Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
Earthing System (Working Draft for NWIP of proposed TS by AHG2)
2011
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 1 / 28
Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
Earthing System (Working Draft for NWIP of proposed TS by AHG2)
2011
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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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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2011
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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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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−
HD 637 S1 :1999，Power Installations Exceeding 1 kV a.c.
−
GB/T17949.1—2000, Guide for Measuring Earth Resistivity, Ground Impedance, and
Earth Surface Potentials of a Ground System Part One: Normal measurement
−
DL/T475—2006, 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 (Ω) through measuring the potentials between two
outer current electrodes and two inner potential electrodes. Then the apparent soil resistivity ρ
(Ω·m)can be calculated by formula (1).
ρ=2πаR
（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 (Ω) 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 ρ (Ω·m)can be calculated by formula (2).
ρ=2π（а+b）R/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 be（0.5～0.6）dCG.
During measurement, electrode P is moved three times near （0.5～0.6）dCG 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:
Z = Z '/ [1 − D × (1 / dCG + 1 / d PG − 1 / d CG 2 + d PG 2 − 2d CG d PG cos θ ) / 2]
(3)
where θ 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, θ 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 mΩ, 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 mΩ, 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 mΩ 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 mΩ--200 mΩ, 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 200Ω--1Ω, 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 1Ω, 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
ρ≤100
resistivity
100＜
300＜
500＜
700＜
1000＜
ρ≤300
ρ≤500
ρ≤700
ρ≤1000
ρ≤2000
2～4
4～5
5～6
6～7
7～9
ρ＞2000
ρ（Ω·m）
Spacing
1～2
9～10
(km)
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
ρ≤100
resistivity
100＜
300＜
700＜
1000＜
ρ≤300
ρ≤700
ρ≤1000
ρ≤2000
k=1.41
k=1.40
k=1.34
ρ＞2000
ρ（Ω·m）
dCG=400m
k=1.29
k=1.38
dCG=700m
k=1.20
k=1.28
k=1.35
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Test Power
Railway Integrated
Earthing System
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
ρ（Ω·m）
100≤ρ≤
300＜ρ≤
500＜ρ≤
700＜ρ≤
1000＜ρ
2000＜ρ
300
500
700
1000
≤2000
≤3000
dPG=
dPG=
dPG=
dPG=
dPG=
dPG=
380～326
326～293
293～267
267～239
239～179
179～145
When
dCG=700m
potential
electrode
location (m)
Note: If earth resistivity varies, dPG can be estimated linearly according to location of the section where
earth resistivity is measured.
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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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2011
Test Power
Railway Integrated
Earthing System
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.
Test Power
Railway Integrated
Earthing System
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。
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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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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 dCG≥700m。With 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 6.2.3～6.2.6 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 1MΩ, and the resolution of the voltmeter shall
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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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2011
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.
Test Power
Direction
Direction
End
Edge
Earthing Wire
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
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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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2011
resistance of a human body Rm shall be 1000Ω.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 6.2.3～
6.2.6 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 1MΩ, 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 Formula（5）
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.
Test Power
Equi.
Earthing Wire
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
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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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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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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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2011
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.
rpzp
recorder
mp
Earthing Wire
Figure 10.1 -- Diagram of measurement of rail potential
rpzp
recorder
Equi.
Figure 10.2 -- Diagram of measurement of equipment potential
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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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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.
