Standard
Title: DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV
DISTRIBUTION SYSTEM
EARTHING
Technology
240-130615754
Unique Identifier:
Alternative Reference Number: 34-1985
Area of Applicability:
Engineering
Documentation Type:
Standard
Revision:
1
Total Pages:
63
Next Review Date:
March 2023
Disclosure Classification:
Controlled
Disclosure
Compiled by
Approved by
Authorized by
Bruce Mclaren
Shawn Ramadhin
Riaz Vajeth
Senior Engineer
Chief Engineer
Senior Manager LES
Date:
Date:
Date:
Supported by SCOT/SC
Riaz Vajeth
SCOT/SC Chairperson
Date:
PCM Reference: 240-51017656
SCOT Study Committee Number/Name: OHL Earthing Work Group
Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
Page:
2 of 63
Content
Page
1.
Introduction .................................................................................................................................................. 5
2.
Supporting clauses ...................................................................................................................................... 5
2.1 Scope ................................................................................................................................................. 5
2.1.1 Purpose .................................................................................................................................. 6
2.1.2 Applicability ............................................................................................................................ 6
2.2 Normative/informative references ...................................................................................................... 6
2.2.1 Normative ............................................................................................................................... 6
2.2.2 Informative ............................................................................................................................. 6
2.3 Definitions ........................................................................................................................................... 6
2.3.1 General .................................................................................................................................. 6
2.3.2 Disclosure classification ......................................................................................................... 7
2.4 Abbreviations ...................................................................................................................................... 7
2.5 Roles and responsibilities .................................................................................................................. 7
2.6 Process for monitoring ....................................................................................................................... 7
2.7 Related/supporting documents .......................................................................................................... 8
3.
Requirements .............................................................................................................................................. 8
3.1 Summary of earthing requirements .................................................................................................... 8
3.1.1 Earthing at equipment installations ........................................................................................ 8
3.1.2 LV feeder earthing and service connections .......................................................................... 8
3.1.3 Earth Electrodes .................................................................................................................... 9
3.1.4 Material for earthing applications ........................................................................................... 9
3.2 Earthing of equipment installations .................................................................................................... 9
3.2.1 General installations .............................................................................................................. 9
3.2.2 Transformer installations ........................................................................................................ 9
3.2.3 Pole-mounted switchgear, CT/VT metering units, voltage regulators and shunt
capacitors ............................................................................................................................. 10
3.2.4 Surge arrester installations .................................................................................................. 10
3.2.5 Mini-substation and ground-mounted transformer installations ...........................................10
3.2.6 Ring Main Units (ground-mounted switchgear) and CT/VT metering equipment
installations .......................................................................................................................... 11
3.2.7 Specific resistance values of the equipment earths ............................................................ 11
3.3 LV feeder earthing and service connections .................................................................................... 12
3.3.1 Low voltage feeders ............................................................................................................. 12
3.3.2 Service connections ............................................................................................................. 14
3.4 Earthing of MV overhead lines Anti-climb devices ........................................................................... 15
3.5 Earthing of cables ............................................................................................................................. 15
3.6 Earth electrode ................................................................................................................................. 16
3.6.1 Standard earth electrode configurations .............................................................................. 16
3.6.2 Earth electrode enhancement .............................................................................................. 21
3.6.3 Earth electrode selection and installation procedure ...........................................................22
3.6.4 Earth electrode installation records ..................................................................................... 23
3.7 Connections to earth electrodes ...................................................................................................... 24
3.8 Materials for earthing applications ................................................................................................... 24
3.8.1 Conductors ........................................................................................................................... 24
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DISTRIBUTION STANDARD:
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Revision:
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SECTION 1: MV AND LV DISTRIBUTION SYSTEM
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Page:
EARTHING
3.8.2 Earth rods and accessories ................................................................................................. 25
3.8.3 Connectors ........................................................................................................................... 26
3.8.4 Neutral surge arrester .......................................................................................................... 27
3.8.5 Earth lead fastening ............................................................................................................. 27
3.8.6 Stay insulators ..................................................................................................................... 27
4.
Measurement guide ................................................................................................................................... 27
4.1 Apparatus for earth tests .................................................................................................................. 27
4.1.1 Earth testing instruments ..................................................................................................... 27
4.1.2 Test probes .......................................................................................................................... 29
4.1.3 Test probe resistance .......................................................................................................... 29
4.1.4 Other earth testing accessories ........................................................................................... 29
4.2 Factors affecting measurement accuracy ........................................................................................ 30
4.2.1 Stray alternating currents ..................................................................................................... 30
4.2.2 Coupling between test leads ................................................................................................ 30
4.2.3 Fences and buried metallic objects ..................................................................................... 30
4.3 Soil resistivity measurement ............................................................................................................ 31
4.3.1 Soil resistivity measurement procedure ............................................................................... 31
4.3.2 Interpretation of measured results ....................................................................................... 33
4.3.3 Two layer soils ..................................................................................................................... 33
4.4 Earth electrode resistance measurement ........................................................................................ 33
4.4.1 Methods of electrode resistance measurement ................................................................... 34
4.4.2 The 61,8% method of earth electrode resistance measurement (with verification by the
four potential method) .......................................................................................................... 34
4.4.3 The slope method of earth electrode resistance measurement ..........................................37
4.5 Earth surface potential measurement .............................................................................................. 42
4.5.1 Procedure to calculate the touch potential, Ut, at a certain position ...................................42
4.5.2 Procedure to calculate the step potential, Us, at a certain position .....................................43
4.6 Earth continuity testing ..................................................................................................................... 44
5.
Authorization .............................................................................................................................................. 45
6.
Revisions ................................................................................................................................................... 45
7.
Development team .................................................................................................................................... 45
8.
Acknowledgements ................................................................................................................................... 46
Annex A – Impact Assessment ......................................................................................................................... 47
Annex B – Landing Test Report Sheet ............................................................................................................. 51
Figures
Figure 1: TN-C-S earthing system .................................................................................................................... 14
Figure 2: TT System earthing with a TN-C-S earthing system extension .......................................................15
Figure 3: Connections for the Wenner method of soil resistivity measurement ..............................................31
Figure 4: Connections for the 61,8 % and four potential methods of earth electrode resistance
measurement ..................................................................................................................................... 35
Figure 5: Connections for the slope method of earth electrode resistance measurement ..............................37
Figure 6: Possible results from several slope method tests ............................................................................ 42
Figure 7: Connections to determine touch potential contact resistance..........................................................43
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SECTION 1: MV AND LV DISTRIBUTION SYSTEM
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EARTHING
Figure 8: Connections to determine step potential contact resistance ............................................................ 44
Tables
Table 1: Maximum earth resistance values for transformer LV electrodes .....................................................11
Table 2: Maximum earth resistance values for electrodes at other equipment ...............................................12
Table 3: Standard earth electrode configurations for 30 Ω resistance ............................................................ 17
Table 4: Alternative earth electrode configurations for 30 Ω resistance ..........................................................18
Table 5: Standard earth electrode configurations for 70 Ω resistance ............................................................ 19
Table 6: Alternative earth electrode configurations for 70 Ω resistance .........................................................20
Table 7: Standard earth electrode configurations for 150 Ω resistance ..........................................................21
Table 8: Short time current ratings (3 s) for stranded copper conductors .......................................................25
Table 9: Short time current ratings (3 s) for copper-clad steel conductor .......................................................25
Table 10: Format for a soil resistivity survey results ....................................................................................... 32
Table 11: Results format for the 61,8 % and four potential method of electrode resistance measurement ...36
Table 12: of values of dPT/dc for values of µ .................................................................................................... 38
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DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
1.
Unique Identifier: 240-130615754
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Introduction
Effective earthing is of the utmost importance for the protection of equipment and for safety purposes.
Simultaneously increasing emphasis on safety and reliability of supply dictates careful design,
implementation and maintenance of earthing systems. This section of the Distribution Standard has been
prepared to promote a common understanding throughout Eskom of the characteristics of and the
requirements for LV and MV earthing.
The objective of earthing is to provide a means to dissipate electric currents into the earth under normal and
fault conditions without exceeding any operating and/or equipment limits or adversely affecting continuity of
supply.
2.
Supporting clauses
2.1
Scope
This section of the Distribution Standard applies to all equipment installations and distribution systems to be
equipped with earth electrodes covering a small area namely:
a)
Equipment installations
•
•
•
•
Transformer installations
o
Distribution transformers up to and including 500 kVA, three-phase (3ø) or singlephase (1 ø), at medium, intermediate and low voltage levels.
o
CT/VT Metering units.
Pole mounted switchgear
o
Circuit-breakers
o
Sectionalizers
Pole/surface mounted compensating equipment
o
Shunt capacitor banks
o
Voltage regulators
Surge arrester installations
Note: Details and drawings of earthing arrangements for equipment listed in points (2) to (4) are to be found in DST_34-1192
Distribution Standard, Part 4, Section 1: Light conductors particular requirements for overhead lines up to 33 kV with conductors
up to Hare conductor.
•
b)
Cable system equipment
o
Mini-substations
o
Ground-mounted transformers
o
CT/VT Metering units
o
Ring main units (RMUs)
Medium and low voltage networks
•
Medium voltage distribution lines.
•
Low voltage feeders..
•
MV and LV underground cable networks.
Note 1: For earthing requirements on single-wire earth return (SWER) systems, refer to DST_34-453, Distribution Standard,
Part 4, Section 4: SWER particular requirements for 19 kV single wire earth return (SWER) overhead distribution.
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DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
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Note 2: For LV service cable earthing requirements on LPU (large power users) and SPU (small power users) outdoor
services, refer to DST_34-305, Distribution Standard, Part 8, Section 3: Outdoor LV services for small power users and large
power users.
2.1.1
Purpose
None
2.1.2
Applicability
This document shall apply throughout Eskom Holdings Limited Divisions.
2.2
Normative/informative references
2.2.1
Normative
The following documents contain provisions that, through reference in the text, constitute requirements of
this standard. At the time of publication, the editions indicated were valid. All standards and specifications
are subject to revision, and parties to agreements based on this standard are encouraged to investigate the
possibility of applying the most recent editions of the documents listed below.
[1]
SANS 10199:2004, The design and installation of earth electrodes.
[2]
SANS 10292:2001, Earthing of low-voltage distribution systems.
[3]
SANS 1063:1998, Earth rods and couplers.
[4]
SANS 10198-3:2004, The selection, handling and installation of electric power cables of rating not
exceeding 33 kV.
[5]
SANS 1411-7:2003, Materials of insulated cables and flexible cords – Part 7: Polyethylene (PE).
[6]
SCSASABK3: Rev.0, Distribution Standard – Part 7: Generic substation design.
[7]
DRP_34-1933, Distribution Report – Optimization of MV earth electrode design.
[8]
NRS000-1: Complication of NRS and other definitions used in the electricity supply industry
[9]
DST_34-1192 Distribution Standard, Part 4, Section 1: Light conductors particular requirements for
overhead lines up to 33 kV with conductors up to Hare conductor.
[10]
DST 34-1175, Distribution Standard, Part 22, Section 0: General information and requirements for
medium voltage cable systems.
[11]
Fig 1 – TN-C-S system earthing, SANS 10292:2001, Earthing of low-voltage distribution systems.
2.2.2
Informative
None
2.3
Definitions
2.3.1
General
The definitions and abbreviations in NRS000-1 and the following definitions apply:
Definition
conductive concrete
Description
Concrete consisting of cement and an added electrolyte to conform to D-DT3205. Conductive concrete has applications in earthing in areas where the soil
resistivity is very high.
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DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Definition
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Description
earthing lead (down
lead)
That section of conductor connecting a buried earth electrode to installed
equipment.
electrode (earth
electrode)
One or more conductive parts that are embedded in the earth for the purpose
of making effective electrical contact with the general mass of earth.
PEN conductor
A conductor that functions both as a Protective Earth conductor and a Neutral
conductor.
System earthing
identification code as
defined in SANS 10292
The first letter of the identification code denotes the relationship of the source
of energy to earth as follows:
•
T – One or more parts are connected directly to earth.
•
I – All live parts are isolated from earth or one point is connected to
earth through an impedance.
The second letter of the identification code denotes the relationship of the
exposed conductive parts of the consumer’s installation to earth as follows:
•
T – exposed conductive parts of the consumer’s electrical installation
are connected to earth, independently of the earthing of any point of the
source of energy.
•
N – The exposed conductive parts of the consumer’s electrical
installation are connected direct to the source earth, which, in the case
of an AC system is usually the transformer neutral point.
The designation TN is further subdivided depending on the arrangement of the
neutral and protective conductors. That arrangement is denoted by a further
letter or letters, as follows:
2.3.2
•
C – The neutral and protective functions on the LV distributor and in the
consumer’s electrical installation are combined in a single conductor.
