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Ground Resistance
and Measurement
Terry Klimchak
Revised 11/19/13
ERICO has met the standards and requirements of the Registered Continuing Education Providers
Program. Credit earned on co...
Copyrighted Materials
This educational activity is protected by copyright laws. Reproduction, distribution,
display and us...
Presentation Outline
• Applicable IEEE Standards
• Soil Resistivity
• Measuring Soil Resistivity
• Measuring Ground Resist...
IEEE Standard
• ANSI/IEEE Std 81-2012
“IEEE Guide for Measuring Earth
Resistivity, Ground Impedance, and Earth
Surface Pot...
IEEE Std 81-2012
• Scope
– Establishing safe testing conditions
– Measuring earth resistivity
– Measuring the power system...
7
IEEE Std 81-2012
• Purpose
– The purpose of this guide is to present practical instrumentation
methods that may be used ...
8
IEEE Std 81-2012 (Cont.)
• Purpose
– This guide is intended to assist the engineer or technician in
obtaining and interp...
IEEE Std 81- 2012
• Testing Methods Covered Include:
– Measurement of Earth Resistivity
– Measurement of the Resistance an...
Earth Resistivity
Soil Resistivity - Effect of Moisture
14
Soil Resistivity - Effect of Temperature
16
Resistance Variation With Seasons
Seasonal Variation of Earth Resistance With an
Electrode of 3/4" Pipe in Stony Clay Soil...
Measuring Soil Resistivity
Wenner’s or Four Pin Method
• Also Known as Equally Spaced Method
• Most Widely Used Method
• Small Test Probes Are Instal...
Wenner’s or Four Pin Method
20I
V
R =
aR
la
a
la
a
aR
π
π
ρ 2
4
2
1
4
2222
=
+
−
+
+
=
Wenner’s or Four Pin Method
• Test Probes (Pins) Placed in a Straight Line at
Intervals “a” Driven to a Depth “l” (“l” <
0...
Wenner’s or Four Pin Method
23
Measuring Ground
Resistance
Measuring Ground Resistance
• Purpose:
– To Determine Actual Resistance Ground Connections
– To Check Calculations
– To De...
Fall-of-Potential or 3-Point Method
30
FALL OF POTENTIAL TEST
• Must have complete
isolation from utility ground
system
• Measure DIAGONAL length
of ground syste...
Fall-of-Potential or 3-Point Method
Plot shows 62% of homogenous soil
32
Stakeless Measurements
• Simple and fast
• No auxiliary rods or
spacing requirements
• Direct reading of
continuity and gr...
Lowering Ground Resistance
Lowering Ground Resistance
• What Affects the Grounding
Resistance?
– Diameter of the Ground Electrode
– Length / Depth of...
Lowering Ground Resistance
Resistance vs. Rod Depth
0%
20%
40%
60%
80%
100%
120%
0.50 0.63 0.75 0.88 1.00 1.13 1.25 1.38 1...
Lowering Ground Resistance
Resistance vs. Rod Depth
0
100
200
300
400
500
600
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
...
Lowering Ground Resistance
38
l
r
Radius (r ) in
Meters
Percent of
Resistance
0.03 25%
0.06 38%
0.09 46%
0.15 52%
0.3 68%
...
Lowering Ground Resistance
39
Concentric Shell
Overlap Decreases
Efficiency of
Ground Rod
Resistance
Lowering Ground Resistance
• Add More Rods
• Deep Driven Rods
– Threaded Couplings
– Compression Couplings
– Exothermic Gr...
Lowering Ground Resistance
• Ground Enhancement
– Chemical Ground Rods
– Bentonite Clay
– Ground Enhancement Material
41
Ground Enhancement
• Chemicals (Salts) and Chemical Ground Rods
– Expensive
– May Need to Be Periodically Recharged
– Typi...
Chemical Ground Rods
43
Bentonite Clay
• Advantages
– Effective When Wet
– Low Initial Cost
• Disadvantage
– May Shrink and Pull Away From Rod or ...
Ground Enhancement Materials
• Permanent, Stable, Low
Resistivity Backfill
Material Used to
Improve Grounding
Effectivenes...
New IEC 62561-7 Standard for Ground
Enhancement Materials
• Leaching test requirements
• Sulfur determination requirements...
IEC 62561-7
47
5.2 Leaching Test
5.2.3 Passing Criteria:
The criteria are given by national or international regulations.
...
IEC 62561-7
48
5.4 Determination of Resistivity
5.4.4 Passing Criteria:
Specimens are deemed to have passed the test if th...
49
IEC 62561-7
5.5.5 Passing Criteria:
• For copper-plated earth electrodes, the polarization
resistance shall be: > 4Ω x ...
IEC 62561-7
5.6 Marking and Indication
Each package unit shall be marked in an indelible way
1.The name of the manufacture...