Engineering
phase
Constructio
n phase
Commission
ing phase
Operation
phase
⎯
Project Start
⎯
(Soil resistivity at selected locations)
⎯
Soil resistivity at selected locations
⎯
Certificate of rail insulation
⎯
Certificate of embedded conductors per structure and per each section of
construction before pouring the concrete
⎯
Resistance to earth per structure at one reference terminal
⎯
Test of continuity and completeness of all terminals per structure related
to the reference terminal for earthing and LPS
⎯
Certificate of bonding of trackside installations inside and outside of
OCL zone and pantograph zone
⎯
Certificate of bonding for LPS
⎯
Certificate of bonding of further subsystems
⎯
Certificate of traction power (rail potential)
⎯
Certificate of service power (initial verification)
⎯
Monitoring for maintenance (type of cyclic tests and test interval)
Figure A.1 Cycle of measurement
22 / 28
By client
or railway
E&M supplier
By Civil Works
By Railway
E&M Supplier
By Operator
Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
Earthing System (Working Draft for NWIP of proposed TS by AHG2)
2011
Annex B Measurement of surface potential gradient of earthing connections
(Informative)
Curve 1
Curve 2
C
u
r.
5
Curve 3
C
u
r.
C
u
r.
7
6
Curve 4
Note: * the reference point of curve
Figure B.1—diagram of measurement of surface potential gradient of earthing connections
Potential difference (mV)
Curve 1
Curve 2
Curve 3
Curve 4
Distance (m)
Figure B.2—distribution 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.
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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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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.
overhead earth wire
Signal
Running
Rails
Fence
shielded cables
Platform
Return Circuit
Substation
Station
Traction power supply
Structure
Earth
Station power supply
Earthing
Systems
pipe with insulating joint
Railway installations
Non-railway installations
Figure C.1 Earthing circuit of railway integrated earthing system in DE
24 / 28
Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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2011
AT
(auto-transformer)
T (contact wire)
Impedance bond
R (rail)
Neutral wire
CPW
F (feeder)
PW (protective wire)
GP (S type
discharger)
RPCD
Feeding transformer
Teaser
Surge arrester
AT
Steel pipe mast
Main
phase
GP (S type
discharger)
Station
(steel
structure)
GP (ground fault
protective discharger)
Steel pipe mast
Steel structure / frame
GP
Distribution cubicle
RTU (remote
terminal unit)
Insulation hat
Communication cable
50m or more
Building
3-pole surge arrester
Substation
Figure Ｆ.2 A.C. traction system earthing (open section)
(Informative)
Figure C.2 Earthing circuit of railway integrated earthing system in JP
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Figure C.3 Earthing circuit of railway integrated earthing system in CN for high speed railway
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Railway applications – Fixed Installations –Measuring Methods for Railway Integrated
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2011
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 Code：Part 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
27 / 28
Suggested Project Plan
WBS
2011-5-30
9(AHG2)-CONV503
2010
1
2
3
4
5
6
7
2011
8
9 10 11 12
1
2
3
4
5
6
7
2012
8
9 10 11 12
1
2
3
4
5
6
7
2013
8
9 10 11 12
1
2
3
Call for Experts and convenor of AHG2
Preparation of TR text
1st AHG2 meeting (GENEVA,07/2010)
A1
Preparation 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
NWIPD
TC9 CAG meeting (IT,04/2011)
CAG
Submission of NWIP to TC9
NWIP
Circulation of NWIP with Working Draft
1st PT-WD meeting (CN,07/2011)
1
Preparation of CD text
2nd PT-CD meeting (JP,09/2011)
2
Preparation of CD text
TC9 Plenary Meeting (JP,11/2011)
Submission of CD to TC9
PL
CD
Circulation of CD
Preparation of FDIS text
3rd PT-FDIS meeting (CN,05/2012)
3
Preparation of FDIS text
Submission of FDIS to TC9
FDIS
Translation of FDIS
Circulation of FDIS
TC9 Plenary Meeting (11/2012)
PL
4th PT-FDIS meeting (02/2013)
4
Preparation of TS text
Submission of TS to TC9
Translation of TS
Publishing of TS
TS
4
5
6
7
8
9 10 11 12
For IEC
use only
9(AHG2)-CONV-504
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
page 1 of 23
2.2.1 Over the years grounding design procedures have been developed as well as appropriate
standards, most notable are,
−
rules
IEC 61936-1 First edition，2002-10，Power Installations Exceeding 1 kV a.c. –Part 1: Common
−
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 :1999，Power 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 Code：Part 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.
page 2 of 23
Appendix
Survey of Measuring Methods for Railway Integrated Grounding System
-Empty Column: The contents of the sub-classification are not included in the specification.