•
S – The neutral and protective functions on the LV distributor and in the
consumer’s electrical installation are provided by separate conductors.
•
C-S - The neutral and protective functions on the LV distributor are
combined in a single conductor and in the consumer’s electrical
installation are provided by separate conductors.
Disclosure classification
Controlled disclosure: controlled disclosure to external parties (either enforced by law, or discretionary).
2.4
Abbreviations
Abbreviation
ECC
2.5
Description
Earth continuity conductor
Roles and responsibilities
Not applicable.
2.6
Process for monitoring
Not applicable.
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SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
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Related/supporting documents
Not applicable.
3.
Requirements
3.1
Summary of earthing requirements
The earthing practice applicable to urban and rural distribution systems is discussed below. The different
types of distribution systems are defined in Appendix C and also see section 3.6.3.1.
3.1.1
Earthing at equipment installations
a)
Transformer MV and LV earths may be combined only where their overall resistance to earth does
not exceed 1 Ω or where there is an ECC (earth continuity conductor) back to the source
substation. Otherwise, the practice of earthing involves separation of the medium and low voltage
earths at all transformer installations providing a supply to a customer at nominal voltages up to
and including the intermediate voltage (IV) range, i.e. for nominal voltages up to and including
1 900 V, single-phase and 3 300 V, three-phase.
b)
There is an exception to the general rule that the MV and LV earths may not be combined unless
the total resistance of the combined electrode to remote earth is less than 1 Ω or unless there is an
ECC back to the source substation. This is when a remote transformer would require a very
expensive MV earth electrode to achieve an MV electrode impedance of less than 30 Ω. For the
purpose of this clause, a remote transformer is defined as a transformer that supplies a single
unmanned installation and the installation is suitably far from any place where people are often
present to ensure that the risk of a person being in the vicinity of the transformer during an earth
fault is extremely low. In this case the MV and LV earth electrode of the transformer can be
combined into one electrode. The combined electrode installed shall have sufficiently low
impedance to allow the sensitive earth fault protection to operate. This is to ensure that a fault will
not remain on the network for an extended period of time which would increase the risk of a person
being in the vicinity of the installation while a fault is present. The limits of the earth electrode
impedance that should not be exceeded in order to ensure that the sensitive earth fault protection
will operate in the event of a fault are given in Table 2.
Note: In underground cable networks, the metallic sheath or armouring of the MV cable generally serves as an ECC.
c)
Where the MV and LV earth electrodes are separated at transformer installations, the transformer’s
LV windings shall be protected against insulation breakdown by installing a neutral surge arrester
between the LV neutral terminal and the tank earth.
d)
A minimum separation distance of 5 m shall be maintained between the MV and LV earth
electrodes at transformer installations.
e)
For all other equipment installations in a distribution system a single earth electrode is required.
3.1.2
LV feeder earthing and service connections
a)
LV distribution systems shall be earthed in accordance with the TN-C-S earthing system
philosophy, i.e. the neutral and protective functions are combined in a single conductor between
the source and point of supply and are separated in a consumer’s installation (see SANS 10292).
b)
In urban distribution systems it is often convenient to earth the MV at the transformer and the LV
remotely (one span away on the LV feeder). Where this technique is implemented and multiple LV
feeders issue from a transformer structure, all of the feeders shall be earthed one span away from
the transformer.
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DISTRIBUTION TYPE – PART 2:
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PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
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3.1.3
Earth Electrodes
a)
The impedance of the earth electrode connection shall be within the limits specified in 3.2.7. All
exceptions, i.e. installations where maximum effort does not satisfy the minimum requirements,
shall be recorded by Project Engineering and be made available for investigation whenever
required.
b)
A detailed installation record including the earthing arrangement shall be kept by Project
Engineering. Maintenance shall be based on the principle of plant condition monitoring and shall be
carried out in accordance with Eskom maintenance guidelines.
c)
The buried earthing conductor and earth rods shall be at least 0,5 m below normal ground level.
d)
Earth electrodes may be encased in conductive concrete to reduce the dimensions of a required
configuration. Owing to the high application costs, conductive concrete shall be applied by
exception.
e)
The use of chemicals to improve long term electrode resistance to earth shall be applied by
exception to avoid an unnecessary burden being placed on operating and maintenance staff for
follow up applications.
3.1.4
Material for earthing applications
a)
For transformer and equipment installations copper earth leads to suit the maximum short circuit
level expected within the system shall be used. Solid copper conductor of a minimum 12 mm² cross
section or stranded copper conductor of a minimum of 16 mm² cross section shall be used. See
3.8.1.1. for more information.
b)
Copper-clad steel conductors may be used for earthing applications in areas where copper theft is
a problem. See 3.8.1.2 for more information.
c)
PVC insulated earth leads shall be used to obtain the 5 m separation between the MV and LV
electrodes at a transformer pole. The earth connecting conductors shall be insulated over the full
separation distance between electrodes.
d)
NOTE: For cable networks, if the LV meter panel is less than 5 m away from the transformer, then
the customer’s LV ECC (if applicable) shall be insulated for at least 5 m.
e)
All the relevant design drawings are listed and included in annex F.
3.2
Earthing of equipment installations
3.2.1
General installations
All accessible conductors, portions of electrical plant or apparatus which do not form part of an electrical
circuit and which might become alive accidentally, shall be bonded to earth.
3.2.2
Transformer installations
Distribution equipment associated with transformer installations that is either ground-mounted or polemounted and fed by underground cable or overhead line, shall be installed, connected and earthed in
accordance with the following requirements:
a)
the star point of the transformer LV winding shall be earthed (see also 3.3);
b)
the MV surge arresters, transformer tank and other metalwork shall be bonded to the MV earth
electrode (see D-DT-0627 for pole-mounted transformers, D-DT-0855 for mini-substations and
D-DT- 0862 for ground-mounted transformers );
c)
a combined MV/LV earth electrode may be employed only where the electrode resistance to earth
does not exceed 1 Ω or where there is an ECC back to the source substation or for remote supplies
(see clause 3.1.1.2);
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SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
d)
where separate MV and LV earths are used:
e)
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•
the MV and LV earth electrodes shall be separated by not less than 5 m,
•
a neutral surge arrester in accordance with D-DT-3088 shall be installed between the LV
neutral terminal and the transformer tank, and
•
care shall be exercised to ensure that there is no metallic or other low impedance
conducting path between the MV and LV earths,
An equipotential MV earth loop shall be installed for mini-substations and for ground-mounted
transformer applications irrespective of whether the MV and LV earths are separated or not. This
shall be done in accordance with D-DT-0855 and D-DT -0862, respectively. Further details can be
found in DST 34-1175, Distribution Standard, Part 22, Section 0: General information and
requirements for medium voltage cable systems, clause 4.7.
The philosophy regarding the application of combined or separated MV and LV earths at transformer
installations is provided in annex C.
3.2.3
Pole-mounted switchgear, CT/VT metering units, voltage regulators and shunt
capacitors
The earthing system for pole-mounted switchgear, CT/VT metering units, voltage regulators and shunt
capacitors shall consist of a multiple spike electrode (preferably a three point star) with all connections being
made and bonded to the main earthing lead (see D-DT-0642). The connection leads shall match the short
time rating of the main earthing lead.
Further details and drawings of earthing arrangements for pole-mounted switchgear, metering and
compensating equipment are to be found in DST_34-1192 Distribution Standard, Part 4, Section 1: Light
conductors particular requirements for overhead lines up to 33 kV with conductors up to Hare conductor.
For LV service cable earthing requirements on large power users (LPU) and small power users (SPU)
outdoor services, refer to DST_34-305, Distribution Standard, Part 8, Section 3: Outdoor LV services for
small power users and large power users.
Note: For recloser installations, if a single-phase transformer is used instead of a VT, it shall be earthed according to D-DT1825 (in-line) and D-DT-1829 (out- of-line).
3.2.4
Surge arrester installations
Surge arrester installations shall be earthed as follows:
a)
the earthing system shall consist of a multiple rod electrode (preferably a three point star) with all
connections being made and bonded to the main earthing lead;
b)
the surge arresters shall be connected to earth and to the equipment being protected by the
shortest possible and most practical direct route;
c)
all arresters shall be provided with devices for disconnecting the arresters in the event of failure.
The earth connection shall be flexible enough to allow the disconnecting device to blow clear of the
arrester; and
d)
surge arresters shall be installed where a cable is connected to an overhead line. The cable
termination earth strap and arrester earth tails shall be bonded together.
3.2.5
Mini-substation and ground-mounted transformer installations
Mini-substations and ground-mounted transformers shall be earthed according to DST_34-1175, Distribution
Standard, Part 22, Section 0: General information and requirements for medium voltage cable systems. An
equipotential loop around the plinth is always required for operator safety.
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SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
3.2.6
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Ring Main Units (ground-mounted switchgear) and CT/VT metering equipment
installations
The earthing system for ring main units and CT/VT metering equipment is similar to that of pole-mounted
switchgear except that no earth electrode is required if there is an ECC back to the source substation (see
D-DT-0865). The equipment shall be earthed according to DST_34-1175, Distribution Standard, Part 22,
Section 0: General information and requirements for medium voltage cable systems. An equipotential loop
around the plinth is always required for operator safety.
3.2.7
Specific resistance values of the equipment earths
The derivations of resistance values specified in this section are included in annex C.
3.2.7.1 Transformer earth electrodes
3.2.7.1.1 Transformer MV earth electrode
For both 22 kV and 11 kV MV systems, the maximum allowable resistance of the transformer MV earth
electrode is 30 Ω. This limit will ensure that for a MV line to transformer tank fault:
a)
no dangerous voltages are experienced on the LV neutral;
b)
the LV neutral surge arrester energy absorption limits are not exceeded; and
c)
sufficient fault current flows to operate the MV earth fault protection.
3.2.7.1.2 Transformer LV earth electrode
The overall resistance to earth of the LV electrode at the transformer shall be such as to ensure that the
feeder main earth fault protection at the source will operate in event of a breakdown between the MV and LV
windings of the transformer.
The following maximum resistances apply to the transformer LV electrode:
Table 1: Maximum earth resistance values for transformer LV electrodes
a)
b)
Main earth fault protection
setting
(A)
Transformer
primary 11 kV
Transformer primary
22 kV
Maximum resistance value (Ω)
20
70
150
40
30
70
60
20
40
100
10
20
Note: A factor of safety of approximately 4 has been used to ensure acceptable
protection operation under:
1)
seasonal variations in soil resistivity, and
2)
variations in the effectiveness of MV source earthing.
The resistance values in Table 1 do not apply to single wire earth return (SWER) distribution systems.
If the maximum values for the MV and LV electrodes cannot be achieved with the standard electrode
configurations the Project Engineering Department shall be requested to investigate alternatives, such as
setting protection to a lower operating threshold or providing additional earthing. The expenditure of
exorbitant amounts of money on additional earthing to achieve these values should be avoided. In annex B
possible methods to enhance the earth electrode are also discussed.
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3.2.7.2 Earth electrodes for other equipment
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At equipment installations other than transformers, for example, pole-mounted switchgear and surge arrester
installations, the maximum electrode resistance values are determined by the sensitive earth fault protection
settings shown in Table 2.
Table 2: Maximum earth resistance values for electrodes at other equipment
Sensitive earth fault protection setting
(A)
Nominal voltage
11 kV
Nominal voltage
22 kV
Maximum resistance value (Ω)
5
300
600
10
150
300
Note: 1 A safety factor of approximately 4 has been used for the reasons given in table 1.
Note2: Since sensitive earth-fault protection is not used in cable networks, for ground-mounted equipment (other than
transformers) used in these networks, where there is no ECC, the earth electrode resistance values shall be in accordance with
the requirements of table 1 and are therefore based on the main earth fault protection settings.
3.3
LV feeder earthing and service connections
3.3.1
Low voltage feeders
The earthing practice for LV feeders employs a TN-C-S earthed system with the following characteristics:
a)
the supply is earthed at the source and the protective earth and neutral conductors are combined;
b)
the overall resistance to earth of the LV neutral shall not exceed the values given in 3.2.7.1.2;
c)
the following methods may be used to earth the LV neutral (see D-DT-0637 for overhead lines,
D-DT- 0855 for mini-substations and D-DT-0862 for ground-mounted transformers);
•
the LV earth electrode may be installed at the transformer, in which case insulated earth leads shall
be used to obtain the 5 m separation, or
•
the LV earth electrode may be installed one span away from the transformer. Where multiple LV
feeders issue from a transformer structure, each feeder shall be earthed one span away from the
transformer. Every LV earth electrode shall comply with the resistance requirements stated in
3.2.6,
Note: For overhead lines, alternative 1 is the preferred method of earthing the LV neutral.
d)
for overhead lines, where the required values of resistance cannot be attained, the PEN (combined
earth and neutral) conductor may be earthed at other points along the LV feeder;
e)
e) for overhead lines, in areas where theft of copper is a problem, a redundant LV earth electrode
shall be installed on the LV neutral. The redundant electrode shall be situated away from the main
electrode and shall comply with the resistance requirements stated in 3.2.6.
f)
f) if the PEN conductor is broken, dangerous voltages to earth may exist at the consumer’s earth
terminal. It is therefore essential to pay particular attention to the conductor’s integrity throughout
the design, construction, maintenance and operation of the LV distribution system;
g)
g) for overhead lines, all T-off connections from the feeder PEN conductor shall be made using
two insulation piercing connectors (IPCs). PG clamps shall be used only for the connection of
aluminium conductors to aluminium conductors. Where used, two PG clamps shall be used per
connection.
