9_1595_NP (1)

Railway applications Fixed Installations Measuring Methods for Railway Integrated Earthing System (Working Draft for NWIP of proposed TS by AHG2) 2011

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Contents Foreword............................................................................................................................................. 2

1. Scope .............................................................................................................................................. 3

2. Normative references....................................................................................................................... 3

3 Terms and definitions........................................................................................................................ 4

4. General regulations.......................................................................................................................... 5

5 Measurement of soil resistivity.......................................................................................................... 5

6 Measurement of earthing resistance of independent earthing electrodes ............................................. 7

7 Test of electrical integrity of integrated earthing system................................................................... 10

8 Measurement of ground impedance of railway integrated earthing system ....................................... 12

9 Measurement of surface-potential gradient, step voltage and touch voltage ...................................... 17

10 Measurement of rail potential and equipment potential of railway integrated earthing system......... 20

Annex A Items and cycle of measurement .......................................................................................... 22

Annex B Measurement of surface potential gradient of earthing connections ...................................... 23

Annex C Description of railway integrated earthing system in concept ............................................... 24

Bibliography ..................................................................................................................................... 27


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Foreword

The Situation of the measurement for railway earthing and bonding system right now, is that, - Standards or regulations or norms of measurement methods for very large building structure as earthing system are used in most countries, but no for railways especially which earthing and bounding applications are quite different from other industry purposes. - Different measurement methods have been used in railways for different equipment and subsystems in some national railways. - Chinese Ministry of Railway (MOR) have developed the standards used in recent large scale high speed railways and upgraded railways. - Series of the IEC 62128 standards will be used in accordance. Based on the work of AHG2 from Dec., 2009 to May, 2011 dominated by IEC/TC9, the proposed working draft has been drawn up in to meet the requirements from large scale constructions of high-speed railway system or powerful EMU locomotives upgraded in existing railway application with more accurate test in a much lower value of equivalent earthing resistivity and impendence by practical methods. Annex of this WD are informative for discussions.


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Measurement methods

for railway integrated earthing system

1. Scope

This Technical Specification describes possible methods for measurements of integrated earthing system in a.c. railways as, - soil resistivity, - continuity of electrical interconnection, - resistance to earth of independent earthing electrodes, - impendence to earth of railway integrated - surface-potential gradient, step voltage and touch voltage and - rail potential and equipment potential of the interconnected return circuit and earthing system. This Technical Specification does not specify as, - which measuring methods are compulsory, - limits to be fulfilled, - requirements for design, approval and maintenance.

2. Normative references

Those clauses cited from the following referenced documents are the clauses of the specification. For dated references, all their subsequent modifications (excluding corrected contents) or revised editions shall not apply to this specification, however, those parties who have entered into an agreement based on this specification are encouraged to study whether the latest edition of those referenced documents can be applied. For undated references, the latest edition of the referenced documents applies.

IEC 61936-1 First edition 2002 Power Installations Exceeding 1 kV a.c. -Part 1: Common rules IEC 62128:2003 Railway applications - Fixed installations - Part 1: Protective provisions related to electrical safety and earthing ANSI/IEEE Std 80-2000, IEEE Guide for Safety in AC Substation Earthing. IEEE Std 487-2007, Recommended Practice for the Protection of Wire-Line Communication Facilities Serving Electric Supply Locations. IEEE Std 998-1996, IEEE Guide for Direct Lightning Stroke Shielding of Substations. IEEE Std 1410-2004, IEEE Guide for Improving the Lightning Performance of Electric Power Overhead Distribution Lines. IEEE Std 1243-1997, IEEE Guide for Improving the Lightning Performance of Transmission Lines.


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HD 637 S1 :1999Power Installations Exceeding 1 kV a.c. GB/T17949.12000, Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Ground System Part One: Normal measurement DL/T4752006, Guide for measurement of earthing connection parameters, electric measurement of power TB/T 3074 Technical conditions for protection of railway signaling installations against lightning electromagnetic impulses

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60050-811 , IEC 62128-1 and the following apply. 3.1 earthing connection A connection used in establishing a ground and consisting of a earthing conductor, a earthing electrode and the earth (soil) that surrounds the electrode. 3.2 earthing grid A system of earthing electrodes consisting of interconnected bare conductors buried in the earth to provide a common ground for electrical devices and metallic structures. 3.3 run-through earth conductors Earth conductors connected with all installations and equipment installed along a railway. 3.4 electric integrity of earthing connection Electrical continuality among all kinds of electrical installations and between each part of earthing device and each part of equipment, measured as the d.c current value. 3.5 step potential difference The potential difference between a distance of 1 meter horizontally on the earth surface, when earthing short-circuit current flows through the earthing connection. 3.6 touch potential difference The potential difference between two points of one being 1.0 meter horizontally away from the equipment, and the other 1.8 meter vertically above the earth surface along the covering of the equipment, structure or wall, when short-circuit current flows through the earthing connection. 3.12 current electrode An electrode placed into earth remotely to form a earthing resistance, surface potential distribution for the measurement of earthing connection. 3.13 potential electrode An electrode placed into earth for the selected reference zero potential in the measurement of characteristic parameters of earthing connection .


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4. General regulations

4.1 Items for the measurement The measurement of railway integrated earthing system includes the following: the measurement

of earth resistivity, the measurement of ground resistance of independent earthing electrodes, the measurement of electrical integrity of railway integrated earthing system, the measurement of ground impedance of railway integrated earthing system, the measurement of surface-potential gradient, step voltage and touch voltage, and the measurement of rail potential and equipment potential of railway integrated earthing system. For the items for measurement of railway integrated earthing system at different phases of a project, see Annex A. 4.2 Environmental conditions for measurement

The measurement of railway integrated earthing system for acceptance shall be administered in the dry season and without the earth being frozen as possibly. The measurement shall not be conducted in lightning, rain, snow, or immediately after raining or snowing. Normally the measurement shall be conducted after consecutively 3 fine days or in the dry season. 4.3 Regulations for measurement safety During the measurement of railway integrated earthing system, the safety regulations on the site shall be abided by strictly. During the measurement, no current conductors shall be broken off, and all the current conductors and current electrodes shall be monitored by designated guards. No touch on the metal wire by hand during in the measurement. If lightning clouds should appear above the electrical poles and towers, the measurement shall stop and the measuring team shall evacuate from the site. 4.4 Assessment of the measurement results The assessment of performance and acceptance of railway integrated earthing system shall be in accordance with the each result of the measurement of characteristic parameters of the railway integrated earthing system tested, and the judgment and conclusion shall be made, in combination with the requirements of relevant standards, on the basis of the following characteristic parameters: electrical integrity of earthing system, earth resistivity, touch voltage and track voltage, without overstressing one parameter. For the detailed data, see the following sections. And thermal capacity of the earthing connection shall satisfy the specified requirement.

