Review of Substation Grounding Practices, Safety and Constructability Enhancements

Authors: V. SIMHA, X.WU, M.THAKUR

Agenda

Grounding Study and Analysis:• Substation Grounding Practices• Grounding Concepts – GPR and Touch Potential• AEP Innovative Grounding Study Methods

Grounding Installation:• Traditional Approach and Challenges• Grounding Application and Installation• Change Management

Testing:• Grounding Integrity Testing

Conclusion and Future Vision:

Agenda

Grounding Study and Analysis:• Substation Grounding Practices• Grounding Concepts – GPR and Touch Potential• AEP Innovative Grounding Study Methods

Grounding Installation:• Traditional Approach and Challenges• Grounding Application and Installation• Change Management

Testing:• Grounding Integrity Testing

Conclusion and Future Vision:

Substation Grounding Practices

Category Description IEEE 80 - 2013 AEP DESIGN METHODS

Calculation Method Uses hand calculation, utilizingequations to calculate an actual valueof a touch potential and a steppotential at one point on top of thesurface (not the entire surface area).The threshold values for the touch andstep potentials are also hand-calculated for comparison.

Use computer algorithms toaccurately simulate the siteconditions, power systemconfigurations, power systemoperations, and prevailing orforecasted fault currents withclearing times – and determine theactual potentials throughout thesurface, then compares them tothreshold.

Soil Model, Resistivityand Thickness

Uses uniform soil model with oneresistivity value.

Uses multi-layer soil model.Accounts for the prevailingresistivity and thickness of eachsoil layer.

Fault Clearing time A single fault clearing time isconsidered in the hand calculation.

Segmented clearing times formultiple fault current magnitudescan be analysed.

Split factor calculation Utilizes pre-determined split factorcurves (that may not be applicable to aspecific station) to determine the gridcurrent and shield/neutral wirecurrents.

Calculates the split factor with theprevalent and pertinent conditionsto a specific station site (where theground grid is being designed).

Grid shape and spacing Analysis is limited to a square orrectangular grid shape, and equal gridspacing.

Can analyse all grid shapes andsizes, with no limitation on gridspacing.

Buried objects GPR impact on buried objects cannotbe analysed.

Can analyse buried objects, such aspipelines, above ground hydrants,or telecom interface boxes.

Transfer Potential Provides minimum guidance ontransfer potential impact on aneighbor’s fence, and recommends theinsulation of a fence extending outsidethe substation area.

Can determine transfer potentialimpact on a neighbor’s fence,along with mitigation thatidentifies a non-metallic fencelocation and length that wouldmitigate the transfer potentialfrom the substation fence.

Grounding Concepts - GPR and Touch Potential

Touch potential illustration when a ground fault energizes the ground grid

Touch potential illustration when a ground fault energizes the fence/structure

Grounding Concepts - GPR and Touch Potential

Structure, Equipment, and Fence grounds

AEP Innovative Grounding Study Methods

Single Injection method fault current distribution

AEP Innovative Grounding Study Methods

Multiple Injections method fault current distribution

Agenda

Grounding Study and Analysis:• Substation Grounding Practices• Grounding Concepts – GPR and Touch Potential• AEP Innovative Grounding Study Methods

Grounding Installation:• Traditional Approach and Challenges• Grounding Application and Installation• Change Management

Testing:• Grounding Integrity Testing

Conclusion and Future Vision:

Exothermic Weld and Safety Incidents

Traditional Approach, and Challenges

Challenging site installation (top), quality comparison – welded versus swage (right)

Traditional Approach, and Challenges

Traditional Approach, and Challenges

• Welding process, and safety• Weld quality and consistency issues• Challenges in wet conditions – over 200 wet

days in OH.• Safety incidents• Increasing number of projects• A standardized approach

Grounding Application and Installation

Typical Swage connectors - for 4 / 0 (left), for ground rod (right)

Grounding Application and Installation

Head Assembly (left), Gauge (right)

Swage is the generic term used for a cold forging process when the dimensions of the conductor and connector are altered in a tool die with equal compressive forces while making the connection.

Change Management

Why?• Focus on Safety, Constructability, Efficiency

How?• On site training and awareness• Tracking Projects• Periodic collaborative meetings• Documenting the concerns, and responses.• Determining an issue, and possible resolution.

Agenda

Grounding Study and Analysis:• Substation Grounding Practices• Grounding Concepts – GPR and Touch Potential• AEP Innovative Grounding Study Methods

Grounding Installation:• Traditional Approach and Challenges• Grounding Application and Installation• Change Management

Testing:• Grounding Integrity Testing

Conclusion and Future Vision:

Grounding Grid Integrity Testing

Corroded ground conductor Grounding integrity testing

• Impedance values compared after successive years of testing at the same location.

• Change in impedance values indicates the ground conductor health.

Grounding Grid Integrity Testing

Ground grid integrity testing set-up

Grounding plan drawing

Test LeadRed

Test LeadBlack

Test CurrentAmps

ResistancemΩ

ReactancemΩ

Main Gate CB-G 50 6.93 48.7Main Gate South Fence 50 215.1 104Main Gate New Control House 50 15.18 68.6Main Gate Southeast Fence 50 280 200

Ground grid integrity test data

Agenda

Grounding Study and Analysis:• Substation Grounding Practices• Grounding Concepts – GPR and Touch Potential• AEP Innovative Grounding Study Methods

Grounding Installation:• Traditional Approach and Challenges• Grounding Application and Installation• Change Management

Testing:• Grounding Integrity Testing

Conclusion and Future Vision:

Conclusions and Future Vision

• Recommends an optimally-designed safe ground grid that uses accurate modeling techniques, and enables possible material and labor savings – while meeting all IEEE 80 safety requirements.

• The use of a swage ground connection improves field safety, facilitates a better quality installation, improves constructability and project efficiency with time and labor savings in all-weather site conditions.

• This paper also details a ground grid integrity testing method that can be deployed to track the health of the ground grid conductors over the service lifetime.

Bibliography

[1] IEEE 80 – 2013, Guide for Safety in AC Substation Grounding. [2] X.Wu, V.Simha, R.J.Wellman, “Optimal Ground Grid Design for Large EHV Substations with Autotransformer”, Publication No. 978-1-4673-8040-9/15/, IEEE PES General Meeting in Denver, CO in July 2015.[3] CDEGS Software Package, Safe Engineering Services & technologies ltd., link: www.sestech.com/products/softpackages/cdegs.htm.[4] ASPEN Software, Advanced Systems for Power Engineering, Inc., link: www.aspeninc.com/web.[5] BURNDY Exothermic Grounding, link: www.burndy.com/solutions/grounding-superstore/exothermic-grounding.[6] DMC Power Swage Ground Connectors, link: dmcpower.com/connectors/ground-connectors.

Questions ?

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