Standard
Standard
Standard
Content
Page
Foreword ....................................................................................................................................... 2
Introduction .................................................................................................................................... 3
Keywords ....................................................................................................................................... 3
1 Scope ......................................................................................................................................... 3
2 Normative references .................................................................................................................. 4
3 Definitions and abbreviations....................................................................................................... 5
4 Requirements.............................................................................................................................. 5
4.1 Statutory Requirements ........................................................................................................ 5
4.2 Environmental considerations ............................................................................................... 6
4.3 Performance and operability requirements ............................................................................ 6
4.4 Insulation co-ordination and bonding ................................................................................... 89
4.5 Structures ........................................................................................................................... 14
4.6 Conductors ......................................................................................................................... 20
4.7 Clearances ......................................................................................................................... 21
4.8 Crossings ........................................................................................................................... 23
4.9 Marking and labelling ...................................................................................................... 2930
4.10 Visual inspection testing and hand over requirements ....................................................... 30
4.11 Particular requirements for 33 kV overhead reticulation. .................................................... 32
Annex A Impact assessment ....................................................................................................... 36
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Distribution Standard Reference: 34-1191
Part 4: Medium voltage reticulation Type: DSP
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Foreword
The Distribution Standard is a multi-part document whose total structure is defined in Part 0. This part
of the Distribution Standard consists of the following sections under the general title Medium Voltage
Reticulation:
34-1191, Section 0: General - General information and requirements for overhead lines up to 33kV
34-1192, Section 1: Light conductors - Particular requirements for overhead lines up to 33 kV with
conductors up to Hare conductor
34-1193, Section 2: Heavy conductors - Particular requirements for overhead lines up to 33 kV with
conductors larger than Hare and up to Kingbird conductor
34-225, Section 3: Auxiliary equipment - Particular requirements for auxiliary equipment and structures
up to 33 kV
34-453, Section 4: SWER - Particular requirements for 19kV Single Wire Earth Return (SWER)
overhead reticulation
34-1198 & 34-1197, Section 5: Rural reticulation protection
The notices in Part 0 of the Distribution Standard are also applicable to this part.
Any recommendations for corrections, additions or deletions to this standard should be sent to:
The Power Plant Technologies Development Manager
Industry Association Resource Management
Private Bag X1074
GERMISTON
1400
Telephone (011) 871-2416
Fax (011) 871-2352
Email: vinod.singh@eskom.co.za
Revision history
This edition cancels and replaces edition no. 0 of specification no. SCSASABE7.
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Authorisation
Name Designation
MN Bailey Corporate Manager Divisional Technology
V Singh Power Plant Technology Development
B McLaren Senior Engineer
This specification shall apply throughout Eskom Holdings Limited, its divisions, subsidiaries and
entities wherein Eskom has a controlling interest.
Development team
B Hill, R Theron, B McLaren
Introduction
This section of Part 4 of the Distribution Standard has been prepared to establish and promote uniform
designs for medium voltage (MV) overhead distribution systems.
This section of the Distribution Standard has been prepared to establish and promote uniform designs
for MV overhead distribution systems. The requirements in this section (0) are often related to
separate standards and procedures. In these cases the most pertinent extracts and tables have been
included in the relevant Part.
Keywords
Wayleaves, Environmental impact , Insulation coordination, Overhead line structures, Wood poles,
Stays and anchors, Insulators, Conductors, Clearances, Crossings, Telkom, Inspections, Marking and
labelling.
1 Scope
This part of the Distribution Standard covers the construction of bare wire MV overhead reticulation
systems using wood-poles. These systems are normally fed from HV/MV substations and may be
used to supply individual customers at MV or individual customers at LV through a step-down
substation and LV network.
The objective of the standard is to ensure that all Eskom MV reticulation systems are built utilizing the
specified standard structures and materials. The standardized materials are fully specified in
SCSPVAAT6 - Distribution Standard Part 9 (Buyers guide)
This Section (0) sets out the design rationale, standard practices and requirements for all MV
overhead reticulation lines up to 33 kV using Hare / Oak and smaller conductors.