Suvey in
Point of view of new
Clause
IEC62128-1:2003 &
proposal
of the working draft
EN50122-1
Scope
4 General regulations
for ground
measurement of railway
integrated grounding
system
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.
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
Suvey in
IEC61936-1:2002
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.
No specified.
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.
No specified.
page 3 of 23
Suvey in
HD 637 S1 :1999
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
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.
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
Clause
of the working draft
Point of view of new
proposal
Suvey in
IEC62128-1:2003 &
EN50122-1
Suvey in
IEC61936-1:2002
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-dist
ance method, and when the
arrangement of measuring
electrodes is restricted by
local environmental
page 4 of 23
Suvey in
HD 637 S1 :1999
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
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
Clause
of the working draft
Point of view of new
proposal
Suvey in
IEC62128-1:2003 &
EN50122-1
Suvey in
IEC61936-1:2002
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
page 5 of 23
Suvey in
HD 637 S1 :1999
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
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
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
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.
5
Measurement of earth
Measurement of earth
resistivity can be performed
No specified.
No specified.
page 6 of 23
Annex N (informative)
Measurements for and on
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
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.
6.7 Partially or completely
buried objects such as rails,
Clause
of the working draft
resistivity Control area
5.1
Measurement
arrangement
Point of view of new
proposal
Suvey in
IEC62128-1:2003 &
EN50122-1
Suvey in
IEC61936-1:2002
Suvey in
HD 637 S1 :1999
earthing systems
N.l Measurement
resistivities
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
of
soil
Commn rules, for example
Wenner-method is
suggested, but no detail
required arrangement being
discribed.
page 7 of 23
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
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.
Clause
of the working draft
5.2
4-point Equally Spaced
Arrangement
Point of view of new
proposal
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.
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 (Ω) through
measuring the potentials
between two outer current
electrodes and two inner
potential electrodes. Then
the apparent earth resistivity
ρ(Ω·m)can be calculated by
formula (1).
ρ=2πаR
（1）
Suvey in
IEC62128-1:2003 &
EN50122-1
No specified.
Suvey in
IEC61936-1:2002
No specified.
Suvey in
HD 637 S1 :1999
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.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
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:
4πaR
ρ =
1 +
2a
a
2
+ 4b
2
-
a
a
2
+ b
2
(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: ρ=2πаR (3)
and gives approximately the
average resistivity of the
page 8 of 23
Clause
of the working draft
5.3
Unequally Spaced
Arrangement
Point of view of new
proposal
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
(Ω) 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
earth resistivity ρ(Ω·m)can
be calculated by formula (2)
ρ=πa(а+b)R/b
Suvey in
IEC62128-1:2003 &
EN50122-1
No specified.
Suvey in
IEC61936-1:2002
No specified.
page 9 of 23
Suvey in
HD 637 S1 :1999
No specified.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
soil to the depth a.
2) Unequally-spaced or
Schlumberger-Palmer
Arrangement. One
shortcoming of the Wenner
method is the rapid
decrease in magnitude of
potential between the two
inner electrodes when their
spacing is increased to
relatively large values.
Often the commercial
instruments are inadequate
for measuring such low
potential values. In order to
be able to measure
resistivities with large
spacings between the
current electrodes the
arrangement shown in Fig
3(b) can be used
successfully. The potential
probes are brought nearer
the corresponding current
electrodes. This increases
the potential value
measured.
