CLAUSE PAGE 1. Purpose................................................................................................................................................................1 2. Scope...................................................................................................................................................................1 3. References...........................................................................................................................................................2 4. Safety Practices...................................................................................................................................................3 4.1 General Precautions ................................................................................................................................... 3 4.2 Safety Aspects of Test Preparations........................................................................................................... 3 4.3 Safety Aspects of Test Measurements....................................................................................................... 4 5. Factors Effecting Grounding System Measurements..........................................................................................4 6. Preliminary Planning and Procedures.................................................................................................................6 6.1 Distance to Current and Potential Test Electrodes..................................................................................... 6 6.2 Selection of TestConductor Routing and TestProbe Locations .............................................................. 6 6.3 Determining the Effect of OverheadGroundWire Shielding on Test Current Distribution .................... 7 6.4 Estimating Grounding Grid Impedance..................................................................................................... 7 6.5 Estimating Minimum Test Current............................................................................................................ 7 6.6 Test Current Sources.................................................................................................................................. 7 6.7 Estimating TestCurrent Source Requirements.......................................................................................... 8 6.8 Remote Rod Electrode Current Capacity................................................................................................... 8 6.9 Potential Input Impedance ......................................................................................................................... 9 6.10 Determining Grounding System Connection Condition............................................................................ 9 6.11 Establishing the Measurement Point on a Grounding System................................................................... 9 7. EarthReturn Mutual Effects When Measuring GroundingSystem Impedance ................................................9 7.1 Introduction................................................................................................................................................ 9 7.2 Measurement Error Due to Earth Mutual Resistances............................................................................. 10 7.3 Measurement Error Due to AC Mutual Coupling.................................................................................... 10 7.4 Mutual Coupling to Potential Lead From Extended Ground Conductors ............................................... 12 8. Measurement of LowImpedance Grounding Systems by TestCurrent Injection...........................................12 8.1 Introduction.............................................................................................................................................. 12 8.2 Signal Generator and Power Amplifier Source........................................................................................ 13 8.3 Portable PowerGenerator Source............................................................................................................ 16 8.4 Power System LowVoltage Source........................................................................................................ 20 9. Measurement of LowImpedance Grounding Systems by Power System Staged Faults.................................23 9.1 Introduction.............................................................................................................................................. 23 9.2 Fault Configurations ................................................................................................................................ 24 9.3 Fault Initiation.......................................................................................................................................... 24 9.4 Current Measurements............................................................................................................................. 25 9.5 Potential Measurements........................................................................................................................... 25 9.6 Interference Reduction............................................................................................................................. 27 9.7 Calibration................................................................................................................................................ 