IEEE Std 81 Tutorial Handouts

Tutorial IEEE Standard 81TM – 2012 IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System IEEE POWER & ENERGY SOCIETY 2014 Annual Substation Committee Meeting Portland, Oregon, USA May 18, 2014

Photo Courtesy of E&S Grounding Solutions (Permission Pending)

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THE INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS, Inc.

Substations Technical Committee Annual Meeting Portland, Oregon, USA May 18-22, 2014 May 18, 2014

IEEE PES Std 81-2012 Tutorial

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IEEE Standard 81TM – 2012 IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System IEEE POWER & ENERGY SOCIETY 2014 Annual Substation Committee Meeting Portland, Oregon, USA May 18, 2014


Presented by • Bryan Beske, PE • Cars on on Day, PE • Dennis Dennis DeCo DeCosta sta,, PE • Lane Lane Garret Garrettt • Jeff Jowett • Carl Carl Mol Moller ler • Steve Palmer • Sashi Patel • Will Sheh • George Vl Vlachos

May 18, 2014

American Transmission Co. NEE TR TRAC/Georgia Tec h Common Commonwea wealth lth Associa Associates tes,, Inc. Inc. Common Commonwea wealth lth Associa Associates tes,, Inc. Inc. Megger CANA ANA High High Volt Voltag agee Safearth Consulting NEETRAC/Georgia Tech TectoWeld Inc. AEMC In Instruments


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THE INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS, Inc.

Substations Technical Committee Annual Meeting Portland, Oregon, USA May 18-22, 2014 May 18, 2014


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IEEE Standard 81TM – 2012 IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System IEEE POWER & ENERGY SOCIETY 2014 Annual Substation Committee Meeting Portland, Oregon, USA May 18, 2014


Presented by • Bryan Beske, PE • Cars on on Day, PE • Dennis Dennis DeCo DeCosta sta,, PE • Lane Lane Garret Garrettt • Jeff Jowett • Carl Carl Mol Moller ler • Steve Palmer • Sashi Patel • Will Sheh • George Vl Vlachos

May 18, 2014

American Transmission Co. NEE TR TRAC/Georgia Tec h Common Commonwea wealth lth Associa Associates tes,, Inc. Inc. Common Commonwea wealth lth Associa Associates tes,, Inc. Inc. Megger CANA ANA High High Volt Voltag agee Safearth Consulting NEETRAC/Georgia Tech TectoWeld Inc. AEMC In Instruments


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Will Sheh Tectoweld, Inc.

May 18, 2014


PRESENTER TUTORIAL OBJECTIVE What we want you to take away from this tutorial: 1.

Understand the basic principles of measuring the electrical characteristics of grounding systems

2. Learn the basic methods of measuring earth resistivity, power frequency impedance to remote earth, step and touch voltages, and verifying the integrity of the grounding system 3. Identify various conditions and instrument limitations that can distort test measurements 4. Recognize that a lethal voltage can exist during testing and implement appropriate safety precautions

May 18, 2014


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AUDIENCE TUTORIAL OBJECTIVE Why are you here today? & What do we want you to take away from this tutorial?: 1. Professional development hours for PE License. 2. Introduce inexperienced engineers/designers to practical methods for ground testing. 3. Provide experienced engineers/designers with an enhanced knowledge of test methods and techniques used for measuring the electrical characteristics of grounding systems.

May 18, 2014


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%$TUTORIAL OUTLINE 1. Introduction 1.1 Test objectives & key key definitions 1.2 Safet Safety y considerati considerations ons 1.3 Understanding the circuit being tested 1.4 Typical problems problems encountered during testing

Wi W ill Sheh George George Vlachos Vlachos & Jeff Jowett Jowett George George Vlachos Vlachos & Jeff Jowett Jowett Ca Carl Moller

2. Test methods 2.1 Earth resisti resistivity vity Break 2.2 Groun Ground d Impedance Impedance 2.3 Earth potentials and step step & touch potentials Lunch 2.4 Ground integrity integrity testing testing 2.5 Surfa Surface ce aggregate aggregate testing testing