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h)
all metalwork, accessible from ground level, forming part of the LV feeder external to the
substation, shall be bonded to the feeder PEN conductor. This includes catch guards, metal poles,
cable sheathing and armouring, metal enclosures of meters and fuse cabinets etc;
i)
no circuit-breakers, isolators, fuses, switches or removable links shall be installed in the earth
conductor of the LV supply feeder;
j)
in single-phase overhead systems the cross sectional area of the PEN conductor of all the LV
feeders shall not be less than that of the phase conductor. In three-phase overhead systems the
cross sectional area of the PEN conductor may be reduced to half that of a phase conductor. The
PEN conductor shall have a minimum cross sectional area of 16mm2;
k)
the PEN conductor shall be insulated from the transformer tank to prevent contact between the MV
and LV earths; and
l)
the PEN conductor is connected to the consumer’s main earthing terminal via the service cable.
m)
Urban and other appropriate low voltage overhead networks may interconnect LV distributor
neutrals to form a low impedance return path. This mitigates the risk of floating neutral/earth
voltages due to broken neutral conductors or poor joint integrity across the consumer’s supply.
Where this is implemented, there is a potential increase in operating risk when disconnecting or
connecting neutrals of apparent “dead” circuits. Field service operators should be consulted and
the technique documented before applying on any project.
A TN-C-S earthing system is illustrated in Figure 1.
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Source of energy
L1
L2
L3
Combined protective
earth and neutral
(PEN) conductor
Source earth
PEN cable
Additional earths
if required
Combined earth & neutral
(PEN) conductor
Consumer earth
terminal
Equipment installation
L
N
E
Single-phase
Exposed conductive parts
PEN cable
Combined protective
earth and neutral
(PEN) conductor
L1
L2
L3
Figure 1: TN-C-S earthing system
Note 1: The neutral and protective functions are combined in a single conductor between the source and the point of supply.
Note 2: All exposed conductive parts of an electrical installation that can become alive are connected to the combined earth
and neutral conductor via the main earthing terminal and a earth conductor via the main earthing terminal and an earth
conductor, which is either the metallic covering of the cable supplying the installation or a separate conductor.
Note 3: The integrity of the PEN conductor is of paramount importance, with an open circuit in the PEN conductor, dangerous
voltages can appear at the consumer’s earth terminal.
Note 4: For further information on the TN-C-S earthing system refer to SANS 10292.
3.3.2
Service connections
Service connections shall comply with the following:
a)
open wire service connections shall not be used;
b)
concentric cable comprising a phase conductor/s and the PEN conductor shall be used for
overhead line service connections;
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c)
the armoured LV cable shall be used for LV underground service connections;
d)
in a single-phase service connection the cross sectional area of the PEN conductor shall be at
least the same as the phase conductor. In the three-phase connection the PEN conductor shall not
be less than half the cross sectional area of the phase conductor; and
e)
the customer’s earthing terminal at the point of supply shall be connected to the PEN conductor on
the supply side of the circuit-breaker.
f)
No earth electrode shall be installed at the customer's premises. According to SANS 10292 (see
Figure 2 below), a break in the neutral of an effective combination of a TT and TN CS systems
can have severe consequences for the customer who has a separate customer’s earth. Therefore
in order to mitigate this, option 4.3.1m) above shall be considered where appropriate. (For example
if a single phase LV network load of 2 kW resistive load and a transformer earth resistance of 70
ohms, the customer earth would have to be below 15 ohms to ensure a safe touch potential of 32
Volts.)
Figure 2: TT System earthing with a TN-C-S earthing system extension
3.4
Earthing of MV overhead lines Anti-climb devices
Steelwork employed on medium voltage wood pole structures is generally not earthed except where
equipment, for example, transformers, pole-mounted auto-reclosers; etc., is installed.
Where the earthing of wood poles is required in order to attain the required BIL, a galvanized steel wire may
be used as the down lead. Copper down leads shall be used where equipment (i.e. surge arrester) earths
are required. In areas prone to copper theft, a conductor of an equivalent material may be used.
3.5
Earthing of cables
The armouring and metal sheath of cables shall be bonded to earth at both ends of the cable. Bonding to
the cable armouring and/or metal sheath shall be performed by means of an approved and type-tested,
solder-less mechanical connection e.g. constant force springs or worm drive clamps, using tinned copper
earth conductor braids of not less than 16 mm² unless local earth fault current levels justify an increase in
cross-section or unless otherwise specified.
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Continuity of the cable armouring and metal sheath shall be maintained at all cable joints. For further details
on the earthing of cables refer to DTS_34-1175, Distribution Standard, Part 22, Section 0: General
Information and requirements for medium-voltage cable systems.
3.6
Earth electrode
3.6.1
Standard earth electrode configurations
Earth electrodes are constructed from buried horizontal conductors or vertically driven rods or a combination
of these. In some applications a conductor may be installed vertically in a bored hole.
Buried horizontal conductors (termed trench electrodes) are easier to install than vertical rods. A further
advantage is that potential gradients at the soil surface which result from current discharge by a trench
electrode are less steep than is the case for vertically installed conductors. If the ground is very difficult to dig
(if it is rock), then a vertical earth electrode should be installed in a drilled hole.
Vertically installed electrodes may be extended to substantial lengths and are often able to make contact
with very low resistivity soils far below the earth’s surface. The resistivity of the soil further below the surface
is less prone to seasonal fluctuation and the resistance of vertical rods is thus very stable.
Earth electrodes exhibit different impedance characteristics for current of different magnitudes and
frequencies. Trench electrodes are known to offer lower impedance at power frequency than do equivalent
vertical conductors. Vertical rods offer superior performance under surge conditions.
Electrodes constructed from a combination of driven rods and radial arrays of buried conductors are installed
in order to ensure a stable resistance value and to minimize the hazard of high surface potentials during
times of current discharge. Combined electrodes also satisfy the objective of having both surge impedances
and 50 Hz impedances as low as possible. Combination also facilitates current division as well as offering
multiple independent paths to reduce the effect of a possible earthing conductor failure.
Earth electrodes shall be installed as deep as possible and not less than 500 mm below the ground surface.
The reason for this specification is that the layer of soil above the conductor forms an important medium into
which the electrode can dissipate current. Deep buried electrodes also exhibit less steep voltage gradients
at the soil surface during times of current discharge. Further, deep burial reduces the possibility of
mechanical damage of the earth electrode.
The four standard electrode types are identified for application:
a)
Non-extendable earth rods used for a multi-rod electrode configuration
Note: A three point star electrode is the preferred configuration. An alternative configuration is a linear trench electrode with
non-extendable earth rods – which is practically more suitable for underground cable network installations.
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b)
Linear trench electrode
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A linear trench electrode is a horizontally applied electrode and may be installed where it is not possible to
install vertical rods.
c)
Extendable earth rods
The use of extendable earth rods is optional; for example, they may be used when a vertical earth electrode
installation is required.
d)
Vertically installed conductor
The installation of a vertical earth conductor is appropriate if there are space constraints that make the
installation of a trench electrode impossible or when the soil at the site has been identified as a two-layer soil
with the top layer having a higher resistivity than the lower layer. It is also appropriate when the ground is
extremely hard to dig (if it is rock) and the electrode is to be installed in a drilled hole.
When the soil is a two-layer soil with the top layer having a higher resistivity that the lower layer; the vertical
electrode is used to reach the more conductive lower layer. For this case, the depth of the upper soil layer
should be added to the length of the vertical conductor required, as read from Table 3a. This is because only
the portion of the vertical electrode in the low resistivity layer has any effect on the electrode resistance.
When this is done, the resistivity of the soil used to determine the length of conductor require can be taken
as the resistivity of the lower soil layer.
The depth of the top layer of soil can be determined by fitting a two layer soil model to the measured data.
The process is outlined in SCSASABK3 (Generic substation design), clause 4.1.8.2.
The dimensions of standard main earth electrodes for required resistances of 30 Ω, 70 Ω and
150 Ω are provided in tables 3, 4 and 5 respectively. These are the preferred configurations for earthing at
equipment installations. Where the standard earth electrode types cannot be installed the appropriate
alternatives in tables 3a or 4a shall be considered.
The electrode dimensions specified in the following tables were derived using the calculation procedure as
described in SANS 10199 and DRP_34-1933 Report: Optimization of MV earth electrode design.
Table 3: Standard earth electrode configurations for 30 Ω resistance
Description
Main earth electrode
Electrode type
1
2
Electrode configuration
Applicable soil resistivity
at a depth of 0,5 m to
1,5m (ρ in Ω m)
5
6
ρ = 300
ρ = 600
ρ = 900
ρ = 1500
Option 1
Option 2
Option 1
Option 2
0,5
0,5
0,5
0,5
0,5
0,5
— Radial length (L)
5,0
13,0
22,0
23,0
40,0
41,0
— Rod length
1,5
1,5
1,5
1,5
1,5
1,5
5,0
6,5
11,0
N/A
20,0
N/A
4
7
7
1
7
1
— Rod
distance
depth
4
Three point star
Electrode dimensions (m)
— Trench
(minimum)
3
separation
Number of rods
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Main earth electrode
Diagrammatic
representation
L
L
L
L
6
L
L
L
L
/
L
L
/
L
L
/
L
L
L
L
L
8
8
8
8
8
Sandy type
soil
L
/
/
Gravel
type soil
Sandy type
soil
Gravel
type soil
Note: Each main earth electrode type is designed for the indicated soil resistivity value. Where intermediate
resistivity values are encountered, an electrode designed for the next higher resistivity value shall be installed.
Table 4: Alternative earth electrode configurations for 30 Ω resistance
Description
Main earth electrode
Electrode type
1
2
Electrode configuration
Right angle turn or in-line
Applicable soil resistivity at a depth of
0,5 m to 1,5 m
ρ = 300
ρ = 600
3
4
ρ = 900
ρ = 1500
(ρ in Ω m)
Alternative 1
Electrode with earth spikes
Electrode dimensions (m)
— Trench depth (minimum)
0,5
0,5
0,5
0,5
— Radial length (L)
8,0
20,0
32,0
58,0
— Rod length
1,5
1,5
1,5
1,5
— Rod separation distance
8,0
20,0
32,0
58,0
Number of rods
3
3
3
3
Diagrammatic representation
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
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Main earth electrode
Alternative 2
Electrode without earth spikes
Electrode dimensions (m)
— Trench depth (minimum)
0,5
0,5
0,5
0,5
— Radial length (L)
19,0
41,0
65,0
120,0
Number of rods
0
0
0
0
Diagrammatic representation
L
L
L
L
Note 1: The earth lead from the equipment should preferably be connected to the centre of the electrode to provide the
best current distribution in the electrode under fault and lightning discharge conditions.
Note 2: The buried horizontal electrode in alternative 2 is suitable for areas where it is difficult to install earth rods.
Description
Electrode type
Main earth electrode
1
Electrode configuration
2
3
4
Drilled-hole vertical conductor
ρ = 300
ρ = 600
ρ = 900
ρ = 1500
— Trench depth (minimum)
0,5
0,5
0,5
0,5
— Vertical conductor length
15,0
33,0
50,0
90,0
1
1
1
1
Applicable soil resistivity at a depth of 0,5
m to 1,5 m
(ρ in Ω m)
Electrode dimensions (m)
Number of rods
Note 1: Drilled-hole vertical conductor electrodes are suitable in areas where space restrictions make it difficult to install
horizontal electrodes.
2
Note 2: The values given are for a bare 16 mm copper conductor laid vertically in a drilled-hole.