Ground Enhancement Material
Specification
Ground enhancement material must be compliant to IEC
62561-7, must be permanent ...
Thank you for your time!
This concludes the educational content of this activity
www.erico.com
52
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Ground Resistance & Measurement

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Ground Resistance & Measurement

  1. 1. Ground Resistance and Measurement 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. Presentation Outline • Applicable IEEE Standards • Soil Resistivity • Measuring Soil Resistivity • Measuring Ground Resistance • Lowering Ground Resistance 4
  5. 5. IEEE Standard • ANSI/IEEE Std 81-2012 “IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System” 5IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  6. 6. IEEE Std 81-2012 • Scope – Establishing safe testing conditions – Measuring earth resistivity – Measuring the power system frequency resistance or impedance of the ground system to remote earth – Measuring the transient (surge) impedance of the ground system to remote earth – Measuring step and touch voltages – Verifying the integrity of the grounding system – Reviewing common methods and procedures for performing ground testing – Reviewing instrumentation characteristics and limitations – Reviewing various factors that can distort test measurements 6IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  7. 7. 7 IEEE Std 81-2012 • Purpose – The purpose of this guide is to present practical instrumentation methods that may be used for measuring soil resistivity, the impedance to remote earth, step and touch voltages, and current distributions in ground grids associated with electric utility facilities. – These grids typically consist of interconnected grounding systems ranging in complexity from a few ground rods to large grids with many ground rods or wells, buried conductors, and external ground connections. External ground connections may include overhead shield/ground/neutral wires, underground cable sheaths/neutrals, counterpoises, grid tie conductors, metallic pipes, and other connections that provide additional paths to remote earth. 7IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  8. 8. 8 IEEE Std 81-2012 (Cont.) • Purpose – This guide is intended to assist the engineer or technician in obtaining and interpreting accurate, reliable data. The factors that influence the choice of instruments are discussed along with a presentation of field techniques for various types of measurements. These factors include the purpose of the measurement, the accuracy required, the types of instruments available, the possible sources of error, and the nature of the ground or grounding system under test. It also describes test procedures that promote the safety of personnel and property, and it seeks to minimize operating interferences with neighboring facilities." 8IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  9. 9. IEEE Std 81- 2012 • Testing Methods Covered Include: – Measurement of Earth Resistivity – Measurement of the Resistance and Impedance to Earth (From Small Rods and Plates to Large Substation Grounding Systems Stations) – Measurement of Step and Touch Voltages and Potential Contour Surveys – Integrity of Grounding Systems 9IEEE is a registered trademark of The Institute of Electrical and Electronics Engineers, Inc.
  10. 10. Earth Resistivity
  11. 11. Soil Resistivity - Effect of Moisture 14
  12. 12. Soil Resistivity - Effect of Temperature 16
  13. 13. Resistance Variation With Seasons Seasonal Variation of Earth Resistance With an Electrode of 3/4" Pipe in Stony Clay Soil 0 20 40 60 80 100 JAN M A R M A Y JUL SE P N O V JAN M A R M A Y Resistamce(Ohms) Buried 3' Buried 10' 17
  14. 14. Measuring Soil Resistivity
  15. 15. Wenner’s or Four Pin Method • Also Known as Equally Spaced Method • Most Widely Used Method • Small Test Probes Are Installed in Depth “L” and Spaced in Intervals “A” • Test Current is Passed Between the Outer Electrodes. The Voltage Drop Is Measured With a High Impedance Volt Meter Connected to the Inner Electrodes 19
  16. 16. Wenner’s or Four Pin Method 20I V R = aR la a la a aR π π ρ 2 4 2 1 4 2222 = + − + + =
  17. 17. Wenner’s or Four Pin Method • Test Probes (Pins) Placed in a Straight Line at Intervals “a” Driven to a Depth “l” (“l” < 0.1”a”) • Assume “l” = 0 and Formula is Simplified as Follows: • The Formula Provides the Average Soil Resistivity (Apparent Resistivity) of the Soil to Depth “a” 21 aRπρ 2=
  18. 18. Wenner’s or Four Pin Method 23
  19. 19. Measuring Ground Resistance
  20. 20. Measuring Ground Resistance • Purpose: – To Determine Actual Resistance Ground Connections – To Check Calculations – To Determine GPR That Results From Ground a Fault Current in a Power System – To Determine the Suitability of a Grounding Connection for Lightning Protection, – To Obtain Data Required for the Design of Protection for Buildings, Equipment and Personnel 29
  21. 21. Fall-of-Potential or 3-Point Method 30