Sh Shashi Patel Ca Carl Moller 12:00 pm Ca C arson Day Br Bryan Beske

3. Test simulations 3.1 Part 1 Break 3.2 Part 2 3. Questions and answers

La Lane Garrett

8:45 am 9:45 am 10:00 am 11:00 am 1:00 am 1:30 pm

St S teve Palmer

2:00 pm 3:30 pm 3:45 pm 5:00 pm

St S teve Palmer

5:30 pm

4. Adjourn

May 18, 2014

8:00 am 8:10 am am 8:20 am am 8:30 am

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QUESTIONS AND ANSWERS

Image Courtesy of Ground Level Systems, LLC (Permission Pending)

May 18, 2014


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%$INTRODUCTION

Test Objectives 1. Earth resistivity measurements 1.1 Estimate the ground impedance of a grounding system 1.2 Estimate potential gradients including step & touch voltages 1.3 Compute inductive coupling to nearby power & communication cables, pipelines and other metallic objects 1.4 Design cathodic protection systems 2. Impedance and potential gradient measurements 2.1 Verify the adequacy of the new grounding system 2.2 Detect changes in an existing grounding system 2.3 Identify hazardous step and touch voltages 2.4 Determine the ground potential rise (GPR)

May 18, 2014


1

INTRODUCTION

Key Definitions Coupling: The association of two or more circuits or systems in such a way that power or signal information is transferred from one to another. Ground electrode: A conductor embedded in the earth and used for collecting ground current from or dissipating ground current into the earth. Ground grid: A system of interconne cted ground electrodes arranged in a pattern over a specified area and buried below the surface of the earth. Ground impedance: The vector sum of resistance and reactance between a ground electrode, grid or system and remote earth. Remote earth: A theoretical concept that refers to a ground electrode of zero impedance placed an infinite distance away from the ground under test. Remote earth is normally assumed to be at zero potential. Soil (earth) resistivity: A measure of how much a volume of soil will resist an electric current and is usually expressed in !-m.

May 18, 2014


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INTRODUCTION

Key Definitions (Continued) Ground potential rise (GPR): The maximum electrical potential that a ground electrode, grid or system might attain relative to a distant grounding point assumed to be at the potential of remote earth. Step voltage: The difference in surface potential that could be experienced by a person bridging a distance of 1 meter with the feet without contacting any grounded object. Touch voltage: The potential difference between the GPR of a grounding grid or system and the surface potential where a person could be standing while at the same time having a hand in contact with a grounded structure or object. Touch voltage measurements can include or exclude the equivalent body resistance in the measurement circuit. Transferred voltage: A special case of touch voltage where a voltage is transferred into or out of the vicinity of a ground electrode from or to a remove point external to the ground electrode.

May 18, 2014


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George Vlachos, Jeff Jowett AEMC Instruments

May 18, 2014

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Safety considerations Three Prime Safety Hazards • Lethal voltage between electrode and ground • Power-system fault during test • Step & Touch Potentials 2

Safety considerations Other Possible Hazards • Ground Potential Rise •

Can reach several thousand volts!

• Lightning Strokes (Strikes)

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%$Safety considerations • Create a test plan that includes Safety Rules • Body prevented from closing circuit between points of potential difference • Gloves and footwear • Isolate exposed leads and electrodes • Keep test signal application brief • Leads and probes kept within sight • Avoid induced voltages from overheads 4

Safety considerations Surge Arrester Testing: • Do not disconnect ground while primary remains connected to energized line! • Lightning & switching currents can exceed 50 kA. • If arrester fails during test, system fault risk.

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Safety considerations Disconnecting Neutral & Shield Wires: • Avoid coupling

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George Vlachos, Jeff Jowett AEMC Instruments

May 18, 2014

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Understanding the circuit being tested • Distinctive complexities • May need to plot multiple points • Interference from stray voltages

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Carl Moller, P.Eng, CANA High Voltage Ltd.