The formula to be used in
this case can be easily
determined [B35]. If the
depth of burial of the
electrodes b is small
compared to their
separation d and c, then the
measured resistivity can be
calculated as follows:
ρ=πc(c+d)R/d
（4）
Clause
of the working draft
6
Test of electrical
integrity of railway
integrated grounding
system
6.1
Testing scope
Point of view of new
proposal
（2）
Measurement of electrical
integrity of railway
integrated grounding
system covers the following:
a) measurement of electrical
integrity of run-through
ground cable connections:
measurement of the integrity
of electrical connections
between run-through cables
and various grounding
electrodes of subgrade,
bridges and tunnels along
the railway; measurement of
the integrity of electrical
connections between
run-through cables and
other installations and
buildings along the railway,
which are connected to the
run-through cables.
b) measurement of electrical
integrity of grounding
connections of traction
substations and power
supply substations:
measurement of electrical
integrity of grounding
connections between
ground grids of various
voltage classes along the
railway; measurement of
electrical integrity of
grounding connections of
both high and low voltage
equipment and installations,
including framework,
distribution boxes, terminal
boxes, power supply units;
measurement of electrical
integrity of grounding
connections between the
grounding trunk of main
Suvey in
IEC62128-1:2003 &
EN50122-1
No specified.
Suvey in
IEC61936-1:2002
No specified.
page 10 of 23
Suvey in
HD 637 S1 :1999
No specified.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
In this test the object is to
determine whether the
various parts of the ground
grid are interconnected with
low-resistance copper. This
copper is shunted by the
surrounding earth, which
usually has a very low
impedance.
Clause
of the working draft
6.2
Testing methods
Point of view of new
proposal
control room and its internal
grounding conductors, the
grounding trunk of
communication cables
within and near the
substation and its internal
grounding conductors, and
microwave relay towers and
railway integrated grounding
system, and grounding
connections between other
necessary parts and railway
integrated grounding
system.
During the measurement, a
grounding lead from an
installation with sound
grounding with railway
integrated grounding
system is taken as the
reference point in order to
measure the DC resistance
between the reference point
and grounding measuring
points of the surrounding
electrical installations.
Special instrumentations
should be used for the
measurement. During the
measurement, a constant
DC current is injected
between the reference point
and the grounding
measuring point of the
installation to be measured,
and then a voltmeter with
high internal resistance is
used to measure the
potential difference of a
metallic conductor between
the reference point and the
grounding measuring point
of the installation to be
measured, then with the
Suvey in
IEC62128-1:2003 &
EN50122-1
No specified.
Suvey in
IEC61936-1:2002
No specified.
page 11 of 23
Suvey in
HD 637 S1 :1999
No specified.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
The best method for making
integrity-of-ground-grid
tests is to use a large but
practical direct current and
some means of detecting
the voltage drop caused by
this current. Direct reading
ohmmeters can be used if
the sensitivity is adequate.
The ammeter-voltmeter
method, using alternating
current, cannot be used
satisfactorily for this test.
The reactance of a large
copper wire in this case is
shunted by the surrounding
earth, a path which may
have slightly less reactance
than the wire. Therefore, a
continuity test for buried
wire would give
indeterminate results if
alternating current were
used.
By extension of this
reasoning, one concludes
that it is practically
impossible to sensibly
lower the impedance
between two ground grids
Clause
of the working draft
6.3 Interpretation and
treatment of the testing
results
Point of view of new
proposal
potential value measured,
the resistance value can be
obtained.
The measurement can be
performed with large DC
current method, or
instruments with DC bridge.
Measurement wiring should
be the 4-point method in
which two current
electrodes and two potential
electrodes are connected
respectively in order to
reduce the contact
resistance and the effect of
resistance in the
measurement leading wires.
The DC resistance
resolution of testing meters
should be 1 mΩ with the
precision not less than
Class 1.0.
If the measured value is
larger than 50 mΩ, then the
measurement should be
repeated for verification of
the result. If the
measurement results of
several installations reveal
poor connections at the
beginning of the
measurement, then it is
recommended that a new
reference point be selected
and the measurement be
performed again.
Interpretation and treatment
of the testing measurement
results may follow the
following methods:
a) The DC resistance value
measured should be less
than 50 mΩ between the
reference point and the
Suvey in
IEC62128-1:2003 &
EN50122-1
No specified.
