COLUMBIAGRID GEOMAGNETIC DISTURBANCE DRAFT STUDY REPORT

COLUMBIAGRID GEOMAGNETIC DISTURBANCE DRAFT STUDY REPORT (NERC Standard TPL-007-1) Revision 1 February 1, 2018 ColumbiaGrid 8338 NE Alderwood Road, Suite 140 Portland, OR 97220 www.columbiagrid.org (503) 943-4940

8338 NE Alderwood Road, Suite 140 Portland, OR 97220 www.columbiagrid.org Disclaimer: The data and analyses contained in this report are not warranted by ColumbiaGrid or any other party, nor does ColumbiaGrid accept delegation of responsibility for compliance with any industry compliance or reliability requirement, including any reliability standard. Any reliance on this data or analyses is done so at the user s own risk.

Table of Contents Executive Summary 1 Introduction 2 Background 3 NERC TPL-007-1 Standard and its requirements 3 TPL-007-1, Attachment 1 5 TPL-007-2 Standard Development 6 Objective and scope of ColumbiaGrid GMD Study 7 ColumbiaGrid GMD Study 8 Data Collection Process 8 Base Case Development 8 Software 10 Study Scenarios, Assumptions and Methodology 10 Study Scenarios 10 Study Assumptions 11 Methodology 11 Technical Study Results 12 Impacts from lower voltage system modeling 12 Study results: GIC Flow Values 14

Executive Summary This draft Geomagnetic Disturbance (GMD) study report documents the scope, assumptions, and study results of the GMD technical studies that were conducted consistent with Requirements R4, R5, and R6 of the NERC TPL -007-1 standard. The study scope was determined by representatives from ColumbiaGrid members, ColumbiaGrid staff and interested parties. Three scenarios covering On-Peak and Off- Peak load conditions within the near-term transmission planning horizon were developed and evaluated for potential Geomagnetically- Induced Current (GIC) impacts. These scenarios represented 2019 Heavy Winter, 2019 Heavy Summer and 2019 Light Spring conditions. During the course of developing the study cases, ColumbiaGrid utilized GMD data from the Western Electricity Coordination Council (WECC) as the starting point. However, since this data was a product of WECC s first effort to collect GMD data, a number of data errors were found and corrected by ColumbiaGrid staff as part of the data review process prior to conducting the study. In addition, more detailed GMD data that was provided by ColumbiaGrid members was incorporated into the cases to improve the quality of the data. As described in the TPL-007-1 standard, the study was conducted using the reference peak geoelectric field value of 8 V/km as the starting point. Two scaling factors (the Geomagnetic Field and Geoelectric Field Scaling Factors) were applied to reflect the impacts from the geomagnetic latitude and ground conductivity at the physical location of each facility. Overall, after incorporating these two scaling factors in the calculation, the peak geoelectric field of transmission facilities in the Pacific Northwest region is generally less than 30% of the reference peak value. The study results identified two transformers with the GIC flow values exceeding 75 Amps in all three scenarios. 75 Amps is the threshold in Requirement R6 of the TPL-007-1 standard for identifying transmission facilities that need to be further assessed for thermal impact by Transmission and Generator Owners. These transformers are the Bell and Hot Spring 500/230 kv transformers. The Hot Springs 500/230 kv transformer showed GIC flows of 118A in the 2019 Heavy Winter, 87A in the 2019 Heavy Summer and 86A in the 2019 Light Spring. The Bell 500/230 kv transformer showed GIC flows of 78A in the 2019 Heavy Winter, 78A in the 2019 Heavy Summer and 78A in the 2019 Light Spring cases. All of these values were peak GIC values when geoelectric field orientation yields the highest GIC values. For the next steps, ColumbiaGrid will continue to track the development of the TPL-007-2 standard and work with its members to determine the scope of any future work based on additional standard requirements. Currently, it is anticipated that this new standard will be finalized in 2018. 1