May 18, 2014


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Not a Simple World • Measurements always come with uncertainty • The world isn’t as simple as we’d like it to be Variability in theory vs. actual installations Trending over time -> clearer picture Once installed, grounding systems can change over time

• Noise Manifests itself in many ways Noise can come and go temporally Buried metallic structures Nearby encroachment of utilities !

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Source: CDEGS 2008 Users’ Group Meeting Conference Proceedings – “Automation and Fall of Potential Testing” by Carl Moller

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Frequency Dependency 50

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• Extend 10x diagonal of ground grid • Vary frequency • Up to 180% Error if not accounting for lead coupling • Low over High resistivity soil

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Buried metallic objects • Pipelines (Cathodic Protection systems) • Rail Lines • Foundations with rebar • Fences • Geologicalvariations • Transmission line tower grounds • Adjacent facility grounding systems • Multi-groundedneutral networks • Telephone/Cable grounds

Source image courtesy of Dr. Bill Carman: DREC2012, 'Vt is not enough

Common Pitfalls • • • •

Hiring an inexperienced contractor Not knowing what to do with the test data. Interpretation of questionable results Dealing with variability in expected measurements • Forgetting to accurately record measurements or locations • Not understanding the test circuit 11

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%$TEST METHODS Earth resistivity Lane Garrett Commonwealth Associates • • • •

General: Safety, Circuit, Problems, Environmental How to perform/basic principles: Wenner, Schlumberger, Driven Rod, Computer-based Multi-meter Interferences Interpretation of results: During testing, Visual, Software

May 18, 2014


1

TEST METHODS General Safety • PPE • Hard-soled (steel toe?) shoes • Safety glasses • Leather gloves • Traffic vest/cones • Voltages/currents during testing • Call before you dig (or drive rods into the ground)

May 18, 2014


2

TEST METHODS General

Circuit • Current source – circulate current into ground between two pins • Voltmeter – measure voltage between two pins • Wire – connects current source and voltmeter to various pins

May 18, 2014


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Problems • Access to site: • New site – grubbed, graded, final soil compaction • Existing site – where to test • Injecting sufficient current – varies with instrument type • Earth is not uniform • Interferences

May 18, 2014

4



Environment • See access to site • Avoiding other construction activities • Near roadway? • When to test • Design schedule/materials delivery dictated? • When is site available? • Wait until final substation grading? • Soil moisture and temperature

May 18, 2014

5



Effect of moisture on soil resistivity 10000 / . , 1 0 0 0 + ) # * # ) ( # ( ' & 10 0 $ # " ! 10 0

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20

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May 18, 2014


40

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Image Courtesy of Southern Company

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Effect of temperature on soil resistivity 10000 . / . , + ) # * # ) ( # ( ' & $ # " !

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100

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Temperature (C) Image Courtesy of Southern Company

May 18, 2014

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TEST METHODS Basic Principles • Inject current into earth to create potentials throughout the earth • Measure voltage between two pins • Apparent resistance is V/I • From test geometry, derive formula to convert apparent resistance to apparent soil resistivity • Simple formulas assume uniform soil resistivity • Apparent soil resistivity: the equivalent, overall resistivity of a volume of soil with varying properties

May 18, 2014

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TEST METHODS Basic Principles -80--60

-60--40

-40--20

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20-40

40-60

60-80

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May 18, 2014


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%$TEST METHODS Wenner 4-pin test

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May 18, 2014

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TEST METHODS Wenner 4-pin test • Measure series of apparent resistivities by varying pin spacings along a straight line (profile) • Run at least two profiles across the site in different directions • For each profile, plot apparent resistivity vs. pin spacing • Use visual method or computer programs to determine layered soil resistivity model • Sample pin spacings: 2’, 4’, 6’, 8’, 16’, 24’ 32’,…96’ (or larger for very large substations or generating plants)

May 18, 2014

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TEST METHODS Wenner 4-pin test - Good test location?