5 Measurement of soil resistivity

5.1 Measurement method 5.1.1 Measurement of soil resistivity can be performed with Four-Point Equally Spaced Arrangement or Four-Point Unequally-spaced Arrangement. The measuring electrodes shall be made from round iron bar with diameter larger than 1.5cm or angle iron L25mm*25mm*4mm, and shall not be less than 40cm in length. The measuring electrode shall be inserted more than 20 mm into the earth closely. The


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measuring lead shall be single-core insulation sheathed conductor, and any joints shall maintain electrical continuity and insulation from the earth. The cross section of measuring lead shall be more than 1.5mm2, and the reliable connection shall be guaranteed between measuring electrode and measurement instruments. 5.1.2 Other methods for measurement of soil resistivity and analytical method of measurement data shall be in accordance with the relevant requirements of GB/T17949.1-2000. 5.1.3 The distance between measuring electrodes a is closely related to the depth of the earth measured. When the area of the site to be measured is large, a shall increase correspondingly. In order to reflect the earth condition of railway integrated earthing system, the maximum distance between the neighboring electrodes a shall not be less than 100m. In order to reduce the effect of railway integrated earthing system on the measurement results of soil resistivity, the minimum distance between the measuring electrodes shall be placed 100 m away from the subgrade of the railway. In order to ensure the reliability of soil resistivity measurement, the measurement shall be conducted twice, vertically and horizontally with respect to tracks each, and then the average of the two results is taken as the final result. If considerable discrepancy is found between two measurements, or obvious discrepancy is found between the results obtained and those in the previous measurements, new measurements shall be administered by changing the directions of measuring electrodes arrangement or increasing the distance between electrodes. If soil resistivity changes suddenly or changes clearly with vertical stratums, the measurement distance and measuring points may be increased appropriately on the basis of geotechnical soil investigation and the distribution of buildings along the railway. 5.1.4 Figure 5.1 is the wiring diagram of four-point equally-spaced method, where the distance between electrodes is a (m) and the measuring electrode is inserted not more than 1a during measurement. When the measuring current flows into the two outer electrodes, the measuring meter of ground impedance obtains the earthing resistance R () through measuring the potentials between two outer current electrodes and two inner potential electrodes. Then the apparent soil resistivity (m)can be calculated by formula (1).

=2R 1

Figure 5.1 Four-point equally-spaced method 5.1.5 Figure 5.2 is the wiring diagram of four-point unequally-spaced method, where a (m) is the distance between the current electrode and the potential electrode, and b (m) is the space between potential electrodes. When the distance between electrodes is considerably large, the measuring meter


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of earthing resistivity usually cannot measure or cannot measure precisely such a small potential difference, because the potential difference between the two inner electrodes drops rapidly. In this case, unequally spaced arrangement shown in Figure 5.2 can be used where the potential electrodes are placed closer to corresponding current electrode, which can increase the potential difference measured. The measuring meter of earthing resistivity obtains the earthing resistance R () through measuring the potentials between two outer current electrodes and two inner potential electrodes. If the burial depth of electrodes is comparatively small with respect to its distance to a and b, then the apparent soil resistivity (m)can be calculated by formula (2). =2+bR/b 2

Figure 5.2 Four-point unequally-spaced method

6 Measurement of earthing resistance of independent earthing electrodes

6.1 The scope of measurement The earthing grids of each administrative sub-branch of electrification railway, sub-substation, communication base station, room of signaling facilities, earthing electrode of bridge piers and power pole and towers, and earthing grids of tunnels less than 500 meter which are not incorporated with the railway integrated earthing system fall into the category of independent earthing electrodes. 6.2 The arrangements for the measurement 6.2.1 Measurement of earthing resistance of independent earthing electrodes can be administered with three-point arrangement where current electrode, potential electrode and injection point of measurement current shall not be placed in parallel with the tracks. The distance between current electrode, potential electrode and the injection point of measurement current shall be the linearly geometrical distance between electrodes, and shall be measured precisely. 6.2.2 Other methods for measurement of earthing resistance of independent earthing electrodes shall be in accordance with the relevant requirements of international or national standards. 6.2.3 During the measurement, the measurement circuit shall avoid rivers and lakes, avoid underground metallic pipes and power transmission line in operation as far as possible and running in parallel with them for a long distance. In soil-frozen area, the measuring electrodes shall be driven below the freezing line.


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6.2.4 The distance between the measuring electrodes and the underground metallic objects shall not be less than that between the measuring electrodes in order to reduce the effect of underground metallic objects. The measuring electrodes shall not be placed into the non-uniform earth evidently with rocks, cracks and slops to reduce the effect of non-uniformity of earth composition. 6.2.5 The measuring electrodes shall be made from round iron bar with diameter larger than 1.5cm or angle iron L25mm*25mm*4mm, and shall not be less than 40cm in length. The measuring electrode shall be inserted more than 20 cm into the earth closely. The measuring lead shall be single-core insulation sheathed conductor, and any joints shall maintain electrical continuity and insulation from the earth. The cross section of measuring lead shall be more than 1.5mm2, satisfying the requirement for heat capacity of test current, and the reliable connection shall be guaranteed between measuring electrode and measurement instruments. 6.2.6 The resistance between the current electrode and the earth shall be possibly small. In order to increase the measurement current effectively, it is advisable to place current electrode in the ponds, increase the number of current electrodes or sprinkle water around the current electrodes to reduce the resistance between the current electrode and the earth. 6.3 Measurement instruments Measurement of earthing resistance of independent earthing electrodes may be administered by use of 4-terminal earthing resistance meter which is powered by an independent power source or through an isolation transformer. The measurement meter shall have precision grade higher than 1.0 and the resolution of the voltmeter shall not be less than 1mV. When power source of different frequencies is used, the tester shall have a good property of frequency-selection to avoid the noise interference on the measurement. 6.4 Three-point straight line method When three-point straight line method is used to measure the earthing resistance of independent earthing electrode, current electrode and potential electrode shall be placed in the same direction as the track, as shown in Figure 6.2. The current electrode measuring the earthing resistance of independent earthing electrode shall be placed possibly far, normally the distance between current electrode and the border of the earthing connection to be measured dCG shall be 4 or 5 times the length of the maximal diagonal of the earthing connection D. If there is a difficulty in remote alignment, dCG shall be taken 2D in the area of uniform earth resistivity, whereas dCG shall be taken 3D in the area of non-uniform earth resistivity, and normally dPG shall be0.50.6dCG. During measurement, electrode P is moved three times near 0.50.6dCG in the direction of earthing connection G and current electrode C, the movement distance shall be 5% dCG approximately. If the error of the results of three measurements is within 5%, then the results shall be accepted as the earthing resistance of earthing electrode. During measurement, the current wire and potential wire shall be kept far away as possible to reduce the effect of mutual induction coupling on the measurement results.


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G: independent earthing electrode under test; C: potential electrode; D: maximal diagonal length of independent earthing electrode under test; dPG: distance between potential electrode and the border of the earthing electrode under test; dCG: distance between current electrode and the border of the earthing electrode under test

Figure 6.1---Diagram of 3 point straight line method 6.5 Three point included angle method If conditions permit, measurement of earthing resistance of independent earthing electrodes may be conducted with 3 point included angle method in which the distance between current electrode and injection point of measuring current and the that between potential electrode and injection point of measuring current form an included angle, as shown in Figure 6.2. The distance between current electrode and the border of the earthing electrode under test dCG shall be 4 or 5 times the length of the maximal diagonal of the earthing connection D, and dCG and dGP shall be similar in length. Then the earthing resistance Z can be calculated by formula 3:

2 2'/ [1 (1/ 1/ 1/ 2 cos ) / 2]CG PG CG PG CG PGZ Z D d d d d d d = + + (3) where is the include angle between the potential wire and current wire; Z the value of earthing

resistance measured, Z=UPG/I; UPG the potential between potential electrode and earthing electrode under test G; I the measuring current injected into the earthing electrode. In the area of uniform earth resistivity, an isosceles triangle arrangement may be used with dCG being equal to dGP. In this case, is taken as approximately 30, and dPG=dCG=2D, then the earthing resistance Z can still be calculated by formula 3.