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2 Normative references
Parties using this document shall apply the most recent edition of the documents listed below:
ANSI/IEEE C57.15: 1986, Standard requirements terminology and test-code for step-voltage and
induction-voltage regulators.
SANS 60815: 1986, Guide for the selection of insulators in respect of polluted conditions.
NRS 027:1994, Distribution transformers — Completely self-protecting type for rated a.c.voltages up
to and including 33 kV.
NRS 033:1996, Guidelines for the application, design, planning and construction of medium voltage
wood-pole overhead lines above 1 kV and up to and including 22 kV.
NRS 043:1997, Code of Practice for the joint use of a pole route for power and telecommunication
lines.
DSP_34-1647: Rev.0, Specification for creosote treated wood-poles, cross-arms and spacer blocks.
Dsp0035: Rev.3, Current carrying compression fittings for overhead reticulation systems.
DISSCAAO1: Rev.2, Specification for conventional stay planting, percussion stay and rock anchor
installation testing.
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4 Requirements
4.1 Statutory Requirements
The requirements of the Occupational Health and Safety Act, Act 85 of 1993, (OHS Act) and all
subsequent amendments and regulations shall be observed and adhered to except where exemption
has been obtained from the Chief Factories Inspector.
If any text or drawings in the standard are in conflict with the OHS Act and no exemption has been
obtained, the OHS Act requirements shall take precedence over the standard.
a) National roads,
b) Provincial roads,
d) Civil aviation,
e) TLCs, and
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As a general guide staggered vertical (perching), intermediate T (perching) and H pole suspension
(perching and mid span collision) structures are considered most bird friendly. Typical examples of
pole top configurations are given in drawing D-DT-0311. The EIA shall take these possible structure
configurations into account when making a recommendation although the best solution shall always be
a line route that avoids sensitive areas.
The application of this covered jumper shall in no way reduce the safety clearances that shall be
observed. For safety considerations these conductors shall be treated as if they were bare.
b) The above devices are costly and it shall be the responsibility of the line designer to ensure that
this requirement is considered to ensure that the most appropriate, cost effective solutions are
implemented.
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capacity are generally the most important considerations. The following factors shall also be
considered when placing additional auto-reclosers and auto-sectionalisers:
a) lines performing poorly due to lightning. The installation of an additional sectionalising point may be
justified to improve the line performance and reduce nuisance outages to upstream customers;
b) a local knowledge of forests, sugar cane fields, irrigation systems, hills, thick vegetation and areas
prone to high winds, pollution etc. may provide sufficient justification for the application of a further
sectionalising point; and
c) additional switching points shall be provided in the MV line to facilitate the operation of the MV
system. The positions of the switching points shall be determined after considering the number of
customers affected, demand, and accessibility. These switching points may either be solid or fuse
links in accordance with local area philosophies.
The main considerations for system configuration shall be based on the following:
a) the use of auto-reclosers at the supply substation to protect MV lines and isolate the MV line from
the system in the case of a permanent fault;
b) the use of fuses to isolate T-offs downline from the main feeder protection and in-line auto-
reclosers / auto-sectionalisers;
c) the installation of individual 20A MV type ‘K’ fuses for transformers connected to the main MV line;
d) the group-fusing of transformers connected to T-offs with not more than 500 kVA of installed
transformer capacity for each fuse, depending on physical limitations;
e) the installation of downline auto-reclosers if the line load exceeds 5MVA or the line length exceeds
80 km; and
f) the installation of sectionalizers if the line load exceeds 3MVA or the line length exceeds 40 km.