Introduction Space weather has historically demonstrated the potential to effect the reliable operation of the Bulk-Power System. During a geomagnetic disturbance (GMD) event, Geomagnetically- Induced Current (GIC) flow in transformers may cause half-cycle saturation, which can increase absorption of reactive power, generate harmonic currents, and cause transformer hot spot heating that could shorten the lifespan or damage the equipment. Increased transformer reactive power demand and harmonic currents associated with GMD events can also cause potential reliability issues to the power grid including protection system misoperations and loss of reactive power sources. System performance issues caused by individual or a combination of these potential impacts could result in voltage instability and possible voltage collapse. NERC standard TPL-007-1 contains seven requirements designated R1 through R7. At the request of its members, ColumbiaGrid has completed a GMD Study to support its members compliance with parts of Requirements R4, R5 and R6 of this standard. This report provides a detailed summary of the ColumbiaGrid GMD study including the background of related studies, development of GIC study cases, study assumptions and methodology, and results of its transformer GIC flow assessment from three study scenarios. The North American Electric Reliability Corporation s (NERC) TPL-007-1 standard was created with the intention of establishing requirements for transmission system planned performance during GMD events. The standard applies to any transmission facilities that include power transformer(s) with a high side, wyegrounded winding with a terminal voltage greater than 200 kv. This includes all such facilities within a Planning Coordinator or Transmission Planner s planning area as well as Transmission or Generator Owners that own facilities meeting these criteria. 2

Background This section provides a summary of the TPL-007-1 standard, basic principles of GMD assessment, and an overview of the upcoming TPL-007-2 standard. NERC TPL-007-1 STANDARD AND ITS REQUIREMENTS The NERC TPL-007-1 standard is intended to establish requirements for transmission system planned performance during GMD events. The standard applies to any transmission facilities that include power transformer(s) with a high side, wye-grounded winding with a terminal voltage greater than 200 kv. This includes all such facilities within a Planning Coordinator or Transmission Planner s planning area as well as Transmission or Generator Owners that own facilities meeting these criteria. Standard TPL-007-1 contains seven requirements designated R1 through R7 as summarized below. The requirements that are addressed within the scope of ColumbiaGrid s study are shown in bold. Requirements R1 and R2 require the responsible functional entities to establish responsibility for maintaining GIC system models and performing the studies needed to complete GMD Vulnerability Assessments. Requirement R3 mandates that each responsible entity shall have criteria for acceptable system steady state voltage performance for its system during the benchmark GMD event. Requirement R4 states that responsible entities must complete a GMD Vulnerability Assessment of the near-term transmission planning horizon at least once every 60 calendar months. These studies must include both on-peak and off-peak load conditions and be conducted based on the benchmark GMD event described in Attachment 1 of the standard. The goal of the vulnerability assessment is to determine whether the system meets the performance requirements shown in Table 1. In Requirement R5, responsible entities must provide GIC flow information to each transmission owner or generator owner that owns an applicable BES power transformer in the planning area. The GIC flow information will provide the maximum effective GIC value for the worst case geoelectric field orientation for the benchmark GMD event described in Attachment 1. Requirement R6 requires transmission or generator owners to conduct a thermal impact assessment for BES power transformers where the maximum effective GIC values 3

Standard TPL-007-1 Table 1: Transmission System Planned Performance for Geomagnetic Disturbance Events provided in Requirement R5, Part 5.1, is 75 A per phase or greater. Finally, in Requirement R7, if a responsible entity concludes that, through the GMD Vulnerability Assessment conducted in Requirement R4, their system does not meet the performance requirements of Table 1, they shall develop a Corrective Action Plan to address identified system performance deficiencies and any actions necessary to achieve the required system performance. The effective date of standard TPL-007-1 was July 1, 2017. Implementation of the seven requirements are phased-in over the next 54 months with full compliance required by January 1, 2022. For example, requirement R1 s compliance date was July 1, 2017 with the next compliance date for R2 at July 1, 2018. In addition, the screening assessment of transformer GIC flows for the planning region (R5) has a completion date of January 1, 2019. Any transformer thermal impact assessments required under R6 must be completed by January 1, 2021. The remaining standard requirements have a phased-in implementation date of January 1, 2022. 4