G: independent earthing electrode under test; C: potential electrode; D: maximal diagonal length of independent earthing electrode under test; dPG: distance between potential electrode and the border of the earthing electrode under test; dCG: distance between current electrode and the border of the earthing electrode under test

Figure 6.2---Diagram of 3 point included angle method


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7 Test of electrical integrity of integrated earthing system

7.1 Testing scope The measurement of electrical integrity of railway integrated earthing system covers the following: a) the measurement of electrical integrity of railway integrated earthing system: measurement of electrical integrity of connections between various earthing electrodes of subgrade, bridges and tunnels along the railway and railway integrated earthing; the measurement of electrical integrity between the earthing connections of the installations and buildings along the railway which are incorporated into railway integrated earthing system and railway integrated earthing system. b) the measurement of electrical integrity of earthing connections of traction substations and power supply substations: measurement of electrical integrity of earthing connections between ground grids of various voltage classes along the railway; measurement of electrical integrity between earthing electrodes of both high and low voltage equipment and installations, including framework, distribution boxes, terminal boxes, power supply units; measurement of electrical integrity between various earthing trunks of main control room and its internal earthing conductors and railway integrated earthing system, and electrical integrity between other necessary parts and railway integrated earthing system. c) the measurement of electrical integrity of earthing connections of communication and signaling system: the measurement of electrical integrity between the earthing connections of communication and signaling system; measurement of electrical integrity between the earthing connections of communication and signaling system and the railway integrated earthing system. 7.2 Measurement method 7.2.1 During the measurement, a earthing electrode which has a sound connection with the earthing system under test is taken as the reference point, then the D.C. resistance is measured between the reference point and the earthing point of the electrical equipment which is 300 meter or so away from the reference point, and the ambient temperature is measured and recorded. 7.2.2 If the resistance measured is found to be above 50 m, then the measurement shall be repeated for verification of the result. If the measurement results of several installations reveal poor connections, it is recommended that a new reference point be selected and the measurement be performed again. During the measurement, due attention shall be paid to the reduction of the influence of contact resistance. 7.3 The Constant Current test method In the constant current test, the test current comes from the substation, and it flows in the contact lines and the rails. The circuit is completed by an electric locomotive which is converted so that it can take a constant current from the contact line. This is achieved by disconnecting the traction motors, and replacing them in the locomotive's power circuit by resistors. The converted locomotive is hauled along the railway, at approximately constant speed, by a diesel


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locomotive. The important currents and voltages, in the Railway Integrated Earthing System, are recorded in data-loggers. Measurements should be made of quantities including:

The current in the substation earthing electrodes The current in the important independent earthing electrodes and equipotential bonds The rail potential, and the step and touch voltages, at places where it is important to limit these

quantities to the safe levels.

Please see Figure 7.1. The advantage of this method, is that it can be done when the Railway Integrated Earthing System is in its normal configuration. If a converted locomotive, for the constant current, is not available, a normal train can be used instead, but the assessment of the results is then more difficult. The same measurements can be made during the every-day operation of the railway. NOTE: In the construction of the railway, the important equipotential bonding conductors and similar connections should be arranged so that it will be convenient to measure the current which flows in them, using split-core transducers.

Figure 7.1 Principle of the Constant Current test method

7.4 Instruments for measurement D.C. circuit resistance tester shall be used for the measurement of electrical integrity, the resolution of the tester shall be 1 m, measurement precision shall not be less than Grade 1.0, and the rated output current shall be larger than 100 mA. Tester based on DC bridge principle may be used. In the method, constant D.C. power source is applied to the earthing electrode and the reference point, the potential


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difference of that section of metal conductor on the earthing connection of the equipment under test is measured by the voltmeter with high internal resistance, then the potential difference measured can be converted into resistance value. In the measurement of electrical integrity, 4- terminal method shall be used, with two current electrodes and two potential electrodes connected separately to reduce the contact resistance and the influence of resistance of leading wire. The cross section of measuring lead shall be more than 1.5mm2, and the reliable connection shall be guaranteed between measuring electrode and measurement instruments. 7.5 Interpretation and treatment of the testing results Interpretation and treatment of the testing measurement results shall follow the following methods: a) The DC resistance value measured shall be less than 50 m between the reference point and the earthing measuring point of an installation with sound earthing connections; b) If the DC resistance between the reference point and the earthing measuring point of an installation varies between 50 m--200 m, which indicates that the earthing connections just meet the working requirements, due attention shall be paid to its variation in the routine measurements thereafter, and important installations or cables shall be inspected in due time; c) If the DC resistance between the reference point and the earthing measuring point of an installation varies between 200--1, which indicates that the earthing connections are poor, important installations shall be inspected as soon as possible proper measures taken, and other installations or cables shall be inspected in due time; d) If the DC resistance between the reference point and the earthing measuring point of an installation is more than 1, which indicates that the installation measured is not connected with the railway integrated earthing system, immediate inspection shall be performed and proper measures taken; e) If the relative value of an installation obtained from the measurement is obviously larger than that of other installations, while the absolute value is not large, then the earthing connection of the installation under test shall be deemed as just meeting the working requirements.

8 Measurement of ground impedance of railway integrated earthing system

8.1 The selection of measurement methods 8.1.1 The measurement of earth resistivity shall be conducted before the measurement of ground impedance of railway integrated earthing system, and then the length of alignment of measurement wire can be determined in accordance with the earth resistivity measured. 8.1.2 The measurement of ground impedance of railway integrated earthing system shall employ reversed-current-long-distance method, shown as in Figure 5; if the arrangement of measuring


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electrodes is restricted by the environmental conditions, The measurement of ground impedance of railway integrated earthing system can may use compensation method, shown as in Figure 6; potential drop method shown as in Figure 7, may be used when the earth resistivity measured is comparatively uniform and the site is suitable for long measuring wire arrangement vertical to the track. When compensation method or potential method is employed, the leading wires of current electrode and potential electrode shall be kept as far away as possible to reduce the effect of mutual induction coupling on the measurement results. 8.13 Should obvious discrepancy be found between the measurement result and those previously measured, inspection shall be made to check the electrical connection of test circuit and rationality of selection of the measurement points, and different measurement methods may be used for verification of the results, if necessary. 8.2 Measurement arrangement The measurement of ground impedance of railway integrated earthing system shall use the three-point arrangement method, in which the arrangement of current electrode, potential electrode and current injection point of railway run-through earth conductor shall be on a straight line which is vertical to the tracks. The distance between the current electrodes, potential electrode and current injection point of railway run-through earth conductor shall be linearly geometric and measured precisely. Other requirements shall be the same as specified in sub-clause 6.2.3 to 6.2.6 of 6.2. 8.3 Test current In the measurement of ground impedance of railway integrated earthing system, a earthing electrode with sound connection with the railway integrated earthing system shall be selected as the injection point of test current. The test current shall meet the following requirements: 8.3.1 Different-frequency current method is recommended to measure ground impedance of railway integrated earthing system, the testing current shall vary within 3 A -20 A, the frequency shall be within 40Hz and 60Hz, which differs from power frequency but approaches power frequency possibly closely. 8.3.2 When ground impedance of railway integrated earthing system is measured with power-frequency large-current method, an independent power source or isolation transformer shall be used for power supply, and the test current shall be as big as possible, and shall not be less than 50A. Care shall be paid to the test safety, such as guarding the current electrode and potential electrode. 8.4 Test instruments Ground impedance measurement meter with 4 terminals shall be used for the measurement of ground impedance of railway integrated earthing system, and the power supply shall be provided by an independent power source or isolation transformer. The precision class of the meter shall not be less than Class 1.0, and the resolution of the voltmeter shall not be less than 1 mV. The measuring meter shall have a sensitive frequency-selection when different-frequency power source is applied. 8.5 Measurement spacing The measurement results of ground impedance of railway integrated earthing system indicate the


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ground impedance of railway integrated earthing system of a certain length of railway. Table 8.1 shows effective measurement spacing of railway integrated earthing system corresponding to different earth resistivity.

