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Fundamentals of Grounding - Erico Seminar

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Fundamentals of Grounding - Erico Seminar

  1. 1. Fundamentals of Grounding and Bonding Terry Klimchak Revised 11/19/13
  2. 2. ERICO has met the standards and requirements of the Registered Continuing Education Providers Program. Credit earned on completion of this program will be reported to RCEPP. A certificate of completion will be issued to each participant. As such, it does not include content that may be deemed or construed to be an approval or endorsement by NCEES or RCEPP.”
  3. 3. Copyrighted Materials This educational activity is protected by copyright laws. Reproduction, distribution, display and use of the educational activity without written permission of the presenting sponsor is prohibited. Copyright ERICO International Corporation, 2013
  4. 4. Learning Objectives At the end of this presentation you will be able to: • Discuss the basics of electrical grounding and bonding. • Discuss electrical engineering principles and relevant specifications. • Discuss the basic design criteria for grounding systems. • Understand and learn how to limit STEP AND TOUCH potentials • Observe and describe exothermic welded grounding connections 4
  5. 5. Outline • Basic Electricity and Materials • Utility Grounding • C & I – Residential Grounding • Telecommunications Systems Considerations 5
  6. 6. Relevant Standards for Utility Grounding • IEEE Std 80: Guide for Safety in AC Substation Grounding • IEEE Std 837: Standard for Qualifying Permanent Connections Used on Substation Grounding • IEEE Std 142: Grounding of Industrial and Commercial Power Systems • IEEE Std 81: Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System • IEEE 1246: Guide for Temporary Protective Grounding Systems used in Substations • IEEE 1268: Guide for Safe Installation of Mobile Substation Equipment • IEEE C2: National Electrical Safety Code (NESC) 6•IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  7. 7. Purpose of System Grounding 7 IEEE 142 - 2007 1.3 Purposes of system grounding: System grounding is the intentional connection to ground of a phase or neutral conductor for the purpose of: a) Controlling the voltage with respect to earth, or ground, within predictable limits, and b) Providing for a flow of current that will allow detection of an unwanted connection between system conductors and ground. Such detection may then initiate operation of automatic devices to remove the source of voltage from these conductors. •IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  8. 8. Purpose of Grounding • Limit potential difference of neutral for system stability • Allow for operation of relays and system protections devices • Personnel safety This is different from most grounding presentations; if you do the first two, you will get safety for free. 8
  9. 9. Grounding (IEEE 100) • Definition: “A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the Earth, or to some conducting body of relatively large extent that serves in place of the Earth.” • Purpose: Used for establishing and maintaining the potential of the Earth (or other conducting body) or approximately that potential, on conductors connected to it, and for conducting ground current to and from the Earth (or other conducting body). 9•IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  10. 10. Bonding (IEEE 100) • Definition: “The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.” • Conclusion: A Grounding System Is Made up of Both Grounding and Bonding Elements. 10•IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  11. 11. First: Some Basic Electrical Theory Resistivity is the intrinsic property of a material to impede the flow of electrical current. It is the resistance factored by the length and cross sectional area. It is also referred to as volume resistivity. 11 l RA =ρ m m m Ω= Ω = 2 ρ A l R
  12. 12. Volume Resistivity of Materials 12 10-8 10-2 104 1012 102 All in mΩ Metals Soils Wood Insulators
  13. 13. Soil Resistivity Loam Clay Sand & Gravel Surface Limestone Shale Sandstone Granites, Basalt Slates 1 to 50 ohm-m 20 to 100 ohm-m 50 to 1000 ohm-m 100 to 10,000 ohm-m 5 to 100 ohm-m 20 to 2000 ohm-m 10,000 ohm-m 10 to 100 ohm-m 13