Table 5: Standard earth electrode configurations for 70 Ω resistance
Description
Electrode type
Main earth electrode
1
Electrode configuration
2
3
4
Three point star
ρ = 300
ρ = 600
ρ = 900
ρ = 1500
— Trench depth (minimum)
0,5
0,5
0,5
0,5
— Radial length (L)
2,0
4,0
8,0
15,0
— Rod length
1,5
1,5
1,5
1,5
— Rod separation distance
N/A
4,0
9,0
15,0
4
4
4
4
Applicable soil resistivity at a
depth of 0,5 m to 1,5 m
(ρ in Ω m)
Electrode dimensions (m)
Number of rods
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Main earth electrode
Diagrammatic representation
L
L
L
L
L
L
L
L
/
L
L
L
L
8
Note: Each main earth electrode type is designed for the indicated soil resistivity value. Where intermediate
resistivity values are encountered, an electrode designed for the next higher given resistivity value shall be
installed.
Table 6: Alternative earth electrode configurations for 70 Ω resistance
Description
Main earth electrode
Electrode type
1
2
Electrode configuration
3
4
Right angle turn or in-line
ρ = 300
Applicable soil resistivity at a depth of
0,5 m to 1,5 m
ρ = 600
ρ = 900
ρ = 1500
(ρ in Ω m)
Alternative 1
Electrode with earth spikes
Electrode dimensions (m)
— Trench depth (minimum)
0,5
0,5
0,5
0,5
— Radial length (L)
3,0
6,5
12,0
22,0
— Rod length
1,5
1,5
1,5
1,5
— Rod separation distance
N/A
6,5
12,0
22,0
1
3
3
3
Number of rods
Diagrammatic representation
L
L
L
L
L
L
L
L
L
L
L
Alternative 2
L
L
L
L
L
Electrode without earth spikes
Electrode dimensions (m)
— Trench depth (minimum)
0,5
0,5
0,5
0,5
— Radial length (L)
7,0
16,0
26,0
46,0
0
0
0
0
Number of rods
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Main earth electrode
Diagrammatic representation
L
L
L
L
Note 1: The earth lead from the equipment should preferably be connected to the centre of the electrode to provide
the best current distribution in the electrode under fault and lightning discharge conditions.
Note 2: The buried horizontal electrode in alternative 2 is suitable for areas where it is difficult to install earth rods.
Table 7: Standard earth electrode configurations for 150 Ω resistance
Description
Main earth electrode
Electrode type
1
2
Electrode configuration
3
4
Three point star
ρ = 300
ρ = 600
ρ = 900
ρ = 1500
— Trench depth (minimum)
0,5
0,5
0,5
0,5
— Radial length (L)
1,0
2,0
3,5
6,5
— Rod length
1,5
1,5
1,5
1,5
— Rod separation distance
N/A
N/A
N/A
N/A
Applicable soil resistivity at a
depth of 0,5 m to 1,5 m
(ρ in Ω m)
Electrode dimensions (m)
Number of rods
1
1
1
1
Diagrammatic representation
L
L
L
/
L
L
/
L
L
/
L
/
L
L
L
L
8
8
8
8
Note: Each main earth electrode type is designed for the indicated soil resistivity value. Where
intermediate resistivity values are encountered, an electrode designed for the next higher given resistivity
value shall be installed.
3.6.2
Earth electrode enhancement
Methods of electrode enhancement (described in annex B) include the encasement of the electrode in
conductive concrete and the chemical treatment of the soil surrounding the electrode. These methods may
be considered in certain circumstances as a possible solution to the problem of high electrode resistance to
earth. They may also be applied in areas where a considerable variation of electrode resistance is
experienced due to seasonal climatic changes.
Encasing earth electrodes in conductive concrete is a costly means of reducing the electrode resistance to
true earth. The practice may, however, find application where space limitations inhibit the use of expansive
electrode designs. Encasing electrodes in concrete has the added benefit of improved resistance to theft.
Full details regarding the application of conductive concrete are presented in annex B.1.
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The option of chemical treatment of the soil is to be applied by exception to avoid an unnecessary burden
being placed on operating and maintenance staff for follow-up treatment applications. Details regarding the
application of chemical treatment are given in annex B.2.
3.6.3
Earth electrode selection and installation procedure
The following procedure shall be followed when establishing a main earth electrode installation:
a)
a soil resistivity survey shall be undertaken to establish suitable electrode sites;
b)
an electrode type appropriate for the soil conditions shall be selected; and
c)
the electrode shall be installed. If the installed electrode is non-standard, its impedance shall be
measured. Standard electrodes are described in section 3.6.1 and annex B.1.
d)
for minor works only, the process may start from b) and the impedance of installed electrode shall
be measured.
3.6.3.1 Soil resistivity survey
The resistance to earth of an electrode is influenced by the resistivity of the surrounding soil. The
measurement of soil resistivity is therefore an extremely important function and shall form an integral part of
the overall earthing process. A soil resistivity survey shall be implemented as follows:
a)
Rural transformers
For a single transformer installation, e.g. a rural point of supply, a soil resistivity survey is required to
establish the location best suited and most practically feasible for the transformer installation. The results
are also used to select an earth electrode suitable for those specific soil conditions. The procedure to select
a suitable electrode is described above shall be followed.
b)
Urban transformers
To establish a network of transformer installations, e.g. a township electrification project, a separate soil
resistivity survey shall be conducted at each proposed location for a transformer installation. These results
are used to select for each transformer an earth electrode that is suitable for the specific soil conditions at
the equipment location.
The soil resistivity survey shall be performed using the Wenner method as described in 5.3.
The soil resistivity value (ρ) measured in ohm metres (Ω m) at a depth of 0,5 m to 1,5 m below ground level
is used for the selection of an appropriate earth electrode. This depth range is important as the soil that is
close to the electrode has the greatest positive effect on its final resistance value.
Identification of the type of soil that is encountered can give a rough indication as to the expected soil
resistivity. Annex A includes information regarding soil identification and the expected resistivity ranges of
different types of soil.
3.6.3.2 Earth electrode selection
A standard earth electrode type is selected from table 3, 3a, 4, 4a or 5 on the basis of the required
resistance value and the result of the apparent soil resistivity measurement (taken at 0,5 m to 1,5 m below
ground level). A three point star electrode configuration is preferred.
Where the measured resistivity value does not correspond to one of the four “standard” values specified in
the tables: 300 Ω m, 600 Ω m, 900 Ω m and 1500 Ω m, an electrode designed for the next highest standard
resistivity value should be selected. For example, if the soil resistivity survey yielded a result of 400 Ω m, a
standard electrode designed for 600 Ω m should be selected.
The Project Engineering Department shall be consulted in those cases where it is impractical to install any of
the main or alternative electrode types and the methods of electrode enhancement described in annex B are
not deemed appropriate.
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3.6.3.3 Installation of an earth electrode
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Earth electrode components are installed as follows:
a)
Horizontal conductors
Horizontal conductors are buried in trenches no less than 500 mm below ground level. After horizontal
conductors have been installed in the trenches, the trenches shall be back-filled (usually using the material
that was excavated from the trenches). During the back-fill process, the soil shall be added in 300 mm thick
layers and then be compacted before the next layers are added. Care shall be taken to ensure that no
stones are placed close to the horizontal conductor, as these could damage the conductor when the soil is
compacted.
b)
c)
d)
Single earth rods
•
each earth rod shall be driven into undisturbed soil. The general rule is that if a foundation
hole can be excavated by mechanical means, then it will be reasonably easy to drive in an
earth rod,
•
earth rods shall be driven a minimum of 1000 mm from the structure and the rod top shall
be not less than 500 mm below ground level,
Extendable earth rods
•
the coupling and driving bolt shall be attached to the top end of the sectional rod,
•
this assembly shall be driven vertically into the ground using a special impact-resisting
steel driving pipe or mechanical hammer until the coupling on the rod reaches the ground
level,
•
the driving bolt shall be removed,
•
the lower end of the second rod shall be fitted to the coupling,
•
another coupling shall be attached to the top end of the second rod,
•
the driving bolt shall be attached to the second coupling,
•
driving shall be continued until the second section reaches ground level.
connections between horizontal conductors and vertical rods
Details regarding the interconnection of vertical rods and horizontal conductors in earth electrodes are
presented in D-DT-0642. D-DT-0642 applies to copper conductors and copper-clad steel conductors.
Notice that for copper-clad steel conductor tails must protrude from the main junction point connection by
100mm.
Joints and terminations of copper and copper-clad steel conductors used in earthing applications need not
be covered with denso tape or bitumen.
e)
Vertical electrodes
Install the vertical conductor in the drilled hole. The hole should then be back-filled with a slurry formed by
mixing water with the excavated soil (after the excavated soil has been sifted to remove any large stones).
3.6.3.4 Measurement of the earth electrode’s resistance to earth
The electrode’s resistance to earth need only be measured in the event that a non-standard electrode is
installed. Where this is the case, the resistance measurement shall be conducted as described in 5.4.
Standard electrodes are described in section 3.6.1 and annex B.1.
3.6.4
Earth electrode installation records
A detailed installation record, including details of the earthing arrangement, shall be kept of all equipment
installations where a main earth electrode configuration has been implemented.
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a)
soil resistivity survey results;
b)
earth electrode configuration and dimensions;
c)
equipment details;
d)
measured resistance of the earth electrode installation to earth (where required); and
e)
Project Engineering Department investigation results and recommendations (where applicable).
Annex E contains recommended formats of installation records and medium voltage equipment
commissioning sheets. Refer to annex A for guidance on soil identification.
3.7
Connections to earth electrodes
Connections to earth electrodes shall comply with the following:
a)
all normally accessible earthing terminations to equipment shall be made with compression lugs or
bolted clamps;
b)
all earthing connections to equipment shall be so arranged that they can be removed, permanently
or temporarily, independently of any other earth; and
c)
the number of connections to an earth conductor shall be kept to a minimum.
3.8
Materials for earthing applications
Relevant component design drawings are listed in annex F.
The preferred materials to be used for earthing applications are as follows.
3.8.1
Conductors
3.8.1.1 Standard conductors (see D-DT-3137 and D-DT-3139)
The conductor used for earthing leads and earth bonding conductor shall be annealed stranded or solid
copper conductor. A minimum cross sectional area of 16 mm² stranded copper or 12 mm² solid copper shall
be used.
For new installations, the earthing lead shall be a joint-free continuous conductor. For retrofits, permission
shall be obtained from the Project Engineering Department to have joints on the earthing leads.
Conductors for earthing applications are selected according to their maximum allowable temperature rise for
the flow of 50 Hz current. The minimal cross sectional area is specified to ensure mechanical integrity of the
conductor after the application of compressed lugs or exothermic welding.
The short time (3 s) current ratings for stranded copper conductors in accordance with SANS 10198-3, are
listed in table 6.
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Table 8: Short time current ratings (3 s) for stranded copper conductors
Cross sectional area
Stranding/diameter
Maximum current (in A) for given
maximum
1)
2
Final conductor temperature
No./mm
150 °C
450 °C
25
40
7/1,70
7/2,12
7/2,65
1200
1875
3000
1975
3100
4950
63
80
100
7/3,35
7/3,75
19/2,85
4750
6000
7500
7800
9925
12500
mm
16 *
1
2
* Preferred size
1
Applicable to PVC insulated conductors and in areas of dry grass (which may be easily ignited).
2
Applicable to bare conductors with brazed connectors.
3.8.1.2 Alternative conductors
In areas where the theft of copper conductors is a problem, conductors of alternative materials may be
considered. In most situations it should be sufficient to use alternative conductors only for the earthing down
lead. For ease of application at transformer installations, the alternative conductor may also be used to
obtain the 5 m separation between MV and LV transformer earths.
Copper-clad steel conductor (D-DT-3137) is the only recommended alternative material for earthing
applications.
Note 1: Galvanized steel conductor shall not be used for permanent earthing applications. Galvanized steel is prone to
oxidation and corrodes sacrificially to many metals. Galvanic corrosion is an especially serious concern where the galvanized
steel is buried in the vicinity of copper conductors.
Note 2: Galvanized steel conductors used temporarily in earthing applications shall be replaced within three months of
application.
The short time (3 s) current rating for 5,19 mm diameter, 30 % conductivity copper-clad steel conductor is
given in table 6a.
Table 9: Short time current ratings (3 s) for copper-clad steel conductor
1
Diameter (mm)
Maximum current (in A) for 150 °C
Final conductor temperature
5,19
920
1
Applicable to PVC insulated copper-clad steel conductors.
Refer to annex D for details regarding the conductor cross-sectional area specifications presented in tables 6
and 6a.
3.8.1.3 Conductor insulation
The earth leads used to obtain the separation between the MV and LV electrodes at transformer installations
shall be insulated with a black, 1000 V, ultra-violet stabilized, PVC covering. The PVC covering and copper
shall comply with SANS 1411-7.
3.8.2
Earth rods and accessories
Earth rods and accessories shall comply with the following:
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3.8.2.1 Earth rods
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Earth rods (extendable or non-extendable) shall comply with D-DT-3091. See above.