Table 8.1 Effective measurement spacing of earthing impedance of railway integrated

earthing system Earth

resistivity m

100 100300

300500

500700

7001000

10002000

2000

Spacing (km)

12 24 45 56 67 79 910

8.6 Reversed-current-long-distance method for ground impedance measurement Figure 8.1 illustrates the arrangement of electrodes in the ground impedance measurement of railway integrated earthing system with reversed-current-long-distance method, by which the current electrode and potential electrode are placed on each side of the railway integrated earthing system, the distance between current electrode C and the run-through earth conductors is dCG, and the distance between potential electrode P and the run-through earthing cables is dPG .Neither dCG nor dPG includes the width of the run-through earth conductors on both sides of railway integrated earthing system. When ground impedance of railway integrated earthing system is measured with reversed-current--long-distance method, dCG 400m, and dPG = 0.5dCG. After arrangement of the measuring leads of current electrode and potential electrode, the test current is applied, and subsequently the measured potential value U and current value I can be read on the voltmeter and ammeter. Then the ground impedance of railway integrated earthing system can be calculated with the formula Z=k(U/I), where k is the correction coefficient k of ground impedance at different earth resistivity of reversed-current-long-distance method, k values are listed on Table 8.2. And the appropriated k value is determined in accordance with earth resistivity measured and regulations in Table 8.2.

Table 8.2 Correction coefficient k of ground impedance at different earth resistivity of reversed-current-long-distance method

Earth resistivity m

100 100300

300700

7001000

10002000

2000

dCG=400m k=1.29 k=1.38 k=1.41 k=1.40 k=1.34 k=1.25 dCG=700m k=1.20 k=1.28 k=1.35


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G: current injection point; C----current electrode P---potential electrode

dPG---- the linear distance between potential electrode P and the run-through earth conductor; dCG--- the linear distance between current electrode C and the run-through earth conductor Figure 8.1 Arrangement of electrodes of reversed-current-long-distance method in measurement

of ground impedance of railway integrated earthing system 8.7 Compensation method for ground impedance measurement Figure 8.2 shows the arrangement of electrodes in the ground impedance measurement of railway integrated earthing system with compensation method, where the current and potential electrodes are placed on the same side of the run-through earth conductor of railway integrated earthing system, the linear distance between current electrode C and the run-through earth conductor is dCG, and the linear distance between potential electrode P and the run-through earth conductor is dPG. When ground impedance of railway integrated earthing system is measured with compensation method, dCG should be equal to or larger than 700m, and the arrangement of potential electrode should be determined according to earth resistivity and meet the requirements set in Table 8.2. After arrangement of measuring lengths of current electrode and potential electrode based on the corresponding earth resistivity measured, the test current is applied, and subsequently the measured potential value U and current value I can be read on the voltmeter and ammeter. Then the ground impedance of railway integrated earthing system can be calculated with the formula Z=U/I.

Table 8.3 Potential electrode locations at different Earth resistivity Earth

resistivity m

100300

300500

500700

7001000

10002000

2000 3000

When dCG=700m potential electrode

location (m)

dPG= 380326

dPG= 326293

dPG= 293267

dPG= 267239

dPG= 239179

dPG= 179145

Note: If earth resistivity varies, dPG can be estimated linearly according to location of the section where earth resistivity is measured.

Test Power

Railway Integrated Earthing System


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G: current injection point; C----current electrode P---potential electrode

dPG---- the linear distance between potential electrode P and the run-through earth conductor; dCG--- the linear distance between current electrode C and the run-through earth conductor

Figure 8.2 Arrangement of electrodes of compensation method in measurement of ground impedance of railway integrated earthing system

8.8 Potential drop method for earthing impedance measurement Figure 8.3 shows the arrangement of electrodes in the ground impedance measurement of railway integrated earthing system with potential drop method, where electrode C and electrode P are placed on the same side of the run-through earthing conductor of railway integrated earthing system, the linear distance between current electrode C and the run-through earth conductor is dCG, and the linear distance between potential electrode P and the run-through earth conductor is dPG.

G: current injection point; C----current electrode P---potential electrode; D: measurement interval;

dPG---- the linear distance between potential electrode P and the run-through earth conductor; dCG--- the linear distance between current electrode C and the run-through earth conductor

Figure 8.3 Arrangement of electrodes of potential drop method in measurement of ground impedance of railway integrated earthing system

Test current is injected between the railway integrated earthing system G and the current electrode C, causing the change of earth potential. Then potential electrode P is moved from the border of G in the direction of return current, potential drop between P and G is measured at each interval d (10m or 20m) and draw up the variation curve of U and X. The point where the curve levels off is the point of zero potential. The potential drop between the point of zero potential and the starting point of the curve is the uplift of potential of the railway integrated earthing system under test current I, and the earthing impedance of railway integrated earthing system can be obtained by the formula: Z= Um/I

Test Power


Test Power




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In order to achieve the leveling-off of the change curve of U and X, the current electrode C shall be placed out of sphere of the effect of railway integrated earthing system and dCG700mWith potential drop method, comparatively correct results can be obtained when the change curve has a clear leveling-off section, to which particular attention shall be paid. If it is difficult to determine the point at which the change curve of potential levels off, the cause may be the effect of the railway integrated earthing system or the current electrode, or may be the complicated underground conditions. One solution is to extend the length of current electrode wire as long as possible. Otherwise, other measurement method may be used.

9 Measurement of surface-potential gradient, step voltage and touch voltage

9.1 Method for measurement of surface-potential gradient 9.1.1 The distribution curve of surface potential gradients can indicate the distribution of surface potentials in the earthing connections. The earthing connection performance of the earthing grid of large stations or traction substations can be analyzed by measuring surface potential gradients. Measurement of surface potential gradients can be conducted for some crucial locations. 9.1.2 Figure 9.1 shows the measurement of surface potential. The current electrode for the measurement of surface potential shall be placed possibly far away, the linear distance from the current electrode C to the run-through earth conductor dCG shall be larger than or equal to 700m. And other requirements are the same with those specified in 6.2.36.2.6 of sub-clause 6.2. 9.1.3 The test area shall be divided rationally, and surface potential distribution is represented with several curves, see Figure B.1 in Annex B. The curves are arranged in accordance with the factors such as the number of equipment, the importance of the equipment, and normally the space between curves shall not be larger than30m. 9.1.4 In the mid of tracks of curves, an earth terminal of a device is selected, which has a sound connection with the main earthing grid of the site, as the reference point, from which measurement of surface potential gradient U shall be carried out at equal interval d (normally 1m or 2m) between measuring surface and the reference point, until the end edge of site, and then the distribution curve of surface gradient shall be drawn. 9.1.5 The measuring electrodes shall be made from round iron bar with diameter larger than 1.5cm or angle iron L25mm*25mm*4mm, and shall not be less than 40cm in length. The measuring electrode shall be inserted more than 20 cm into the earth closely. If the site is of cement concrete pavement, then the measuring electrode may be a round metal plate of 20cm in diameter wrapped with wet cloth, pressed by 40 kg or more weight. Attention shall be given to the electromagnetic interference if the measuring wire is comparatively long. 9.1.6 For the measurement of surface potential gradient, the precision class of the meter shall not be less than Class 1.0, its internal impedance not less than 1M, and the resolution of the voltmeter shall


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not be less than 1 mV. In order to avoid the noise influence, the measuring meter shall have a sensitive frequency-selection when different-frequency power source is applied.

G: current injection point; C----current electrode P---potential electrode; D: measurement interval

Figure 9.1 Diagram of measurement of surface potential gradient 9.1.7 When d is 1m, the surface potential gradient UT when the system is in fault can be calculated with the following formula

UT= UT Is/Im 4 where UT is the potential difference between two neighboring points on the surface potential

curve; Is is the single phase earthing fault resistance of the earthing connections of the device under test; Im the measuring current injected into the earthing grid.

