SIST EN 50341-2-20:2019

SLOVENSKI STANDARD
01-april-2019
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Overhead electrical lines exceeding AC 1 kV - Part 2-20: National Normative Aspects
(NNA) for ESTONIA (based on EN 50341-1:2012)
Ta slovenski standard je istoveten z: EN 50341-2-20:2018
ICS:
29.240.20 Daljnovodi Power transmission and
distribution lines
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 50341-2-20

NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2018
ICS 29.240.20 Supersedes EN 50341-2-20:2015
English Version
Overhead electrical lines exceeding AC 1 kV - Part 2-20:
National Normative Aspects (NNA) for ESTONIA (based on EN
50341-1:2012)
This European Standard was approved by CENELEC on 2018-11-26.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50341-2-20:2018 E
Contents
European foreword .6
0 Introduction .7
0.7 Language .7
1 Scope .7
1.1 General .7
1.2 Field of application .7
2 Normative references, definitions and symbols .8
2.1 Normative references.8
3 Basis of design . 10
3.2 Requirements of overhead lines . 10
3.2.2 Reliability requirements. 10
3.2.3 Security requirements . 11
3.2.5 Strength coordination . 11
3.2.6 Additional considerations . 11
3.3 Limit states . 11
3.3.3 Serviceability limit states . 11
3.4 Actions . 11
3.4.2 Classification of actions by their variation in time . 11
4 Actions on lines . 12
4.1 Introduction . 12
4.3 Wind loads . 12
4.3.1 Field of application and basic wind velocity . 12
4.3.2 Mean wind velocity . 12
4.3.3 Mean wind pressure . 12
4.3.5 Wind forces on any overhead line component . 12
4.4 Wind forces on overhead line components . 13
4.4.1 Wind forces on conductors . 13
4.4.2 Wind forces on insulator sets . 13
4.4.3 Wind forces on lattice towers . 14
4.4.4 Wind forces on poles . 14
4.5 Ice loads . 14
4.5.1 General . 14
4.5.2 Ice forces on conductors . 14
4.6 Combined wind and ice loads . 14
4.6.1 Combined probabilities . 14
4.6.2 Drag factors and ice densities . 15
4.7 Temperature effects . 15
4.8 Security loads . 15
4.8.4 Mechanical conditions of application . 15

Estonia 3/49 EN 50341-2-20:2018
4.9 Safety Loads . 15
4.9.1 Construction and maintenance loads . 15
4.9.2 Loads related to the weight of linesmen . 16
4.10 Forces due to short-circuit currents . 16
4.11 Other special forces . 16
4.11.1 Avalanches, creeping snow . 16
4.11.2 Earthquakes . 16
4.11.3 Floating of ice, accidents of vessels . 16
4.11.4 Mining out areas . 17
4.12 Load cases . 17
4.12.1 General . 17
4.12.2 Standard load cases . 17
4.13 Partial factors for actions . 18
5 Electrical requirements . 19
5.1 Introduction . 19
5.2 Currents . 19
5.2.1 Nominal current . 19
5.2.2 Short-circuit currents . 19
5.3 Insulation co-ordination. 19
5.4 Classification of voltages and overvoltages. 19
5.4.1 General . 19
5.5 Minimum air clearance distances to avoid flashover . 20
5.5.1 General . 20
5.6 Load cases for calculation of clearances. 21
5.6.2 Maximum conductor temperature . 21
5.6.3 Wind loads for determination of electric clearances . 21
5.6.4 Ice loads for determination of electric clearances . 22
5.6.5 Combined wind and ice loads . 22
5.8 Internal clearances within the span and at the top of support . 22
5.9 External clearances . 22
5.9.1 General . 22
5.9.2 External clearances to ground in areas remote from buildings, roads, etc. . 23
5.9.3 External clearances to residential and other buildings . 23
5.9.5 External clearances to adjacent traffic routes. 25
5.9.6 External clearances to other power lines or overhead telecommunication lines. 25
