Geomagnetically Induced Currents and Magnetometer ProjectNovember 2, 2016

Nick Marquardt & Darnez GreshamMidAmerican Energy Company

• MidAmerican Energy has installed GIC monitors and a magnetometer through the EPRI Sunburst program to study the induced magnetic fields that drive these currents.

• Iowa State and USGS researchers, under EPRC, will study the relationship between observed magnetic field changes and GIC to refine the one-dimensional earth conductivity model.

• Refinement of the one-dimensional model will allow more accurate prediction of the effects of solar storms, stopgap until 3D modeling is available.

Introduction

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• Geomagnetic Disturbances (GMD) are caused by solar flares and Coronal Mass Ejections (CMEs), commonly referred to as space weather.

• Severe geomagnetic events have potential to cause electrical system damage or grid voltage collapse.

Background

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TPL-007-1: Transmission Planned Performance for Geomagnetic Disturbance Events

• Maintain System models and GIC System models of the responsible entity’s planning area to be used to complete a GMD Vulnerability assessment

• Provide GIC flow (GIC(t)) to TO and GO to be used for the transformer thermal impact assessment specified in the standard

• Develop criteria for acceptable System steady state voltage performance during the benchmark GMD event

• Develop a Corrective Action Plan as needed to address how the performance requirements will be met.

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TPL-007-1 Implementation Plan

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TPL-007-1: Future NERC Activites

FERC directs NERC to develop changes:

• modify the benchmark GMD event so that it is not based solely on spatially-average data

• develop a GMD research work plan to further analyze spatial averaging, earth conductivity models, thermal impact assessments

• modify the standard to require the collection of GIC monitoring and magnetometer data and make such data publicly available

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• GMD manifests on the electrical system in the form of quasi-DC currents on transformers, referred to as Geomagnetically Induced Current (GIC).

• Magnitude of induced current depends on strength of the induced electric field. This depends on:– Rate of change of magnetic field.– Resistance of lines and power transformer cores.– Distance between grounded locations.– The conductivity of the earth between two grounded locations.

• One-dimensional GIC modeling uses scaling factors based on geomagnetic latitude and ground conductivity to correlate magnetic field changes from GMD with current.

GIC on the system

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• Various equipment in substations is bonded to grounding grids including transformers, structures, conduits.

Electrical System Grounding

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• Substation ground rods extend ~15 feet underground, around the perimeter of the conductive grid system.

• Grounding resistance depends on local soil conditions as well as grid design. (See ANSI/IEEE Std. 80-1986)

Electrical System Grounding

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• EPRI Sunburst is a network of GIC-measuring nodes. MidAmerican has two such nodes installed.

• Node at Oak Grove (south of Quad Cities) is DoE-funded; other DoE funded nodes in the Midwest are WAPA Sioux City node and KCPL LaCygne node.

EPRI Sunburst Program

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EPRI Sunburst Program

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• Overland Trail monitor installation

EPRI Sunburst Program

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• A magnetometer (actually variometer) was installed through the EPRI Sunburst project in order to better understand correlation between magnetic field changes ( ) and observed currents.

• Installation was completed in Fall, 2015 near the Oak Grove Substation in Milan, Illinois. This substation is also the site of a Sunburst Program GIC node.

• Variometer installation was partially funded by US Department of Energy, and MidAmerican is working with Iowa State University to analyze data..

Variometer Project

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• Oak Grove Variometer Site (completed)– the node interface is identical to the Sunburst node.

Variometer Project

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• GIC module, licensed from Siemens. Part of PSSE– MidAmerican uses PSSE to run planning-level power flow studies.– GIC module uses 1-D model to calculate current flows.– Latest version can use NERC benchmark event storm strength to produce

effective GIC flows to insert directly into the GIC Time Series.

• Data not normally needed for power flow is contained in a special GIC file to be read by PSSE– Buses up to 2 away from MidAmerican– Ground grid resistance, latitude-longitude, etc.– Some already available, some had to be found or calculated.

• Module uses Python, and latest version can produce results exported into Excel.

Modeling GIC

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One-Dimensional Earth Model

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• Why a one-dimensional model?– It’s what we have available today.– Our existing tools (i.e., PSSE) use it.– It’s simple and quick to use for calculations

• Three-dimensional model is superior, but...– The tools to calculate GIC using a 3-D model aren’t

available.– The 3-D model itself is still in development.

One-Dimensional Earth Model

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Conductivity regions of the lower 48 United States – from the NERC TPL-007-1 standard documentation.

• Analysis of variometer data will allow MidAmerican and other utilities to replace old conductivity data with a new model that has a finer granularity.

• This is a stop-gap until modeling tools are able to use 3-D earth models.

• EPRC research will look into the correlation between magnetic field fluctuations and observed GIC measurements.

• Methods used to verify and refine model parameters will benefit entire electric utility industry.

Data Analysis

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• MidAmerican has installed a variometer to measure geomagnetic field variations along with induced currents in transformers.

• Refinement of the geomagnetic model will allow more accurate modeling of the effects of GMD.– EPRC project will refine the 1-D model significantly enough that it can be

used until there is a viable alternative.

Summary

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Questions?Nick Marquardt

Engineer II, Electric System Planning(563) 333-8509 – NPMarquardt@midamerican.com

Darnez GreshamSenior Engineer, Compliance and Standards

(563) 333-8633 – DJGresham@midamerican.com

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