  14. 14. Impedance Impedance is the sum (and much more complex mathematical operations) of a circuit resistance elements and the REACTANCE which is caused by inductors and capacitive elements in the circuit. IT IS AFFECTED BY FREQUENCY f in Hz. Transients or faults in electrical systems look like very high frequency events, not 60 hz. ωLXL = ωC XC 1 = fπω 2= Inductive Reactance Capacitive Reactance 14
  15. 15. Electrical Systems – Transients • CLOSED ELECTRICAL SYSTEM: • Generators, Transformers, and Utilization devices • Use the earth as a reference for system stability • The EARTH IS NOT a destination of currents • The System Neutral is the destination for currents • Earth is sometimes a conductor during transients • NON SYSTEM TRANSIENTS: • Lightning is a Non System Transient • The EARTH IS a destination for currents and they are large magnitude currents. 15
  16. 16. Utility Electrical Systems • GENERATION – Transforms mechanical energy to electricity P = 1,300MW @ 30 kV • TRANSMISSION – P = V x I – Losses are proportional to I so V is increased, I is decreased for efficient transmission. V >130kV • DISTRIBUTION – Requires lower voltage for practical handling of components. Substations transform voltage to 15-25kV and then to 480 or 240/120V 16
  17. 17. 17 1,000 MW 30 kV XFMR 500 kV GENERATION TRANSMISSION DISTRIBUTION 500 kV XFMR 15-25 kV SUBSTATION 15-25 kV 25 kV XFMR 480V 3Φ 25 kV XFMR 240/120V 1Φ
  18. 18. Typical Utility System 18
  19. 19. Utility Grounding Summary • Establish Reference to Earth – Allows for Protection devices to operate – Keeps metallic and structures at the potential of the earth • Creates Equipotential Plane – Significantly reduces risk of step and touch potential • Provides Low Impedance Path – Especially for SYSTEM and NON SYSTEM transients 19
  20. 20. Purpose of Grounding • Establish a reference for the system by intentionally connecting the neutral to the earth • Limit potential difference of neutral for system stability • Allow for operation of relays and system protections devices • Personnel safety – Establish an equipotential plane 20
  21. 21. AC Three Phase 21 3 PHASE VOLTAGE -1.5 -1 -0.5 0 0.5 1 1.5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 Angle (/10) Phase A Phase B Phase C Ground System Reference
  22. 22. Utility Substation Grounding Substations have high fault currents and potential for voltages caused by that current. Fault Currents > 50kA 22 RIV ∗= SAFETY: At 50-60 Hz 60-100mA can cause ventricular fibrillation. Threshold voltage can be as low as 50 V.
  23. 23. Typical Substation Grounding • 4/0 Cu buried at 18” • 10-20’ grid, welded • Ground Rods every 20’ typical. • Extremely low R • Meets the requirements of IEEE Standard 80 23 Typ
  24. 24. • Provides a Molecular Bond Between Conductors – Current Carrying Capacity Equal to that of the Conductor – Permanent - Cannot Loosen or Corrode to Cause a High-Resistance Connection – Requires No External Source of Power or Heat – Can be Visually Checked for Quality 24 Exothermic Welding for Connections
  25. 25. C & I Grounding • Generally C & I and Residential grounding methods establish a good earth reference • Also grounding elements provide a path for fault currents • All metal parts associated with the electrical system shall be connected to the ground reference for safety (equipotental plane). 25
  26. 26. NEC 250 Definition of Grounding • Intentional permanent low impedance path to carry fault current • Capacity to carry ground fault current • Returns fault current to source, not earth • Is connected to earth for system reference • Used to allow operation of protection devices 26
  27. 27. C & I and Residential System Grounding Elements • Grounded Conductor - Neutral • Grounded Electrode – Several • Grounding Electrode Conductor (GEC) • Service Bonding Jumper • Equipment Grounding Conductor 27
  28. 28. Solidly Grounded 3 Phase Electrical System Other Grounding Electrodes & Bonds 28
  29. 29. NEW – MUST Be Bonded into GEC System 29
  30. 30. Grounding Electrode Sizing • Most Grounding Electrode Conductors are sized to 250.66 as they exist downstream of the service disconnection device. • Ground Rods only require a #6 - this GEC ISN’T intended to carry fault current!