3.8.2.2 Couplings
Couplings (threaded or threadless) shall comply with D-DT-3092.
3.8.2.3 Driving tips
Driving tips shall be manufactured from high strength steel of length adequate to make a contact with the rod
while driving.
3.8.2.4 Driving studs
Driving studs shall be manufactured from high-tensile steel for driving of threaded earth-rods.
3.8.2.5 Driving heads
Driving heads shall be manufactured from high-tensile steel for driving earth rods with unthreaded ends.
3.8.3
Connectors
It is preferred that all bonds within an earthing system be made via a crimped, bolted or exothermic welded
connection. The following connectors are suitable for use on both copper and copper-clad steel conductors.
3.8.3.1 Underground connections
a)
b)
Connections to earth rods:
•
Conductor to rod crimped connection (preferred) (see D-DT-3076),
•
Suitable for use with one 16mm2 conductor and a 16mm diameter earth rod;
•
Exothermic welded connection,
•
Conductor to rod clamp (see D-DT-3093),
•
Suitable for use with conductor of maximum cross sectional area of 70 mm² and a 16 mm
diameter earth rod. The clamp bolt shall be tightened onto the earth rod, not the copper
lead;
Connections for earthing conductors:
•
Crimping ferrule (preferred) (see D-DT-3076)
•
Shall be used with four 16 mm2 conductors. The ferrule is crimped using a 14,5 HEX
across flats die and a half-ton hydraulic crimping tool (the same tool as is used for ABC
joints and terminations);
•
Line tap (see D-DT-3101)
•
Suitable for connection of stranded conductor of diameters up to 9 mm;
3.8.3.2 Connections above ground level
a)
Transformer line tap (see D-DT-3048)
b)
Suitable for connection of stranded conductor of diameters up to 9 mm;
c)
Line tap (see D-DT-3101)
d)
Crimping lug (see D-DT-3102) Suitable for 16 mm conductor diameter for attachment to M12
earthing stud on a transformer tank.
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3.8.4
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Neutral surge arrester
The specification of the neutral surge arrester (see D-DT-3088) required at transformer installations with
separate MV and LV earths is as follows:
a)
type:
Metal oxide;
b)
class:
Distribution;
c)
MCOV *:
5 kV;
d)
operating voltage:
6 kV;
e)
discharge current:
10 kA; and
f)
protective level # :
19,5 kV.
Note 1: Maximum continuous operating-voltage.
Note 2 # Derived for a 10 kA ; 8/20 µs impulse.
3.8.5
Earth lead fastening
Earth leads shall be fastened to wood poles using galvanized wire staples (see D-DT-3129) spaced every
500 mm.
3.8.6
Stay insulators
Stays on all MV distribution networks and LV feeders shall be fitted with a stay insulator.
4.
Measurement guide
4.1
Apparatus for earth tests
4.1.1
Earth testing instruments
4.1.1.1 Requirements of an earth testing instrument
An earth testing instrument shall comply with the following requirements:
a)
special earth testing instruments designed for the particular form of measurement shall be used;
b)
the principle of earth tester operation is to measure current passing through the circuit containing
the resistance under test and the voltage across this resistance. The measured quantities shall
then be processed by the instrument to give the value of the resistance in ohms;
c)
the instrument shall contain its own source of supply, either a hand-driven generator or internal
batteries. An alternating current shall be generated. In situations where the soil resistivity is high,
standard earth testers may not be able to generate enough voltage to drive an adequate test
current. See 4.1.2 for further details;
d)
the instrument shall have four terminals to which the test leads can be connected. Two terminals
shall be for passing the current to the circuit and two shall be for detecting the potential drop across
the measured resistance. The current terminals shall be marked C1 and C2 and the potential
terminals shall be marked P1 and P2;
e)
for ease of operation and elimination of possible reading errors the "direct reading" Liquid Crystal
Display (LCD) testers are preferred. Testers operating on the "null-balance" principle are
acceptable;
f)
resistance readings from 0,01 Ω to 1999 Ω shall be obtainable;
g)
an instrument shall be able to record measurements in the order of 20 Ω, 200 Ω and 2000 Ω;
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h)
optional features are available on some earth testers indicating:
•
the current probe resistance being too high,
•
the potential probe resistance being too high,
•
the battery capacity being low or the generator being turned too slowly, and
•
the excessive noise interference in the soil being tested.
As a cost effective alternative for teams concerned with routine maintenance testing of the earth connection
continuity and earth electrode resistance, a three terminal direct reading tester with one measurement range
and readings of resistance of 0,2 Ω to 500 Ω will be sufficient.
4.1.1.2 Operation of a typical earth testing instrument
The instrument shall be connected for the specific test required. The operation of typical instruments is
described below. For more detailed instructions consult the operating manual for the specific instrument.
a)
b)
Operation of "Null-balance" instruments
•
set the range switch to × 0,01 and the balancing resistor dials to 999 Ω,
•
turn the generator slowly, press the test button and note the galvanometer deflection,
•
if deflection is positive (towards +), increase range factor to × 0,1 (or higher) until the
deflection becomes negative (towards −),
•
when deflection is negative decrease the value of the resistor, digit by digit, starting with
the left knob, then the centre and finally the right knob. Continue until the galvanometer
pointer is central. Speed up the revolutions of the generator to about 160 rpm for
maximum sensitivity and to avoid the effects of stray currents, and
•
the value of resistance under test is established by reading the balance resistor dials and
multiplying it by the range factor.
Operation of direct reading instruments
•
set the range switch to its lowest setting,
•
turn the generator or press the test button and note the resistance value on the scale,
•
if the reading is going out of range, change the range switch to the higher value, and
•
the value of resistance under test is read directly from the scale.
4.1.1.3 Calibration of a typical earth testing instrument
Every earth testing instrument shall maintain an appropriate measurement accuracy. To verify this accuracy,
earth testers shall be calibrated by a National Calibration Service (NCS) laboratory on an annual basis.
Calibration certificates shall contain the following information:
a)
the serial number, type and accuracy of equipment used in the calibration;
b)
the serial number, type and accuracy of equipment being calibrated;
c)
the date of calibration and date for recalibration; and
d)
the signature of an approved staff member of the NCS laboratory.
Note: Only equipment that has been calibrated by an NCS laboratory is recognized as being accurate in terms of the law.
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4.1.2
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Test probes
The methods of testing described in the following sections, require the use of current and voltage test
electrodes along with the earth testing instrument. The test probes are normally supplied together with the
measuring instrument.
An earth testing kit shall contain at least four steel probes of minimum length 450 mm and minimum crosssectional area 140 mm².
Test probes shall be hammered into the ground in various configurations and to various depths depending
on the specific measurement being undertaken.
4.1.3
Test probe resistance
The resistances to earth of the potential probes have little influence on resistance and resistivity
measurements since voltmeters operate with very high internal resistances.
In all the tests described in this section, current is injected into the earth through the earth electrode under
test or a current probe and extracted through a current probe. The magnitude of the test current for a
constant voltage source is dependent on the sum of the electrode and probe resistances. In the case that
this combined resistance is very large, the magnitude of test current that flows may be lower than the
measuring instrument’s sensitivity. Measurements taken using small test currents are also more likely to be
distorted by the presence of stray currents (see 4.2.1).
The problem of insufficient test current may be alleviated by one of two courses of action:
4.1.3.1 Decrease the current probe/s resistance to earth
The resistance of a test probe can be decreased by driving the rod deeper into the soil, pouring water around
the rod or by driving additional rods and interconnecting them in parallel. The addition of salt to the water
poured around the test electrodes does little to decrease the electrode resistance.
In some cases care shall be exercised when installing an expansive current probe. With particular reference
to the Wenner method of soil resistivity measurement, the technique is based on an assumption that the
current probes have specific dimensions. Use of electrodes of different dimensions will thus introduce a
measurement error. In many cases, the likelihood of such errors shall be weighed against the alternative of
obtaining no measurement at all.
4.1.3.2 Increase the voltage of the power supply
Increasing the power supply voltage is not possible when using a hand driven generator of the type
incorporated in some measuring instruments. In cases where it is not possible to adequately decrease the
probe resistance, earth testing may be carried out by using a selectable frequency power source together
with a step-up transformer. The test current is calculated by measuring the voltage across a known
resistance.
When this solution is practical, care shall be taken to avoid contact across dangerous potentials on the
electrodes and test leads.
As a general rule the resistance values of the current and potential electrodes shall meet the requirements of
the instruments used. With commercial instruments, a potential electrode resistance of 1 kΩ may be used.
Some manufacturers claim that their instrument will permit 10 kΩ in the potential electrode.
4.1.4
Other earth testing accessories
Together with the measuring instrument and test probes, a minimum earth testing kit shall comprise the
following:
a)
two 50 m and two 100 m leads each with two types of connectors – a spade connector for
attachment to the tester terminals on one side and the "crocodile" type clip for attachment to the
earth rod at the other end;
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b)
two 3 m leads also with connectors;
c)
one hammer,13 kg (2,5 lb.);
d)
two probe extractors;
e)
one non-metallic, 60 m tape measure; and
f)
a commissioning sheet (installation record).
4.2
Factors affecting measurement accuracy
4.2.1
Stray alternating currents
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Stray alternating currents that flow in the earth may originate from a number of different sources. These
sources include:
a)
differential salination in soils;
b)
differential aeration of soils;
c)
bacteriological action in soils;
d)
different materials in contact with one another, for example, galvanic action;
e)
power supply systems;
f)
traction systems, tramways, rapid transit systems, railways; and
g)
domestic supplies that employ neutral or earth conductors (or both) that are connected to earth at
multiple locations.
Stray currents tend to distort the measurements of earthing related quantities by introducing voltage drops
across the electrode or soil sample under test that are not related to the applied test current. Stray currents
are thus responsible for the exaggerated resistance and resistivity measurements.
The effects of stray alternating current may be reduced in earthing related measurements by utilizing a test
frequency that is not present in the stray current. Most measuring devices use frequencies within a range of
50 Hz to 100 Hz. The use of filters or narrow band measuring instruments is another method of overcoming
the effects of stray alternating currents.
4.2.2
Coupling between test leads
In cases where current and voltage leads of substantial length are laid adjacently as in all test procedures
described herein, there is a distinct possibility that leakage current may be induced in the potential lead.
This current leakage is an important factor that gives rise to measurement errors.
The most obvious precaution to reduce the likelihood of induced currents is to ensure that the lead insulation
is in good condition.
The effect of the measurement error resulting from coupling between the test leads is likely to be most
pronounced when measuring low resistance values. In these cases it is good practice to ensure a 100 mm
separation between current and potential leads.
4.2.3
Fences and buried metallic objects
Metallic structures near to the test area may invalidate the test results. Where possible, testing shall be
carried out away from man-made structures such as pipelines and fences. If a pipeline or fence crosses the
test site, the direction of the line formed by the test probes shall be chosen to be perpendicular to the
direction of the metal structure.
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4.3
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Soil resistivity measurement
The resistivity of soil is dependent on its composition and moisture content. These factors show wide
variance from place to place and over time. The resistivity of the soil surrounding an earth electrode has a
significant impact on the resistance of an earth electrode. Soil resistivity also has a bearing on the potential
gradients that are to be expected at the soil surface during times of fault current discharge through the earth
electrode.
The measurement of soil resistivity is an important function that plays a crucial role in the application of an
earth electrode. Soil resistivity measurements are also useful in the calculation of the extent of inductive
coupling between adjacent power and communication circuits.
Several methods are available by which soil resistivity may be measured. The preferred technique is the
Wenner method.
The Wenner method of soil resistivity measurement
The Wenner method (also known as the “four electrodes method”) is the favoured technique for measuring
soil resistivity at a location where an earth electrode covering a small area will be installed.
The Wenner method operates under the assumption that the soil in which the measurement is made is
homogenous: that is, a soil of uniform material, consistency, grain size and density. It will be seen presently
that the method has some application in soils consisting of layers of differing resistivity.
4.3.1
Soil resistivity measurement procedure
The measurement procedure is as follows:
a)
Four test probes shall be driven into the soil in a straight line at equal distances "a" and to a depth
of not more than 10 % of "a" (refer to figure 3).
b)
The leads between the measuring instrument and test probes are connected as shown in Figure 2.
Care shall be exercised to ensure that the insulated leads are in good working order as damaged
or non-insulated leads may result in incorrect values being recorded.
a
a
a
a
10
C1
P1
P2
C2
C1 P1 P2 C2
EARTH TESTER
Figure 3: Connections for the Wenner method of soil resistivity measurement
c)
The earth tester is operated and a resistance measurement, R, is recorded.
d)
The average soil resistivity to a depth, D, in the vicinity of the voltage probes is calculated
according to the relation:
Average resistivity to depth D:
ρ = 2πaR (Ωm)
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where "a" is the test probe spacing in metres and "R" is the earth
given as eighty percent of the probe spacing (i.e. D = 0,8 × a).
