ee4503 electrical systems design
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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EE4503Electrical Systems Design
Grounding
1
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Topics
• Introduction to Grounding
• Grounding of Electrical Systems
• Grounding Systems
• Grounding Resistant
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Grounding
3
• Grounding or Earthing
• Make the potential difference become the same as ground/earth.
• For human safety and equipment safety
• Follow NEC Article 250
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GroundingCategory
4
• 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
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GroundingComponents
5
• Grounding Electrode (System)
• Grounding Electrode Conductor
• Grounded Conductor
• Main Bonding Jumper
• Equipment Grounding Conductor
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GroundingComponents
6
Electrical Systems Design: ประสทิธิ ์พทิยพฒัน์
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GroundingComponents
7
http://cr4.globalspec.com/thread/40145/Grounded-Neutral
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GroundingCommon Grounding Systems
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• System Grounding
• Service Equipment Grounding
• Separately Derived System
• Equipment Grounding
• Computer Grounding
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GroundingAC System Grounding
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“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
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GroundingAC System Grounding – 50V
10
• 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
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GroundingAC System Grounding – 50 to 1kV
11
• Usually at the distributed transformer
• Neutral is grounded
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GroundingAC System Grounding – Electrode
12
• Grounding Electrode Conductor
• Connected to three parts– Grounded Conductor: usually neutral line
– Equipment Grounding Conductor
– Main Bonding Jumper
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GroundingAC System Grounding – Electrode
13
• Cable: continuous copper cable with insulator
• Installation: connect to a surface, recommend conduit
• EMC: metal component needed to be connect to ground
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GroundingAC System Grounding – Electrode
14
• 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
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GroundingAC System Grounding – Exothermic Welding
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http://www.youtube.com/watch?v=CqixbTQG13M
AllTec Corp Exothermic Weld.flv
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GroundingAC System Grounding – Cable Size
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http://www.kroo-suchat.com/File_data/ground.pdf
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GroundingAC System Grounding – Cable Size
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http://irrigation.rid.go.th/rid17/Myweb/machanical/type%20lamp.html
Meter(A) MCB (A)
Cable Sizing (sq.mm.)
Voltage (V)
Incoming Cable in Air (Grounding)
Incoming Cable in Conduit (Grounding)
5 (15) 1 16 4 (10) 4,10**(10) 30015 (45) 1 50 10 (10) 16 (10) 300
30 (100) 1 100 25 (10) 50 (16) 30050 (150) 1 125 35 (10) 70 (25) 30015 (45) 3 50 10 (10) 16 (10) 750
30 (100) 3 100 25 (10) 50 (16) 75050 (150) 3 125 35 (10) 70 (25) 750
200 3 250 95 (25) 150 (35) 750400 3 500 240 (50) 500 (70) 750
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GroundingService Equipment Grounding
18
• 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”
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GroundingSeparately Derived System
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• 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
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GroundingEquipment Grounding
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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
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GroundingEquipment Grounding – What to be grounded?
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• 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)
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22
• 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
GroundingEquipment Grounding – What to be grounded?
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23
• Continuity
• Low Impedance
• High Ampacity
GroundingEquipment Grounding – Effective Grounding
• Copper: with or without insulator
• Busware: that specified for grounding
• Metal Armor of some cables: AC, MI, MC
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GroundingEquipment Grounding – Effective Grounding
http://www.iaei.org/magazine/2006/09/new-form-of-mc-cable-crosses-application-boundaries/
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GroundingEquipment Grounding – Sizing
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• 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
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GroundingEquipment Grounding – Sizing
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Rated Circuit Breaker or Overload Protector(A)
Ground Cable Size (mm2)
16 1.5 (recommended 2.5)20 2.540 470 6
100 10200 16400 25500 35
Electrical Systems Design: ประสทิธิ ์พทิยพฒัน์
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GroundingComputer Grounding
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• 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
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Grounding Electrode SystemEarth
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• 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
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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
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Grounding Electrode SystemGround Rod
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• Copper rod with at least 16mm in diameter and 2.4 m in length
• Few longer rods are better than many short rods
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Earthing Scheme
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• 2,3 or 4 characters
• 1st: relation between distribution system and earth
– T means single point connecting to earth
– I means isolated from earth
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Earthing Scheme
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• 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)
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Earthing Scheme
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• 3rd(if any): arrangement of neutral (N) and protective conductor (PE)– S means separation between N & PE
– C means common between N & PE
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Type of Earthing SystemIT
34
http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf
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Type of Earthing SystemTT
35
http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf
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Type of Earthing SystemTN-C
36
http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf
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Type of Earthing SystemTN-S
37
http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf
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Type of Earthing SystemTN-C-S
38
http://www.electrical-installation.org/enw/images/5/5e/EIG_chap_E-2010_1.pdf
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Resistance to Ground
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• By E.I.T. standard 5 Ohm
• Some area, authority might allow up to 25 Ohm
• If cannot achieve, try adding extra electode
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• Electrical Systems Design: ประสทิธิ ์พทิยพฒัน์
Reference
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