Mitsubishi Electric Power Products Inc. and Duquesne Light Co.

Transcription

1 Mitsubishi Electric Power Products Inc. and Duquesne Light Co. Overview on Geomagnetically Induced Current Revision #00 March 2017 Presented by: Elizabeth Cook (DLC) and Wesley Terek (MEPPI)

2 Overview on Geomagnetically Induced Current Background Why is Geomagnetically Induced Current Important? The Astrophysics Understanding the Cause of GIC: Geomagnetic Disturbance Phenomena The Geophysics Translating CMEs to GICs The Engineering Problem Calculating GIC Flow through the EHV System Quantifying the Impact of GIC Flows Asymmetrical Transformer Saturation Reactive Power Losses and Steady State Voltage Stability Transformer Thermal Heating Harmonic Distortion

3 Background Why is Geomagnetically Induced Current Important? 3

4 NERC Order 779 Ref:TPL Technical Conference, July 17, 2014 NERC

5 NERC EOP-10-1

6 NERC TPL Ref:TPL Technical Conference, July 17, 2014 NERC

7 The Astrophysics Understanding the Cause of GIC Geomagnetic Disturbance Phenomena 7

8 Coronal Mass Ejections (CME) Geomagnetic Disturbances are driven by Coronal Mass Ejections, which are masses of energized particles expelled from the sun and traveling towards earth. The earth directed mass of particles distort the earth s magnetosphere and ionosphere (the magnetosphere s inner edge), creating the geomagnetic disturbance on earth. CME originate from sunspots, which are area s of intense magnetic activity on the sun s surface. CME velocity varies (transit time to earth typically ranges between 14 and 96 hours) and there is limited correlation between it and GIC. Ref: 2012 Special Reliability Assessment, Interim Report: Effects of Geomagnetic Disturbances on the Bulk Power System, NERC 8

9 Sunspot Correlation Current Solar Cycle is falling short of predictions. However, the prediction of solar activity is still beyond our present capabilities and the Sun s activity is quite random when considering sub Solar Cycle (11 year) time frame. The big event could occur at any point in time. Source: 9

10 NOAA Space Weather Scales All historically significant storms are G5 level. Transit (warning) time in hours to days timeframe. Correlated to GMD/GIC events. Source: 10

11 March 12, 2012 Coronal Mass Ejection NASA SOHO Satellite Imagery Source: 11

12 March 12, 2012 Coronal Mass Ejection NASA Goddard integrated SPACE WEATHER ANALYSIS SYSTEM Forecast Source: 12

13 March 11, 2015 Coronal Mass Ejection Source:

14 March 11, 2015 Coronal Mass Ejection Source:

15 DLC Weather Emergencies Plan

16 PJM Emergency Message Sent Reports

17 The Geophysics Translating CMEs to GICs 17

18 How db/dt translates to E Disturbances to the Earth s magnetic field (db/dt) produce ionospheric currents, referred to as electrojet currents. The ionospheric currents produced couple with the Earth s resistive grounding structure and circulate through all low-resistance man-made conductive paths tied to earth ground (transmission lines and pipe lines). Source: 2012 Special Reliability Assessment, Interim Report: Effects of Geomagnetic Disturbances on the Bulk Power System, NERC 18

19 E is the Key Component for Calculating GIC From a power engineering perspective, the electric field (E) on the Earth s surface is the key parameter for calculating geomagnetically induced currents. When calculating GIC the changing magnetic field db/dt) can be ignored, provided that reasonable assumptions are made for E. Most commercially available software utilizes E for GIC calculations. Prediction Theoretical maximums (worst case scenarios) can be developed with historical data. Calculated with a GIC Model db/dt E GIC Monitoring Measured using magnetometers Extrapolated using magnetometer data Measured using neutral current monitoring 19

20 Simplification of Maxwell s Equations Mathematically, E can be calculated by simplifying Maxwell s Equations. Using the Complex Image Method (CIM), which assumes that currents equal to the induced ionosphere currents are superimposed on the earth, and an adequate ground conductivity model. The calculation is further simplified by using frequency domain analysis. Maxwell s Equations CIM Ground Conductivity Structure (ohm m) Change in Earth s Magnetic Field with Respect to Time (nt or Vs/m 2 ) Electric Field (V/m) Vacuum Permeability (Vs/Am) Ref: Geomagnetically Induced Currents as Ground Effects of Space Weather, 2012, R. Pirjola 20

21 USGS 1-D Ground Conductivity Regions Source: 21

22 Example USGS 1-D Ground Resistivity Model Source: 22

23 Important Notes on Ground Models Ground modeling is an important part in determining E for a given system area. The low frequency and the corresponding deep skin depth of the ground induced currents requires detailed earth conductivity models that extend to depths of several hundred kilometers. The success of present geophysical research and the validity of the present State of the Art GIC modeling techniques are greatly dependent on the accuracy of the ground conductivity models being used. The USGS has just recently completed a 1-D Ground Conductivity survey of the continental United States. This data is now incorporated into NERC Draft Standard TPL There is a concern that 1-D ground modeling is insufficient and that even more detailed 3-D ground modeling may be necessary. A second concern not well addressed with the USGS 1-D models is the costal boundary effect. Measurement data is suggesting that land bordering highly conductivity bodies of salt water is subject to more intense electrojet current induction and hence higher E. 23

24 Geomagnetic Latitudes Magnetic north pole presently tilted over northern Canada. In general GMDs pose a greater risk for North America Source: 24

25 E Field Variations with Respect to Latitude Worst case is generally at lat. > 50 and < 50 Approximate Mean Recent work suggests the Equatorial Electrojet Intensification is a the cause and indicates this is a valid measurement, meaning high GIC could be seen at southern latitudes. Source: Generation of 100-year Geomagnetically induced Current Scenarios A. Pulkkinen et al. 25

26 Statistically Determined NERC TPL /100 Year Event E Field Magnitude Linearized Tails are the indicators for Extreme Value Statistics Max Error 3 8 V/km Ref:TPL Technical Conference, July 17, 2014 NERC 26

27 Using the Benchmark GMD Event from TPL Statistically determined upper bound for the 1/100 year event (8 V/km) Scaling factor for regional earth conductivity Scaling factor for location (latitude) Source: NERC TPL

28 Spatial Averaging of the Benchmark Event Ref: Benchmark Geomagnetic Disturbance Event Description, May 12, 2016 NERC

29 Sample Short Term Storm Profile Storm E Field Peak Max Intensity ~ 2 minutes E V/km Rotation Phase (Deg)

30 Sample Long Term Storm Profile Moderate Intensity ~ 7 Hours E V/km Direction Constantly Changing Phase (Deg)