1 2 3 4 5
Minimum 11 kV 22 kV
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The following aspects are relevant with regard to the minimum ratings in Table 4.4.1:
a) A derating factor of approximately 1,2 is recommended for group fuses to account for excitation
current composition.
b) The smaller the fuse link rating, the more efficient the fuse in terms of earth fault detection and the
easier the fuse-protection co-ordination; at the same time the fuse will be more prone to transient
current deterioration effects. Transient insensitivity for fuses is attained with a characteristic
resembling that of a 25 K fuse. In order to minimise nuisance operations, 20 K and 30 K fuses are
recommended. K-type fuses (and the inclusion of the 10 K) are recommended to allow for the
appropriate fuse/fuse co-ordination applications discussed in the next section.
c) Where fuse/fuse co-ordination is applicable, the maximum clearing time of the downstream fuse
closest to the fault shall be less than about 75 % of the minimum melting time of the upstream
fuse. This requirement inherently sets an upper fault current limit for successful fuse/fuse co-
2
ordination, this margin being a function of the I t energy capabilities of the fuses in question. The
fuse co-ordination selections in Table 4.3.4-2 are recommended, considering the spread of fault
currents for earth and phase faults as well as the ratings of devices protected:
1 2 3
30 K 20 K ± 500 A
30 K 10 K ± 1050 A
20 K 10 K ± 550 A
a) High fault current conditions may result in both fuse elements experiencing damage and thereby
resulting in a loss of fuse/fuse co-ordination. This is also true for protection / fuse co-ordination in
this time region (<70 ms to 100 ms), with the provision that the recloser will normally initiate a
successful reclose under such conditions.
b) The higher the upstream (i.e. “section-fuse”) fuse rating, the higher the probability of
protection/section-fuse loss of co-ordination at low fault levels. While the use of section-fuses
enables lower system capital expenditure, extensive systems with rapid phase fault current drop-
off (and non-effectively earthed systems) may incur larger operating costs and customer disruption
due to nuisance tripping.
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Unless otherwise stated, insulation co-ordination and bonding shall be performed in accordance with
Table 5.1 below. It is advisable however for the owner of the network to specifically state his
requirements so that they match the philosophy employed on the rest of the network.
1 2 3
2
Lightning activity (strikes/km /year)
Pollution level Low (2 or less) High ( more than 2)
• No bonding of insulator • Provide a 500 mm gap between the BIL downwire
Low/medium
required and lowest/nearest MV insulator
(Few / no
• No BIL downwire required • No bonding between insulators is required unless
pollution related
vertical or staggered vertical bonding is required
incidents) • Use a 1,2 MV BIL
• Use a 300 kV BIL
• Bond between insulators • Provide a 500 mm gap between the BIL down wire
High/very high
and the lowest/nearest MV insulator
• No BIL downwire required
(Frequent
• Bond between insulators
pollution related • Use a 1,2 MV BIL
incidents) • Use a 300 kV BIL
NOTE 1 — Refer to annex B for details of lightning strike activities in South Africa
4.4.1 General
Insulation co-ordination is achieved when the insulation strengths of all components of the electricity
system are adequate to withstand the electrical stresses of service within selected reliability margins.
The three conditions that system components are designed to meet are.
a) To withstand indefinitely the normal and maximum system operating voltages at supply frequency.
b) To withstand temporary supply frequency overvoltages up to the rated short duration power
frequency withstand voltage.
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4.4.6 Bonding
The practice of electrically connecting all the hardware and insulator ‘dead’ ends is known as bonding.
In polluted environments small leakage currents may cause the burning of unbonded cross-arms and
poles. Bonding the ‘dead’ ends of phase insulators and stay wires can prevent this. In the case of the
longer cross-arms being used the bonding wire will also act as a BIL wire and prevent cross-arm
splitting. Separate bonding designs are provided for all applicable structures. See D-DT-0310.
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The insulation which provides the best overall performance in a high lightning area has been proved
on test sites to be between 200 kV BIL and 300 kV BIL. This allows direct strikes to flashover while
containing induced surges. This BIL is achieved in the following way:
b) On stayed structures this is due to the BIL of the long rod insulator, stay insulators and the position
of the stays. On these structures the stay is acts as the BIL downwire.
If there are a number of surge arresters in close proximity on the line it effectively reduces the BIL of
that line and the design of insulation for a reticulation line thus falls into two categories.
a) Townships or areas protected from lightning affects by a relatively high density of surge arresters
In these areas,structures, of which the maximum BIL is that of the insulator (170 kV), may be used
i.e. Concrete or conductive structures. Wood poles need not have a BIL wire.
b) Sparsely populated, high lightning rural areas with long lines and few surge arresters
In these areas co-ordinated wood pole structures with 300 kV BIL will perform better in high
lightning conditions. The application of down wires will reduce the BIL from 1,2 kV to the desired
levels. The incidence of pole damage will be greatly reduced if the practice is employed.
