EN 50341-2-20:2015

SLOVENSKI STANDARD
01-april-2016
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Overhead electrical lines exceeding AC 45 kV - Part 2-20: National Normative Aspects
(NNA) for ESTONIA (based on EN 50341-1:2012)
Ta slovenski standard je istoveten z: EN 50341-2-20:2015
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
February 2015
ICS 29.240.20
English Version
Overhead electrical lines exceeding AC 45 kV -
Part 2-20: National Normative Aspects (NNA) for ESTONIA
(based on EN 50341-1:2012)
This European Standard was approved by CENELEC on 2015-01-06.
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, 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: Avenue Marnix 17, B-1000 Brussels
© 2015 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50341-2-20:2015 E
CONTENTS
0 Introduction .5
0.7 Language .5
1 Scope .5
1.1 General .5
1.2 Field of application .5
2 Normative references, definitions and symbols .6
2.1 Normative references.6
3 Basis of design .8
3.2 Requirements of overhead lines .8
3.3 Limit states .9
3.4 Actions .9
3.6 Design values .9
4 Actions on lines .9
4.1 Introduction .9
4.3 Wind loads .9
4.4 Wind forces on overhead line components . 10
4.5 Ice loads . 11
4.6 Combined wind and ice loads . 11
4.7 Temperature effects . 11
4.8 Security loads . 11
4.9 Safety Loads . 12
4.10 Forces due to short-circuit currents . 13
4.11 Other special forces . 13
4.12 Load cases . 13
4.13 Partial factors for actions . 14
5 Electrical requirements . 16
5.1 Introduction . 16
5.2 Currents . 16
5.4 Classification of voltages and overvoltages . 16
5.5 Minimum air clearance distances to avoid flashover . 17
5.6 Load cases for calculation of clearances . 17
5.8 Internal clearances within the span and at the top of support . 18
5.9 External clearances . 18
5.10 Corona effect . 26
6 Earthing systems . 27
6.1 Introduction . 27
6.2 Ratings with regard to corrosion and mechanical strength. 27
6.4 Dimensioning with regard to human safety . 27
7 Supports . 28
7.2 Materials . 28
7.3 Lattice steel towers . 28
7.4 Steel poles . 29
7.5 Wood poles . 29
7.9 Corrosion protection and finishes . 30
7.10 Maintenance facilities. 30
8 Foundations . 30
8.1 Introduction . 30
8.2 Basis of geotechnical design . 30
8.3 Soil investigation and geotechnical data. 31
9 Conductors and earth-wires . 32
9.2 Aluminium based conductors . 32
9.3 Steel based conductors . 32
9.5 Conductors and ground wires containing optical fibre telecommunication circuits . 32

Estonia 3 / 42 EN 50341-2-20:2015
9.6 General requirements . 32
10 Insulators . 32
10.2 Standard electrical requirements . 32
10.4 Pollution performance requirements . 33
10.7 Mechanical requirements. 33
10.10 Characteristics and dimensions of insulators . 33
11 Hardware . 34
11.6 Mechanical requirements. 34
12 Quality assurance, checks and taking-over . 34
Annex B (informative) Conversion of wind velocities and ice loads . 35
Annex C (informative) Application examples of wind loads – Special forces . 36
Annex E (normative) Theoretical method for calculating minimum air clearances . 37
Annex F (informative) Empirical method for calculating mid span clearances . 38
Annex G (normative) Calculation methods for earthing systems . 39
Annex H (informative) Installation and measurements of earthing systems . 40
Annex M (informative) Geotechnical and structural design of foundations . 42