TPL-007-1, ATTACHMENT 1 Attachment 1 of the TPL-007-1 standard provides fundamental technical background information for GMD assessments. This section focuses on the methodology to determine the maximum field strength as described in Attachment 1. In order to obtain the maximum effective GIC value for the worst case geoelectric field orientation required in R5, Part 5.1, the TPL-007 standard requires transformer GIC flow information to be evaluated through the application of a benchmark GMD event as described in Attachment 1 of TPL-007-1. The benchmark GMD event defines the geoelectric field values used to compute GIC flows that are needed to conduct a GMD Vulnerability Assessment. The geoelectric field value at each study area in the system varies due to the impacts from several major elements as shown below. A reference peak geoelectric field amplitude. Currently, the standard suggests a peak value of 8 V/km derived from statistical analysis of historical magnetometer data to be used as the starting point; Scaling factors to account for local geomagnetic latitude; Scaling factors to account for local earth conductivity; and A reference geomagnetic field time series or waveshape to facilitate timedomain analysis of GMD impact on equipment. The benchmark GMD event is defined for geomagnetic latitude of 60 o and it must be scaled to account for regional differences based on geomagnetic latitude. In order to address this issue, the geomagnetic latitude scaling factor α correlates the peak geoelectric field of the benchmark event to the geomagnetic latitude of the transmission facilities in the study area. The scaling factor α is computed with the empirical expression: α = 0.001e (0.115L) Where L is the geomagnetic latitude in degrees. In addition, the benchmark GMD event is defined for the reference Quebec earth model described in TPL-007-1, Table 4. The earth conductivity scalar for each location in the study can be determined by applying the earth conductivity factor (β) from TPL-007-1, Table 3 to reflect the impacts from ground conductivity corresponding to the regions shown in Figure 1 or Figure 2. The regional geoelectric field peak amplitude used in the GMD Vulnerability Assessment, E peak, can be obtained from the reference geoelectric field value of 8 V/km using the following relationship: E peak = 8 X (α) X (β) (V/km) 5

TPL-007-2 STANDARD DEVELOPMENT On September 22, 2016, FERC issued Order No. 830 approving Reliability Standard TPL-007-1 - Transmission System Planned Performance for Geomagnetic Disturbance Events. In the order, FERC also directed NERC to develop certain modifications to the Standard, or to develop other new or revised Standards. The revisions include: Modify the benchmark GMD event definition used for GMD Vulnerability Assessments; Make related modifications to requirements pertaining to transformer thermal impact assessments; Require collection of GMD-related data; and Require deadlines for Corrective Action Plans (CAPs) and GMD mitigation actions. Attachment 1 of the TPL-007-1 standard FERC established a deadline of 18 months from the effective date of Order No. 830 for completing the revisions, which is May 2018. In response to FERC s directives, the proposed TPL-007-2 standard includes requirements for entities to perform two types of GMD Vulnerability Assessments to evaluate the potential impacts of GMD events on the Bulk Electric System (BES). The benchmark GMD Vulnerability Assessment is based on the benchmark GMD event associated with TPL-007-1 which was approved by the Federal Energy Regulatory Commission (FERC) in Order No. 830 in September 2016. The benchmark GMD event is derived from spatially-averaged geoelectric field values to address potential wide-area effects that could be caused by a severe 1-in-100 year GMD event. The supplemental GMD Vulnerability Assessment, based on the supplemental GMD event will be used by entities to evaluate localized enhancements of the geomagnetic field during a severe GMD event that could potentially affect the reliable operation of the BES. The purpose of the supplemental GMD event is to assess system performance during a GMD event which includes a local enhancement of the geomagnetic field. In addition to varying with time, geomagnetic fields can be spatially non-uniform with higher and lower strengths across a region. This spatial non-uniformity has been observed in a number of GMD events, so localized enhancement of field strength above the average value must be considered. The supplemental GMD event defines the geomagnetic and geoelectric field values to be used for computing GIC flows for a supplemental GMD Vulnerability Assessment. 6

The proposed TPL007-2 standard also includes requirements for responsible entities to: Implement a process to obtain GIC flow data from at least one GIC monitor located in the planning area. Implement a process to obtain geomagnetic field data for the planning area. Objective and Scope of ColumbiaGrid GMD Study screening assessment with a maximum effective GIC value of 75A per phase or greater. Requirement R6 mandates that each responsible entity shall conduct a thermal impact assessment for any transformers that meet or exceed the 75A screening threshold. ColumbiaGrid staff consulted with its Members and Planning Participants during regularly scheduled planning meetings in 2017 to determine the scope of ColumbiaGrid s GMD study. ColumbiaGrid reached agreement with its members by consensus to: The objective of the ColumbiaGrid GMD study is to support its members compliance with parts of Requirements R4, R5 and R6 of the TPL-007 standard. This effort included: Development of GIC study base cases meeting the requirements of R4, Part 4.1 Develop three GIC study cases in PowerWorld (PW) format and, Use the PW Simulator with the GIC add on tool to compute transformer GIC values for all applicable Bulk Electric System (BES) power transformers in the Northwest region. Determination of the maximum effective GIC values at the worst case geoelectric field orientation for the benchmark GMD event per Requirement R5, Part 5.1. This system screening assessment for transformer GIC flows was completed for all applicable BES power transformers in the Northwest planning region. The ColumbiaGrid GMD study identified any BES power transformers in the previous Requirement R5, Part 5.1 7