Table 4.4.9-1 Insulation co-ordination and bonding guide
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1 2 3
2
Lightning activity (strikes/km /year)
Pollution level Low (2 or less) High ( more than 2)
• No bonding of insulator • Provide a 500 mm gap between the BIL downwire
Low/medium
required and lowest/nearest MV insulator
(Few / no
• No BIL downwire required • No bonding between insulators is required unless
pollution related
vertical or staggered vertical bonding is required
incidents) • Use a 1,2 MV BIL
• Use a 300 kV BIL
• Bond between insulators • Provide a 500 mm gap between the BIL down wire
High/very high
and the lowest/nearest MV insulator
• No BIL downwire required
(Frequent
• Bond between insulators
pollution related • Use a 1,2 MV BIL
incidents) • Use a 300 kV BIL
NOTES
1. Refer to table B2 below for details of lightning strike activities in South Africa
2. The isochronic graphs are somewhat generalized and it is possible to find a relatively high
lightning incidence pocket within a low rated area. The insulation co-ordination and bonding of a line
shall take cognizance of performance requirements. In a contract situation the ultimate owner of the
network shall decide what insulation co-ordination and bonding practice should be employed.
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The values supplied in the table below are representative of the number of lightning ground
flashes per km2 per year. (With acknowledgement to the C.S.I.R.).
Aberdeen 1.8 East London 1.6 Ladybrand 7.5 Richards Bay 5.2
Beaufort West 1.7 Flagstaff 4.9 Lydenburg 5.0 Schweizer Reneke 5.6
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De Aar 2.5 King William’s Town 1.1 Port Elizabeth 0.9 Walvis Bay 0.2
4.5 Structures
4.5.1 Structures selection
Accepted distribution phase/phase voltage levels in this standard are 11 kV, 22 kV and 33 kV. 11 kV
overhead lines are built to 22 kV specifications. The additional BIL achieved by the use of 22 kV
insulation greatly improves the general performance of 11 kV lines in lightning at a marginal extra cost.
33 kV has been introduced with the dual purpose of better load transfer with relatively small
conductors and the derivative, 19 kV serves as the standard single wire earth return (SWER) voltage.
33 kV lines are built using 33 kV insulation and 22 kV structures that have sufficient clearances to
accommodate the higher clearance requirements.
A structure selection guide is included as annex to sections 2 and 3 of Part 4 of the Distribution
Standard to assist the user to select the most appropriate family of structures based on the type of
conductor and the terrain. Four categories of terrain are used for each conductor type. Structure
strength tables are also set out as an annex to these sections to give the user a guide of what
parameters may be used in the design of the line.
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used and three-phase structures of which only two phases are conductored must be used. In this
case the three-phase structure designs and strength tables shall be used with either the centre or
bottom phases not being conductored. The initial construction shall ensure that the upgrade exercise
will not require the removal or moving of any existing stays, equipment or conductor ties.
Some structure configurations are not practically compatible (i.e. vertical intermediate and 4,5m x-arm
H-pole suspension) and should only be used adjacent to each other with due consideration of the
effect on the conductors. It is good practice to utilise strain structures when changing between very
different pole top configurations.
4.5.4 Poles
Wood poles shall be used as the standard pole for overhead lines. Concrete poles may be used for
special applications.
a) Concrete poles are conductive to lightning surges and shall not be used in exposed rural areas with
high lightning incidence. They are also more expensive than wood poles.
b) Concrete poles shall be manufactured in accordance with DTC 0106 and designed in accordance
with drawings D-DT-0001 to D-DT-0007 which can be found in SCSPVAAT6;
c) Wood-poles shall have a fibre strength of at least 55 MPa and shall be in accordance with
DSP_34-1647, Rev 0.
d) 75 MPa poles may be used on condition the mechanical loading of the poles is calculated and
approved by a suitably qualified engineer.
e) CCA treated wood-poles shall not be used for rural lines. CCA treated wood-poles shall only be
used in urban applications; and
NOTES
1. Concrete and wood-poles of the same height are not interchangeable without considering the stresses and stiffness
of both for compression loads.