5.9.7 External clearances to recreational areas (playgrounds, sports areas, etc.) . 26
5.9.8 External clearances to line crossing pipelines or adjacent pipelines, including gas and oil
pipelines . 30
5.9.9 Overhead lines adjacent to aerodromes. 31
5.10 Corona effect . 32

5.10.2 Audible noise . 32
5.10.3 Corona loss . 32
6 Earthing systems . 32
6.1 Introduction . 32
6.1.3 Earthing measures against lightning effects . 32
6.2 Ratings with regard to corrosion and mechanical strength. 32
6.2.1 Earth electrodes . 32
6.2.2 Earthing and bonding conductors . 33
6.4 Dimensioning with regard to human safety . 33
6.4.1 Permissible values for touch voltages . 33
6.4.3 Basic design of earthing systems with regard to permissible touch voltage . 33
7 Supports . 34
7.1 Initial design considerations . 34
7.1.1 Introduction . 34
7.2 Materials . 34
7.2.6 Wood . 34
7.3 Lattice steel towers . 34
7.3.1 General . 34
7.3.6 Ultimate limit states . 34
7.3.8 Resistance of connections . 35
7.4 Steel poles . 35
7.4.8 Resistance of connections . 35
7.5 Wood poles . 35
7.5.3 Materials . 35
7.5.5 Ultimate limit states . 35
7.10 Maintenance facilities. 35
7.10.1 Climbing . 35
7.10.2 Maintainability . 36
7.10.3 Safety requirements . 36
8 Foundations . 36
8.1 Introduction . 36
8.2 Basis of geotechnical design . 37
8.2.2 Geotechnical design by calculation . 37
8.2.3 Design by prescriptive measures . 38
8.2.4 Load tests and tests on experimental models . 38
8.3 Soil investigation and geotechnical data. 38
8.5 Fill, dewatering, ground improvement and reinforcement . 38
8.6 Interactions between support foundations and soil . 38
9 Conductors and earth-wires . 39
9.1 Introduction . 39

Estonia 5/49 EN 50341-2-20:2018
9.2 Aluminium based conductors . 39
9.2.1 Characteristics and dimensions . 39
9.6 General requirements . 40
9.6.2 Partial factors for conductors . 40
10 Insulators . 40
10.2 Standard electrical requirements . 40
10.4 Pollution performance requirements . 40
10.7 Mechanical requirements. 41
10.10 Characteristics and dimensions of insulators . 41
11 Hardware . 42
11.6 Mechanical requirements. 42
12 Quality assurance, checks and taking over . 42
Annex B (informative) Conversion of wind velocities and ice loads . 43
Annex C (informative) Application examples of wind loads – Special forces . 44
Annex E (normative) Theoretical method for calculating minimum air clearances . 45
Annex F (informative) Empirical method for calculating mid span clearances . 46
Annex G (normative) Calculation methods for earthing systems . 47
Annex H (informative) Installation and measurements of earthing systems . 48

European foreword
1 The Estonian National Committee (NC) is identified by the following address
Estonian Centre for Standardisation
Estonian National High Voltage Committee (HVC)
Akadeemia tee 21/6, 12618 Tallinn, Estonia
Phone: +372 605 5050
Fax: +372 605 5070
E-mail: info@evs.ee
2 The Estonian NC has prepared this Part 2-20 (EN 50341) listing the Estonian National Normative
aspects, under its sole responsibility, and duly passed it through the CENELEC and CLC/TC 11
procedures.
NOTE The Estonian NC also takes sole responsibility for the technically correct co-ordination of this NNA
with EN 50341-1. It has performed the necessary checks in the frame of quality assurance/control. However, it
is noted that this quality control has been made in the framework of the general responsibility of a standards
committee under the national laws/regulations.