FOREWORD
1 The Estonian National Committee (NC) is identified by the following address
Estonian Centre for Standardisation
Estonian National High Voltage Committee (HVC)
Aru str. 10, 10317 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 of EN 50341, listing the Estonian national normative
aspects under its sole responsibility, and has 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 Part 2-20 is normative in Estonia and informative for other countries.
4 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 articles 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.
5 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 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.
6 The national Estonian standards/regulations related to overhead electrical lines exceeding AC 1 kV
are identified/listed in Clause 2 of this Part 2-20.
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 5 / 42 EN 50341-2-20:2015
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
(NCPT) EE.1 Application to new lines
This Part 2-20 applies to all new overhead electric lines with nominal system voltages
exceeding AC 1 kV and with rated frequencies below 100 Hz. This standard also applies
to D.C. overhead lines in structural aspects.
(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, for which specific requirements should be defined in the Project
Specification.
1.2 Field of application
(A-dev) EE.1 Application to mounting of telecommunication equipment
The Standard EVS-EN 50341:2012 is applicable to fixing of structural elements for tele-
communication (antennas, satellite dishes, All Dielectric Self Supporting (ADSS)
equipment, 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 line
owner and stated in the Project Specification.
If telecommunication equipment (antennas, dishes, etc.) will be installed in the
transmission line supports, and their size, location or mounting will have major effects on
the loads or design of the structures, the requirements of EVS-EN 1993-3 will also have
to be taken into account. If such structures include conductive parts, the requirements on
clearances in Section 5.8 should be applied.
(NCPT) EE.2 Application to existing overhead lines
The Standard EVS-EN 50341:2012 shall not be applied to maintenance, reconductoring,
tee-offs, extensions or diversions to existing overhead lines in Estonia, unless specifically
required in the Project Specification.
In cases of major revisions of existing lines the degree of application of the Standard
EVS-EN 50341:2012 should be agreed upon by the parties concerned and specified in
the Project Specification.
(NCPT) EE.3 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 National Standard
and to what extent should 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 line route and construction or mounting of high voltage overhead line 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. (RT − Riigi Teataja, RTL – Riigi Teataja
Lisa (supplement). Riigi Teataja is the official publication of the Republic of Estonia).
NAME PUBLICATION CITATION
Asjaõigusseadus Law of Property Act (RT I 1993, 39, 590)
Asjaõigusseaduse rakendamise seadus
Law of Property Act Implementation Act (RT I 1993, 72, 1021)
Elektriohutusseadus Electrical Safety Act (RT I 2007, 12, 64)
Elektrituruseadus Electricity Market Act (RT I 2003, 25, 153)
Elektroonilise side seadus Electronic Communications Act (RT I 2004, 87, 593)
1 1
Ehitusseadus Building Act (RT I 2002, 47, 297)
Jäätmeseadus Waste Act (RT I 2004, 9, 52)
Keskkonnajärelvalve seadus Environmental Supervision Act (RT I 2001, 56, 337)
Keskkonnamõju hindamise ja keskkonnajuhtimissüsteemi
seadus
Environmental Impact Assessment and Environmental
Management System Act (RT I 2005, 15, 87)
Lennundusseadus Aviation Act (RT I 1999, 26, 376)
Looduskaitseseadus Nature Conservation Act (RT I 2004, 38, 258)
Maakatastriseadus Land Cadastre Act (RT I 1994, 74, 1324)
Meresõiduohutuse seadus Maritime Safety Act (RT I 2002, 1, 1)
Muinsuskaitseseadus Heritage Conservation Act (RT I 2002, 27, 153)
Planeerimisseadus Planning Act (RT I 2002, 99, 579)
Raudteeseadus Railways Act (RT I 2003, 79, 530)
Teeseadus Roads Act (RT I 1999, 26, 377)
Tööstusheitmete seadus Industrial Emissions Act (RT I, 16.05.2013, 1)
Veeseadus Water Act (RT I 1994, 40, 655)
Võlaõigusseadus Law of Obligations Act (RT I 2001, 81, 487)
Majandus- ja kommunikatsiooniministri määrus
„Elektripaigaldise kaitsevööndi ulatus ja kaitsevööndis
tegutsemise kord“
Regulation of the Minister of Economic Affairs and
Communications “Extent of protection zone for an electrical
installation and practical arrangements in a protection zone” (RTL 2007, 27, 482)

Estonia 7 / 42 EN 50341-2-20:2015
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)