2. If poles are taken into an area where the mean annual equilibrium moisture content of timber is less than 100
grams/kg, the poles shall be stored for at least 6 months after arrival. Where the mean annual equilibrium
moisture content of timber is less than 80 grams/kg, the poles shall be stored for one year prior to use. In
situations where the above recommendations are impractical, the line configuration shall be designed to
ensure that problems caused by pole twisting are minimized.
When selecting pole sizes for a level terrain the above may be applied but undulating terrain may
require the wind, weight electrical spans to be longer than the level ground spans. In all cases the
smallest pole that meets all the required parameters shall be selected.
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a) Maximum span length is the lesser of the actual ground clearance span, electrical span, wind span
and weight span. This is restricted by the strength of the poles and cross arms used and depends
on the combinations and configuration of MV, LV and Telkom conductors used. The maximum
span lengths for single circuit lines under certain limiting conditions are set out in the structure
strength tables. The strengths for multi-circuit structures shall be calculated individually.
b) When changing between different configurations, the phasing shall be in accordance with
D-DT-0311 and the maximum spacing span permitted shall be the same as that of the lower of the
two adjacent structures;
c) Windspan values are based on pole strength and the soil foundations will be adequate in type 1
soils. If this is not the case and poor soil is suspected, individual calculation shall be done using the
bearing pressures received from actual tests. This is particularly important when construcing heavy
conductor 3-phase lines.
4.5.7 Phasing
Phasing on all pole top configurations shall be in accordance with drawing D-DT-0311 — “Phase
configurations for standard pole top designs”
NOTE — The phase configuration is as viewed from the normal source substation i.e. looking from the
source substation towards the structure in question.
The standard MV stay assembly is 96kN. This assembly is adequate for all stayed structures. The
number of stays used for each structure may vary to suit the structure type, conductor size and line
deviation angle. When 600 deviation is exceeded on an H-pole structure, bisector stays must be fitted
to both uprights.
Power installed stays may be used in suitable soils if the strength criterion is met.
The most cost effective stay assembly shall be used. This may be conventional, rock or percussion.
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1 2 3 4 5
m mm m mm mm
12 160/200 2000
13 160/200 2200
14 180 2200
16 180 2200
18 180 2400
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4.5.10.2 General
a) The wind pressure is 700 Pa.
j) The minimum span length is 50 m. If span lengths are calculated to be less than 50 m, then the
structure is exceeding the design limit.
4.5.10.3 Conductors
a) The projected conductor area is equal to 60 % of the conductor diameter * L.
4.5.10.4 Insulators
a) The post insulator length is 300 mm.
b) The rod penetration depth for post insulators is 50 mm for a threaded rod and 35 mm for a swivel
spindle.
d) The distance from the pole to the base of the insulator is 70 mm when a swivel spindle is used.
e) The distance between the base of the L-bracket and the pole top is 50 mm.
h) For the vertical strain structure (0° to 5°), the insulator has an angle of 10° to the horizontal plane.
4.5.10.5 Structures
a) A wooden pole has a taper of 5 mm/m.
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e) The cross-arm diameters are 120mm (2,5m), 140mm (3,5m), 160mm (4,5m).
q)h)The projected area that the wind pressure is acting on is 60 % of the pole diameter multiplied by Formatted: Bullets and Numbering
the pole length.
r)i) The average diameter of the pole is equal to the diameter of the pole at a height of 2/3 of the
crippling length, measured from ground level.
s)j) The maximum design load that a swivel spindle can take is 40 kg (392 N).
t)k) The maximum design moment capacity of the threaded rod is 150 Nm.
u)l) For H-poles, the total transverse force is divided equally between the transverse reaction forces.