3 This revision supersedes EVS-EN 50341-2-20:2015.
The most significant technical changes with respect to the previous edition are:
— requirements for low voltage lines are included;
— telecommunication lines located on common structures with power lines are taken into
account;
— the last amendments of Estonian legal documents are taken into account.
4 This Part 2-20 is normative in Estonia and informative for other countries.
5 This Part 2-20 has to be read in conjunction with EN 50341-1, referred to hereafter as Part 1. All
clause numbers used in this Part 2-20 correspond to those in Part 1. Specific subclauses, which
are prefixed “EE”, are to be read as amendments to the relevant text in Part 1. Any necessary
clarification regarding the application of Part 2-20 in conjunction with Part 1 shall be referred to the
Estonian NC that will, in cooperation with CLC/TC 11, clarify the requirements.
When no reference is made in Part 2-20 to a specific subclause, Part 1 applies.
6 In the case of “box values” defined in Part 1, amended values (if any), which are defined in
Part 2-20, shall be taken into account in Estonia.
However any boxed value, whether in Part 1 or in Part 2-20, shall not be amended in the direction
of greater risk in the Project Specification.
Terms with prepositions “from” and “up to”, denoting boundaries of values, always include the
boundary values itself, as it is common in other Estonian normative documents.
7 The national Estonian standards/regulations related to overhead electrical lines are listed in Clause
2.
NOTE All national standards referred to in this Part 2-20 will be replaced by the relevant European
Standards as soon as they become available and are declared by the Estonian Centre for Standardisation to
be applicable and thus reported to the secretary of CLC/TC 11.

Estonia 7/49 EN 50341-2-20:2018
0 INTRODUCTION
0.7 Language
(snc) EE.1 Language
This Part 2-20 is published in English and in Estonian.
1 SCOPE
1.1 General
(snc) EE.1 Application to new lines
In Estonia the standard EN 50341-1 (Part 1) can only be applied using this NNA
(EN 50341-2-20) containing National Normative Aspects for Estonia.
This Part 2-20 applies to all new overhead electric lines with nominal system voltages
exceeding AC 1 kV and also for low voltage (below 1 kV AC) overhead lines performed
by aerial cables. The requirements of the structural design are applicable also for DC
overhead lines, where the electrical requirements are given in the Project Specification.
(ncpt) EE.2 “New overhead line”
A “new overhead line” means a completely new line between two points, A and B. A new
branch line of the existing power line should be considered as a new power line including
the junction support. Specific requirements for junction support should be defined with the
Project Specification.
1.2 Field of application
(ncpt) EE.1 Application to covered conductors and aerial cables
The standard includes requirements for the design and construction of overhead lines
with nominal system voltages up to 45 kV AC equipped with covered conductors and
aerial cables. Additionally, the requirements of the equipment standards and
manufacturers’ instructions shall be followed.
(A-dev) EE.2 Application to mounting of telecommunication equipment
The Standard EVS-EN 50341:2013 is applicable to fixing of structural elements for tele-
communication (antennas, All Dielectric Self Supporting (ADSS) equipment, junction
boxes, etc.), if mounted on power line supports (towers), especially regarding wind forces
and ice loads on such fixed elements. The design and installation should be done under
the due control of the line owner and/or the competent authority. Mounting of
telecommunication equipment on power line supports must be coordinated with the line
owner and stated in the Project Specification.
This standard applies to telecommunication lines only in the case of their common
installation with power lines. This standard does not apply to separately installed
telecommunication overhead lines.
If telecommunication equipment (antennas, dishes, etc.) will be installed in the
transmission line supports, and their size, location or mounting may have major effects on
the loads or design of the structures, the requirements of EVS-EN 1993-3-1/NA:2009
shall also to be taken into account. If such structures include conductive parts, the
requirements on clearances in subclause 5.8 should be applied.