ColumbiaGrid GMD Study This section describes the background and assumptions of GMD study that was conducted by ColumbiaGrid in conjunction with its members. It includes details of the data collection process, base case development, software and tools that were used in the study, study assumptions and methodology, and the study results. Data Collection Process In order to build study base cases which include a GIC system model, ColumbiaGrid obtained the Western Electricity Coordinating Council (WECC) Master GIC data for the entire western interconnection to use as a starting point. This data was contained in an Excel spreadsheet with separate tabs for: Substations Latitude/longitude coordinates and grounding resistance Transformers Winding configurations, winding resistances, core type, autotransformer Buses Power flow bus/substation associations Lines DC Resistance (ohms per phase) In section 4.2.1 of the TPL-007-1 standard, the stated applicability is for facilities that include power transformers with a high side, wyegrounded winding with terminal voltage greater than 200 kv. Consequently, some entities did not include data for substation and transmission facilities below 200 kv in their GIC system models. For this study, ColumbiaGrid incorporated additional more detailed GIC system model data provided by its members into the GIC study cases it developed. This data consisted primarily of additional latitude and longitude coordinates for lower voltage buses (<200 kv). This enabled ColumbiaGrid to develop GIC system model information to add substation data for over 400 existing buses in the Puget Sound area at voltages below 200 kv. Base Case Development Under Requirement R4 of the TPL-007 Standard, Each responsible entity, as determined in Requirement R1, shall complete a benchmark GMD Vulnerability Assessment of the Near-Term Transmission Planning Horizon at least once every 60 calendar months. Part 4.1 of this requirement states that the study shall include at least one system on-peak load condition and one off-peak load condition within the near-term transmission planning horizon. Shunts Shunt reactor winding connection type and DC resistance (ohms per phase) In order to be compliant with the requirements under R4, Part 4.1.1 and 4.1.2, ColumbiaGrid developed 3 GIC study cases based on the 8

2019 Light Spring, 2019 Heavy Summer and 2019 Heavy Winter system assessment cases that were developed for its 2017 study program. This meets the requirement to include at least one system on-peak load condition and one offpeak load condition within the near-term transmission planning horizon. After importing the WECC Master GIC data into these power flow base cases, ColumbiaGrid performed several data validation checks to verify the integrity and accuracy of the GIC system model. Numerous errors were found and corrected before the study was conducted. Below are some examples of these issues: Incorrect bus/substation associations: Some substations were mapped to the wrong buses. This resulted in errors of the study results due to inaccurate locations. Incorrect latitude/longitude coordinates: This also results in errors due to inaccurate scaling factors and line lengths being applied. Other issues also include instances where the WECC Master GIC data did not match up with corresponding power flow model data. This resulted in a significant amount of the WECC Master GIC data being imported to the power flow cases either incorrectly or not at all. ColumbiaGrid staff manually corrected all of the data issues that were identified through its data validation checks for the northwest planning region plus some of the Idaho and Montana regions that are adjacent to the northwest. This included correcting all instances of erroneous bus/substation associations and latitude/ longitude coordinates as well as adding transformer GIC data which was not imported due to circuit ID mismatches or bus configuration differences. Correcting data errors for other western interconnection planning regions outside the northwest was considered beyond the scope of this study. Therefore, GIC flow analysis in this study was only conducted for the corrected northwest regional GIC model. In section 4.2.1 of the TPL-007-1, the stated applicability of this standard is for facilities that include power transformers with a high side, wye -grounded winding with terminal voltage greater than 200 kv. As a result, some entities did not include data for substation and transmission facilities below 200 kv in their GIC system models. ColumbiaGrid requested and received additional GIC system model information from its members including latitude and longitude coordinates for most of Puget Sound Energy s lower voltage (< 200 kv) BES buses. This enabled ColumbiaGrid to develop GIC model information to add substation data for over 400 existing buses in the Puget Sound area at voltages below 200 kv. ColumbiaGrid incorporated this more detailed GIC system model into all three of the GIC study cases it developed. 9