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4.6 Conductors
4.6.1 Conductor selection
Bare conductors shall be used for MV overhead reticulation. The structures have been designed for
conductors up to Hare (Oak). Conductors shall be predominantly ACSR types, Squirrel, Fox, Mink and
Hare. AAAC conductor types, Acacia, 35, Pine and Oak conductors shall only be used in high marine
pollution areas. Magpie and single strand 1350 MPa steel wire may be used for very low load spurs as
a cost-effective alternative. Magpie dead-end fittings are the same size as those for Squirrel but are
not interchangeable. Steel conductors require armour rods to allow fixing onto a post insulator. The
conductor choice shall be based on the least life-cycle cost of transferring power. Information on the
recommended conductors is given in Table 4.6.1-1.
Cigre studies are proving that the most effective way to determine tensions in undamped conductors is
by considering the tension divided by mass per unit length constant or ‘C’ value. In accordance with
this study, RSAT utilises a ‘C’ value of 1425 for ACSR and AAAC conductors. Lines constructed using
the information in these tables will not require dampers. Extra strength ACSR ‘C’ value is set at 2712
and steel wire at 2242. These ‘C’ values have been chosen to reduce the risk of conductor fatigue
without using dampers. If lines are designed for special applications exceeding these ‘C’ values,
damping shall be considered. Over and above the ‘C’ values RSAT design tensions are limited to the
OHS Act design limits of 40 % of UTS on final tension and 50 % of UTS for initial tension (stringing).
Only persons who have passed Eskom approved compression jointing training and have proof of this
are permitted to perform this work on the Eskom network.
No joints shall be placed in crossing spans.
Joints shall, as far as possible, be made in the middle third of a span. No joint shall be placed within
20m of a structure.
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4.7 Clearances
4.7.1 Clearances on a structure
4.7.1.1 Shared structures
The minimum clearances for shared services on a structure are:
NOTE – The clearance requirement dimensions refer to all structures in townships (See D-DT-0348).
For further details refer to NRS043.
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This is a minimum requirement and may well be supplemented in future by a Telkom training
department manual.
1 2 3 4 5 6
Clearance
( kV r.m.s.) m m m m m
NOTES
1 Clearances above water (dams, rivers etc.) will, as a general rule, be as given in column 2. However, if the water is used
for recreational or commercial purposes, the users may require a greater clearance.
2 In terms of an exemption obtained from the chief inspector, auxiliary equipment such as transformers, reclosers and
sectionalisers may be mounted 4,0 m above ground. While the clearance value applies to the bushings of the equipment, for
ease of application and consistency this measurement will in all cases apply to the base of the equipment.
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a) not less than 0,2 m between insulated LV power cables and telecommunication cables;
b) not less than 1,5 m between bare MV power conductors and telecommunication cables at the worst
conditions of sag; and
Note:
Clearances shall be determined for a minimum power conductor temperature of 50 °C and a swing angle co rresponding to a
wind pressure of 700 Pa. In applications where the power conductor may operate at a temperature above 50°C, that
temperature shall be used to calculate the sag and clearances of the power conductor. In the case of telecommunication lines a
maximum temperature of 30°C shall be used for the T elkom sag calculation.
4.8 Crossings
Crossings shall comply with section 20 of the Electrical Machinery Regulations of the OHS Act
(see SCSASAAM0) and the requirements set out in annex B.
NOTE – This annex has been extracted from a pre-publication copy of NRS 033
4.8.1 Scope
This annex covers overhead power line crossings of proclaimed roads, railway lines, tramways and
important communication lines, and shall be read in conjunction with the undermentioned regulations.
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Figure 4.8.22-2 — Helically formed arcing horn for horizontally mounted long rod insulator
Figure 4.8.22-3 — Helically formed arcing horn for horizontally mounted disc insulator
Ties
10 kN Insulator
Figure 4.8.22-1 — Helically formed, armoured, road crossing twin tie for vertically mounted pin
or post insulator
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Figure 4.8.22-2 Helically Formed arcing horn for horizontally mounted long rod insulator
Figure 4.8.22-3 Helically Formed arcing horn for horizontally mounted disc insulator
4.8.2.3 Purpose
The sketches listed above depict the most common crossing configurations. Should other
configurations be used, it shall be borne in mind that the main purpose of applying the above-
mentioned precautions at crossings is to ensure that flashovers to overhead line conductors and
hardware, adjacent to the crossing, will not jeopardise the integrity of the crossing span. The crossing
span conductors shall not be lower than 4,5 m above ground in case of a broken phase conductor in a
span other than the crossing span as stipulated in the Occupational Health and Safety Act.