May 18, 2014


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%$TEST METHODS Schlumberger-Palmer test

!a= " c(c+d)R/d Image Courtesy of Southern Company

“depth” = (2c + d)/2 May 18, 2014

13


TEST METHODS Schlumberger-Palmer test • Vary potential (inner) pin separation, keeping distances between potential and current pins equal • Can leave current pins in one place, moving only potential pins • Could speed up measurement process – move 2 pins instead of 4 pins • Might better detect changes in soil resistivity vs. depth • Associate each apparent resistivity measurement with depth (spacing) computed using (2c + d)/2 • Run at least two profiles across the site in different directions • For each profile, plot apparent resistivity vs. pin spacing • Use visual method or computer programs to determine layered soil resistivity model

May 18, 2014

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TEST METHODS Driven-rod test I

Test Rod Diameter “d”

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May 18, 2014


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%$TEST METHODS Driven-rod test • Drive ground rod to varying depths. For each depth: • Circulate current between ground rod and remote current pin • Measure voltage between ground rod and potential pin • Resistance is V/I • See section 2.2 for testing ground rod impedance • Use simple (uniform soil assumption) formula to compute apparent resistivity • Sample depths: 2’, 4’, 6’, 8’, 10’, 15’ 20’,…100’ (or refusal) • Drive test rods at multiple locations across the site • For each test rod location, plot apparent resistivity vs. pin spacing • Use visual method or computer programs to determine layered soil resistivity model

May 18, 2014

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TEST METHODS Driven-rod test - Don’t do this!


May 18, 2014


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TEST METHODS Computer-based Multimeter

Image Courtesy of Advanced Grounding Concepts

May 18, 2014


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%$TEST METHODS Computer-based Multimeter

• Injects “white noise” current – as high as several Amperes • Automatically switches between the multiple potential probes • Each measurement is actually several Schlumberger-Palmer measurements • Software automatically displays 2-layer soil and parameter errors

May 18, 2014


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TEST METHODS Errors due to limited probe spacing

May 18, 2014


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TEST METHODS Interferences • Any conductive “object” in the vicinity that can divert the test current or distort the soil potentials • Metal fences • Buried pipes (metal) • Grounding systems • Transmission or distribution pole grounds, especially i f connected to other pole grounds • Distribution cables with bare concentric neutrals • Any circuit that can induce voltages onto test leads • Transmission or distribution lines • Outside sources of current in the soil • Lack of space to achieve desired maximum pin spacing

May 18, 2014


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%$TEST METHODS Example of interference – 3 ft parallel to grid

• 4-pin resistance at 10 ft spacing = 9.45 • Interference-free resistance = 15.11

May 18, 2014


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TEST METHODS Example of interference – perpendicular to grid

• 4-pin resistance at 10 ft spacing = 14.12 • Interference-free resistance = 15.11

May 18, 2014


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TEST METHODS Interpretation of results - software “Perfect 2-layer soil: !2< !1

May 18, 2014


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%$TEST METHODS Interpretation of results - software “Perfect 2-layer soil: !2> !1

May 18, 2014

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TEST METHODS Interpretation of results - software Cancel

Wenner Method Field Data RUNMEASUREMENTSFOR300,100,20 SOILMODEL

Print

Accept

Copy

GroundingSystem/ GeometricModel

Import

Export

I

Sort

Default*

Update

Update Apparen Resis iviy Ohm-Meers

ProbeSpacing inee (a)

ProbeLeng h ininches(L)

Resisance inOhms(V/I)

1

1. 0000

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151. 40

289 95 .

2

3. 0000

3. 0000

51. 940

298 41 .

3

5. 0000

3. 0000

31. 130

298 09 .

4

10. 000

3. 0000

15. 110

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5

15. 000

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9.4 530

271 55 .

6

20. 000

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6.4 930

248 70 .

7

30. 000

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3.5 270

202 64 .

8

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144 11 .