(ncpt) EE.3 Application to installation of other equipment
Only equipment belonging to the line (electric or telecommunication line) can be installed
on the overhead lines. However, with the permission of the owner of the line, equipment
serving communal services or environmental protection like road signs, warning signs or
warning balls, etc., may also be installed. The installation height of equipment meant to
be installed and maintained by an instructed person shall be such that the work can be
done without climbing the support and the distances of safe electrical work can be
followed. The additional loads due to this equipment on the line supports shall be taken
into account if necessary.
(ncpt) EE.4 Application to existing overhead lines
The Standard EVS-EN 50341:2013 shall not be applied to maintenance, branch lines,
extensions or diversions of existing overhead lines in Estonia, unless specifically required
in the Project Specification.
Overhead lines that meet the mechanical and electrical requirements in force at the time
of their construction can be continually operated if this does not cause obvious danger.
Such lines may be repaired and upgraded according to previously valid requirements.
Thereat repair means replacing a damaged element with a similar new one; renovation
means a more extensive improvement of the line with the aim of extending its life, while
preserving the basic construction of the line.
Any modification of existing lines shall be subject to this standard, but previous norms
and standards can also be used. It shall be made sure that the changes do not have a
significant impact on the line's load. Modification means, for example, the relocation of
some of the supports or the development of the line provided for in the initial design - for
example, adding a circuit or reconductoring on existing supports.
In cases of major revisions of existing lines the degree of application of the Standard
EVS-EN 50341:2013 should be in any case agreed upon by the parties concerned and
specified in the Project Specification.
(ncpt) EE.5 Application to installations under construction or design
Installations in the design and construction stage may be completed by using the
standard valid at the beginning of planning unless otherwise agreed with the line owner
and/or any other competent authority.
It must also be determined in the Project Specification which previous Standard and to
what extent shall be applied to the project in question.
2 NORMATIVE REFERENCES, DEFINITIONS AND SYMBOLS
2.1 Normative references
(A-dev) EE.1 Application of references in Part 1
References in EN 50341-1 apply without change.
(A-dev) EE.2 References to Estonian national laws, regulations and standards
Choice of lines’ route and construction or mounting of high voltage overhead lines is
regulated by the following Estonian laws and government regulations. These laws and
regulations are indispensable for the application of this document. For dated references,
only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
In addition to Part 1 the following Estonian standards and acts should be taken into
account:
Estonia 9/49 EN 50341-2-20:2018
EVS 814:2003. Normaalbetooni külmakindlus. Määratlused, spetsifikatsioonid ja
katsemeetodid. Frost resistance of normal-weight concrete. Definitions, specifications
and test method
EVS 843:2016. Linnatänavad. Urban streets
EVS 884:2017. Maagaasitorustik. Projekteerimise põhinõuded üle 16 baarise töörõhuga
torustikele. Natural gas pipeline systems – Pipelines for maximum operating pressure
over 16 bar – General requirements for design
EVS-EN 1991-1-4/A1:2010/NA:2010. Eurokoodeks 1: Ehituskonstruktsioonide
koormused. Osa 1-4: Tuulekoormus. Eesti standardi rahvuslik lisa. Eurocode 1: Actions
on structures – Part 1-4: General actions – Wind actions. Estonian National Annex
EVS-EN 1991-1-4/NA:2007. Eurokoodeks 1: Ehituskonstruktsioonide koormused.
Osa 1-4: Üldkoormused. Tuulekoormus. Eesti standardi rahvuslik lisa. Eurocode 1:
Actions on structures – Part 1-4: General actions – Wind actions. Estonian National
Annex
EVS-EN 1993-3-1/NA:2009. Eurokoodeks 3: Teraskonstruktsioonide projekteerimine.
Osa 3-1: Tornid, mastid ja korstnad. Tornid ja mastid. Eesti standardi rahvuslik lisa.