9.1.8 Judgment of the measurement results of surface potential gradient The distribution curves of surface potential gradients in the earthing grid of excellent performance look flat, normally with two ends rising slightly. Rapid fluctuation or rapid change of the curves indicates the poor performance of the earthing grid. For reference see the Figure B.2 in Annex B. When the maximal single phase earthing short-circuit current of the effective earthing system does not exceed 35 kA in the earthing grid, the surface potential gradient per unit is less than 20V and may not be larger than 60. If the surface potential gradient per unit approaches or exceeds 80V, then the cause shall be found out and due measures taken. 9.2 Measurement of step potential difference, touch potential difference, step voltage and touch voltage. 9.2.1 Step potential difference, touch potential difference, step voltage and touch voltage shall be measured of installations and traction substation along the railway, devices and equipment the staff of power distribution substation may contact, such as framework, earthing lead-in wire, and covering of equipment. 9.2.2 Figure 9.2 shows the diagram of measurement of step potential difference, touch potential difference, step voltage and touch voltage. The current electrode for the measurement of surface potential shall be placed possibly far away, the linear distance from the current electrode C to the run-through earth conductor dCG shall be larger than or equal to 400m. In Figure 9, the equivalent

Test Power

Earthing Wire

Direction Direction

End Edge


19 / 28

resistance of a human body Rm shall be 1000.When the switch K breaks and Rm is not connected into the circuit, the touch potential difference and step potential difference are measured; when K closes, and Rm is connected into the circuit, touch voltage and step voltage are measured. 9.2.3 The measuring electrodes shall be made from round iron bar with diameter larger than 1.5cm or angle iron L25mm*25mm*4mm, and shall not be less than 40cm in length. The measuring electrode shall be inserted more than 20 cm into the earth closely. If the site is of cement concrete pavement, then the measuring electrode may be a round metal plate of 20cm in diameter wrapped with wet cloth, pressed by 40 kg or more weight. And other requirements are the same with those specified in 6.2.36.2.6 of sub-clause 6.2. 9.2.4 For the measurement of step potential difference, touch potential difference, step voltage and touch voltage, the precision class of the meter shall not be less than Class 1.0, its internal impedance not less than 1M, and the resolution of the voltmeter shall not be less than 1 mV. In order to avoid the noise influence, the measuring meter shall have a sensitive frequency-selection when different-frequency power source is applied. 9.2.5 The measured values of step potential difference, touch potential difference, step voltage and touch voltage can be calculated in accordance with Formula5

Us=Us Is/Im 5 Where, UT is the measured values of step potential difference, step potential, step voltage and touch voltage; Is is the single phase earthing fault resistance of the earthing connections of the device under test; Im the measuring current injected into the earthing grid.

9.2.6 The judgment of measurement results of step potential difference, touch potential difference, step voltage and touch voltage: For the permissible values of step potential difference, step potential, step voltage and touch voltage, refer to the limits in relevant standards and Annex C.

G: current injection point; C----current electrode P---potential electrode; D: measurement interval Figure 9.2 Diagram of measurement of step potential difference, step potential difference, step

voltage and touch voltage

Test Power

Earthing Wire

Equi.


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10 Measurement of rail potential and equipment potential of railway integrated earthing system

10.1 Basic requirements 10.1.1 Measurement of rail potential and equipment potential of railway integrated earthing system shall be administered when locomotive runs in operating condition. The measurement shall cover the characteristic locations of power supply section and performance of locomotive in characteristic operating conditions, such as single train operation at a large interval, and the tracking operation of trains. The effective data of the measurement of each typical operating condition shall not be less than 5 sets. The results of measurement of rail potential and equipment potential shall be the effective values. 10.1.2 In the measurement of rail potential and equipment potential of railway integrated earthing system, digital storage oscilloscope with wave form storage or digital transient recorder shall be used, and the transmission band, vertical resolution, and measurement sampling rate of these equipment shall meet the precision requirement of the measurement of transient waveforms, and the length of measurement data record shall satisfy the time requirement for the dynamic operation of trains in this section. Digital storage oscilloscope or digital transient recorder shall be powered by an independent power source or an isolation transformer. 10.1.3 When rail potential and equipment potential are measured, track current, current in the integrated earthing conductor and current in the overhead protection conductor shall be measured at the same time. The measurement of rail potential, equipment potential, and track current, current in the integrated earthing conductor and current in the overhead protection conductor at a measurement point shall be conducted with the same digital storage oscilloscope or digital transient recorder, so as to reveal the dynamic variation of each signal. If the digital storage oscilloscope or digital transient recorder does not have enough channels, synchronized trigger shall be used. The measurement data shall reflect the maximal values of performance of locomotive in each typical operating condition. The trigger level of digital storage oscilloscope or digital transient recorder shall be tuned down gradually from high level, or have enough record length to reflect the maximal value of performance of locomotive in typical operating conditions. 10.2 Measurement method 10.2.1 The measurement of rail potential and equipment potential of railway integrated earthing system is related to the selection of the reference point of zero potential. The reference point of zero potential shall be placed possibly far away, and the linear distance from the reference point of zero potential to the run-though earth conductor on the same side of the railway shall not be less than 400m, or not less than 200m if the geotechnical conditions on site restrict the setting out of measurement line. 10.2.2 Method for measurement of rail potential: A point on the track is selected as measuring point, and the potential between the measuring point and the reference point of zero potential is the rail potential at that point. In the measurement, a terminal of a divider (or an attenuator probe) is connected


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to the track, and the other terminal to the reference point of zero potential, and the potential difference between the two terminals is the rail potential. Figure 10.1 is the wiring diagram. At the same time recorded are the performance of the locomotive, the measurement time, and track current, current in the integrated earthing conductor and current in the overhead protection conductor. 10.2.3 Method for the measurement of equipment potential: A point ( an metal terminal with a sound connection to the covering of the equipment ) on the equipment under test is selected as measuring point, and the potential between the measuring point (mp) and the reference point of zero potential (rpzp) is the equipment potential of that equipment. In the measurement, a terminal of a divider (or an attenuator probe) is connected to the measuring point of the equipment under test , and the other terminal to the reference point of zero potential, and the potential difference between the two terminals is the equipment potential of the equipment. Figure 10.2 is the wiring diagram. At the same time recorded are the performance of the locomotive, the measurement time, and track current, current in the integrated earthing conductor and current in the overhead protection conductor.

Figure 10.1 -- Diagram of measurement of rail potential

Figure 10.2 -- Diagram of measurement of equipment potential

rpzp

Earthing Wire

mprecorder

recorder

rpzp

rpzp

Equi.


22 / 28

Annex A Items and cycle of measurement

(Informative) In the design phase of railway integrated earthing system, earth resistivity measurement would be carried out in traction substations and distribution substation of capacity of 10 kV and above. More measuring points would be added in the area of high earth resistivity, sections of complicated geotechnical conditions, and sections of bridges and tunnels of importance. Measurement of earthing resistance and electrical integrity of independent earthing electrode would be administered after the completion of construction of one item in the construction phase. Acceptance measurement would be conducted when the project meets the requirements for acceptance. In the phase of operation and maintenance, electrical integrity measurement of the system would be performed once every 1 to 2 years, and all measurements of the system would be competed every 4 to 5 years. In the case of severe earth erosion (such as alkaline and acid soils) earthing resistance of independent earthing electrode would be carried out once every 1 to 2 years. If the railway integrated earthing system is renovated or if it is necessary for other reasons, specific measurements would be carried out.

