoperate. Such devices would not be included as reactive power support in ac power flow cases 14

15 Assessment Criteria Geomagnetic Field Geoelectric Field Potential Mitigation Measures B(t) Earth Conductivity Model E(t) dc System Model GIC(t) Transformer Model (Electrical) Transformer Model (Thermal) vars Power Flow Analysis Temp(t) Hot Spot Temp. Bus Voltages Line Loading & var Reserves Assessment Criteria Fail Pass Operating Procedures and Mitigation Measures (if needed) The objective of the GMD Vulnerability Assessment is to prevent instability, uncontrolled separation, or Cascading failure of the System during a GMD event. System performance is evaluated based on System steady-state voltage limits established by the Transmission Planner and Planning Coordinator Cascading and uncontrolled islanding shall not occur 15

16 Mitigation Strategies If the requirements of the standard can not be met, actions to mitigate the effects of the Benchmark GMD event must be taken Mitigation options might include: Operating Procedures (if supported by system study) GIC reduction or blocking devices protection upgrades equipment replacement 16

17 17

18 Purpose This presentation provides an overview of a technically sound approach to assessing the thermal impact of GIC in power transformers A draft technical whitepaper is being developed by the Standard Drafting Team to accompany the Reliability Standard 18

19 Half Cycle Saturation GIC produces in offset in ac sinusoidal flux within the transformer resulting in thermal effects: λ λ dc λ m λ L air-core Hot-spot heating of windings due to stray flux Hot-spot heating of noncurrent carrying parts due to stray flux o π/2 θ o o L u i m i m o Fitch-plate o Tie-plate o Tank walls θ = ωt π θ GIC i bias V m π/2 19

20 Thermal Effects Hot-spot heating is dependent upon Transformer thermal time-constant (on the order of 2 to 10 minutes) GIC peak amplitude and duration GIC waveshape Loading Ambient temperature Transformer cooling mode 20

21 2 min 2 min Same event Different transformers 2 min 5 min GIC A/phase Hot spot Temperature C Time (min) 21

22 Thermal Effects Effects vary based on age, condition, and type of Transformer Technically-sound sources of temperature thresholds include Manufacturer-provided information Limits for safe transformer operation such as those found in IEEE Std C for hot-spot heating during short-term emergency loading 22

23 Considerations in a Transformer Thermal Assessment In the absence of manufacturer-specific information, use the temperature limits for safe transformer operation suggested in the IEEE Std. C standard,for hot spot heating during short-term emergency operation. The C57.91 standard does not suggest that exceeding these limits will result in transformer failure, but rather that it will result in additional aging of cellulose in the paper-oil insulation, and the potential for the generation of gas bubbles in the bulk oil. From the point of view of evaluating possible transformer damage due to increased hot spot heating, these thresholds can be considered conservative for a transformer in good operational condition. 23

24 Considerations in a Transformer Thermal Assessment To be consistent with IEEE Std. C suggested temperature limits, the worst case temperature rise for winding and metallic part (e.g., tie plate) heating should be estimated taking into consideration the construction characteristics of the transformer as they pertain to dc flux offset in the core (e.g., single-phase, shell, 5 and 3-leg threephase construction). Temperature increases due to ambient temperature and transformer loading. For planning purposes, maximum ambient and loading temperature should be used unless there is a technically justified reason to do otherwise. 24

25 Considerations in a Transformer Thermal Assessment Time series or waveshape of the reference GMD event in terms of peak amplitude, duration and frequency of the geoelectric field Take into consideration the effective current in autotransformers, reflecting the different GIC ampere-turns in the common and the series windings. I I ) V / V dc, eq = I H + ( I N / 3 H X H I H is the dc current in the high voltage winding; I N is the neutral dc current; V H is the rms rated voltage at HV terminals; V X is the rms rated voltage at the LV terminals. 25

26 Assessment Approaches Calculate steady-state GIC for every transformer for the benchmark E peak (GIC E and GIC N Calculate GIC(t) for every transformer using the reference geoelectric field waveshape 26 { GIC E sin( θ ) GIC cos( )} GIC ( t) = E + θ N

27 Assessment Approaches { GIC E sin( θ ) GIC cos( )} GIC ( t) = E + θ N 27

28 Assessment Approaches Each transformer will see a different GIC(t) Assess if each transformer will be affected by GIC(t) Winding hot spot Metallic part hot spot Adjust thresholds according to age and condition Three ways to do this Peak GIC(t) is so low compared to the transformer s GIC capability that a detailed assessment is unnecessary. Technical justification required. Manufacturer-provided GIC capability curves relating permissible peak GIC pulses of a given duration and loading for a specific transformer. Transformer thermal response simulation of hot-spot temperature to GIC time-series data 28

29 GIC Capability Curve Flitch Plate Temp = 180 C for 2 Minutes Flitch Plate Temp = 160 C for 30 Minutes 80 % MVA Rating GIC, Amps/Phase Sample GIC manufacturer capability curve of a large single-phase transformer design using the Flitch plate temperature criteria. (Girgis and Vedante, IEEE PES Meeting 2013)