  31. 31. Main Bonding Jumper Neutral – Grounded Conductor Equipment Grounding Conductors Typical Grounding Connections in Small Main Service Panel 31
  32. 32. Difference between Neutral (Grounded) and Grounding Conductor 32
  33. 33. NEC 250 Resistance Requirement • Section 250.53 requires < 25 Ω resistance for pipe, rod or plate electrodes OR • Add another electrode > 6’ away from the first, WITHOUT FURTHER MEASUREMENT       = d l l RO 4 ln 2π ρ rodofResistance=OR 33 Using this formula for resistance (from MIL Handbook 419) diameterRod=d lengthrod=l yResistivitVolumeSoil=ρ Source : http://www.mikeholt.com/newsletters.php?action=display&letterID=407 A ¾” by 10’ in 500 Ω M soil would have a resistance of over 160 Ω
  34. 34. Practical Ground Resistance • Most rods have much less than 160 Ω • Typical rod resistances will be less than 25 Ω in most soils because of the existence of proximate utility ground references. Low ground resistance (< 10 Ω ) can be achieved with – Multiple Rods bonded together – Counterpoise system – Coupled rods – Conductive Enhancement Materials – Chemical Rods 34
  35. 35. Beware of False Claims 35 UL 467 Bend Test Results Galvanized Rod
  36. 36. Copper Electroplated Rod 36 UL 467 Bend Test Results - Cu Electroplated Rod
  37. 37. Bonding • 2011 NEC® Article 250.94 – Intersystem Bonding Termination • Interconnecting of all Ground Electrode Systems – Electrical Power Grounding System – Lightning Grounding System – Telecommunications Grounding System – Cable TV Grounding System • Connect all conductive objects together both internal and external to the facility • Provides near zero voltage difference during ground potential rise 37
  38. 38. Intersystem Bonding Termination 38
  39. 39. Other Grounding and Bonding Applications • Signal Reference Grids • Grounding Bus Bars • Equipotential Mesh • Rebar Clamps • Swimming Pool Grounding • Wind Turbine Grounding 39
  40. 40. SRG for Low Impedance Ground • Stops noise from interfering with low voltage digital signals. • Provides a lower impedance ground reference than signal conductors and shields. • Minimizes voltage potential difference between interconnected equipment. 40
  41. 41. SRG Impedance vs. Freq 41
  42. 42. Signal Reference Grids & Sensitive Electronics Grounding 42
  43. 43. • Applications: – Reduce step & touch potential – Signal Reference Grid – Antenna ground screen – Electronic shielding • Configuration: – Wire: #6 to #12 - 30 %CW, 40% CW, Cu – Mesh size: 2” x 2” up to 48” x 24” – 20’ maximum width - 500 lb maximum weight – Wire overhang for field splicing using PG style connection. 43 Prefabricated Wire Mesh
  44. 44. EIA/TIA Ground Bars and Ground Plates 44
  45. 45. TGB and TMGB Grounding Bus Bars 45
  46. 46. Main Elements of Telecom Grounding and Bonding Equipment • Bonding Conductor for Telecommunications • Telecom Main Grounding Busbar (TMGB) ----------------------------------------------------- • Telecomm Bonding Backbone (TBB) • Telecomm Grounding Busbar (TGB) • Telecomm Bonding Backbone Interconnecting 46
  47. 47. Bonding Conductor for Telecommunications 47 Bonding conductor for telecommunications Equipment Telecommunications Entrance Facility Electrical Entrance Facility TMGB Grounding Electrode Conductor Service Equipment N G TBB Outside the scope of this Standard Within the scope of this Standard
  48. 48. 48
  49. 49. Grounding and Bonding Summary • Discussed basic electricity • Understand resistivity • Should know why utilities ground their systems • Should know elements of commercial, industrial, & residential grounding • Should know elements of telecom bonding and grounding 49
  50. 50. Thank you for your time! This concludes the educational content of this activity www.erico.com

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