28 Authorized licensed use limited to: MULTIMEDIA UNIVERSITY. Downloaded on August 12, 2009 at 05:04 from IEEE Xplore. Restrictions apply. vi CLAUSE PAGE 10. Current Distribution in Extended Grounding Systems.....................................................................................30 10.1 Introduction........................................................................................................................................... 30 10.2 Test Considerations................................................................................................................................ 31 10.3 Analysis of Current Distribution in a Grounding System (See B25 and B44)................................. 33 10.4 Induced Current in the Angled Overhead Ground Wire........................................................................ 37 10.5 Current Distribution During a Staged Fault Test (See B44)............................................................... 41 11. Transfer Impedances to Communication or Control Cables.............................................................................49 12. Step, Touch, and VoltageProfile Measurements .............................................................................................51 12.1 General Requirements............................................................................................................................ 51 12.2 Grid Safety Requirements...................................................................................................................... 52 12.3 FootprintElectrode Method................................................................................................................... 52 12.4 TestProbe Method................................................................................................................................. 52 12.5 SimulatedPersonnel Method (See B24)............................................................................................. 54 13. Instrumentation Components............................................................................................................................56 13.1 Introduction............................................................................................................................................ 56 13.2 DirectReading Ohmmeters ................................................................................................................... 57 13.3 Electromagnetic Oscillograph................................................................................................................ 57 13.4 Tuned Voltmeter.................................................................................................................................... 58 13.5 Fast Fourier Transform Analyzer........................................................................................................... 58 13.6 Sine Wave Network Analyzer................................................................................................................ 58 13.7 Staged Fault............................................................................................................................................ 59 13.8 Switched PowerFrequency Source....................................................................................................... 59 13.9 Welding Set or Portable Power Generator............................................................................................. 59 13.10 LowPower Sine Wave Source............................................................................................................. 60 13.11 LowPower Random Noise Source....................................................................................................... 60 13.12 Periodic (Nonsinusoidal) Generator...................................................................................................... 60 13.13 PowerSystem Switching Transient ......................................................................................................60 13.14 Pulse Generator..................................................................................................................................... 61 13.15 Current Transformer (CT)..................................................................................................................... 61 13.16 Resistive Shunt...................................................................................................................................... 61 13.17 Inductive Current Pickup...................................................................................................................... 61 13.18 HallEffect Probe .................................................................................................................................. 62 13.19 Remote Synchronization of Test Signal................................................................................................ 62 13.20 Measurement Environment and Signal Transmission........................................................................... 62 14. Instrument Performance Parameters.................................................................................................................64 14.1 Reading Accuracy................................................................................................................................... 64 14.2 Selectivity................................................................................................................................................ 64 14.3 Impedance Phase Discrimination............................................................................................................ 67 14.4 Current Level .......................................................................................................................................... 68 14.5 Test Frequency and Current Waveform.................................................................................................. 68 14.6 Measurement Error Reduction (See B25)............................................................................................ 69 15. Bibliography......................................................................................................................................................69