Suvey in
IEC61936-1:2002
No specified.
page 12 of 23
Suvey in
HD 637 S1 :1999
No specified.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
which are any distance
apart, each of which has an
impedance in the order of
0.1 W at 60 Hz. The addition
of copper connectors,
however large, will not
lower the reactance
between the two ground
grids. The resistive
component can be lowered
by additional connectors,
and this component is used
to determine the integrity of
the ground grid.
One practical integrity test
consists of passing about
five amperes into the
ground grid between two
points to be checked. The
voltage drop across these
points is measured with a
milli-voltmeter or portable
Clause
of the working draft
Point of view of new
proposal
Suvey in
IEC62128-1:2003 &
EN50122-1
Suvey in
IEC61936-1:2002
grounding measuring point
of an installation with sound
grounding connections;
b) If the DC resistance
between the reference point
and the grounding
measuring point of an
installation varies between
50 mΩ-200 mΩ, which
indicates that the grounding
connections just meet the
working requirements, due
attention should be paid to
its variation in the routine
measurements thereafter,
and important installations
should be inspected in due
time;
c) If the DC resistance
between the reference point
and the grounding
measuring point of an
installation varies between
200 mΩ -1Ω, which indicates
that the grounding
connections are poor,
important installations
should be inspected as soon
as possible proper
measures taken, and other
installations should be
inspected in due time;
d) If the DC resistance
between the reference point
and the grounding
measuring point of an
installation is more than 1Ω,
which indicates that the
installation measured is not
connected with the railway
integrated grounding
system, immediate
inspection should be
performed and proper
page 13 of 23
Suvey in
HD 637 S1 :1999
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
potentiometer and the
effective resistance is
calculated from the current
and voltage readings. From
these readings and the
calculated resistance of
copper it can be determined
whether there is an
adequate connection. For
those ground systems that
have
a direct voltage between
points, the change of
voltage caused by the test
current is used to calculate
the resistance.
Clause
of the working draft
7
Measurement of ground
impedance of railway
integrated grounding
system
7.1
Measurement
arrangement
Point of view of new
proposal
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 grounding
connection of the
installation under test
should be deemed as just
meeting the working
requirements.
The measurement of ground
impedance of railway
integrated grounding
system should use the
three-point arrangement
method, in which the
arrangement of current
electrode, potential
electrode and current
injection point of railway
run-through grounding
cable should 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 grounding
cable should be measured
precisely, and the distance
between the current
electrode, potential
electrode and current
injection point of railway
run-through grounding
cable should be linearly
geometry.
During the measurement of
ground impedance, the
location of measurement
Suvey in
IEC62128-1:2003 &
EN50122-1
No specified.
Suvey in
IEC61936-1:2002
10.5 Measurements
Measurements shall be
carried out after
construction, where
necessary, to verify the
adequacy of the design.
Measurements may
include the earthing
system impedance,
prospective touch and
step voltages at relevant
locations and transfer
potential, if appropriate.
When measuring touch
and step voltages under
test conditions, two
choices are possible.
Either measure the
prospective touch and
step voltages using a high
impedance voltmeter or
measure the effective
touch and step voltages
appearing across an
appropriate resistance
which represents the
human body.
page 14 of 23
Suvey in
HD 637 S1 :1999
Annex N (informative)
Measurements for and on
earthing systems
N.2 Measurement of
resistances to earth and
impedances to earth
Examples for suitable
methods of measurements
and types of instniments are
given such as
z
Fall-of-potential
method with the earth
tester
z
High frequency earth
tester
z
Heavy-current injection
method
No detail required
arrangement are discribed
specially for railway
integrated earthing system.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
With development and
industrial growth adjacent
to power substations, it
becomes increasingly
difficult to choose a suitable
direction or locations for
test probes to make a
resistance test. Moreover,
the connection of overhead
ground wires, buried water
pipes, cable sheaths, etc, all
have the effect of physically
distorting and enlarging the
ground grid.