Figure A.1 Cycle of measurement

By OperatorMonitoring for maintenance (type of cyclic tests and test interval)Operation phase

Certificate of service power (initial verification)Certificate of traction power (rail potential)Certificate of bonding of further subsystemsCertificate of bonding for LPS

By Railway E&M Supplier

Certificate of bonding of trackside installations inside and outside of OCL zone and pantograph zone

Commissioning phase

Test of continuity and completeness of all terminals per structure related to the reference terminal for earthing and LPS

Resistance to earth per structure at one reference terminal

Certificate of embedded conductors per structure and per each section of construction before pouring the concrete

Certificate of rail insulation

By Civil Works

Soil resistivity at selected locations

Construction phase

By clientor railway

E&M supplier(Soil resistivity at selected locations) Engineering phase

Project Start

By OperatorMonitoring for maintenance (type of cyclic tests and test interval)Operation phase

Certificate of service power (initial verification)Certificate of traction power (rail potential)Certificate of bonding of further subsystemsCertificate of bonding for LPS

By Railway E&M Supplier

Certificate of bonding of trackside installations inside and outside of OCL zone and pantograph zone

Commissioning phase

Test of continuity and completeness of all terminals per structure related to the reference terminal for earthing and LPS

Resistance to earth per structure at one reference terminal

Certificate of embedded conductors per structure and per each section of construction before pouring the concrete

Certificate of rail insulation

By Civil Works

Soil resistivity at selected locations

Construction phase

By clientor railway

E&M supplier(Soil resistivity at selected locations) Engineering phase

Project Start


23 / 28

Annex B Measurement of surface potential gradient of earthing connections

(Informative)

Note: * the reference point of curve Figure B.1diagram of measurement of surface potential gradient of earthing connections

Figure B.2distribution curve of surface potential gradient of earthing connections The 4 curves in Figure B.2 are typical ones measured of surface potential gradient of earthing connections. Curve 1 indicates the surface potential gradients are comparatively even distributed which means that the earthing connections work well; the tail of Curve 2 rises rapidly and Curve 3 has a big fluctuation, which means the earthing connections may not work well, whereas Curve 4 presents 2 abnormally sharp rises and rapid rise of its tail, indicating there may be likely serious defects in the underground earthing connections.

Curve 1

Curve 2

Curve 3

C u r. 5

C u r. 7

C u r. 6

Curve 4

Curve 1 Curve 2 Curve 3 Curve 4

Distance (m)

Potential difference (mV

)


24 / 28

Annex C Description of railway integrated earthing system in concept

Railway integrated earthing system, is a grid earthing system consisting of traction line-feeder-and-return-circuit system, power supply system, signaling system, communication, and other electronic information system, buildings, track-beds, platforms, bridges, tunnels and sound barriers, all of which need earthing and are integrated by run-through earth conductors as a whole, and functioning as discharging current and equalizing potential as well. There are different earthing circuits in different countries based on the protection provisions of earthing and bonding for safety concept described in IEC62128-1. See Figure C.1 to C.3.

Railway installationsNon-railway installationspipe with insulating joint

RunningRails

StructureEarth

shielded cables

FenceSignaloverhead earth wire

Substation Station

Platform

Station power supplyTraction power supply

Return Circuit

EarthingSystems

Figure C.1 Earthing circuit of railway integrated earthing system in DE


25 / 28

CPW

R (rail)

Neutral wire

T (contact wire)

F (feeder)

PW (protective wire)

GP (S typedischarger)


Steel pipe mast Steel pipe mast

Station(steelstructure)

GP

Mainphase

Teaser

Feeding transformer

AT Surge arrester

GP (ground faultprotective discharger)

Building

Steel structure / frame

Distribution cubicle

RTU (remoteterminal unit)

Communication cable

Insulation hat

50m or more3-pole surge arrester

Impedance bond

Figure .2 A.C. traction system earthing (open section) (Informative)

Substation

RPCD

AT(auto-transformer)

CPW

R (rail)

Neutral wire

T (contact wire)

F (feeder)

PW (protective wire)



Steel pipe mast Steel pipe mast

Station(steelstructure)

GP

Mainphase

Teaser

Feeding transformer

AT Surge arrester

GP (ground faultprotective discharger)

Building

Steel structure / frame

Distribution cubicle

RTU (remoteterminal unit)

Communication cable

Insulation hat

50m or more3-pole surge arrester

Impedance bond

Figure .2 A.C. traction system earthing (open section) (Informative)

Substation

RPCD

AT(auto-transformer)

Figure C.2 Earthing circuit of railway integrated earthing system in JP


26 / 28

Figure C.3 Earthing circuit of railway integrated earthing system in CN for high speed railway


27 / 28

Bibliography

ASTM B 539-2002 Standard Test Methods for Measuring Resistance of Electrical Connections (Static Contacts) ANSI/IEEE td 81 -1983 IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potential of a Earthing system. ANSI/IEEE Std 81.2-1991 IEEE Guide for Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Earthing systems. United States National Electrical Code BS 7430 Code of Practice for Earthing. BS 6651 Protection of Structures against Lightning. IEC 60364-1: Electrical installations of buildings Part 1: Fundamental principles, assessment of general characteristics, definitions. International Electrotechnical Commission, GB/T 17949.1-2000 Guide for measuring earth resistivity, ground impedance and earth surface potentials of a ground system--Part 1: Normal measurements, Chinese National Electrical Code Canadian Electrical CodePart 1, Safety Standard for Electrical Installations CSA Standard C22.1-06, Canadian Standards Association, Mississauga, Ontario 2006, ISBN 1-55436-923-4 IEEE Std 1474.1:2004, Communications-based Train Control (cbtc) Performance and Functional Requirements

Suggested Project Plan 9(AHG2)-CONV503

1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12

Call for Experts and convenor of AHG2

Preparation of TR text

1st AHG2 meeting (GENEVA,07/2010) A1Preparation of TR text

TC9 Plenary Meeting (CN,10/2010) PL

Circulation of GP, Call for more Experts

2nd AHG2 meeting (FR,01/2011) A2

Preparation of NWIP text

Submission of NWIP Draft to TC9 CAG meeting NWIPDTC9 CAG meeting (IT,04/2011) CAG

Submission of NWIP to TC9 NWIPCirculation of NWIP with Working Draft

1st PT-WD meeting (CN,07/2011) 1Preparation of CD text

2nd PT-CD meeting (JP,09/2011) 2Preparation of CD text

TC9 Plenary Meeting (JP,11/2011) PL

Submission of CD to TC9 CDCirculation of CD

Preparation of FDIS text

3rd PT-FDIS meeting (CN,05/2012) 3Preparation of FDIS text

Submission of FDIS to TC9 FDISTranslation of FDIS

Circulation of FDIS

TC9 Plenary Meeting (11/2012) PL

4th PT-FDIS meeting (02/2013) 4Preparation of TS text

Submission of TS to TC9 TSTranslation of TS

Publishing of TS

2011-5-30

2013WBS 2010 2011 2012

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9(AHG2)-CONV-504

For IEC use only 2011-04-06

INTERNATIONAL ELECTROTECHNICAL COMMISSION TECHNICAL COMMITTEE 9: ELECTRICAL EQUIPMENT AND SYSTEMS FOR RAILWAYS AHG2 : Measuring Methods for Railway Integrated Grounding System

NWIP_ANNEX4_

Final Report of the Survey of Measuring Methods for Railway Integrated Earthing System 1. Background In recent years, earthing measurement for the railway application is important technical method to get the correct and accurate data for design of the safety for equipment and human, construction quality inspection, commission, safety evaluation and maintenance in future operation, because of the application of powerful traction projects and long distance railway systems. As National Electrical Code & National Electrical Safety Code, there are many items concerned the general regulations for ground measurement and most of them are focused on the earth resistivity in control area instead of the grounding system. The most notable and represent code is ANSI/IEEE td 81 series. As an international standard in the field of grounding system of railway application is only the IEC 62128-1:2003 transfered according to EN50122-1, which is practical in measurement of grounding very simply in annex , but is lack of detailed earthing measurement methods for different railway integrated grounding system and different structures and parts in railway application. Another international standard IEC 61936-1 provides, in a onvenient form, common rules for the design and the erection of electrical power installations in systems with nominal voltages above 1 kV a.c. and nominal frequency up to and including 60 Hz, so as to provide safety and proper functioning for the use intended.This standard does not apply for electrical railways except the substations, neither for overhead and underground lines between separate installations. IEC 61936-1 is transferred from HD637, and in HD 637 there is ANNEX N give some guides and suggestions for the common meausrement methods for earthing system, also not applies for electrical railways whit no detail required arrangement. But in IEC61936-1, the relative annex is deleted.