IEEE Std 81.2-1991 IEEE Guide for Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Grounding Systems Sponsor Power System Instrumentationand Measurements Committee of the IEEE Power Engineering Society Approved December 5, 1991 IEEE Standards Board Abstract: Practical instrumentation methods are presented for measuring the ac characteristics of large, extended or interconnected grounding systems Measurements of impedance to remote earth, step and touch potentials, and current distributions are covered for grounding systems ranging in complexity from small grids (less than 900 m2), with only a few connected overhead or direct burial bare concentric (2) neutrals, to large grids (greater than 20 000 m2), with many connected neutrals, overhead ground wires (sky wires), counterpoises, grid tie conductors, cable shields, and metallic pipes This standard addresses measurement safety; earth-return mutual errors; low-current measurements; power-system staged faults; communication and control cable transfer impedance; current distribution (current splits) in the grounding system; step, touch, mesh, and profile measurements; the foot-equivalent electrode earth resistance; and instrumentation characteristics and limitations Keywords: Grounding systems, impedance, safety The Institute of Electrical and Electronics Engineers, Inc 345 East 47th Street, New York, NY 10017-2394, USA Copyright © 1992 by the The Institute of Electrical and Electronics Engineers, Inc All rights reserved Published 1992 Printed in the United States of America ISBN 1-55937-187-0 No part of this publication may be reproduced in any form, in an electronic retrieval system or other wise, without the prior written permission of the publisher Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply IEEE Standards documents are developed within the Technical Committees of the IEEE Societies and the Standards Coordinating Committees of the IEEE Standards Board Members of the committees serve voluntarily and without compensation They are not necessarily members of the Institute The standards developed within IEEE represent a consensus of the broad expertise on the subject within the Institute as well as those activities outside of IEEE that have expressed an interest in participating in the development of the standard Use of an IEEE Standard is wholly voluntary The existence of an IEEE Standard does not imply that there are no other ways to produce, test, measure, purchase, market, or provide other goods and services related to the scope of the IEEE Standard Furthermore, the viewpoint expressed at the time a standard is approved and issued is subject to change brought about through developments in the state of the art and comments received from users of the standard Every IEEE Standard is subjected to review at least every Þve years for revision or reafÞrmation When a document is more than Þve years old and has not been reafÞrmed, it is reasonable to conclude that its contents, although still of some value, not wholly reßect the present state of the art Users are cautioned to check to determine that they have the latest edition of any IEEE Standard Comments for revision of IEEE Standards are welcome from any interested party, regardless of membership afÞliation with IEEE Suggestionsfor changes in documents should be in the form of a proposed change of text, together with appropriate supporting comments Interpretations: Occasionally questions may arise regarding the meaning of portions of standards as they relate to speciÞc applications When the need for interpretations is brought to the attention of IEEE, the Institute will initiate action to prepare appropriate responses Since IEEE Standards represent a consensus of all concerned interests, it is important to ensure that any interpretation has also received the concurrence of a balance of interests For this reason IEEE and the members of its technical committees are not able to provide an instant response to interpretation requests except in those cases where the matter has previously received formal consideration Comments on standards and requests for interpretations should be addressed to: Secretary, IEEE Standards Board 445 Hoes Lane P.O Box 1331 Piscataway, NJ 08855-1331 USA IEEE Standards documents are adopted by the Institute of Electrical and Electronics Engineers without regard to whether their adoption may involve patents on articles, materials, or processes Such adoption does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the standards documents Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply Foreword (This foreword is not a part of IEEE Std 81.2-1991, IEEE Guide for Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Grounding Systems.) During the late 1970's, in an effort to increase its usefulness, this guide was divided into two parts The Þrst part is entitled IEEE Std 81-1983, IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System It covers the majority of Þeld measurements that not require special high-precision equipment and measuring, and that not encounter unusual difÞculties such as may be found with extensive grounding systems, abnormally