Eurocode 3 - Design of steel structures - Part 3-1: Towers, masts and chimneys - Towers
and masts. Estonian National Annex
Asjaõigusseadus ja muudatused. Law of Property Act (RT I 1993, 39, 590) and
amendments
NOTE RT − Riigi Teataja (The State Gazette), an official online publication of the Republic
of Estonia, RTL – Riigi Teataja Lisa (Supplement of the State Gazette). The translations published
in Riigi Teataja are unofficial texts – they do not have legal force and you cannot rely on them in
judicial or any other official proceedings. In Estonia, legislation has legal force only in Estonian.
Asjaõigusseaduse rakendamise seadus ja muudatused. Law of Property Act
Implementation Act (RT I 1993, 72, 1021) and amendments
Ehitusseadustik ja muudatused. Building Code (RT I 05.03.2015, 1) and amendments
Ehitusseadustiku ja planeerimisseaduse rakendamise seadus ja muudatused. An Act to
Implement the Building Code and the Planning Act (RT I, 23.03.2015, 3) and
amendments
Elektrituruseadus ja muudatused. Electricity Market Act (RT I 2003, 25, 153) and
amendments
Elektroonilise side seadus ja muudatused. Electronic Communications Act
(RT I 2004, 87, 593) and amendments
Jäätmeseadus ja muudatused. Waste Act (RT I 2004, 9, 52) and amendments
Keskkonnajärelevalve seadus ja muudatused. Environmental Supervision Act
(RT I 2001, 56, 337) and amendments
Keskkonnamõju hindamise ja keskkonnajuhtimissüsteemi seadus ja muudatused.
Environmental Impact Assessment and Environmental Management System Act
(RT I 2005, 15, 87) and amendments
Lennundusseadus ja muudatused. Aviation Act (RT I 1999, 26, 376) and amendments
Looduskaitseseadus ja muudatused. Nature Conservation Act (RT I 2004, 38, 258) and
amendments
Maakatastriseadus ja muudatused. Land Cadastre Act (RT I 1994, 74, 1324) and
amendments
Meresõiduohutuse seadus ja muudatused. Maritime Safety Act (RT I 2002, 1, 1) and
amendments
Muinsuskaitseseadus ja muudatused. Heritage Conservation Act (RT I 2002, 27, 153)
and amendments
Planeerimisseadus ja muudatused. Planning Act (RT I 26.02.2015, 3) and amendments
Raudteeseadus ja muudatused. Railways Act (RT I 2003, 79, 530) and amendments
Seadme ohutuse seadus ja muudatused. Equipment Safety Act (RT I 23.03.2015, 4) and
amendments
Majandus- ja taristuministri määrus „Ehitise kaitsevööndi ulatus, kaitsevööndis
tegutsemise kord ja kaitsevööndi tähistusele esitatavad nõuded“. Regulation of the
Minister of Economic Affairs and Infrastructure “Extent of a structure protection zone,
procedures for operating in the protection zone and requirements for the protection zone
designation” (RT I, 28.06.2015, 4)
Majandus- ja taristuministri määrus „Tee projekteerimise normid”. Regulation of the
Minister of Economic Affairs and Infrastructure “Road design regulations”
(RT I, 07.08.2015, 14)
Sotsiaalministri määrus „Müra normtasemed elu- ja puhkealadel, elamutes ning
ühiskasutusega hoonetes ja mürataseme mõõtmise meetodid“.
Regulation of the Minister of Social Affairs “Audible noise limits in residential and
recreational areas, residential and social buildings and noise level control methods”
(RTL 2002, 38, 511)
Other valid relevant normative regulatory documents should also be taken into account.
Internal normative documents of a utility may be referred to in the Project Specification.
3 BASIS OF DESIGN
3.2 Requirements of overhead lines
3.2.2 Reliability requirements
(ncpt) EE.1 Selection of reliability levels
Three reliability levels are used, as shown in the following table:
Table EE.3.1 — Reliability levels
Reliability level Nominal system voltage Line type
Un < 110 kV Normal lines
Un = 110 kV Unimportant lines
= 110 kV
2 Un Normal lines
Un ≥ 110 kV Important lines, including all 330 kV lines
NOTE  The type of line is considered normal unless otherwise specified in the Project Specification.

