critical facilityyg grounding - bicsi – common groundcommon ground – importance /...

Download Critical Facilityyg Grounding - BICSI  – Common GroundCommon Ground – Importance / PyramidImportance / Pyramid – Grounding Resistance – Defined – Site Specific Design – Achieving 5 Ohms?

Post on 13-Mar-2018

212 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • Critical Facility Groundingy g

    XIT GROUNDINGXIT GROUNDING

  • Agenda

    Common Ground Importance / PyramidCommon Ground Importance / Pyramid

    Grounding Resistance Defined

    Site Specific Design Achieving 5 Ohms?

    Electrode Choices Pros / Cons

    Ground System Testing Why 95% is Invalid

  • Why Ground?

    Equipment Protectionq p

    Satisfy Warranty Requirements

    Service Protection

    System Performance

    Personnel Safety (NEC)

  • Electrical Protection Systems

    Protection Pyramid

    Surge C ll t

    RFCollectorsAC Surge

    Telco / Data

    LightningGroundingGrounding

    Surge Dissipater

  • Typical Performance Reqs

    National Electrical Code (NEC) < 25 OHMS a o a ec ca Code ( C) 5 O S

    IEEE Standard 142 Equipment D d t

    Practical Safeguarding of..

    Dependent IEEE Standard 1100 < 5 OHMS

    Motorola Standard R-56 < 10 OHMS

    Verizon Wireless 8501 < 5 OHMS

    Typical Telecom Switch < 2 OHMSTypical Telecom Switch 2 OHMS

  • Ground System Resistance

    Defined!!Ground System Resistance?

    Finite Resistance between the Ground System and Remote EarthGround System and Remote Earth

  • Ground System Resistance

    What Two Factors Determine Ground System Resistance??

    Soil Resistivity ( P )

    Size of the Grounding System ( A )

  • Ground System Resistance

    How Are They Related? The Relationship

    R P / A

    y p/ Simple Formula

    R = P / AR = Ground System ResistanceR = Ground System Resistance

    P = Soil ResistivityP Soil ResistivityA = Effective Cross Sectional

    Area of The Ground System

  • Ground System Resistance

    With Only Two Elements, Why is

    P

    y yResistance Difficult to Design/Predict?

    P - Varies with Depth/Location Of SoilOf Soil

    A - Determined by Size / ConfigurationOf The Grounding System

  • T fTypes ofGrounding ElectrodesGrounding Electrodes

  • Types of Grounding Systems

    Driven Rods Ground Enhancement Materials

    Copper Platespp Chemical Wells Ufer GroundsUfer Grounds Building Steel

    Ground Ring Ground Ring Water Pipes

    XIT El t l ti S t XIT Electrolytic Systems++

  • S il R i i iSoil ResistivityTestingTesting

    (Determining P)

  • Soil Resistivity Testing

    4-Pt. WENNER METHOD

    R=E/I

    METHOD

    4-Pole Digital

    R=E/Ig

    Ground Tester

    Voltage Drop

  • = 1 915 ARSoil Resistivity Testing

    5 52 00 497 90

    = 1.915 ARProbe Spacing Meter Reading Resistivity

    5 52.00 497.90

    10 19.68 370.87

    15 10 16 292 0015 10.16 292.00

    20 6.53 250.10

    30 4.30 247.04

    40 10.80 827.28

    60 7.40 850.26

    80 5.58 855.60

    100 4.44 850.26

  • Soil Resistivity Testing

    Site Area

    Direction of Test

  • Grounding System Design

    Grounding Calculationsg

  • Grounding System Design

    The Simple Formula:

    R = P / Ap

    R = Ground System Resistance P = Soil ResistivityA = Effective Cross Sectional

    Area of The Ground SystemArea of The Ground System

  • Grounding System Design

    The Simple Formula:

    R = P / Ap

    R Is Known (Required Ohms, 5?)P P Is Known (Soil Resistivity)P & R A U d T D t i A

    A P / R P & R Are Used To Determine A

    A = P / R

  • Grounding System Design

    Design Alternatives?