high stray ac or dc currents, etc IEEE Std 81 (Part I) has been extensively revised and updated Part I was approved in 1983 and reafÞrmed in 1991 This part of the guide (Part II) is entitled IEEE Std 81.21991, IEEE Guide for Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Grounding Systems This new part covers measurement of very low values of ground impedance (less than W) The extensive use of specialized instrumentation, measuring techniques, and safety aspects are incorporated This guide was prepared by the Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Grounding Systems Working Group of the RLC Measurements Subcommittee of the Power Systems Instrumentation and Measurements Committee of the IEEE Power Engineering Society At the time that this standard was completed, the working group had the following membership: D Mukhedkar, Chair J White, Secretary E Rogers, Technical Editor G Y R Allen M J Anna E P Dick J Fortin W Hardy P Kouteynikoff J F Laidig R Malewski A Pessonen R H Reynolds H Sarmiento A N Sharaf E Smithson L Thione W Velazquez At the time that it balloted and approved this standard for submission to the IEEE Standards Board, the Power Systems Instrumentation and Measurements Committee had the following membership: A Abramowitz J Anderson J M Belanger J M Carr C Carrara L Coffeen S W Crampton F C Creed V DaGrosa A E Emmanuel G J Fitzpatrick R E Hebner R Hopkins P B Jacob W A Keagle, Jr H Kirkham J A Kise S R Knudsen J Kuffel D W Lenk F J Levitsky R Malewski D McAuliff T R McComb J H Moran D Mukhedkar O Petersons R Reid P H Reynolds R L Richardson A F Rohlfs H M Schneider J C Smith E So G E Stemler D Train R S Turgel J M Vanderleck C F Von Herrmann B H Ward D L Whitehead iii Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply When the IEEE Standards Board approved this standard on December 5, 1991, it had the following membership: Marco W Migliaro, Chair Donald C Loughry, Vice Chair Andrew G Salem, Secretary Dennis Bodson Paul L Borrill Clyde Camp James M Daly Donald C Fleckenstein Jay Forster* David F Franklin Ingrid Fromm Thomas L Hannan Donald N Heirman Kenneth D Hendrix John W Horch Ben C Johnson Ivor N Knight Joseph Koepfinger* Irving Kolodny Michael A Lawler John E May, Jr Lawrence V McCall T Don Michael* Lloyd A ỊPet Morley Stig L Nilsson John L Rankine Ronald H Reimer Gary S Robinson Terrance R Whittemore *Member Emeritus Also included are the following nonvoting IEEE Standards Board liaisons: Fernando Aldana Satish K Aggarwal James Beall Richard B Engelman Stanley Warshaw Adam Sicker IEEE Standards Project Editor iv Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply CLAUSE PAGE Purpose Scope References Safety Practices 4.1 General Precautions 4.2 Safety Aspects of Test Preparations 4.3 Safety Aspects of Test Measurements Factors Effecting Grounding System Measurements Preliminary Planning and Procedures 6.1 Distance to Current and Potential Test Electrodes 6.2 Selection of Test-Conductor Routing and Test-Probe Locations 6.3 Determining the Effect of Overhead-Ground-Wire Shielding on Test Current Distribution 6.4 Estimating Grounding Grid Impedance 6.5 Estimating Minimum Test Current 6.6 Test Current Sources 6.7 Estimating Test-Current Source Requirements 6.8 Remote Rod Electrode Current Capacity 6.9 Potential Input Impedance 6.10 Determining Grounding System Connection Condition 6.11 Establishing the Measurement Point on a Grounding System Earth-Return Mutual Effects When Measuring Grounding-System Impedance 7.1 7.2 7.3 7.4 Measurement of Low-Impedance Grounding Systems by Test-Current Injection 12 8.1 8.2 8.3 8.4 Introduction Measurement Error Due to Earth Mutual Resistances 10 Measurement Error Due to AC Mutual Coupling 10 Mutual Coupling to Potential Lead From Extended Ground Conductors 12 Introduction 12 Signal Generator and Power Amplifier Source 13 Portable Power-Generator Source 16 Power System Low-Voltage Source 20 Measurement of Low-Impedance Grounding Systems by Power System Staged Faults 23 9.1 9.2 9.3 9.4 9.5 9.6 9.7 Introduction 23 Fault Configurations 24 Fault Initiation 24 Current Measurements 25 Potential Measurements 25 Interference Reduction 27 Calibration 28 v Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply CLAUSE 10 PAGE Current Distribution in Extended Grounding Systems .30 10.1 10.2 10.3 10.4 10.5 Introduction 30 Test Considerations 31 Analysis of Current Distribution in a Grounding System (See [B25] and [B44]) 33 Induced Current in the Angled Overhead Ground Wire 37 Current Distribution During a Staged Fault Test (See [B44]) 41 11 Transfer Impedances to Communication or Control Cables 49 12 Step, Touch, and Voltage-Profile Measurements .51 12.1 12.2 12.3 12.4 12.5 13 General Requirements 51 Grid Safety Requirements 52 Footprint-Electrode Method 52 Test-Probe Method 52 Simulated-Personnel Method (See [B24]) 54 Instrumentation Components 56 13.1 Introduction 56 13.2 Direct-Reading Ohmmeters 57 13.3 Electromagnetic Oscillograph 57 13.4 Tuned Voltmeter 58 13.5 Fast Fourier Transform Analyzer 58 13.6 Sine Wave Network Analyzer 58 13.7 Staged Fault 59 13.8 Switched Power-Frequency Source 59 13.9 Welding Set or Portable Power Generator 59 13.10 Low-Power Sine Wave Source 60 13.11 Low-Power Random Noise Source 60 13.12 Periodic (Nonsinusoidal) Generator 60 13.13 Power-System Switching Transient 60 13.14 Pulse Generator 61 13.15 Current Transformer (CT) 61 13.16 Resistive Shunt 61 13.17 Inductive Current Pickup 61 13.18 Hall-Effect Probe 62 13.19 Remote Synchronization of Test Signal 62 13.20 Measurement Environment and Signal Transmission 62 14 Instrument Performance Parameters 64 14.1 14.2 14.3 14.4 14.5 14.6 15 Reading Accuracy 64 Selectivity 