Estonia 11/49 EN 50341-2-20:2018
(A-dev) EE.2 Wind load on temporary lines
In accordance with the Estonian National Annex of EVS-EN 1991-1-4 the recommended
value of the seasonal coefficient cseason is 1,0.
(snc) EE.3 Ice load on temporary lines
When designing temporary lines intended for use between April and October, where ice
accretion does not occur, the ice load doesn’t need to be considered.
3.2.3 Security requirements
(snc) EE.1 Distance between tension supports
In lines with nominal system voltage exceeding AC 1 kV up to 20 kV, the distance
between tension supports must not be greater than 2 km unless specified otherwise in
the Project Specification. For lines with nominal system voltage exceeding AC 20 kV the
distance between tension supports shall be specified in the Project Specification.
3.2.5 Strength coordination
(ncpt) EE.1 Specific requirements
The strength coordination is based on the principles of IEC 60826, which are presented in
Annex A of Part 1 of this Standard. Specific requirements for strength coordination may
be specified in the Project Specification if necessary.
3.2.6 Additional considerations
(ncpt) EE.1 Location of overhead lines
The overhead line route shall be chosen as easily accessible as possible for operation as
well as for reparations.
The construction of overhead lines in a densely built-up area shall be avoided.
(A-dev) EE.2 Environmental aspects
Consideration of an overhead line as an element in the environment shall take into
account the environmental and legal situations in that particular region of Estonia.
(ncpt) EE.3 Safety and protection of wildlife and livestock
Specific requirements on safety of human beings and protection of wildlife and livestock
(e.g. birds, cattle, etc.) may be specified in the Project Specification, if necessary.
(ncpt) EE.4 Protection of birds
Crossarms, insulators and other components of overhead line poles shall be designed so
that the birds cannot stay above insulators and cannot find possibilities for nesting in a
dangerous proximity to the live conductors.
3.3 Limit states
3.3.3 Serviceability limit states
(ncpt) EE.1 Criteria of serviceability
Criteria of serviceability limit states are defined in clauses relating to particular line
components. Additional requirements may be presented in the Project Specification.
3.4 Actions
3.4.2 Classification of actions by their variation in time
(ncpt) EE.1 Variable actions
Wind loads and ice loads as well as applicable temperatures are assessed by applying
the reliability concept.
4 ACTIONS ON LINES
4.1 Introduction
(snc) EE.1 Climatic data
For assessment of the climatic data to determine numerical values for actions, the first
approach is applied, i.e. Estonian and European standards are used. Specific references
shall be given in the corresponding subsections.
4.3 Wind loads
4.3.1 Field of application and basic wind velocity
(A-dev) EE.1 Basic wind velocity
For all territory of Estonia the following value shall be used for basic wind velocity (V )
b,0
according to the Estonian National Annex EVS-EN 1991-1-4/A1:2010/NA:2010:
V = 21 m/s
b,0
For overhead lines with nominal system voltages up to 20 kV, according to long-term
experience, the value 18.5 m/s for the basic wind velocity V shall be used.
b,0
4.3.2 Mean wind velocity
(A-dev) EE.1 Wind directional factor
According to the Estonian National Annex EVS-EN 1991-1-4/A1:2010/NA:2010, the value
of the directional factor cdir is 1,0.
(A-dev) EE.2 Orography factor
According to the Estonian National Annex EVS-EN 1991-1-4/A1:2010/NA:2010, the value
of the orography factor co is 1,0.
4.3.3 Mean wind pressure
(A-dev) EE.1 Air density
According to the Estonian National Annex EVS-EN 1991-1-4/A1:2010/NA:2010, the
conservative value for air density ρ = 1,25 kg/m regardless of temperature is used in
Estonia.