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Cognisance of these precautionary requirements, and the Regulations detailed in E.2.1 above, shall
be taken into account when designing every crossing.
4.8.4 Structures
4.8.4.1 Where there are strain structures on either side of the crossing, intermediate structures without
any special precautions can be erected beyond the crossing (see D.5.4).
4.8.4.2 Where there is one strain structure at the crossing, special precautions shall be taken on the
first three intermediate structures on the opposite side of the crossing (see D.5.5).
4.8.4.3 Where there are no strain structures at the crossing, special precautions shall be taken on the
first three intermediate structures on both sides of the crossing. (see D.5.6).
Telkom Road
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C C B B C C
Stays if required
Telkom Road
C A A A C C
B
Figure D.5 — Crossing with an intermediate structure on one side and a strain structure
on the other side
Telkom Road
A C
C A A A A A
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4.8.4.5 Requirements for intermediate structures (C) in figures D.4, D.5 and D.6
a) Alternative 1: With rigid post or pin insulators.
Or
4.8.4.6 Requirements for intermediate structures (A) in figures D.5 and D.6
a) Alternative 1: With rigid post or pin insulators.
2) Use special helically formed road crossing twin tie in accordance with figure D.1. or,
Note:
if suspension insulators are used, the following “broken conductor” formula shall be used to calculate
the clearance:
D = (d 2 + 3 pl/ 8 )
where
It is a requirement of the OHS Act that all controlling apparatus shall be permanently marked or
labelled so as to identify the system or part of the system on the electrical machinery which it controls,
and, where such control apparatus is accessible from the front and back, these markings shall be on
both the front and the back.
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YES NO N/A
E.2 MV Lines
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E3 Pole-mounted equipment(continued)
E.3.2 Isolators/A.B.switch YES NO N/A
1 Are the insulators sound ?
2 Is the equipment aligned correctly (open and close) ?
3 Is the arcing horn alignment correct?
4 Is the equipment mounted to the manufacturer’s specification?
5 Are the locking mechanisms (if fitted) operable?
6 Is the footplate for hand-operated gang-isolators installed and
correctly earthed?
7 Does the earthing conform to requirements?
The requirements of this section are particular to 33 kV overhead lines and are integral to those
stated in DSP_34-1191. A working knowledge of the requirements in DSP_34-1191 is required
in order to apply this section.
It will be noted that 33 kV lines are similar in many ways to 22 kV lines and that most of the structures
used for 22 kV lines are also used for 33 kV lines. The insulators, and in some cases the pole
insulation co-ordination, being the only major difference between the two line voltages.
Single-wire earth return (SWER) as described in DSP_34-453 (Section 4 of Part 4) can be connected
directly to 33 kV lines which are sourced from a substation with a solidly earthed neutral. The user is
referred to DSP_34-453 for further information.
4.11.2 Scope
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This sub section sets out the standard practices and particular requirements for all 33 kV reticulation
lines utilizing Hare/Oak and smaller conductors.
The standard does not contain the actual structure drawings unless they are only particular to 33 kV
lines. The general arrangement drawings refer to detailed assembly drawings which in turn refer the
material or Buyers’ Guide drawings.
4.11.3.3 Insulators
The insulators for 33 kV lines differ from those used on 22 kV lines in respect of the creepage distance
and the impulse voltage withstand. A 25 mm/kV 22 kV insulator will have a creepage of 16,6 mm/kV
when used at 33 kV hence it is essential that 33 kV lines are constructed using approved 33 kV
insulators.
Strain structures, without a post insulator supporting a jumper, will have a minimum BIL of 250 kV and
those with a post insulator will have a minimum BIL of 200 kV. This is considered to be sufficient BIL
for most high lightning areas. Refer to annex A of DSP_34-1191 for further information.
