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EE4503 Electrical Systems Design

EE4503 Electrical Systems Design. Grounding. Topics. Introduction to Grounding Grounding of Electrical Systems Grounding Systems Grounding Resistant. Grounding. Grounding or Earthing Make the potential difference become the same as ground/earth. For human safety and equipment safety

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EE4503 Electrical Systems Design

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  1. EE4503Electrical Systems Design Grounding

  2. Topics • Introduction to Grounding • Grounding of Electrical Systems • Grounding Systems • Grounding Resistant

  3. Grounding • Grounding or Earthing • Make the potential difference become the same as ground/earth. • For human safety and equipment safety • Follow NEC Article 250

  4. GroundingCategory • System Grounding: connect the “live” portion of the electrical system to ground, e.g. neutral • Equipment Grounding: connect a part (having no current) of the equipment to ground, e.g. case

  5. GroundingComponents • Grounding Electrode (System) • Grounding Electrode Conductor • Grounded Conductor • Main Bonding Jumper • Equipment Grounding Conductor

  6. GroundingComponents Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

  7. GroundingComponents http://cr4.globalspec.com/thread/40145/Grounded-Neutral

  8. GroundingCommon Grounding Systems • System Grounding • Service Equipment Grounding • Separately Derived System • Equipment Grounding • Computer Grounding

  9. GroundingAC System Grounding “live” portions of the electrical system • Protect Overvoltage: specially from lightning • Stabilize voltage level referring to ground • Be part of protection circuit: be part of the short-circuit current 50V, 50 to 1kV, more than 1kV

  10. GroundingAC System Grounding – 50V • NEC Standard • The source • is stepped down from more than 150V • is stepped down from the ungrounded system • Cable in over the ground outside the building

  11. GroundingAC System Grounding – 50 to 1kV • Usually at the distributed transformer • Neutral is grounded

  12. GroundingAC System Grounding – Electrode • Grounding Electrode Conductor • Connected to three parts • Grounded Conductor: usually neutral line • Equipment Grounding Conductor • Main Bonding Jumper

  13. GroundingAC System Grounding – Electrode • Cable: continuous copper cable with insulator • Installation: connect to a surface, recommend conduit • EMC: metal component needed to be connect to ground

  14. GroundingAC System Grounding – Electrode • Cable: continuous copper cable with insulator • Installation: connect to a surface, conduit (recommended) • EMC: metal component needed to be connect to ground • Connection: Exothermic Welding, or other recommended methods

  15. GroundingAC System Grounding – Exothermic Welding http://www.youtube.com/watch?v=CqixbTQG13M

  16. GroundingAC System Grounding – Cable Size http://www.kroo-suchat.com/File_data/ground.pdf

  17. GroundingAC System Grounding – Cable Size http://irrigation.rid.go.th/rid17/Myweb/machanical/type%20lamp.html

  18. GroundingService Equipment Grounding • Usually two points of grounding: at the transformer and at the main distribution box • “Main Bonding Jumper” connects the metal part of the main distribution box to ground • “Main Bonding Jumper” (now) connects to the grounded conductor • Same calculation as “System Grounding”

  19. GroundingSeparately Derived System • Electrical systems that are separated inside the facility (after the utility): e.g. from utility and generator • Common Neutral: grounded only at the main distribution box • Isolated Neutral: grounded separately and have the isolated ground rod

  20. GroundingEquipment Grounding Grounding for the “non-live” metal portion • The enclosure has the same potential level as the ground (protected for human contact) • Improve short-circuit protection: conductor touching enclosure • Path for the leakage current

  21. GroundingEquipment Grounding – What to be grounded? • Metal enclosure & Protected Fence: metal conduit, panelboard enclosure, electric crane, elevator’s enclosure • Protected fence: HV station • Electrical Appliance specially with outlet: more than 150V, except having proper insulator (e.g. double insulator)

  22. GroundingEquipment Grounding – What to be grounded? • Fixed Equipment with hard wires specially able to be touched • Close contact to human: grounded within 2.4m from ground and 1.5m from wall • Electrical contact to metal • Wet area

  23. GroundingEquipment Grounding – Effective Grounding • Copper: with or without insulator • Busware: that specified for grounding • Metal Armor of some cables: AC, MI, MC • Continuity • Low Impedance • High Ampacity

  24. GroundingEquipment Grounding – Effective Grounding http://www.iaei.org/magazine/2006/09/new-form-of-mc-cable-crosses-application-boundaries/

  25. GroundingEquipment Grounding – Sizing • Tables (if common ground cable, take maximum one) • In general: according to rating of CB • For motor: according to the rating of overload protection. http://www.cable.alcan.com/NR/rdonlyres/19FC4111-742D-47B7-9A28-06DF8AB4023D/0/EquipmentGroundingConductor.pdf

  26. GroundingEquipment Grounding – Sizing Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

  27. GroundingComputer Grounding • Power Distribution Grounding • Single Ground Point to protect “Ground Loop” • High Frequency Grounding • in the order of kHz or MHz • 60cm x 60cm conductor grid Recommend common ground electrode

  28. Grounding Electrode SystemEarth • Refered as 0 • Deeper in the ground (more humidity)  lower resistance • Good for make the reference voltage as 0 • ** not capable enough to conduct high current

  29. Grounding Electrode SystemElectrode Existing Electrode • Underground metal pipes • Building structures • Pile • Under ground metal structures Made Electrode • Ground Rods • Concrete Encased Electrode • Buried Plate • Ring • Grid

  30. Grounding Electrode SystemGround Rod • Copper rod with at least 16mm in diameter and 2.4 m in length • Few longer rods are better than many short rods

  31. Earthing Scheme • 2,3 or 4 characters • 1st: relation between distribution system and earth • T means single point connecting to earth • I means isolated from earth

  32. Earthing Scheme • 2nd: relation exposed conductive part and earth • T means no connection to the electrical system • N means there is a connection between the exposed conductive and electrical system (neutral)

  33. Earthing Scheme • 3rd(if any): arrangement of neutral (N) and protective conductor(PE) • S means separation between N & PE • C means common between N & PE

  34. Type of Earthing SystemIT http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

  35. Type of Earthing SystemTT http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

  36. Type of Earthing SystemTN-C http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

  37. Type of Earthing SystemTN-S http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

  38. Type of Earthing SystemTN-C-S http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf

  39. Resistance to Ground • By E.I.T. standard 5 Ohm • Some area, authority might allow up to 25 Ohm • If cannot achieve, try adding extra electode

  40. Reference • Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

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