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tester readings in ohms. The depth, D, is
Readings shall be taken and resistivity calculated for progressively widened probe spacings to obtain
resistivity values at various depths. The centre position of the spike system shall be kept constant whilst the
probe spacings are increased. The recommended values for “a” are:
a)
1 m;
b)
2 m;
c)
3 m;
d)
5 m;
e)
10 m; and
f)
15 m.
The depth to which the test probes are driven shall never be more than 10 % of the spacing "a" between the
electrodes.
The results shall be tabulated as shown in table 7.
calculated as:
The specific depth, D, for a given spacing, a, is
D = 0,8 × a
For easy calculation a geometric factor given by K = 2πa is presented in the table.
On completion of the table, a curve of resistivity (in ohm metres) against depth (in metres) is plotted on a
logarithmic scale. The format of the graph is displayed in graph 1 and reproduced in annex E.
In an area, readings shall be taken in a minimum of two different directions.
Table 10: Format for a soil resistivity survey results
1
2
3
4
5
Probe spacing
a (m)
Specific depth
D=0,8 a (m)
Tester reading
Geometric factor K
Resistivity
R(Ω)
K = 2πa
(Ω × m)
p = RK
1
0,8
6,28
2
1,6
12,57
3
2,4
18,85
5
4,0
31,42
10
8,0
62,83
15
12,0
94,25
1000
Resistivity
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ohm-m
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100
Probe spacing (m)
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15
Specific depth (m)
0,8 1,6 2,4 3,2 4,0 4,8 5,6 6,4 7,2 8,0 8,8 9,6 10,8 11,6 12,0
Graph 1 – Format for an apparent soil resistivity graph
4.3.2
Interpretation of measured results
The results obtained from a soil resistivity measurement give some indication of the nature of the underlying
soil. If the resistivity is found to increase rapidly with increase of "a", one may deduce that there are layers of
soil having a higher resistivity than that at the surface. A very rapid increase may indicate the presence of
rock. In this case it could be difficult to install a vertical earth electrode and a horizontal electrode type
should be considered.
If the resistivity decreases rapidly with increased depth, the conclusion can be drawn that the deeper layers
of soil have a lower resistivity and advantage will be gained by installing a deep earth electrode, for example,
a vertical earth rod.
If the results indicate abnormalities in the soil, a second set of tests shall be conducted with the probes lined
up in a different direction.
4.3.3
Two layer soils
If the apparent soil resistivity graph shows significant variation of the soil resistivity with depth then it will be
necessary to construct a two-layer soil model for the soil. This will give an indication of the resistivity of the
upper soil layer ( ρ1 ) the resistivity of the lower soil layer ( ρ 2 ) and the depth of the top layer (h). Software
such as CDEGS may be used to determine the model.
4.4
Earth electrode resistance measurement
According to procedure to install an earth electrode discussed in section 4.6.3, after installing a standard
electrode , the electrode’s resistance need not be measured. However, where a non-standard electrode is
installed, a resistance measurement shall be performed. Earth resistance measurements are useful to:
a)
verify the adequacy of a new earthing system;
b)
detect changes in an existing earthing system; and
c)
check on design parameters and calculations.
Note: n the case of a multiple earthed system, the total effective resistance may be calculated using the
relation:
1
R total
=
1
1
1
1
+
+
+ ..... +
Ri R 2 R 3
Rn
where
•
Rtotal
•
Ri is the resistance of electrode i.
is the total resistance of ‘n’ parallel electrodes; and
It should be noted that the effective resistance of an earth electrode to earth may decrease by up to 30 %
after the first 6 months to 12 months after installation. This effect is largely due to the settling of the soil
around the electrode.
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Calculations for the earth resistance of an electrode configuration make the assumption of homogeneous soil
having a constant resistivity. In practice, this assumption is rarely, if ever, found to hold true and
considerable discrepancies can arise between a calculated and measured value of earth resistance.
4.4.1
Methods of electrode resistance measurement
Depending on the application, one of two methods of electrode resistance measurement shall be used. A
third method of measurement is used for verification of the measured results.
The method, known as the “61,8 % rule”, is the simplest method of measurement and is ideal for application
to relatively small earth electrode systems. Strictly speaking, this method requires knowledge of the
electrical centre of the electrode to be tested. Unless the electrode is symmetrical about a given point, the
electrical centre may not be easily found, much less accessed. Nevertheless, this method has application to
small unsymmetrical electrode configurations. For example, this method may be used to measure the
resistance of a three point star earth electrode at a transformer installation.
Apart from the issue of accessing the electrical centre of the electrode, the use of the 61,8 % rule on large
systems is limited by the large distances required for current injection (see 4.4.2.1 to 4.4.2.6).
It is recommended that the results from a resistance measurement by the 61,8 % method are verified by the
“four potential method”. This procedure does not require that measurements are made from the electrical
centre of the electrode to be tested. The disadvantage of requiring large distances for current probe spacing
remains.
The “slope method” of resistance measurement is more accurate than the methods described above. As the
current probe need not be positioned very far from the electrode, this method is suitable for use on large
electrode systems. This method has the advantage that its use does not depend upon the knowledge of the
location of the earth system electrical centre.
4.4.2
The 61,8% method of earth electrode resistance measurement (with verification by
the four potential method)
Equipment connections for the 61,8 % method are illustrated in Figure 4.
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X = 5 x D BUT > 50m
POSITIONS OF THE POTENTIAL PROBE
0,2X
0,4X
0,5X
0,6X
0,7X
0,8X
C2
P2
EARTH ELECTRODE
UNDER TEST:
Three point star or
Single rod
CURRENT
PROBE
D
C1 P1 P2 C2
EARTH TESTER
Figure 4: Connections for the 61,8 % and four potential methods of earth electrode resistance
measurement
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The measurement procedure is as follows:
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a)
Establish the physical layout of the earthing system and type of electrodes being used, for example
in the figure the earth electrode is in a three point star configuration.
b)
Disconnect the earth electrode from the earthed equipment, preferably at the point where the wire
from the equipment connects to the earth electrode. Dangers associated with disconnecting the
earth electrode shall be noted and precautionary measures shall be taken when disconnecting the
earth electrode.
c)
Identify the position of the current probe C2. The measurement shall be taken away from the line of
any known trench earth, metallic pipe or underground cables. The distance between the electrode
under test and the current probe C2 shall be five times the length of the longest earth rod, longest
horizontal length or the longest diagonal of the earthing system but not less than 50 m. For
standardization purposes it is proposed that a distance of 100 m be used.
d)
Set the potential probe P2 in line with the tested electrode and the current probe C2 at a distance
equal to 0,618 of the distance to the current probe. Water the area around the current probe C2 to
reduce its resistance. High probe resistance reduces the amount of current that the test set can
inject into the soil.
e)
Connect the earth tester terminals C1 and P1 to the tested electrode, terminal P2 to the potential
probes P2 and the terminal C2 to the current probe C2. Operate the earth tester and obtain the
resistance reading. By the 61,8% method, this reading is the resistance of the electrode under
test.
f)
The result obtained in 4.4.2.6 shall be verified using the following procedure (known as the four
potential method):
1)
with the current probes set up as before, measure the resistance with the potential
electrode P2 set up at the distances: 0,2; 0,4; 0,5; 0,6; 0,7; and 0,8 of the distance to the
current electrode;
2)
the values obtained by measurement at the six positions (designated R1 to R6) shall be
tabulated. The format for this table is given in table 8.
Table 11: Results format for the 61,8 % and four potential method of electrode resistance
measurement
1
2
3
4
Definition
Position
Distance
(m)
Measured resistance
X
Probe C2
R1
Probe P2 at 0,2X
R2
Probe P2 at 0,4X
R3
Probe P2 at 0,5X
R4
Probe P2 at 0,6X
Total resistance
Probe P2 at 0,618X
R5
Probe P2 at 0,7X
R6
Probe P2 at 0,8X
(Ω)
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3)
four values for electrode resistance are derived from the four potential method according to
the formulas:
4)
4.4.3
1)
R=
− 0,1187 R1
− 0,4667 R2
+ 1,9816 R4
− 0,3961 R6
2)
R=
− 2,6108 R2
+ 4,0508 R3
− 0,1626 R4
− 0,2774 R6
3)
R=
− 1,8871 R2
+ 1,1148 R3
+ 3,6837 R4
− 1,9114 R5
4)
R=
− 6,5225 R3
+ 13,6816 R4
− 6,8803 R5
+ 0,7210 R6
the four values of R , obtained from (c), shall agree substantially and an average of the
results may then be calculated. However, it is possible that the result from equation (1) will
be less accurate than the others. If the result of (1) does prove to be at variance with the
others it can be ignored and an average obtained from the three more agreeable values.
The slope method of earth electrode resistance measurement
Equipment connections for the slope method are illustrated in figure 5.
Arbitrary
position on
E electrode
Position of
C probe
dc
dp = 0,6dc
dp = 0,4dc
dp = 0,2dc
R2
R1
R3
C1 P1 P2 C2
EARTH TESTER
Figure 5: Connections for the slope method of earth electrode resistance measurement
The measurement procedure is as follows:
a)
The current probe C2 is placed a distance dc from the point of current injection at the earth
electrode to be tested. The distance dc must be greater than 50 m.
b)
The potential probe is placed in line with the current probe and earth electrode in each of three
positions. Distances from the earth electrode of 0,2; 0,4; and 0,6 times the distance dc are to be
used.
c)
The earth tester terminals C1 and P1 are connected to the earth electrode. The current probe is
connected to terminal C2 of the tester. The potential probe is connected to terminal P2.
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d)
For each position of potential probe: 0,2 dc; 0,4 dc; and 0,6 dc; the earth tester is operated and
resistance values R1, R2 and R3 are obtained respectively.
The slope coefficient, , is ca lcula te d a ccording to the m e a s ure d re s is ta nce va lue s us ing the
formula:
e)
µ=
R3−R2
R 2 − R1
A value for the term dPT/dc corresponding to the calculated  va lue is re a d from ta ble 9. If the
calculated value of µ falls outside those given in the table, it will be necessary to move the current
probe further away from the earthing system and repeat the tests.
f)
Note: The numbers in the first row of table 9 represent the third decimal of the µ value in the first column. For example, the
dPT/dc value corresponding to µ = 0,403 is 0,6428.