Preliminary versions of the ColumbiaGrid GIC study base cases were posted for members review and comment in December 2017. Software PowerWorld Simulator version 19 with the GIC add on tool was used to perform the steady state powerflow studies to determine transformer GIC flow information resulting from the benchmark GMD events. Microsoft Excel was used to perform post-processing of the results and to format the results. Study Scenarios, Assumptions and Methodology Requirement R5 of the TPL-007-1 Standard mandates that Each responsible entity, as determined in Requirement R1, shall provide GIC flow information to be used for the benchmark thermal impact assessment of transformers specified in Requirement R6 to each Transmission Owner and Generator Owner that owns an applicable Bulk Electric System power transformer in the planning area. Part 5.1 requires that the GIC flow information include the maximum effective GIC value for the worst case geoelectric field orientation for the benchmark GMD event described in Attachment 1 of the TPL-007 Standard. Requirement R6 states that Transmission Owners and Generator Owners must conduct a thermal impact assessment for BES power transformers where the maximum effective GIC value provided in Requirement R5, Part 5.1, is 75A per phase or greater. In order to support its members compliance with these requirements, ColumbiaGrid conducted a screening assessment of all applicable Northwest region BES transformers to identify any transformers with potential maximum perphase effective GIC values of 75A or greater. ColumbiaGrid conducted this assessment using the GIC add on tool in PowerWorld Simulator. STUDY SCENARIOS ColumbiaGrid s GMD study focused on the assessment of GIC flows for applicable BES transformers in the Near-Term Transmission Planning Horizon. It utilizes system models and GIC System models that were developed by ColumbiaGrid members and other utilities as part of WECC-wide GMD data development process. The following base cases were used to simulate potential impacts from GMD events in the relevant areas: 1) 2019 Heavy Summer: This base case represents an on-peak load condition within the Near-Term planning horizon when electricity demand in the Pacific Northwest region is very high. 2) 2019 Heavy Winter: This base case also represents an on-peak condition within the Near-Term planning horizon during the winter season when the highest electricity demand in the Pacific Northwest region usually occurs. 10

3) 2019 Light Spring: This base case represents an off-peak load condition within the Near-Term planning horizon. STUDY ASSUMPTIONS Transformer GIC flow information was evaluated for the benchmark GMD event described in Attachment 1 (Calculating Geoelectric Fields for the Benchmark GMD Event) of the TPL-007-1 Standard. Below are the key assumptions of this study: The benchmark GMD event is defined for a geomagnetic latitude of 60 o with a reference peak geoelectric field amplitude of 8 V/km derived from statistical analysis of historical magnetometer data. The benchmark GMD event is also defined for the reference Quebec earth model described in TPL-007-1, Table 4. To account for local differences based on geomagnetic latitude, the Geomagnetic Field Scaling Factors 1 which correlates the peak geoelectric field of the benchmark event to the geomagnetic latitude of the transmission facilities in the study area were used. In general, for the focused study area in this study which encompasses the Pacific Northwest region, the scaling factors that are associated with geomagnetic latitudes between 48-54.5 degrees (values between 0.25-0.53) were used. To account for earth conductivity in the study area, the Geoelectric Field Scaling Factors 2 which capture the impacts from local earth conductivity for each transformer and its connected transmission facilities. For the focused study area in this study, the scaling factors that area associated with the physiographic regions PB-1, PB-2, CS-1, CO -1 and RM were used. For study areas that cover more than one geomagnetic latitude scaling factor or multiple earth conductivity models, the assessment was based on a peak local geoelectric field amplitude scaled from the reference peak by using a methodology to calculate induced voltages in transmission lines through interpolation along the line path. METHODOLOGY Requirement R5, Part 5.1 requires that the maximum effective GIC values for the worst case geoelectric field orientation for the benchmark GMD event must be determined for all applicable BES power transformers in the planning area. The GIC flow assessment showed that there were more than 300 applicable BES transformers in the northwest region with peak calculated GIC values greater than 1A in at least one of the GIC study cases. In order to document the peak calculated GIC values for applicable BES transformers, ColumbiaGrid calculated the peak effective GIC values for all northwest transformers at various geoelectric field orientations ranging from zero to 165 degrees in 15 degree increments for all three 1 The values of Geomagnetic Field Scaling Factors from Equation (2) in Attachment 1 of TPL-007-1 were used 2 The values of Geoelectric Field Scaling Factors from Table 3 in Attachment 1 of TPL-007-1 were used

