Review of Substation Grounding Practices, Safety and Constructability Enhancements. Authors: V. SIMHA, X.WU, M.THAKUR

Transcription

1 Review of Substation Grounding Practices, Safety and Constructability Enhancements Authors: V. SIMHA, X.WU, M.THAKUR

2 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:

3 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:

4 Substation Grounding Practices Category Description IEEE AEP DESIGN METHODS Calculation Method Uses hand calculation, utilizing equations to calculate an actual value of a touch potential and a step potential at one point on top of the surface (not the entire surface area). The threshold values for the touch and step potentials are also handcalculated for comparison. Soil Model, Resistivity and Thickness Uses uniform soil model with one resistivity value. Fault Clearing time A single fault clearing time is considered in the hand calculation. Split factor calculation Utilizes pre-determined split factor curves (that may not be applicable to a specific station) to determine the grid current and shield/neutral wire currents. Grid shape and spacing Analysis is limited to a square or rectangular grid shape, and equal grid spacing. Buried objects GPR impact on buried objects cannot be analysed. Transfer Potential Provides minimum guidance on transfer potential impact on a neighbor s fence, and recommends the insulation of a fence extending outside the substation area. Use computer algorithms to accurately simulate the site conditions, power system configurations, power system operations, and prevailing or forecasted fault currents with clearing times and determine the actual potentials throughout the surface, then compares them to threshold. Uses multi-layer soil model. Accounts for the prevailing resistivity and thickness of each soil layer. Segmented clearing times for multiple fault current magnitudes can be analysed. Calculates the split factor with the prevalent and pertinent conditions to a specific station site (where the ground grid is being designed). Can analyse all grid shapes and sizes, with no limitation on grid spacing. Can analyse buried objects, such as pipelines, above ground hydrants, or telecom interface boxes. Can determine transfer potential impact on a neighbor s fence, along with mitigation that identifies a non-metallic fence location and length that would mitigate the transfer potential from the substation fence.

5 Grounding Concepts - GPR and Touch Potential Touch potential illustration when a ground fault energizes the ground grid

6 Grounding Concepts - GPR and Touch Potential Touch potential illustration when a ground fault energizes the fence/structure

7 Structure, Equipment, and Fence grounds

8 AEP Innovative Grounding Study Methods Single Injection method fault current distribution

9 AEP Innovative Grounding Study Methods Multiple Injections method fault current distribution

10 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:

11 Traditional Approach, and Challenges Exothermic Weld and Safety Incidents

12 Traditional Approach, and Challenges Challenging site installation (top), quality comparison welded versus swage (right)

13 Welding process, and safety Traditional Approach, and Challenges Weld quality and consistency issues Challenges in wet conditions over 200 wet days in OH. Safety incidents Increasing number of projects A standardized approach

14 Grounding Application and Installation Typical Swage connectors - for 4 / 0 (left), for ground rod (right)

15 Grounding Application and Installation 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. Head Assembly (left), Gauge (right)

16 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.

17 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:

18 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.

19 Grounding Grid Integrity Testing Ground grid integrity testing set-up Grounding plan drawing Test Lead Red Test Lead Black Test Current Amps Resistance mω Reactance mω Main Gate CB-G Main Gate South Fence Main Gate New Control House Main Gate Southeast Fence Ground grid integrity test data

20 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:

21 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.

22 Bibliography [1] IEEE , 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 /15/, IEEE PES General Meeting in Denver, CO in July [3] CDEGS Software Package, Safe Engineering Services & technologies ltd., link: [4] ASPEN Software, Advanced Systems for Power Engineering, Inc., link: [5] BURNDY Exothermic Grounding, link: [6] DMC Power Swage Ground Connectors, link: dmcpower.com/connectors/groundconnectors.

23 Questions?

24 Thank you!