2. Contents of survey The ANSI/IEEE td 81 series ,the IEC 61936-1,IEC62128-1/EN50122-1, HD 637 S1, and the GB/T Chinese code are studied in the field of specific differences Results of the survey are shown as tables on the following pages. 2.1 Survey items

General regulations for ground measurement of railway integrated grounding system Measurement of earth resistivity in Control area Measurement arrangement 4-point Equally Spaced Arrangement Unequally Spaced Arrangement Test of electrical integrity of railway integrated grounding system

Testing scope Testing methods Interpretation and treatment of the testing results Measurement of ground impedance of railway integrated grounding system

Measurement arrangement Test current and measurement instrumentations Measurement spacing Reversed-current-&-long-distance method for ground impedance measurement Compensation method for ground impedance measurement

2.2 Specifications surveyed

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2.2.1 Over the years grounding design procedures have been developed as well as appropriate standards, most notable are, IEC 61936-1 First edition2002-10Power Installations Exceeding 1 kV a.c. Part 1: Common rules IEC 62128:2003/ EN 50122-1:(1997) Ed.1: Railway applications - Fixed installations - Part 1: Protective provisions related to electrical safety and earthing, CDV 2008-10. FDIS 2009-12 ANSI/IEEE Std 80-2000, IEEE Guide for Safety in AC Substation Grounding. IEEE Std 487-2007, Recommended Practice for the Protection of Wire-Line Communication Facilities Serving Electric Supply Locations. IEEE Std 998-1996, IEEE Guide for Direct Lightning Stroke Shielding of Substations. IEEE Std 1410-2004, IEEE Guide for Improving the Lightning Performance of Electric Power Overhead Distribution Lines. IEEE Std 1243-1997, IEEE Guide for Improving the Lightning Performance of Transmission Lines. HD 637 S1 :1999Power Installations Exceeding 1 kV a.c. 2.2.2 For the purpose of verifying designs, testing procedures have Been also developed. Most notable are, ASTM B 539-2002 Standard Test Methods for Measuring Resistance of Electrical Connections (Static Contacts) ANSI/IEEE td 81 -1983 IEEE Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potential of a Grounding System. ANSI/IEEE Std 81.2-1991 IEEE Guide for Measurement of Impedance and Safety Characteristics of Large, Extended or Interconnected Grounding Systems. United States National Electrical Code BS 7430 Code of Practice for Earthing. BS 6651 Protection of Structures against Lightning. IEC 60364-1: Electrical installations of buildings Part 1: Fundamental principles, assessment of general characteristics, definitions. International Electrotechnical Commission, GB/T 17949.1-2000 Guide for measuring earth resistivity, ground impedance and earth surface potentials of a ground system--Part 1: Normal measurements, Chinese National Electrical Code Canadian Electrical CodePart 1, Safety Standard for Electrical Installations CSA Standard C22.1-06, Canadian Standards Association, Mississauga, Ontario 2006, ISBN 1-55436-923-4 IEEE Std 1474.1:2004, Communications-based Train Control (cbtc) Performance and Functional Requirements Technical requirements of the Canadian Electrical Code are very similar to those of the US National Electrical Code. Specific differences still exist and installations acceptable under one Code may not entirely comply with the other. Correlation of technical requirements between the two Codes is ongoing. 3. Survey in AHG2 According to the 1st meeting of AHG2 in Geneva, Convener of AHG2 has finished the survey between the working draft prepared for the new proposal with the specifications as mentioned above, and made out the survey results through the examination of the Chinese WG's survey and most of the AHG2 members as in the appendix, and incorporate additions and corrections should be modified by experts of new proposal team in future phases. 4. Conclusion There is no specified standard or report or specification in detail for the measuring methods of large earthing system especially of railway application either in IEC level. IEC 62128 specified the eveluation of the safety requirements of the earthing system in railway evaluated by the rail potentail without detail and accurate measuring methods for different situations, in the annex. IEC 61936-1 specified the general requirement and the necessary of measuring the touch and step voltages and trasfer potentail after the construction of an structure containing power installations exceeding 1 kV a.c, and metioned 2 choices of the measuring, using a high impedance voltmeter to measure the prospective touch and step voltages, or to measure the effective touch and step voltages appearing across an appropriate resistance which represents the human body, in one paragraph with 3 rows. For national standards or codes, US has the specifications of measuring methods for earthing system of power substation, new revision is now planned to include those for large earthing system of large substation; China has the code in the earthing measuring methods of railway application, according to the investigation in several railways with long distances and large comprehensive intergrated earthing system which is conformed by the structures and earthing parts inside the railway applications, based on requirements of the safety specified in IEC62128, and also refering to the ANSI of US. Convener of AHG2 strongly recommends to starting the new proposal of IEC standard or as technical specification (TS) which will be needed to call for more experts to join in.

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Appendix Survey of Measuring Methods for Railway Integrated Grounding System -Empty Column: The contents of the sub-classification are not included in the specification.

Clause of the working draft

Point of view of new proposal

Suvey in IEC62128-1:2003 &

EN50122-1

Suvey in IEC61936-1:2002

Suvey in HD 637 S1 :1999

Suvey in ANSI/IEEE Std 81-1983 &

ANSI/IEEE Std 81.2-1991 & GB/T 17949.1-2000

Scope

The code defines the terms and definitions of the measurement of a.c. traction railway integrated grounding system, general regulations for the measurement of railway integrated grounding system, the method for measurement of earth resistivity, the method for measurement of electrical integrity railway integrated grounding system, the method for measurement of ground resistance of independent grounding electrodes, the method for measurement of surface-potential gradient, step voltage and touch voltage, and the method for measurement of rail potential and equipment potential of railway integrated grounding system.

Specifies requirements for the protective provisions relating to electrical safety in fixed installations associated with a.c.- and d.c.-traction systems and to any installations that may be endangered by the traction power supply system. Also applies to all fixed installations that are necessary to ensure electrical safety during maintenance work within electric traction systems.

This part of IEC 61936 provides, in a onvenient form, common rules for the design and the erection of electrical power installations in systems with nominal voltages above 1 kV a.c. and nominal frequency up to and including 60 Hz, so as to provide safety and proper functioning for the use intended. This standard does not apply for electrical railways except the substations, neither for overhead and underground lines between separate installations.

This standard contains the requirements for the design and erection of electrical installations, in systems with nominal voltage above 1 kV ax., so as to provide safety and proper functioning for the use intended. This standard does not apply for electrical railways except the substations, neither for overhead and underground lines between separate installations.

4 General regulations for ground measurement of railway integrated grounding system

The guide defines the method for measuring earth resistivity, the method for measuring electrical integrity of railway integrated grounding system and the method for measuring ground impedance. The characteristic parameters of grounding system are closely related to the earth moisture to a considerable extent, and

No specified.