Table 12: of values of dPT/dc for values of µ
µ
0
1
2
3
4
5
6
7
8
9
0,40
0,6432
0,6431
0,6429
0,6428
0,6426
0,6425
0,6423
0,6422
0,6420
0,6419
0,41
0,6418
0,6416
0,6415
0,6413
0,6412
0,6410
0,6409
0,6408
0,6406
0,6405
0,42
0,6403
0,6402
0,6400
0,6399
0,6437
0,6396
0,6395
0,6393
0,6392
0,6390
0,43
0,6389
0,6387
0,6386
0,6384
0,6383
0,6382
0,6380
0,6379
0,6377
0,6376
0,44
0,6374
0,6373
0,6372
0,6370
0,6369
0,6367
0,6366
0,6364
0,6363
0,6361
0,45
0,6360
0,6359
0,6357
0,6356
0,6354
0,6353
0,6351
0,6350
0,6348
0,6347
0,46
0,6346
0,6344
0,6443
0,6341
0,6340
0,6338
0,6337
0,6336
0,6334
0,6333
0,47
0,6331
0,6330
0,6328
0,6327
0,6325
0,6324
0,6323
0,6321
0,6320
0,6318
0,48
0,6317
0,6315
0,6314
0,6312
0,6311
0,6310
0,6308
0,6307
0,6305
0,6304
0,49
0,6302
0,6301
0,6300
0,6298
0,6297
0,6295
0,6294
0,6292
0,6291
0,6289
0,50
0,6288
0,6286
0,6285
0,6283
0,6282
0,6280
0,6279
0,6277
0,6276
0,6274
0,51
0,6273
0,6271
0,6270
0,6268
0,6267
0,6265
0,6264
0,6262
0,6261
0,6259
0,52
0,6258
0,6256
0,6255
0,6253
0,6252
0,6252
0,6248
0,6347
0,6245
0,6244
0,53
0,6242
0,6241
0,6239
0,6238
0,6236
0,6235
0,6233
0,6232
0,6230
0,6229
0,54
0,6227
0,6226
0,6224
0,6223
0,6221
0,6220
0,6218
0,6217
0,6215
0,6214
0,55
0,6212
0,6210
0,6209
0,6207
0,6206
0,6204
0,6203
0,6201
0,6200
0,6198
0,56
0,6197
0,6195
0,6194
0,6192
0,6191
0,6189
0,6188
0,6186
0,6185
0,6183
0,57
0,6182
0,6180
0,6179
0,6177
0,6176
0,6174
0,6172
0,6171
0,6169
0,6168
0,58
0,6166
0,6165
0,6163
0,6162
0,6160
0,6159
0,6157
0,6156
0,6154
0,6153
0,59
0,6151
0,6150
0,6148
0,6147
0,6145
0,6144
0,6142
0,6141
0,6139
0,6138
0,60
0,6136
0,6134
0,6133
0,5131
0,6130
0,6128
0,6126
0,6125
0,6123
0,6121
0,61
0,6120
0,6118
0,6117
0,6115
0,6113
0,6112
0,6110
0,6108
0,6107
0,6105
0,62
0,6104
0,6102
0,6100
0,6099
0,6097
0,6096
0,6094
0,6092
0,6091
0,6089
0,63
0,6087
0,6086
0,6084
0,6083
0,6081
0,6079
0,6076
0,6076
0,6074
0,6073
0,64
0,6071
0,6070
0,6068
0,6066
0,6065
0,6063
0,6061
0,6060
0,6058
0,6057
0,65
0,6055
0,6053
0,6052
0,6050
0,6049
0,6047
0,6045
0,6044
0,6042
0,6040
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µ
0
1
2
3
4
5
6
7
8
9
0,66
0,6039
0,6037
0,6036
0,6034
0,6032
0,6031
0,6029
0,6027
0,6026
0,6024
0,67
0,6023
0,6021
0,6019
0,6018
0,6016
0,6015
0,6013
0,6011
0,6010
0,6008
0,68
0,6006
0,6005
0,6003
0,6002
0,6000
0,5998
0,5997
0,5995
0,5993
0,5992
0,69
0,5990
0,5989
0,5987
0,5985
0,5984
0,5982
0,5980
0,5979
0,5977
0,5976
0,70
0,5974
0,5973
0,5971
0,5969
0,5967
0,5965
0,5964
0,5962
0,5960
0,5959
0,71
0,5957
0,5955
0,5953
0,5952
0,5950
0,5948
0,5947
0,5945
0,5943
0,5942
0,72
0,5940
0,5938
0,5936
0,5935
0,5933
0,5931
0,5930
0,5928
0,5926
0,5924
0,73
0,5923
0,5921
0,5920
0,5918
0,5916
0,5914
0,5912
0,5911
0,5909
0,5907
0,74
0,5906
0,5904
0,5902
0,5900
0,5899
0,5897
0,5895
0,5894
0,5892
0,5890
0,75
0,5889
0,5887
0,5885
0,5883
0,5882
0,5880
0,5878
0,5877
0,5875
0,5873
0,76
0,5871
0,5870
0,5868
0,5866
0,5865
0,5863
0,5861
0,5859
0,5858
0,5856
0,77
0,5854
0,5853
0,5851
0,5839
0,5847
0,5846
0,5844
0,5842
0,5841
0,5839
0,78
0,5837
0,5835
0,5834
0,5832
0,5830
0,5829
0,5827
0,5825
0,5824
0,5822
0,79
0,5820
0,5818
0,5817
0,5815
0,5813
0,5812
0,5810
0,5808
0,5806
0,5805
0,80
0,5803
0,5801
0,5799
0,5797
0,5796
0,5794
0,5792
0,5790
0,5788
0,5786
0,81
0,5785
0,5783
0,5781
0,5779
0,5777
0,5775
0,5773
0,5772
0,5770
0,5768
0,82
0,5766
0,5764
0,5762
0,5760
0,5759
0,5757
0,5755
0,5753
0,5751
0,5749
0,83
0,5748
0,5746
0,5744
0,5742
0,5740
0,5738
0,5736
0,5735
0,5733
0,5731
0,84
0,5729
0,5727
0,5725
0,5723
0,5722
0,5720
0,5718
0,5716
0,5714
0,5712
0,85
0,5711
0,5709
0,5707
0,5705
0,5703
0,5701
0,5699
0,5698
0,5696
0,5694
0,86
0,5692
0,5690
0,5688
0,5686
0,5685
0,5683
0,5681
0,5679
0,5677
0,5675
0,87
0,5674
0,5672
0,5670
0,5668
0,5666
0,5664
0,5662
0,5661
0,5659
0,5657
0,88
0,5655
0,5653
0,5651
0,5650
0,5648
0,5646
0,5644
0,5642
0,5640
0,5638
0,89
0,5637
0,5635
0,5633
0,5631
0,5629
0,5627
0,5625
0,5624
0,5622
0,5620
0,90
0,5618
0,5616
0,5614
0,5612
0,5610
0,5608
0,5606
0,5604
0,5602
0,5600
0,91
0,5598
0,5596
0,5594
0,5592
0,5590
0,5588
0,5586
0,5584
0,5582
0,5580
0,92
0,5578
0,5576
0,5574
0,5572
0,5570
0,5568
0,5565
0,5563
0,5561
0,5559
0,93
0,5557
0,5555
0,5553
0,5551
0,5549
0,5547
0,5545
0,5543
0,5541
0,5539
0,94
0,5537
0,5535
0,5533
0,5531
0,5529
0,5527
0,5525
0,5523
0,5521
0,5519
0,95
0,5517
0,5515
0,5513
0,5511
0,5509
0,5508
0,5505
0,5503
0,5501
0,5499
0,96
0,5497
0,5495
0,5493
0,5491
0,5489
0,5487
0,5485
0,5483
0,5481
0,5479
0,97
0,5477
0,5475
0,5473
0,5471
0,5469
0,5467
0,5464
0,5462
0,5460
0,5458
0,98
0,5456
0,5454
0,5452
0,5450
0,5448
0,5446
0,5444
0,5442
0,5440
0,5438
0,99
0,5436
0,5434
0,5342
0,5430
0,5428
0,5426
0,5424
0,5422
0,5420
0,5418
1,00
0,5426
0,5414
0,5412
0,5409
0,5407
0,5405
0,5403
0,5400
0,5398
0,5396
1,01
0,5394
0,5391
0,5389
0,5387
0,5385
0,5383
0,5380
0,5378
0,5376
0,5374
1,02
0,5371
0,5369
0,5367
0,5365
0,5362
0,5360
0,5358
0,5356
0,5354
0,5351
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µ
0
1
2
3
4
5
6
7
8
9
1,03
0,5349
0,5347
0,5345
0,5344
0,5340
0,5338
0,5336
0,5333
0,5331
0,5329
1,04
0,5327
0,5325
0,5322
0,5320
0,5318
0,5316
0,5313
0,5311
0,5309
0,5307
1,05
0,5305
0,5302
0,5300
0,5298
0,5296
0,5293
0,5291
0,5289
0,5287
0,5284
1,06
0,5282
0,5280
0,5278
0,5276
0,5273
0,5271
0,5269
0,5267
0,5264
0,5262
1,07
0,5260
0,5258
0,5255
0,5253
0,5251
0,5249
0,5247
0,5244
0,5242
0,5240
1,08
0,5238
0,5235
0,5233
0,5231
0,5229
0,5229
0,5224
0,5222
0,5219
0,5217
1,09
0,5215
0,5213
0,5211
0,5209
0,5206
0,5204
0,5202
0,5200
0,5197
0,5195
1,10
0,5193
0,5190
0,5188
0,5185
0,5183
0,5189
0,5178
0,5175
0,5173
0,5170
1,11
0,5168
0,5165
0,5163
0,5160
0,5158
0,5155
0,5153
0,5150
0,5148
0,5145
1,12
0,5143
0,5140
0,5137
0,5135
0,5132
0,5130
0,5127
0,5125
0,5122
0,5120
1,13
0,5118
0,5115
0,5113
0,5110
0,5108
0,5105
0,5203
0,5100
0,5098
0,5095
1,14
0,5093
0,5090
0,5088
0,5085
0,5083
0,5080
0,5078
0,5075
0,5073
0,5070
1,15
0,5068
0,5065
0,5062
0,5060
0,5057
0,5055
0,5052
0,5050
0,5047
0,5045
1,16
0,5042
0,5040
0,5037
0,5035
0,5032
0,5030
0,5027
0,5025
0,5022
0,5020
1,17
0,5017
0,5015
0,5012
0,5010
0,5007
0,5005
0,5002
0,5000
0,4997
0,4995
1,18
0,4992
0,4990
0,4987
0,4985
0,4982
0,4980
0,4977
0,4975
0,4972
0,4970
1,19
0,4967
0,4965
0,4962
0,4960
0,4957
0,4955
0,4952
0,4950
0,4947
0,4945
1,20
0,4942
0,4939
0,4936
0,4933
0,4930
0,4928
0,4925
0,4922
0,4919
0,4916
1,21
0,4913
0,4910
0,4907
0,4904
0,4901
0,4899
0,4896
0,4893
0,4890
0,4887
1,22
0,4884
0,4881
0,4878
0,4875
0,4872
0,4870
0,4867
0,4864
0,4861
0,4858
1,23
0,4855
0,4852
0,4849
0,4846
0,4843
0,4841
0,4838
0,4835
0,4832
0,4829
1,24
0,4826
0,4823
0,4820
0,4817
0,4814
0,4812
0,4809
0,4806
0,4803
0,4800
1,25
0,4797
0,4794
0,4791
0,4788
0,4785
0,4783
0,4780
0,4777
0,4774
0,4771
1,26
0,4768
0,4765
0,4762
0,4759
0,4756
0,4754
0,4751
0,4748
0,4745
0,4742
1,27
0,4739
0,4736
0,4733
0,4730
0,4727
0,4725
0,4722
0,4719
0,4716
0,4713
1,28
0,4710
0,4707
0,4704
0,4701
0,4698
0,4696
0,4693
0,4690
0,4687
0,4684
1,29
0,4681
0,4678
0,4675
0,4672
0,4669
0,4667
0,4664
0,4661
0,4658
0,4655
1,30
0,4652
0,4649
0,4645
0,4642
0,4638
0,4635
0,4631
0,4628
0,4625
0,4621
1,31
0,4618
0,4616
0,4611
0,4607
0,4604
0,4601
0,4597
0,4594
0,4590
0,4586
1,32
0,4583
0,4580
0,4577
0,4573
0,4570
0,4566
0,4563
0,4559
0,4556
0,4553
1,33
0,4549
0,4546
0,4542
0,4539
0,4535
0,4532
0,4529
0,4525
0,4522
0,4518
1,34
0,4515
0,4511
0,4508
0,4505
0,4501
0,4498
0,4494
0,4491
0,4487
0,4484
1,35
0,4481
0,4477
0,4474
0,4470
0,4467
0,4463
0,4460
0,4457
0,4453
0,4450
1,36
0,4446
0,4443
0,4439
0,4436
0,4432
0,4429
0,4426
0,4422
0,4419
0,4415
1,37
0,4412
0,4408
0,4405
0,4402
0,4398
0,4395
0,4391
0,4388
0,4384
0,4381
1,38
0,4378
0,4374
0,4371
0,4367
0,4364
0,4360
0,4357
0,4354
0,4350
0,4347
1,39
0,4343
0,4340
0,4336
0,4333
0,5330
0,4326
0,4323
0,4319
0,4316
0,4312
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µ
0
1
2
3
4
5
6
7
8
9
1,40
0,4309
0,4305
0,4301
0,4296
0,4292
0,4288
0,4284
0,4280
0,4275
0,4271
1,41
0,4267
0,4263
0,4258
0,4254
0,4250
0,4246
0,4242
0,4237
0,4233
0,4229
1,42
0,4225
0,4221
0,4216
0,4212
0,4208
0,4204
0,4200
0,4195
0,4191
0,4187
1,43
0,4183
0,4178
0,4174
0,4170
0,4166
0,4162
0,4157
0,4153
0,4149
0,4145
1,44
0,4141
0,4136
0,5132
0,4128
0,4124
0,4120
0,4115
0,4111
0,4107
0,4103
1,45
0,4099
0,4094
0,4090
0,4086
0,4082
0,4077
0,4073
0,4069
0,4065
0,4061
1,46
0,4056
0,4052
0,4048
0,4044
0,4040
0,4035
0,4031
0,4027
0,4023
0,4018
1,47
0,4014
0,4010
0,4005
0,4001
0,3997
0,3993
0,3989
0,3985
0,3980
0,3976
1,48
0,3972
0,3968
0,3964
0,3959
0,3955
0,3951
0,3947
0,3943
0,3938
0,3934
1,49
0,3930
0,3926
0,3921
0,3917
0,3913
0,3909
0,3905
0,3900
0,3896
0,3892
1,50
0,3888
0,3883
0,3878
0,3874
0,3869
0,3864
0,3859
0,3854
0,3850
0,3845
1,51
0,3840
0,3835
0,3830
0,3825
0,3820
0,3816
0,3811
0,3806
0,3801
0,3796
1,52
0,3791
0,3786
0,3781
0,3776
0,3771
0,3766
0,3760
0,3755
0,3750
0,3745
1,53
0,3740
0,3735
0,3730
0,3724
0,3719
0,3714
0,3709
0,3704
0,3698
0,3693
1,54
0,3688
0,3683
0,3677
0,3672
0,3667
0,3662
0,3656
0,3651
0,3646
0,3640
1,55
0,3635
0,3630
0,3624
0,3619
0,3613
0,3608
0,3602
0,3597
0,3591
0,3586
1,56
0,3580
0,3574
0,3569
0,3563
0,3557
0,3552
0,3546
0,3540
0,3534
0,3528
1,57
0,3523
0,3517
0,3511
0,3506
0,3500
0,3494
0,3488
0,3482
0,3477
0,3471
1,58
0,3465
0,3459
0,3453
0,3447
0,3441
0,3435
0,3429
0,3423
0,3417
0,3411
1,59
0,3405
0,3399
0,3393
0,3386
0,3380
0,3374
0,3368
0,3362
0,3355
0,3349
g)
The dPT/dc value is multiplied by dc, the distance from the electrode to the current probe, to obtain
the distance dPT. This distance represents the distance away from the electrode that the potential
probe shall be placed so that the earth tester reads the actual resistance of the earth electrode.