9 10

70. 000 90. 000

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11

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14 15 16

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DeleteMeasur ement DeleteAllMeasurements

M ar k/ Unmar k

ProbeDiameter

0.560

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3.00

inches

72.00

Hz

*Default ProbeLength InducedVoltageCorrection OperatingFrequency V/ILead Separation

20.00

feet

Un m ak r Al l AlgorithmControls Distance

NoCorrection RealPartOnly Real+Reactive

Raw-Meas

Model

Corrected Plot

Upper Rho:

300.64

Lower Rho:

100.04

m

Layer Depth:

19.94

feet

Model/Data

View CorrectedData

m

Sensitivit

3Layer

ModelFit

SoilModel

Advanced Grounding Concepts

May 18, 2014

STOP

StateLimits

Process

Objectiv e:

0.000000

Form SOIL_WENNER - Copyright© A. P. Meliopoulos 1998-2013

26


TEST METHODS Interpretation of results - software Close

Wenner Method Soil Parameters Case Name 300-100-SOIL-MEASUREMENTS

Wenner Method Model Fit Report

Close

File: RUNMEASUREMENTSFOR300,100,20SOIL MODEL

Description RUNMEASUREMENTSFOR300,100,20SOILMODEL

Description: GroundingSystem/ GeometricModel

GroundingSystem/GeometricModel

SoilResistiv ityModel Exp.Value

Tolerance

UpperS oil Resistivity

300.9

0.8

Ohm Meters

Lower Soil Resistivity

100.1

0.3

Ohm Meters

19.9

0.1

Feet

SoilResistivityModel

Upper Layer Thickness

AtConfidence Level

Resultsare validtodepth of

Conf:

Error:

Conf:

ProgramWinIGS - FormSOIL_RA

May 18, 2014

Error:

Conf:

90.0

%

225.0

Feet

PlotCursors

U pp er S oi l Re si st iv it y

300.9

L ow er S oi l Re si st iv it y

100.1

O hm Me te rs

Measured

U ppe r Laye r Thi ckn es s

19.9

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O hm Me te rs

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%$TEST METHODS Interpretation of results - software D rivenRodMethodFieldData

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RUNMEASUREMENTSFOR300,100 ,20SOIL MODEL-3 -PINTEST DrivenGround Rod

Table Operations Print

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C op y

Probe Parameters

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Ex po rt

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0.000

feet

Y(feet)

0.000

feet

Diameter

0.625

inches

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RodLengthinContact w ih t S oi l i n F e e th ()

Resistance i n Oh ms ( V / I )

V h VoltageProbe

CurrentReturn

X

1000.002

-1000.002

feet

Y

0.000

0.000

feet

Diameter

0.625

0.625

inches

Length

4.000

4.000

feet

Update ApparentResisti vity OhmMeters

1

10 . 0 0 0

64 7.7 0

3 07.4 6

2

30 . 0 0 0

27 0.7 0

3 03.0 0

3

50 . 0 0 0

17 7.2 0

3 00.6 5

4

1 0 . 0 0 0

97 7 . 10

2 95.2 9

5

1 5 . 0 0 0

67 9 . 30

2 89.4 2

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2 77.3 2

7

3 0 . 0 0 0

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1 68.8 3

8

5 0 . 0 0 0

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1 32.4 3

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7 0 . 0 0 0

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Ope ra it ng Fre quency

72.00

Hz

V/ILead Separation

20.00

feet

RealPartOnly Real+Reactive

Distance

ft

Model

Raw Meas Corrected

Plot

Upper Rho:

Model/DataF

LowerRho:

307.77 101.78

LayerDepth:

Model Fit

Soil Model

STOP

Process

StateLimits

Objective:

20.04

m m feet

0.000000

ProgramW inIGS - FormS OIL_DRIVENROD

May 18, 2014

28


TEST METHODS Interpretation of results - software

Driven Rod Method Soil Parameters

Close

Case Name 3-PIN-300-100-SOIL-MEASUREMENTS

Driven Rod Method Model Fit Report

Close

File: RUNMEASUREMENTSFOR300,100,20SOILMODEL-3-PINTEST

Description RUNMEASUREMENTSFOR300,100,20SOILMODEL-3-PIN TEST

Description: GroundingSystem/GeometricModel


SoilResistivityModel SoilResistivityModel Upper Soil Resistivity Lower Soil Resistivity

Exp.Value

Tolerance

307.0

0.5

Ohm Meters

101.8

0.2

Ohm Meters

20.0

0.0

Feet

Upper Layer Thickness

AtConfidenceLevel

Resultsare validto depthof

Conf:

Error:

Conf:

ProgramWinIG S- FormSOIL_RA

May 18, 2014

Error:

Conf:

90.0

%

300.0

Feet

PlotCursors

U pp er S oi l Re si st iv it y

307.0

O hm M et er s

L ow er S oi l Re si st iv it y

101.8

O hm M et er s

Measured

20.0

F ee t

Computed

Up pe r La ye r Th c i k ne ss

RodLength

XScale

Linea Log

Error:

Program WinIGS - Form SOIL_RB


29

TEST METHODS Interpretation of results - visual • The computed apparent resistivities are always positiv e. • As the actual resistivity increases or decreases with greater depth, the apparent resistivities also increase or decrease with greater probe spacings. • The maximum change in apparent resistivity occurs at a spacing larger than the depth at which the corresponding change in actual resistivity occurs. Thus, the changes in apparent resistivity are always plotted to the right of the probe spacing corresponding to the change in actual resistivity. • The amplitude of the curve is always less than or equal to the amplitude of the actual resistivity vs. depth curve. • In a multi-layer model, a change in the actual resistivity of a thick layer results in a similar change in the apparent resistivity curve.

May 18, 2014


30

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%$TEST METHODS Interpretation of results - visual

May 18, 2014

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TEST METHODS Interpretation of results – during testing • If using software, input data in laptop while at site • If using visual techniques, plot measurements by converting measured resistance to apparent resistivity • Does apparent resistivity profile match expected based on soil type and environmental conditions? • If results jump all over, check connections and/or look for interferences

May 18, 2014

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TEST METHODS Interpretation of results – during testing The good – driven rod test DrivenRodMethodFieldData

Cancel

Accept

T14067-PIEDMONTTSGPR

DrivenGroundRod

TableOperations Print

X(feet)

Import

C op y

Ex po rt Sort

0.000 0.625

feet inches

h VoltageProbe

CurrentReturn

X

62.000

100.000

feet

Y

0.000

0.000

feet

0.625

0.625

inches

1.000

1.000

feet

Update

R e sis at n ce i n O hm s ( V / I )

ApparentResistivity OhmMeters

1

2.0 0 00

1600 0 .

1 2 96.3

2

4.0 0 00

1000 0 .

1 4 13.2

3

6.0 0 00

730.0 0

1 4 39.8

4

8.0 0 00

560.0 0

1 4 03.3

5

10. 0 00

490.0 0

1 4 80.9

6

12. 0 00

400.0 0

1 4 10.1

7

14. 0 00

330.0 0

1 3 25.8

8

16. 0 00

290.0 0

1 3 05.5

9

18. 0 00

250.0 0

1 2 44.5

10

20. 0 00

230.0 0

1 2 53.1

11

22. 0 00

200.0 0

1 1 82.6

12

24. 0 00

190.0 0

1 2 10.8

13

26. 0 00

170.0 0

14

28. 0 00

160.0 0

15

30. 0 00

150.0 0

DeleteMeasurement

V

feet

0.000

Y(feet) Diameter

Update

R od L e ng h t i n C on a t ct wih t S oi l i n F ee t ( h)

Probe Parameters

I

Groundin gSystem/ GeometricModel

Diameter Length

1 1 60.8 1 1 64.7 1 1 59.0

BadMeasurements

DeleteAllMeasurement s

M ar k / Un ma rk

AlgorithmContr ols

U nm ar k Al l

ViewCorrected Data

InducedVoltage Correction

NoCorrection

Ope a r it ng Fre que ncy

72.00

Hz

V/I LeadSeparation

20.00

feet

RealPartOnly Real+Reactive

Distance

ft

Model

Raw Meas Corrected

Plot

Model/DataF

Upper Rho: LowerRho: LayerDepth:

Model Fit

Soil Model

STOP

Process

StateLimits

Objective:

1438.22 824.33 19.00 0.000000

m m feet


ProgramWinIG S- FormSOIL_DRIVENROD

May 18, 2014


33

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IEEE Std 81 Tutorial Handouts

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