NOTE — Overhead ground
wires may be insulated
either deliberately or by
clamp corrosion and
therefore low-voltage tests
may give answers different
from actual fault tests.
Often the most effective
way of increasing the test
current is to decrease the
current electrode
resistance. This can be
done by driving the rod
deeper into the soil, pouring
water around the rod, or by
driving additional rods and
interconnecting them in
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
circuit should be placed
away from rivers and lakes,
and be kept away from
underground metallic pipes
and alive power
transmission lines, and
avoid placing the
measurement circuit parallel
with the transmission line
for a long section.
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 measuring
electrodes should be driven
into the earth more than
20cm in depth. The
resistance between the
current electrode and the
earth should be as small as
possible in order to increase
the testing current
effectively. It is advisable to
increase the conductor
number of current electrode
or sprinkle water around the
current electrode to reduce
the resistance between the
current electrode and the
earth.
7.2
Test current and
measurement
instrumentations
During the measurement of
ground impedance of
railway integrated grounding
system, it is advisable to
select the lead from an
No specified.
No specified.
page 15 of 23
No specified.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
parallel. The addition of salt
to the water poured around
the test electrodes is of very
little value; the moisture is
the main requirement.
The most practical
electrodes are ground rods.
Steel ground rods are
preferred to lightweight
aluminum rods since
aluminum rods may be
damaged if a hammer is
used to drive them in hard
soil. Screw type rods
should not be used. The
screw type rod fluffs up the
soil and creates air in the
area of the rod above the
screw which results in high
contact resistances. The
driven rod compacts the
soil giving minimum contact
resistance.
The current electrode
resistance is in series with
the power source and is,
therefore, one of the factors
governing the testing
current. If this current is
low, it may be necessary to
obtain a lower current
electrode resistance by
driving additional ground
rods. In rocky soil it is a
good practice to drive rods
at an angle with respect to
the vertical. Inclined rods
will slide over the top of a
rock.
If direct current is used, the
effects of inductance and
mutual impedance are
eliminated, but electrolysis
can be very troublesome.
Clause
of the working draft
Point of view of new
proposal
Suvey in
IEC62128-1:2003 &
EN50122-1
Suvey in
IEC61936-1:2002
installation with sound
grounding connections with
the railway integrated
grounding system or a
grounding terminal of the
run-through grounding
cable as the injection point
of test current. The testing
current should meet the
following requirements:
a) When ground impedance
of railway integrated
grounding system is
measured with
different-frequency method,
the testing current should
not be less than 0.2 A,
frequency should be within
40Hz and 60Hz, which differs
from power frequency but
approaches power
frequency possibly closely.
b) When ground impedance
of railway integrated
grounding system is
measured with power
frequency large current
method, an independent
power source or isolated
transformer should be used
for power supply, and the
testing current should be
increased possibly and
should not be less than 20A.
Ground impedance
measurement meter with 4
terminals should be used for
the measurement of ground
impedance of railway
integrated grounding
system, and the power
supply should be provided
by an independent power
source or isolated
page 16 of 23
Suvey in
HD 637 S1 :1999
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
This problem can be solved
by reversing the direct
current periodically. The
effects of inductance and
mutual impedance are then
evident only as transients
which will be negligible, if
the time constants of the
various circuits are
sufficiently low. Periodically
reversed direct current, with
a complete break in the
circuit between reversals is
the best power source for
resistance or resistivity
measurements. However, it
is not adequate for
impedance measurements.
For measuring the 60 Hz
grounding-system
impedance, the test-current
frequency should be
between 50-70 Hz.
One of the following
instruments can be used
(see Section 12).
1) Power supply with
ammeter and high
impedance voltmeter
2) Ratio ohmmeter
3) Double-balance bridge
4) Single-balance
transformer
5) Induced-polarization
receiver and transmitter.