The following Estonian standards should be taken into account:
EVS-EN 1991-1-4:2005+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 1991-1-4:2005/A1:2010+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 50522:2010. Üle 1 kV nimivahelduvpingega tugevvoolupaigaldiste maandamine.
Earthing of power installations exceeding 1 kV a.c.
EVS 814:2003. Normaalbetooni külmakindlus. Määratlused, spetsifikatsioonid ja
katsemeetodid. Frost resistance of normal-weight concrete. Definitions, specifications
and test method
EVS 843:2003. Linnatänavad. Town streets
EVS 884:2005. 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 14229:2010. Ehituspuit. Õhuliinide puitpostid. Structural timber – Wood poles for
overhead lines.
EVS-EN 61773:2002. Overhead lines – Testing of foundations for structures
EVS-EN 1997-1:2005+NA:2006. Eurokoodeks 7: Geotehniline projekteerimine. Osa 1:
Üldeeskirjad. Eurocode 7: Geotechnical design – Part 1: General rules
EVS-EN 1997-1:2005/A1:2013. Eurokoodeks 7: Geotehniline projekteerimine. Osa 1:
Üldeeskirjad. Eurocode 7: Geotechnical design – Part 1: General rules
EVS-EN 60071-1. Insulation co-ordination – Part 1: Definitions, principles and rules
EVS-EN 60071-2. Insulation co-ordination – Part 2: Application guide
EVS-EN 61284:2002. Overhead lines – Requirements and tests for fittings
Other valid relevant normative regulatory documents should also be taken in 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 Lines exceeding AC 1 kV
1 Normal lines
2 Important lines
3 Very important lines
NOTE If line reliability is not specified in the Project Specification, the requirements of Level 1
apply.
(A-dev) EE.2 Wind load on temporary lines
In accordance with the Estonian National Annex of EVS-EN 1991-1-4:2005+NA:2007, the
recommended value of the seasonal coefficient c = 1,0.
season
(NCPT) 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 need not be considered.
3.2.3 Security requirements
(NCPT) EE.1 Distance between tension supports
In lines with nominal voltage exceeding AC 1 kV up to and including 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 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.
3.2.6 Additional considerations
(A-dev) EE.1 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.2 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.
3.2.7 Design working life
(NCPT) EE.1
In general, design working life of lines with nominal voltage exceeding AC 1 kV up to and
including 20 kV is 30 years; for lines with nominal voltage exceeding AC 20 kV it is
50 years. A different design working life may be specified in the Project Specification.

Estonia 9 / 42 EN 50341-2-20:2015
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.
3.6 Design values
3.6.3 Design value of a material property
(NCPT) EE.1 Partial factors for actions
Partial factors for a material property higher than those stated in Eurocodes 2, 3, 5, 7, and
8 may be specified in the Project Specification.
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 speed
The following value shall be used for basic wind velocity (V ) according to the Estonian
b,0
National Annex of EVS-EN 1991-1-4:2005+NA:2007:
V = 21 m/s
b,0
Other values of basic wind speed based on long-term statistics and local conditions can
be specified in the Project Specification.
4.3.2 Mean wind velocity
(A-dev) EE.1 Wind directional factor
According to the Estonian National Annex of EVS-EN 1991-1-4:2005+NA:2007, the
recommended value of the directional factor c = 1,0.
dir
(A-dev) EE.2 Orography factor
According to the Estonian National Annex of EVS-EN 1991-1-4:2005+NA:2007, the
recommended value of the orography factor c = 1,0.
o
4.3.3 Mean wind pressure
(A-dev) EE.1 Air density
According to EVS-EN 1991-1-4:2005+NA:2007, the conservative value for air density
ρ = 1,25 kg/m is used in Estonia.