  22. 22. FALL OF POTENTIAL TEST • Must have complete isolation from utility ground system • Measure DIAGONAL length of ground system (10m x 10m grid would be 14m diagonal) • Probe Z is driven at a distance of 10X diagonal • Probe Y is driven at 1X Diagonal, then 2X,3X etc. up to 9x • Results are plotted, FALL of resistance should be 62% 31
  23. 23. Fall-of-Potential or 3-Point Method Plot shows 62% of homogenous soil 32
  24. 24. Stakeless Measurements • Simple and fast • No auxiliary rods or spacing requirements • Direct reading of continuity and ground loop resistance. 33
  25. 25. Lowering Ground Resistance
  26. 26. Lowering Ground Resistance • What Affects the Grounding Resistance? – Diameter of the Ground Electrode – Length / Depth of the Ground Electrode – Number of Ground Electrodes – Ground System Design / Electrode Placement 35
  27. 27. Lowering Ground Resistance Resistance vs. Rod Depth 0% 20% 40% 60% 80% 100% 120% 0.50 0.63 0.75 0.88 1.00 1.13 1.25 1.38 1.50 Resistance (%) Rod Diameter Has Minor Effect On Resistance 36
  28. 28. Lowering Ground Resistance Resistance vs. Rod Depth 0 100 200 300 400 500 600 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 Rod Depth (ft) Resistance(ohms) 1/2" Rod (ohms) 1" Rod (ohms) Doubling Rod Depth Reduces Resistance 40% In Uniform Soil 37
  29. 29. Lowering Ground Resistance 38 l r Radius (r ) in Meters Percent of Resistance 0.03 25% 0.06 38% 0.09 46% 0.15 52% 0.3 68% 1.5 86% 3 94% Effective Resistance Area
  30. 30. Lowering Ground Resistance 39 Concentric Shell Overlap Decreases Efficiency of Ground Rod Resistance
  31. 31. Lowering Ground Resistance • Add More Rods • Deep Driven Rods – Threaded Couplings – Compression Couplings – Exothermic Ground Rod Splice 40
  32. 32. Lowering Ground Resistance • Ground Enhancement – Chemical Ground Rods – Bentonite Clay – Ground Enhancement Material 41
  33. 33. Ground Enhancement • Chemicals (Salts) and Chemical Ground Rods – Expensive – May Need to Be Periodically Recharged – Typically Need Bentonite – May Have Environmental Concerns Depending on Materials Used 42
  34. 34. Chemical Ground Rods 43
  35. 35. Bentonite Clay • Advantages – Effective When Wet – Low Initial Cost • Disadvantage – May Shrink and Pull Away From Rod or Soil When It Dries 44
  36. 36. Ground Enhancement Materials • Permanent, Stable, Low Resistivity Backfill Material Used to Improve Grounding Effectiveness Regardless of Soil Conditions • Composed of Chemically Stable Materials 45
  37. 37. New IEC 62561-7 Standard for Ground Enhancement Materials • Leaching test requirements • Sulfur determination requirements • Resistivity determination results • Additional corrosion testing 46IEC is a registered trademark of The International Electrotechnical Commission
  38. 38. IEC 62561-7 47 5.2 Leaching Test 5.2.3 Passing Criteria: The criteria are given by national or international regulations. (GEM25A was tested to Environmental Protection Agency) 5.3 Sulfur Determination 5.3.2 Passing Criteria: The material is deemed to have passed the test if all measured values are less than 2%. The recorded value resulting from this test shall be indicated within the product documentation. IEC is a registered trademark of The International Electrotechnical Commission
  39. 39. IEC 62561-7 48 5.4 Determination of Resistivity 5.4.4 Passing Criteria: Specimens are deemed to have passed the test if the obtained resistivity value from the three samples are equal or less than the resistivity value claimed by the manufacturer IEC is a registered trademark of The International Electrotechnical Commission
  40. 40. 49 IEC 62561-7 5.5.5 Passing Criteria: • For copper-plated earth electrodes, the polarization resistance shall be: > 4Ω x m2 for non-aggressive environments and > 8Ω x m2 for aggressive environments • For galvanized earth electrodes, the polarization resistance shall be: > 3Ω x m2 for non-aggressive environments and > 7.6Ω x m2 for aggressive environments IEC is a registered trademark of The International Electrotechnical Commission
  41. 41. IEC 62561-7 5.6 Marking and Indication Each package unit shall be marked in an indelible way 1.The name of the manufacturer or his trademark 2.The type or serial number of the batch of ground enhancing compound 3.The installation instructions 4.The resistivity value and test apparatus used 5.The conformity statement to the present standard 50IEC is a registered trademark of The International Electrotechnical Commission
  42. 42. Ground Enhancement Material Specification Ground enhancement material must be compliant to IEC 62561-7, must be permanent and maintenance-free (no recharging with salts or chemicals, which may be corrosive) and maintain its earth resistance with time. It must set up firmly and not dissolve or decompose, or otherwise pollute the soil or the local water table. It should not depend on the continuous presence of water to maintain its conductivity, and in its set form will have a resistivity of not more than 2 ohm-cm. 51
  43. 43. Thank you for your time! This concludes the educational content of this activity www.erico.com 52

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