h)
The potential probe is moved a distance dPT from the electrode and the resistance value is
recorded.
i)
Verification of the measured result may be carried out using the following procedure:
1)
additional sets of test results may be obtained with different values of ‘dc’ or even different
directions of ‘C’ from ‘E’;
2)
from the results obtained at various values of ‘dc’, a graph may be plotted which shows how
the resistance decreases asymptotically as the distance chosen for ‘dc’ is increased. A
sample curve is illustrated in figure 6;
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Measured
Resistance
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Test 1
Test 2
Test 3
Test 4
Distance dc for each test
Figure 6: Possible results from several slope method tests
4.5
3)
this curve shows that distances chosen for ‘dc’ in Test 1 and Test 2 were insufficient
because the value is falling, and that those chosen for Test 3 and Test 4 yielded the more
correct value of earth resistance;
4)
it is unreasonable to expect an accuracy of readings better than 5 % because of variation
due to the soil moisture content and its non-homogeneity. Reading accuracy of 10 % is
more realistic; and
5)
the best guarantee of a satisfactory measurement is to achieve spacing between the tested
electrode, the potential probe and the current probe, such that the mutual resistances are
sufficiently small and the plotted curve flattens out before rising again.
Earth surface potential measurement
To find an approximate value of step and touch potentials to which a person might be subjected during
current discharge through an earth electrode, the earth fault current level must be known and the earth
resistance at the particular point must be measured.
It is important to note that step and touch potentials are specific to the position at which they are measured.
4.5.1
Procedure to calculate the touch potential, Ut, at a certain position
The earth tester connections to measure the contact resistance, Rt, between hand and foot are illustrated in
figure 7.
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MINI SUBSTATION
MV COMPARTMENT
LV COMPARTMENT
EARTHING
BAR
POTENTIAL PROBE P2
1m
30m
EARTH
ELECTRODE
CURRENT PROBE C2
C2 P2 P1 C1
EARTH TESTER
Figure 7: Connections to determine touch potential contact resistance
The measurement procedure is as follows:
a)
Connect terminal C1 to the earth electrode. Connect terminal P1 to the metalwork or any
conductive part of the earthed structure being tested.
b)
Connect terminal P2 to the potential probe which is driven into the ground about 1 m away from the
metal work being tested, adjacent to the point of test on the metalwork.
c)
Connect terminal C2 to the current probe which shall be set up 30 m away.
d)
Operate the instrument and record the resistance reading.
The prospective maximum touch potential during fault conditions is given as the product of the fault current,
If, and the contact resistance, Rt:
U t (V) = R t (Ω) × I f (A)
4.5.2
Procedure to calculate the step potential, Us, at a certain position
The earth tester connections to measure the contact resistance, Rs, between two feet, 1 m apart, are
illustrated in figure 8.
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MINI SUBSTATION
MV COMPARTMENT
LV COMPARTMENT
EARTHING
BAR
POTENTIAL
PROBE P1
30m
POTENTIAL
PROBE P2
EARTH
ELECTRODE
CURRENT
PROBE C2
C2 P2 P1 C1
1m
EARTH TESTER
Figure 8: Connections to determine step potential contact resistance
The measurement procedure is as follows:
a)
Connect terminals C1 and C2 as described for determining touch potential value.
b)
Two potential probes are driven into the ground with a 1 m separation at the point where the
measurement is required. It is not necessary for the potential probes to be in line with the current
probe and earth electrode. Terminal P1 of the earth tester is connected to the probe nearest the
earth electrode. Terminal P2 is connected to the other potential probe.
c)
Operate the instrument and record the resistance reading.
The prospective maximum step potential during fault conditions is given as the product of the fault current, If,
and the contact resistance, Rs:
U s (V) = R s (Ω) × I f (A)
4.6
Earth continuity testing
The objective of the earth continuity test is to check if the continuity path throughout the whole installation is
complete and of acceptably low (< 100 mΩ) resistance. This is so that in the event of an earth fault sufficient
current will flow to operate the appropriate protection device.
a)
The earth tester can be used to conduct an earth continuity test as follows:
b)
bridge earth tester terminals C1 and P1 as well as P2 and C2 ;
c)
connect terminals C1 and C2 to the opposite ends of the resistance under test;
d)
operate the tester to obtain the resistance reading (R1);
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EARTHING
e)
disconnect the test leads from the measured object and connect them together. Operate the tester
to obtain a second resistance reading, R2. R2 is the resistance of the test leads; and
f)
the measured resistance value is calculated by deducting the test lead resistance R2 from the
value, R1:
•
5.
R = R1 − R2
Authorization
This document has been seen and accepted by:
Name and surname
Designation
MN Bailey
Corporate Manager Divisional Technology
V Singh
Power Plant Technologies Manager
B McLaren
MVLV Study Committee Chairman
6.
Revisions
Date
Rev
Compiler
March 2018
Draft 0.1
A Roopnarain
June 2010
0
T Nkambule
July 1999
1
SJ van Zyl
7.
Remarks
Content copied from old template to current
Document number changed
Overall document revised.
-Earthing of cable system equipment was included.
-Information on the interconnection of the LV
distributor neutrals of urban and other appropriate LV
overhead networks to form a low impedance return
path according to SANS 10292 was included.
-The common field procedure of testing of minor
works was incorporated.
- The unique identifier of the standard was changed
from SCSASAAL9 to DST_34-1985.
-The title of the standard was changed from ‘MV and
LV Reticulation Earthing’ to ‘MV and LV Distribution
System Earthing’
Overall document revised
Original issue
Development team
The following people were involved in the development of this document:
T Nkambule
IARC
B McLaren
IARC
D Delly
Central Region
H Geldenhuys
IARC
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J Maudu
IARC
R Kelly
IARC
R Sander
North West Region
R Theron
IARC
8.
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Acknowledgements
Not applicable.
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Annex A – Impact Assessment
1)
Guidelines
•
All comments must be completed.
•
Motivate why items are not applicable (n/a).
•
Indicate actions to be taken, persons or organizations responsible for actions and deadline for
action.
•
Change control committees to discuss the impact assessment and, if necessary, give feedback to
the compiler regarding any omissions or errors.
2)
Critical Points
2.1
Importance of this document, e.g. is implementation required due to safety deficiencies,
statutory requirements, technology changes, document revisions, improved service quality,
improved service performance, optimized costs.
Comment: Document renumbered and reformatted.
2.2
If the document to be released impacts on statutory or legal compliance, this needs to be
very clearly stated and so highlighted.
Comment: n/a
2.3
Impact on stock holding and depletion of existing stock prior to switch over.
Comment:
2.4
When will new stock be available?
Comment: n/a
2.5
Has the interchangeability of the product or item been verified, i.e. when it fails, is a straight
swap possible with a competitor’s product?
Comment: n/a
Identify and provide details of other critical (items required for the successful implementation of this
document) points to be considered in the implementation of this document.
Comment: n/a
2.6
Provide details of any comments made by the Regions regarding the implementation of this
document.
Comment: (n/a during commenting phase).
3)
Implementation Time Frame
3.1
Time period for implementation of requirements.
Comment: n/a
3.2
Deadline for changeover to new item and personnel to be informed of DX wide changeover.
Comment: n/a
4)
Buyer’s Guide and Power Office
4.1
Does the Buyer’s Guide or Buyer’s List need updating?
Comment: n/a
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4.2
What Buyer’s Guides or items have been created?
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Comment: n/a
4.3
List all assembly drawing changes that have been revised in conjunction with this
document.
Comment: n/a
If the implementation of this document requires assessment by CAP, provide details under paragraph 5).
4.4
Which Power Office packages have been created, modified or removed?
Comment: n/a
5)
CAP/LAP Pre-qualification Process-related Impacts
5.1
Is an ad hoc re-evaluation of all currently accepted suppliers required as a result of
implementation of this document?
Comment: n/a
5.2
If NO, provide motivation for issuing this specification before Acceptance Cycle Expiry date.
Comment: n/a
5.3
Are ALL suppliers (currently accepted per LAP) aware of the nature of changes contained in
this document?
Comment: n/a
5.4
Is implementation of the provisions of this document required during the current supplier
qualification period?
Comment: n/a
5.5
fully?
If Yes to paragraph 0, what date has been set for all currently accepted suppliers to comply
Comment: n/a
5.6
If Yes to paragraph 0, have all currently accepted suppliers been sent a prior formal
notification informing them of Eskom’s expectations, including the implementation date deadline?
Comment: n/a
5.7
Can the changes
material/equipment?
made,
potentially
impact
upon
the
purchase
price
of
the
Comment: n/a
5.8
Material group(s) affected by specification (refer to Pre-qualification invitation schedule for
list of material groups).
Comment: n/a
6)
Training or Communication
6.1
Is training required?
Comment: (If NO, then paragraphs 0 to 0 will be n/a.)
6.2
State the level of training required to implement this document (e.g. awareness training,
practical/on job, module).
Comment: n/a
6.3
State designations of personnel that will require training.
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6.4
Is the training material available? Identify person responsible for the development of
training material.
Comment: n/a
6.5
If applicable, provide details of training that will take place (e.g. sponsor, costs, trainer,
schedule of training, course material availability, training in erection/use of new equipment,
maintenance training).
Comment: n/a
6.6
Was Technical Training Section consulted regarding module development process?
Comment: n/a
6.7
State communications channels to be used to inform target audience.
Comment: n/a
7)
Special Tools, Equipment, Software
7.1
What special tools, equipment, software, etc. will need to be purchased by the Region to
effectively implement?
Comment: n/a
7.2
Are stock numbers available for the new equipment?
Comment: n/a
7.3
What will be the cost of these special tools, equipment, software?
Comment: n/a
8)
Finances
8.1
What total costs would the Regions be required to incur in implementing this document?
Identify all cost activities associated with implementation, e.g. labour, training, tooling, stock,
obsolescence.
Comment: n/a
Impact assessment completed by:
Name: V Singh
Designation: Power Plant Technologies Manager
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Annex B – Landing Test Report Sheet
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PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
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Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
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56 of 63
ESKOM COPYRIGHT PROTECTED
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to ensure it is in line with the authorized version on the WEB.
Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
Page:
57 of 63
ESKOM COPYRIGHT PROTECTED
When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
to ensure it is in line with the authorized version on the WEB.
Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
Page:
58 of 63
ESKOM COPYRIGHT PROTECTED
When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
to ensure it is in line with the authorized version on the WEB.
Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
Page:
59 of 63
ESKOM COPYRIGHT PROTECTED
When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
to ensure it is in line with the authorized version on the WEB.
Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
Page:
60 of 63
ESKOM COPYRIGHT PROTECTED
When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
to ensure it is in line with the authorized version on the WEB.
Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
Page:
61 of 63
ESKOM COPYRIGHT PROTECTED
When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
to ensure it is in line with the authorized version on the WEB.
Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
Page:
62 of 63
ESKOM COPYRIGHT PROTECTED
When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
to ensure it is in line with the authorized version on the WEB.
Document Classification: Controlled Disclosure
DISTRIBUTION TYPE – PART 2:
DISTRIBUTION STANDARD:
PART 2: EARTHING.
SECTION 1: MV AND LV DISTRIBUTION SYSTEM
EARTHING
Unique Identifier: 240-130615754
Revision:
1
Page:
63 of 63
ESKOM COPYRIGHT PROTECTED
When downloaded from the WEB, this document is uncontrolled and the responsibility rests with the user
to ensure it is in line with the authorized version on the WEB.