30 Thermal Step Response Sample of measured GIC thermal step response (Marti et al, IEEE Transactions on Power Delivery,

31 31

32 Using Thermal Response Tools Obtain GIC(t) after scaling the reference magnetic field with α and the geoelectric field with β 32

33 Using Thermal Response Tools Identify the thermal step response for winding and metallic part hot spots 33

34 Using Thermal Response Tools Obtain the thermal response to GIC(t) 34

35 Using Thermal Response Tools Verify that it meets criteria 35

36 Using Capability Curves Identify the correct capability curve from manufacturer For the purposes of this example the capability curve was constructed with the thermal step response and simplified loading curve All modelling assumptions are therefore identical. Only the methodology is different 36

37 Using Capability Curves Obtain GIC(t) after scaling the reference magnetic field with α and the geoelectric field with β 37

38 Using Capability Curves Identify if the relevant part of GIC(t) matches the pulse widths provided in the curve 38

39 Using Capability Curves Identify if the relevant part of GIC(t) matches the pulse widths provided in the curve 39

40 Using Capability Curves Identify the thermal step response for winding and metallic part hot spots 40

41 Using Capability Curves Use engineering judgment or ask your friendly neighbourhood manufacturer when the capability is marginal. In this example, capability is close to thresholds and pencils would probably have to be sharpened for a more detailed assessment. 41

42 Using Capability Curves Remember that not all signatures are created equal and that it is prudent to consider heating by previous GIC pulses 2 min 5 min Temperature GIC A/phase Hot spot Temperature C GIC Time (min) 42

43 43

44 44

45 TPL-007 Require a planning assessment of the system for its ability to withstand a Benchmark GMD Event without causing a wide area blackout, voltage collapse, or damage to transformers. Applicability: PCs,TPs, TOs, GOs Need system models DC (GIC calculation) and AC (power flow) Transformer information-- internal winding resistance Substation grounding information Studies that may be necessary to perform a GMD assessment: Transformer GIC Impact (Reactive Power and Thermal) Power Flow System Studies Impact of Harmonics on Reactive Power compensation devices 45

46 GMD Benchmark Geo-electric Field E peak = E benchmark x α x β (in V/km) where, E peak = E benchmark = α = β = Benchmark Geo-electric field magnitude at System location Benchmark Geo-electric field magnitude at reference location (60 N geomagnetic latitude, resistive ground model) Factor adjustment for geo-magnetic latitude Factor adjustment for regional Earth conductivity model 46

47 Benchmark GMD Event Geo-electric field magnitude (E benchmark ) Take many years of magnetometer data and extrapolate the data to arrive at a statistical probability of a ~1:100 year event at reference location. 3-8 V/km Range at 60⁰ N 8 V/km to be conservative 47

48 Geomagnetic Latitude Scaling Sample α scaling factors for geomagnetic latitudes 1.0 at 60⁰ N Juneau; Winnipeg; Churchill Falls, NL 0.3 at 50⁰ N New York ; St Louis; Salt Lake City 0.1 at 40⁰ N Jacksonville; New Orleans; Tucson LaGrande Complex at James Bay is at ~65⁰ N geomagnetic Factors are illustrative and subject to change Geomagnetic Latitude Chart. Application for converting geographic latitude to geomagnetic latitude is available from NOAA website 48

49 Earth Conductivity Scaling Earth conductivity model factor (β) Scaling Factor: 0.81 Atlantic Coastal (CP-1) (analysis ongoing) 0.30 Columbia Plateau (CO-1) Based on data from USGS and Natural Resources Canada 49

50 Assessment Process Overview New Planning Steps GIC Calculation is now available on most power system analysis software Assemble model and equipment data Create DC model of the system Calculate GICs for each transformer Use GICs to calculate reactive losses Standard TPL Planning Run AC power flow w/ reactive losses included Identify limit violations and system issues Conduct thermal assessment of transformers Corrective Action Plan Investigate mitigation options 50

51 Thermal Assessment of Transformers Thermal limits: IEEE C57.91 (Guide for Loading Mineral-Oil- Immersed Transformers) provides temperature limits Transformer manufacturer capability curves Thermal response simulation 51

52 GICs will vary based on a number of factors geology, geography, topology, proximity to large bodies of water, etc. Assessment Results Example Mitigation strategies Op procedures Blocking devices Selective outages Protection upgrades Equip replacement New equip specs 52

53 NERC GMD Task Force Issued in 2013 GIC Application Guide o GIC Calculation GMD Planning Guide o System Impact Studies o Equipment Assessment o Mitigation and Monitoring In progress in 2014 Transformer modeling and testing 53

54 Challenges Lack of commercially available software tools and validated models for transformers and harmonics analysis Transformer heating has been a hot topic (pun intended) and we won t have a definitive answer to this issue for some time (read: years) We will attempt to address these issues at a high level in the standards Assessment criteria (how do you know if you have an issue?) Less stringent acceptance criteria than standard planning-- this is about preventing a cascade and blackout. What are the necessary criteria in analysis that will prevent a cascade and blackout? [Hint: It is not Table 1 of TPL-001] 54

55 55