GIC study cases. The transformer GIC flow values are documented in spreadsheet format with the peak calculated GIC values for each transformer shown at various geoelectric field orientations on each tab. The maximum losses direction (peak GIC value) calculated by Simulator is also shown for every transformer. Similar spreadsheets were created for each of the three GIC study cases. While this methodology does not quite give the peak GIC value at the exact worst case geoelectric field orientation for each individual transformer, the resulting GIC values are within less than 1% of the GIC values for the worst case geoelectric field orientation which is within the accuracy range of the GIC system model contained in the GMD study base cases. The computation of the worst case geoelectric field orientation in Simulator is based on the latitude and longitude coordinates of the interconnected substations in the model. Since Simulator only knows the geographic locations of the substations where the lines terminate, it is not able to calculate GIC flows based on the actual real-world geographic orientation of the transmission lines connecting the substations. This may not make too much difference for short lines, but the difference could be significant for longer lines. Add to that all the assumptions that go into the calculations plus the auto-generated GIC data that Simulator inserts in place of missing GIC system data and it is not hard to see that the tool can only really provide a rough estimation of possible GIC flows. Technical Study Results The study results summarize the peak GIC flow values (for the maximum losses direction of the geoelectric field) of all applicable transformers in the northwest region. The findings include transformers with GIC values of more than 75 Amps are shown in this section. IMPACTS FROM LOWER VOLTAGE SYSTEM MODELING The purpose of this task was to determine how much the GIC flow values could potentially be impacted by including lower voltage facilities in the GIC system model. For this part of the study, GIC flow values were calculated for applicable transformers before and after adding in the more detailed GIC model information for substation facilities below 200 kv in the 2019 Heavy Summer case. The enhanced GIC model primarily centered around the addition of approximately 400 lower voltage substations in the Puget Sound area. The study results shown in Tables 1 and 2 indicate that the addition of a more detailed GIC model of the system can have a significant effect on the amount of GIC flow in transformers. The study results also showed that, although the more detailed model resulted in significantly more GIC flow for a number of transformers in the Puget Sound area, the increase was not significant enough for any of the transformer GIC flows to exceed the 75A screening threshold specified in TPL-007-1, Requirement R6. 12

Table 1: Comparison of GIC from the case with and without lower voltage system modeling at 15 degree field orientation Table 2: Comparison of GIC from the case with and without lower voltage system modeling at 97 degree field orientation 13

Based on these results, ColumbiaGrid decided to include the more detailed GIC model in all three of the study cases it developed. The GIC flow results from these three cases are showed in the next section. STUDY RESULTS: GIC FLOW VALUES As shown in Table 3, out of over 900 transformers that are located in the study area, there were two applicable transformers identified to have maximum effective GIC values which could potentially exceed 75A for the benchmark GMD event. The Hot Springs 500/230 kv transformer showed GIC flows of 118A in the 2019 Heavy Winter, 87A in the 2019 Heavy Summer and 86A in the 2019 Light Spring. The Bell 500/230 kv transformer showed GIC flows of 78A in the 2019 Heavy Winter, 78A in the 2019 Heavy Summer and 78A in the 2019 Light Spring cases. Since the GIC flows for these two transformers potentially exceed the 75A threshold specified in Requirement R6, a thermal impact assessment must be conducted for these transformers. This thermal impact assessment must be completed within 24 calendar months of receiving GIC flow information specified in Requirement R5, Part 5.1. The thermal impact assessment shall include a description of suggested actions and supporting analysis to mitigate the potential impacts of GICs if necessary. Detailed results of the GIC flow values for all applicable BES transformers in the northwest region have been documented in spreadsheets. Examples of these spreadsheets are shown in Appendix A. These tables were formatted with the calculated GIC flow values for each transformer shown at various geoelectric field orientations on each tab. The maximum losses direction (peak GIC value) calculated by Simulator is also shown for every transformer. Similar spreadsheets were created for each of the three GIC study cases. GIC Values 2019 Heavy Winter 2019 Heavy Summer 2019 Light Spring Bell 500/230 kv 78.1 A 77.9 A 77.9 A Hot Springs 500/230 kv 117.6 A 86.5 A 85.5 A Table 3: Peak GIC flows from the study 3 3 Peak transformer GIC values for the worst case geoelectric field orientation resulting from the benchmark GMD event

Table 4: GIC flow values for geoelectric field orientation of 95 degrees It should be noted that each transformer s maximum effective GIC flow value is based on a different geoelectric field orientation (maximum losses direction) based on the topology of transmission facilities connected to the substation that each particular transformer is located in. To find a transformer s maximum effective GIC flow value, the maximum losses direction (degrees) for that transformer should be noted from the spreadsheet and then the spreadsheet tab closest to that value selected. Table 4 above shows an example of this methodology for the Hot Springs 500/230 kv and Bell 500/230 kv transformers. 15