Clause
of the working draft
7.3
Measurement spacing
7.4
Reversed-current-&-lon
g-distance method for
ground impedance
measurement
Point of view of new
proposal
transformer. The precision
class of the meter should
not be less than 1.0, the
resolution of the voltmeter
should not be less than 1
mV. The frequency-selection
of the measuring meter
should be good when
different-frequency power
source is applied.
The measurement results of
ground impedance of
railway integrated grounding
system indicate the ground
impedance of railway
integrated grounding
system of a certain length
railway section. Figure 3
shows effective
measurement spacing of
railway integrated grounding
system corresponding to
different earth resistivity. In
the measurement, the
spacing should be
determined based on the
local earth resistivity where
the railway is located, and
the spacing should not be
less than the effective
measurement spacing
shown on Figure 3.
Figure 4 illustrates the
arrangement of electrodes in
the ground impedance
measurement of railway
integrated grounding
system with
reversed-current-&-long-dist
ance method, where the
current electrode and
potential electrode are
placed on each side of
railway integrated grounding
Suvey in
IEC62128-1:2003 &
EN50122-1
Suvey in
IEC61936-1:2002
Suvey in
HD 637 S1 :1999
No specified.
No specified.
No specified.
No specified.
No specified.
No specified.
page 17 of 23
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
This method has several
variations and is applicable
to all types of ground
impedance measurements.
As mentioned in 6.5, the
impedance of a large
grounding system may have
an appreciable reactive
component when the
impedance is less than 0.5
Ω，therefore, the measured
value is an impedance and
Clause
of the working draft
Point of view of new
proposal
Suvey in
IEC62128-1:2003 &
EN50122-1
Suvey in
IEC61936-1:2002
system, the distance
between current electrode C
and the run-through
grounding cables is dCG,
and the distance between
potential electrode P and the
run-through grounding
cables is dPG .Neither dCG
nor dPG includes the width
of the run-through
grounding cables on both
sides of railway integrated
grounding system.
When ground impedance of
railway integrated grounding
system is measured with
reversed-current-&-long-dist
ance method, dCG should
be equal to or larger than
400m, and dPG should be
equal to 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 grounding
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-dist
ance method, k values are
listed on Table 1 and k is
determined by earth
resistivity measured.
page 18 of 23
Suvey in
HD 637 S1 :1999
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
should be so considered
although the terminology
often used is resistance.
The method involves
passing a current into the
electrode to be measured
and noting the influence of
this current in terms of
voltage between the ground
under test and a test
potential electrode.
A test current electrode is
used to permit passing a
current into the electrode to
be tested (see Fig 6).
The potential profile along
the C, P, E, direction will
look as in Fig 7. Potentials
are measured with respect
to the ground under test, E,
which is assumed for
convenience at zero
potential.
Preferably, this potential
probe wire should be
extended at an angle of 90°
with respect to the current
injection line to minimize
mutual coupling between
them. When the angle
between the potential and
the current test conductors
is not 90°, the
mutual-impedance
correction methods of
Section 7. require
measurement of the phase
angle between Vs and Is of
Fig 8-1.
As discussed in 6.1,
locating the current and the
potential probes
approximately 6.5 times the
extent of the grounding
Clause
of the working draft
7.5
Compensation method
for ground impedance
measurement
Point of view of new
proposal
Figure 5 shows the
arrangement of electrodes in
the ground impedance
measurement of railway
integrated grounding
system with compensation
method, where the current
and potential electrodes are
placed on the same side of
the run-through grounding
cables of railway integrated
grounding system, the linear
distance between current
electrode C and the
run-through grounding
cables is dCG, and the linear
distance between potential
electrode P and the
run-through grounding
cables is dPG.
When ground impedance of
railway integrated grounding
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 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
Suvey in
IEC62128-1:2003 &
EN50122-1
No specified.