    NomographIEEE T bl

    g

    IEEE Table Software Programs

  • Grounding System Design

    Properly Designed System Benefits? Predictable Results

    p y g y

    Improved Personnel Safety

    Improved Equipment ReliabilityImproved Equipment Reliability

    Improved Equipment Performance

    Improved Power Quality

    Meet Mfgs Warranty RequirementsMeet Mfg s Warranty Requirements

  • Grounding System Resistance Testing

  • Ground System Testing

    Why Test Grounds?y

    Determine Baseline

    Confirm Design Spec Validate Construction

    Satisfied Satisfy Warranty Reqs Ensure Equip Protection & Performance

  • Ground System Testing

    Two Test Methods

    Fall Of Potential Test - Inserting Current / Measuring Voltage

    Clamp-On Test - Inducing Voltage / Measuring Current

  • Fall of Potential Test

    Advantageg Recognized As Accurate Most Commonly Utilized (IEEE Std 81)

    DisadvantagesR lt F tl I lid (75 %)X

    (95+%)

    y ( )

    Results are Frequently Invalid (75+%)X Requires Isolated Ground System Requires Large Area

    Time Consuming Access To Soil

  • Fall of Potential Test

    Required Equipment

    3 / 4 Pole TesterAEMC / Megger

    q q p

    AEMC / Megger

    Test Kit Probes

    Conductor Conductor Tape Measure

  • Fall of Potential Test

    3 Pole MeterCurrent Flow

    R=E/I

    Voltage

    RemoteCurrentEl t d

    Drop

    Earth

    Neutral Electrode

  • Fall of Potential Test

    195

    155165 175

    G d R i t (Pl t )

    185 195

    Resistance

    115125 135 145 155 Ground Resistance (Plateau)

    7585 95

    105 115

    Voltage Probe Spacing (%)

    55 65 75

    0 10 20 30 40 50 60 70 80 90 100

  • Fall of Potential Test

    You are testing every

    d i

    Neutral Connected

    Currentground in parallel.

    Connected

  • Fall Of Potential TestNeutral Connected

    Ohms

    Neutral Connected

    Invalid

    Test With Neutral Connected20

    Test GraphPlot For

    5 Oh G dPlot For

    25 Oh G dPlot For

    100 Oh G dPlot For

    1000 Oh G d

    15

    5 Ohm Ground25 Ohm Ground100 Ohm Ground1000 Ohm Ground

    5

    10

    Distance (Ground-Probe)

  • Clamp-On Resistance Test

    Advantages Quick and Easy

    No Disconnecting Neutral No Disconnecting Neutral

    No Long Leads, Property

    Disadvantage Ground Configuration Ground Configuration

    Finding Proper Location To Test

    Invalid Most Of The Time

  • Clamp-On Resistance Test

    ??? ohms 2 Control Xformers

    R = E / IR = E / I 2 Control Xformers

    One Induces 4 mvOne Induces .4 mv

    One Measures Current Flow

    Current Flow

  • Clamp-On Resistance Test

    Neutral-Ground

    Utility Neutral LineParallel Paths

    Bond

    Grounding G ou d gConductor

    Series Loop

    ???Current Flow R = E/I???Current Flow R = E/I

  • Clamp-On Resistance Test

    Neutral-Ground

    Utility Neutral LineInvalid Ground

    Bond

    Grounding

    Clamp-On Test

    Grounding Conductor

    Additional Grounding Conductor

    ???R = E/I

    Current Flow

    ???R = E/I

  • Clamp-On Resistance Test

    Main Reasons For Invalid Testingg

    Fall Of Potential Test - Must Isolate Ground from Neutral

    Clamp-On Test - Must have Single Point Ground

  • Ground Resistance Testing

    Contributing Reasons For Invalid Testing

    Grounding / Testing Not Taught

    g g

    IEEE G id / P d W k

    Not Many Good Courses Available

    IEEE Guidance / Procedures Weak

    Mfgs Procedures Weak / WrongMfg s Procedures Weak / Wrong

    Old Habits / Bad Assumptions / Pressure

  • Ground Resistance Testing

    How To Improve Testing Results? Insist On Training

    p g

    Dont Insist On Results

    Test Prior To Connecting Power

    Design Facility For Testing

    Dont Depend On Mfgs Procedures

    Test Prior To Connecting Power

    p g

  • Lyncole XIT GroundingPhone 1-800-962-2610

    Fax 1-310-214-1114Fax 1-310-214-1114www.Lyncole.com

    S @Support@Lyncole.com