No specified. No specified. Do not schedule field measurements of either the power system grounding, during periods of forecast lightning activity, in areas (determined by conditions at each utility) that encompass the station being measured or of the power network connected to the station being measured. Do not lay out test leads or connect test leads to

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Suvey in IEC62128-1:2003 &

EN50122-1




ANSI/IEEE Std 81.2-1991 & GB/T 17949.1-2000

therefore, the assessment of performance of railway integrated grounding system and the acceptance of railway integrated grounding system should be administered. The distance between the measuring electrodes and the underground metallic object should not be less than the distance between the measuring electrodes in order to reduce the effect of underground metallic object. The measuring electrodes should not be placed in the non-uniform earth evidently with rocks, faults and slops to reduce the effect of non-uniformity of earth composition. The measurement of earth resistivity should be conducted before the measuring ground impedance of railway integrated grounding system, and the appropriate length of measuring electrodes lead wires should be determined in accordance with the local earth resistivity. The measurement of ground impedance of railway integrated grounding system should be conducted normally with reversed-current-&-long-distance method, and when the arrangement of measuring electrodes is restricted by local environmental

out-of-service transmission lines during a period when lightning is prevalent. When test procedures are not in progress, externally routed test leads should be disconnected and isolated from the grid and treated as being energized. In the event lightning appears in the zone defined above when test procedures are underway, stop all testing, open the test connection to the out-of-service transmission line, and isolate from the grid any temporarily installed test conductors routed externally to the grid. Using high-voltage rated insulated gloves and boots, eye protection, and hard hats. Working on clean, dry crushed rock or an insulating blanket. Avoiding bare hand-to-hand contact between equipment and extended test leads. Sufficiently insulating the voltage or current probe test conductor within the station and its close neighborhood. Ensuring that the cable reel is well insulated or mounted on an insulated platform. Connecting safety grounds (sized for fault levels) to all equipment frames. Making connections to instrumentation only after cable-pulling personnel are

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Suvey in IEC62128-1:2003 &

EN50122-1




ANSI/IEEE Std 81.2-1991 & GB/T 17949.1-2000

conditions, compensation method might be applied for the measurement. A reasonable arrangement of measuring electrodes will improve the validity of the measurement of ground impedance of railway integrated grounding system. The arrangement of measuring electrodes should conform to the regulations of Clause 7.1,7.4 and 7.5. When compensation method is applied, the distance between the leading wire of the measuring current electrode and that of potential electrode should be kept as far away as possible, in order to reduce the effect of mutual induction coupling on the measurement results. If obvious discrepancy is found between the results measured and those in the previous measurements, examination should be made of the electrical connections of measurement circuit, and adequacy of selection of measurement points, and comparative verification can be made between various methods if necessary. The measurement of electrical integrity of railway integrated grounding system should be conducted 2 or 3 times annually. The measurement of ground impedance of

in the clear (radio communication recommended). Removing working grounds on the test circuit last. It is recommended that test procedures, hazardous conditions, and the responsibilities of each person be discussed and understood by everyone taking part in the test. Moreover, the circuit should not be touched after removal of the temporary grounding. From the standpoint of safety rules, a test that applies the 10 to 100 A current injection method should be considered as corresponding to a prolonged earth fault; and an earth-fault test should be considered as corresponding to a fast-tripped earth fault. Thus, the test currents should be such that the rules with regard to the touch-voltage, transferred-potential, and induced-potential limits for earth faults are respected. Electromagnetic interference resulting from mutual coupling Mutual coupling between the current test conductor and the potential test conductor will introduce an error in the measured impedance Mutual coupling between

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Suvey in IEC62128-1:2003 &

EN50122-1




ANSI/IEEE Std 81.2-1991 & GB/T 17949.1-2000

railway integrated grounding system should be conducted once at 5-or-6-year interval. If the railway integrated grounding system is renovated, or other conditions call for measurement, aim-specific measurement should be carried out.

extended ground conductors that conduct the test current to earth and the potential test conductor will give a lower measured impedance Locating the current or potential remote test electrode near grounded metal structures, buried neutrals, aerial neutral grounds, or buried ground conductors that connect to the grounding system under test will result in a lower measured impedance. In urban areas, these components effectively enlarge the power-system grounding and make it difficult to reach remote earth. Because changing weather, power system load variations, and system switching modify many of the above factors, the test environment can change hour-to-hour The current and potential test conductor routings and the location of current and potential remote electrodes should be determined; and test conductor lengths should be estimated from the station plot plan and area maps that show transmission lines, neutrals, buried conductors, communication cables, and piping locations.

5 Measurement of earth

Measurement of earth resistivity can be performed

No specified. No specified. Annex N (informative)Measurements for and on

6.7 Partially or completely buried objects such as rails,

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Suvey in IEC62128-1:2003 &

EN50122-1




ANSI/IEEE Std 81.2-1991 & GB/T 17949.1-2000

resistivity Control area 5.1 Measurement arrangement

with Four-Point Method which has two different variations: Equally Spaced Arrangement and Unequally-spaced Arrangement. The measuring electrodes should be made from round iron bar with diameter larger than 1.5cm or angle iron L25mm*25mm*4mm, and should be longer than 40cm in length. The distance between measuring electrodes a is closely related to the depth of the earth measured. When the area to be measured is large, a should increase correspondingly. In order to reflect the earth condition of railway integrated grounding system, a should not be less than 50m. In order to reduce the effect of railway integrated grounding system on the measurement results of earth resistivity, the measuring electrodes should be placed 50 m or more away from the subgrade of the railway. In order to ensure the reliability of earth resistivity measurement, the measurement should be performed twice, vertically and horizontally with respect to tracks each, and then the average of the two results is taken as the final result. If considerable discrepancy is found between two

earthing systems N.l Measurement of soil resistivities Commn rules, for example Wenner-method is suggested, but no detail required arrangement being discribed.

water, or other industrial metallic pipes will considerably influence the measurement results [B9], [B36]. In earth-resistivity tests a sharp drop in the measured value is often caused by the presence of a metallic object buried close to the test location. The magnitude and extent of the drop gives an idea of the importance and depth of the buried material. The measured resistance of a ground electrode located close to a buried metallic object can be significantly lower than its value if the additional buried metal objects were not present. Wherever the presence of buried metallic structures is suspected in the area where soil resistivity measurements are to be taken and the location of these structures is known, the influence of these structures on the soil resistivity measurement results can be minimized by aligning the test probes in a direction perpendicular to the routing of these structures. Also the location of the test probes should be as far as possible from the buried structures.

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Suvey in IEC62128-1:2003 &

EN50122-1




ANSI/IEEE Std 81.2-1991 & GB/T 17949.1-2000

measurements, or obvious discrepancy is found between the results obtained and those in the previous measurements, new measurements should be performed by changing the directions of measuring electrodes arrangement or increasing the distance between electrodes.

5.2 4-point Equally Spaced Arrangement

Figure 1 is the wiring diagram of equally-spaced arrangement four-point method, where the distance between electrodes is a (m). During measurement, when the measuring current flows into the two outer electrodes, the measuring meter of ground impedance obtains the grounding resistance R () through measuring the potentials between two outer current electrodes and two inner potential electrodes. Then the apparent earth resistivity (m)can be calculated by formula (1).

=2R 1

No specified. No specified. Annex N (informative) Measurements for and on earthing systems N.l Measurement of soil resistivities Commn rules, for example Wenner-method is suggested, but no detail required arrangement are discribed.

1) Equally Spaced or Wenner Arrangement. With this arrangement the electrodes are equally spaced as shown in Fig 3(a). Let a be the distance between two adjacent electrodes. Then, the resistivity r in the terms of the length units in which a and b are measured is:

2 2 2 2

4 a R = 2 a a1 + -

a + 4 b a + b(2) It should be noted that this does not apply to ground rods driven to depth b; it applies only to small electrodes buried at depth b, with insulated connecting wires. However, in practice, four rods are usually placed in a straight line at intervals a, driven to a depth not exceeding 0.1 a. Then we assume b = 0 and the formula becomes: =2R (3) and gives approximately the average resistivity of the

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Suvey in IEC62128-1:2003 &

EN50122-1




ANSI/IEEE Std 81.2-1991 & GB/T 17949.1-2000

soil to the depth a. 5.3 Unequally Spaced Arrangement

Figure 2 is the wiring diagram of unequally-spaced arrangement four-point method, where the space between electrodes is a (m). When the space between electrodes is considerably large, the measuring meter of grounding resistivity usually cannot measure or cannot measure precisely so small potential difference because the potential difference between the two inner electrodes placed as in equally-spaced arrangement four point method drops rapidly. In this case, unequally spaced arrangement shown in Figure 2 can be used. In this arrangement, the potential electrodes are placed nearer the corresponding current electrodes, which can increase the potential difference measured. The measuring meter of grounding resistivity obtains the grounding resistance R () through measuring the potentials between two outer current electrodes and two inner potential electrodes. If the burial depth of electrodes is comparatively small with respect to its distance to a and b, th

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