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The reader is referred to the SAIEE publication “Insulation co-ordination for overhead distribution lines
from 1 kV to 36 kV” by C T Gaunt, A C Britten, H J Geldenhuys.
4.11.4.2 Phase-to-phase
The minimum phase-to-phase clearance used for 33 kV lines is 500 mm. The structures are designed
for this clearance. This phase-to-phase clearance is also used in calculations to establish the
maximum electrical span for a particular structure.
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Conductor Type
3.66Steel Squirrel/Fox Mink Hare
Undulating retic lines
Formal townships
Formal townships
Rural townships
Rural townships
Rural townships
Rural townships
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Annex A
(informative)
Impact assessment
Impact assessment form to be completed for all documents.
1 Guidelines
o All comments must be completed.
o Motivate why items are N/A (not applicable)
o Indicate actions to be taken, persons or organisations responsible for actions and deadline for
action.
o Change control committees to discuss the impact assessment, and if necessary give feedback to
the compiler of 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, optimised costs.
Comment: To provide for standardised implementation of overhead line technologies.
2.2 If the document to be released impacts on statutory or legal compliance - this need to be
very clearly stated and so highlighted.
Comment: The MV standard has a significant bearing on compliance with the OHS Act.
2.3 Impact on stock holding and depletion of existing stock prior to switch over.
Comment: No impact.
2.4 When will new stock be available?
Comment: Not applicable.
2.5 Has the interchangeability of the product or item been verified - i.e. when it fails is a
straight swop possible with a competitor's product?
Comment: Not applicable.
2.6 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:To implemented in a phased release together with associated documents contemplated in
part 4.
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Annex A
(continued)
2.7 Provide details of any comments made by the Regions regarding the implementation of
this document.
Comment: (N/A during commenting phase)
3 Implementation timeframe
3.1 Time period for implementation of requirements.
Comment: Not applicable.
3.2 Deadline for changeover to new item and personnel to be informed of DX wide change-
over.
Comment: To run concurrently with negotiated standard reconfiguration.
4 Buyers Guide and Power Office
4.1 Does the Buyers Guide or Buyers List need updating?
Comment: Not applicable
4.2 What Buyer’s Guides or items have been created?
Comment: None.
4.3 List all assembly drawing changes that have been revised in conjunction with this
document.
Comment: Not applicable.
4.4 If the implementation of this document requires assessment by CAP, provide details
under 5
4.5 Which Power Office packages have been created, modified or removed?
Comment: None.
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: Not applicable.
5.2 If NO, provide motivation for issuing this specification before Acceptance Cycle Expiry
date.
Comment: Not applicable.
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Annex A
(continued)
5.3 Are ALL suppliers (currently accepted per LAP), aware of the nature of changes contained
in this document?
Comment: Not Applicable.
5.4 Is implementation of the provisions of this document required during the current supplier
qualification period?
Comment: No.
5.5 If Yes to 5.4, what date has been set for all currently accepted suppliers to comply fully?
Comment: Not applicable.
5.6 If Yes to 5.4, have all currently accepted suppliers been sent a prior formal notification
informing them of Eskom’s expectations, including the implementation date deadline?
Comment: No.
5.7 Can the changes made, potentially impact upon the purchase price of the
material/equipment?
Comment: No.
5.8 Material group(s) affected by specification: (Refer to Pre-Qualification invitation schedule
for list of material groups)
Comment: None.
6 Training or communication
6.1 State the level of training or communication required to implement this document. (E.g.
none, communiqués, awareness training, practical / on job, module, etc.)
Comment: None.
6.2 State designations of personnel that will require training.
Comment: Not Applicable.
6.3 Is the training material available? Identify person responsible for the development of
training material.
Comment: Not applicable.
6.4 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, etc).
Comment: Not applicable.
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Annex A
6.5 (continued) Was Training & Development Section consulted w.r.t training requirements?
Comment:
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: None.
7.2 Are there stock numbers available for the new equipment?
Comment: Not Applicable.
7.3 What will be the costs of these special tools, equipment, software?
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:
None………………….
……………………………………………………………………………………………………………………….
Impact assessment completed by:
Name: Bruce McLaren
Designation: IARC custodian
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