Suvey in
IEC61936-1:2002
No specified.
page 19 of 23
Suvey in
HD 637 S1 :1999
No specified.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
system will measure 95% of
the grounding impedance
The fall-of-potential method
consists of plotting the ratio
of V/I = R as a function of
probe spacing x. The
potential electrode is moved
away from the ground under
test in steps. A value of
impedance is obtained at
each step. This impedance
is plotted as a function of
distance, and the value in
ohms at which this plotted
curve appears to level out is
taken as the impedance
value of the ground under
test (see Fig 8).
The fall-of-potential method
is the fundamental method
for measuring the ground
impedance of large
grounding systems (see
8.2.1.5 of IEEE Std 81-1983
[2]). As illustrated in Fig 8-1,
this method of measuring
ground impedance requires
circulating a test current, Is,
between the ground system
under study and a remote
current electrode, C, while
at the same time measuring
the voltage, Vs, of the
ground system relative to a
reference potential
electrode, P. In addition to
the impedance, it is
possible to measure the
current distribution in the
grounding system, the
mutual impedance to the
paralleling utility facilities,
and step, touch, and profile
voltages. Note that, to
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
on the voltmeter and
ammeter. Then the ground
impedance of railway
integrated grounding
system can be calculated
with the formula Z=U/I.
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 grounding
connections. The grounding
connection performance of
the grounding 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 8 shows the
measurement of surface
potential. The current
No specified.
No specified.
Annex N (informative)
Measurements for and on
earthing systems
N.3 Determination of the
earth potential rise
N4 Elimination of
interference and disturbance
voltages for earthing
rneasurements
The earth potential rise is
calculted according to the
measurements by formulars.
No detail required methods
are discribed specially for
railway integrated earthing
system.
page 20 of 23
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
eliminate the measurement
error due to the voltage
drop in the test lead, as
shown in Fig 8-1 and all
following measurement
schematics, a separate test
lead is used for connecting
the current loop and the
potential circuit to the grid
(see 6.11). Refer to 13.20 for
a description of transient
voltages that may be
present during test
measurements in energized
substations.
No specified.
Clause
of the working draft
9.2 Measurement of
Point of view of new
proposal
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
6.2.3～6.2.6 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 Appendix 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
than 30m.
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 grounding 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 of site, and then the
distribution curve of surface
gradient shall be drawn.
9.2.1 Step potential
Suvey in
IEC62128-1:2003 &
EN50122-1
Annex C
Suvey in
IEC61936-1:2002
No specified.
page 21 of 23
Suvey in
HD 637 S1 :1999
No specified.
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
No specified.
Clause
of the working draft
step potential
difference, touch
potential difference,
step voltage and touch
voltage
Point of view of new
proposal
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,
grounding lead-in wire, and
covering of equipment.
9.2.2 Figure 9 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 conduct
or dCG shall be larger than
or equal to 400m. In Figure
9, the equivalent resistance
of a human body Rm shall
be 1000Ω.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
Suvey in
Suvey in
IEC61936-1:2002
IEC62128-1:2003 &
EN50122-1
Guiding values for rail
potential gradient.
The value at which the
rail potential for a.c.
traction systems, given
in 9.2 can act as a
touch voltage should
be investigated.
Guiding values for the
rail potential gradient
measured at right angle
away from the track of
a.c. traction systems,
where the running rails
are directly earthed, are
given in Figure C.1 and
Table C.1 for
homogenous soil
resistivity.
page 22 of 23
Suvey in
HD 637 S1 :1999
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000
Clause
of the working draft
Point of view of new
proposal
Suvey in
IEC62128-1:2003 &
EN50122-1
Suvey in
IEC61936-1:2002
iron L25mm*25mm*4mm,
and shall not be less than
40c min 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 maybe
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
6.2.3～6.2.6 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 Class1.0, its
internal impedance not less
than 1MΩ, and the
resolution of the volt meters
hall 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 Formula（5）
Us=Us′ Is/Im
page 23 of 23
Suvey in
HD 637 S1 :1999
Suvey in
ANSI/IEEE Std 81-1983 &
ANSI/IEEE Std 81.2-1991 &
GB/T 17949.1-2000