64 Impedance Phase Discrimination 67 Current Level 68 Test Frequency and Current Waveform 68 Measurement Error Reduction (See [B25]) 69 Bibliography 69 vi Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply CLAUSE PAGE Annex A Mutual Impedance Between Horizontal Earth-Return Conductors and the Self Impedance of a Horizontal Earth-Return Conductor Based on the Complex Image Plane Concept (See [11]) (Informative) 73 Annex B Mutual Impedance Between Finite Length Conductors Lying on the Ground Based on the Campbell/Foster Method (Informative) 84 Annex C Earth Return Impedance of a Grid-Tie Conductor (Informative) 89 Annex D Parallel Impedance of an Overhead Ground Wire and a Buried Counterpoise Conductor (Informative) .91 vii Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply IEEE Guide for Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Grounding Systems Purpose The purpose of this guide is to present practical instrumentation methods that may be used for the measurement of impedance to remote earth, step and touch potentials, and current distributions of large extended or interconnected grounding systems ranging in complexity from small grids (less than 900 m2), with only a few connected overhead or direct burial bare concentric neutrals, to large grids (greater than 20 000 m2), with many connected neutrals, overhead ground wires (sky wires), counterpoises, grid tie conductors, cable shields, and metallic pipes Scope Test methods and instrumentation techniques used to measure the ac characteristics of large grounding systems include the following topics: 1) 2) 3) 4) 5) 6) 7) 8) 9) Measurement safety Earth-return mutual errors Low-current measurements Power-system staged faults Communication and control cable transfer impedance Current distribution (current splits) in the grounding system Step, touch, mesh, and proÞle measurements The foot-equivalent electrode earth resistance Instrumentation characteristics and limitations Grounding electrodes consisting of a single ground rod, arrays of ground rods, tower footings, and many grids (if no external grounding is connected) can be measured, interference voltages permitting, with methods outlined in IEEE Std 81-1983 [2]1 Even if a large grid has an impedance phase angle of 18° the resistance component will be only 5% lower than its impedance However, for large grounding grids in low-resistive earth (> a) Z s = R s + jK s (A7) A s 2C 2w = Cr c + j -7- C ln æ ö Ð A s Ð C + D s è a C + DSø 10 where rC = conductor resistance, in W-m AS = 2hC + d -jd 2 DS = C + ( h c2 + dh c ) Ð j ( 2d + 4dh c ) C = grounding conductor length, in m hC = height of conductor C, in m d = 503.292 r- , in m a = conducter radius, in m, which neglects the internal conductor impedance = 82 f GMR, geometric mean radius (see [B45]), in m (for a round conductor, GMR = 7788 conductor radius, in m) Copyright © 1992 IEEE All Rights Reserved Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply OF LARGE, EXTENDED OR INTERCONNECTED GROUNDING SYSTEMS IEEE Std 81.2-1991 When conductor C is very long (C È 2d and d È hC), Eq A7 reduces to Z S = R S + jX S (A8) ổ 712 r-ử ỹ ỡ ỗ ù 9.87 12.57 fữ ù - f ln ỗ -÷ ý = C í r c + -4- f + j -4 GMR ỗ ữ ù ù 10 10 ố ứ ỵ ợ where C = rC = r = f = GMR = conductor length, in m conductor resistance, in W-m earth resistivity, in W-m frequency, in Hz conductor geometric mean radius, in m When rC is in W/km and C is in km, Eq A8 changes to ZS ỉ 712 r-ư ì ç ï 9.87 12.57 f÷ - f ln ç -÷ = C í r C + -4- f + j -4 ỗ GMR ÷ ï 10 10 è ø ỵ ü ï ý ù ỵ The self impedance, ZS2, of two horizontal, parallel, and identical earth-return conductors can be determined with the self impedance of one conductor, ZS (Eqs A7 or A8), the mutual impedance between them, ZM (Eqs A1 or A2 ), and ZS2 = (ZS + ZM)/2 Copyright © 1992 IEEE All Rights Reserved Authorized licensed use limited to: MULTIMEDIA UNIVERSITY Downloaded on August 12, 2009 at 05:04 from IEEE Xplore Restrictions apply 83 IEEE Std 81.2-1991 IEEE GUIDE FOR MEASUREMENT OF IMPEDANCE AND SAFETY CHARACTERISTICS Annex B Mutual Impedance Between Finite Length Conductors Lying on the Ground Based on the Campbell/Foster Method (Informative) Mutual impedance between parallel or angled conductors lying on the earth surface are derived by the Campbell/ Foster Method, see [14] Depending on earth resistivity and frequency, the limited approximation used in the derivation of the following mutual impedance formulas restrict conductor lengths to less than the skin depth, d, for homogenous earth (d = 503.292 r ¤ f ) B.1 Mutual Coupling Between Parallel Conductors Lying on the Ground Fig B1 shows the parallel orientation of the current conductor, C, and the potential conductor, P When both are lying on the ground (hC = hp = 0), the mutual impedance from C to P, in ohms, is given by Eq B1 For conductor lengths less than the earth skin depth, d, Eq B1 and Eq A1 agree for the reactive component, XM However, RM, calculated by Eq B1, is above the resistive component calculated by Eq A1 The latter difference is not serious because the RM magnitude is small Eq B1 will have signiÞcant error when the conductor length exceeds the earth's skin depth, d Thus, neither RM nor XM approach Carson, see [B5], for increasing parallel lengths Refer to the closure of reference [11] for the inÞnite series general equation for the Campbell/Foster Method Figure B-1ÑParallel Orientation of Current and Potential Conductors (B-1) Z M = R M + jX M w CP CP = -7- - + j æ C ln K + P ln K + Y P + K Ð K Ð K Ð - ö è d 3 d ø 10 where 2 K1 = (C Ð P) + Y P K2 = C + YP K3 = P + YP 2 2 K4 = (C + K 2) Ô (C é P + K 1) K5 = (P + K 3) Ô (P é C + K 1) d = 503.292 r- , in m C f