4.3.5 Wind forces on any overhead line component
(ncpt) EE.1 Nominal wind load
Determination of minimum air clearances in Clause 5 is based on the nominal wind load
which is found, multiplying the extreme wind load (with 50-year return period) Q by
W50
𝐶𝐶 = 0m58, which is the ratio of square of the 10 minutes mean wind velocity with 3-year
𝑇𝑇
return period V3 to square of the 10 minutes mean wind velocity with 50-year return period
V :
QW3 = C T×QW50 = 0,58QW50
For determination of ice and wind forces affecting the mast elements, the wind load Q
W3 I
is calculated as the nominal wind load (with 3-year return period) QW3 multiplied by the
reduction factor B = 0.7 (see Table 4.13 / EE.1 and Part 1, subclause 4.6.6.1):
I
QW3 I = BI×QW3 = BI×C T×QW50 = ΨW×QW50 = 0,4QW50
where
ΨW is the combination factor for wind loads.

Estonia 13/49 EN 50341-2-20:2018
4.4 Wind forces on overhead line components
4.4.1 Wind forces on conductors
4.4.1.1 General
(snc) EE.1 Conductors reference height above ground
For lines with nominal system AC voltage up to 20 kV, reference height above ground h
for the calculation of wind forces on conductors should be determined according to
method 6 in Table 4.3 of Part 1.
For lines with nominal system AC voltage exceeding 20 kV, reference height above
ground h for the calculation of wind forces on conductors should be determined desirably
according to method 2 in Table 4.3 of Part 1.
The mean reference height of spans in the section weighted by their lengths shall be
taken as the reference height above ground of the conductors in the section.
4.4.1.2 Structural factor
(ncpt) EE.1 Span factor
For determination of the span factor in sag and tension analysis the section length shall
be taken as the span length. For analysis of loads on supports and on conductors fixed
on pin or post insulators, the average length of the spans adjacent to the support must be
taken as the span length.
4.4.1.3 Drag factor
(snc) EE.1 Drag factor for conductors
The drag factor CC for conductors and earth wires shall be determined by method 1 in
subclause 4.4.1.3 of Part 1, i.e. C is 1,0 for any conductor, subconductor and earth wire.
C
(snc) EE.2 Drag factor for aerial cables
The value of the drag factor C for aerial bundle cables is 1,2.
C
4.4.2 Wind forces on insulator sets
(ncpt) EE.1 Wind forces on insulator sets
When designing supports wind forces on insulator sets due to wind pressure can be
neglected. If taking them into account the wind forces acting on the insulator sets are
determined in accordance with subclause 4.4.2 of Part 1. The horizontal projection area
A of the insulating set to the vertical plane parallel with the insulator string axis is
ins
calculated as
A = L D sinα,
ins
where
L is the effective length of the insulator string;
D is the external diameter of the insulator;
α is the angle between insulator string and wind direction. The conservative
value α = 90° may be used.
4.4.3 Wind forces on lattice towers
4.4.3.1 General
(snc) EE.1 Method for determining of wind forces
Wind forces on the tower itself can be determined either by method 1 in subclause
4.4.3.1 of Part 1, by which the tower is divided into sections, or by method 2 ibidem, by
which each individual member of the tower is considered separately.
(snc) EE.2 The reference height of lattice tower sections or members
The reference height of lattice tower sections or members can be determined by any
method given in subclause 4.4.3.1 of Part 1: either the same value is used for every
section or member of a lattice tower, which is equal to 60 % of the total height of the
tower, or the reference height for every section or member is determined separately as
the height of the geometric centre of the corresponding section or member above ground.
4.4.4 Wind forces on poles
(snc) EE.1 Method for determining the reference height
The reference height to evaluate wind forces on poles can be determined either by
method 1 or method 2 in subclause 4.4.4 of Part 1.
The value of the structural factor for the pole Gpol shall be ta
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