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 voltage up to AC 20 kV, reference height above ground h shall be
taken as 10 m regardless of the actual height, provided that the structure height is a
maximum of 20 m.
For lines with nominal voltage exceeding 20 kV, reference height above ground h for the
calculation of wind forces on conductors shall be determined according to method 2 in
Table 4.3.
(NCPT) EE.2 Mechanical tension in a section
For calculating the mechanical tension in a section, the section length should be used as
the span length.
The mean reference height of spans in the section weighted by their lengths should be
taken as the reference height above ground of the conductors in the section.
4.4.1.3 Drag factor
(snc) EE.1 Drag factor for conductors
The drag factor for the conductor, C , shall be determined by method 1, i.e. C = 1,0.
C C
4.4.2 Wind forces on insulator sets
(NCPT) EE.1 Wind forces on insulator sets
Wind forces due to wind pressure on the insulator sets themselves may be neglected for
the design of supports.
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 by method 1, by which tower is divided
into sections, or by method 2, 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 Clause 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.
Estonia 11 / 42 EN 50341-2-20:2015
4.5 Ice loads
4.5.2 Ice forces on conductors
(snc) EE.1 Extreme ice load per unit length
Extreme ice load per unit length I (N/m) shall be calculated by the following formula:
–3
I = 9,82 × 10 ρ π b (d + b)
I
where
b is the icing thickness, mm;
d is the diameter of conductor or earthwire, mm;
ρ is the ice density, g/cm .
I
Simplified:
I = 0,0277 b (b + d)
Value of the icing thickness should be taken equal to 10 mm and the ice type should be
glaze ice with density 0,90 g/cm , unless specified otherwise in the Project Specification.
4.6 Combined wind and ice loads
4.6.1 Combined probabilities
(snc) EE.1 Load combinations and combination factors
Values of load combinations and combination factors are given in Table 4.13/EE.1.
Load cases 2b*, 2c*, 2d*, 2e* and 3b need not be investigated for lines with nominal
voltage exceeding AC 1 kV up to and including 20 kV.
4.6.2 Drag factors and ice densities
(snc) EE.1 Drag factor and ice density
Drag factor for glaze ice covered conductor C is 1,0.
Ic
4.7 Temperature effects
(snc) EE.1 Ambient temperatures
The following ambient temperatures should be used:
− Minimum temperature with no other climatic action: –40 °C,
on Western Estonian islands: –30 °C;
− Normal ambient temperature (every day temperature): +5 °C;
− Maximum temperature: +35 °C;
− The temperatures applied to different load cases are given in Table 4.13/EE.
4.8 Security loads
4.8.1 General
(NCPT) EE.1 Lines with nominal voltage of AC 20 kV and below
Security loads need not be taken into account for lines with nominal voltages up to and
including AC 20 kV unless specified otherwise in the Project Specification.

4.8.2 Torsional loads
(NCPT) EE.1 Conductor tension
Conductor tension shall be calculated at the normal ambient temperature without any
external load.
(NCPT) EE.2 Load cases
Two load cases are distinguished: interruption of one subconductor, and interruption of all
subconductors mounted to one fixing assembly.
4.8.3 Longitudinal loads
(NCPT) EE.1 Conductor tension
Conductor tension shall be calculated at the normal ambient temperature without any
external load.
(NCPT) EE.2 Longitudinal load
For longitudinal load calculation to all phase conductors and earth wires overloads equal
to their dead load should be applied.
4.8.4 Mechanical conditions of application
(NCPT) EE.1 Reduction factor
For consideration of load reduction resulting from any swing of the insulator sets the
conductor tension can be multiplied by the reduction factor β = 0,5.
4.9 Safety Loads
4.9.1 Construction and maintenance loads
(snc) EE.1 Weather conditions
During installation of conductors temperature should be taken equal to –15 °C, wind and
ice are neglected.
(snc) EE.2 Load cases in construction period
In the construction period three load cases should be taken into account:
− temperature up to –15 °C;
− wind load with a return period of 3 years at the temperature corresponding to wind
load;
− ice load with a return period of 3 years.
(NCPT) EE.3 Loads during construction
During construction of a line the following loads should be considered:
1. Additional horizontal load arising during the installation of conductors.
2. Additional vertical load arising during the installation of conductors due to the coiling
machine. The distance to the coiling machine should be taken as triple the height of
the attachment point of the conductor.
3. Additional vertical load due to anchorage to the ground of installed conductors. The
distance between anchors should be taken as triple the height of the attachment point
of conductors.
4. Double vertical load due to lifting conductors. The weight of installation equipment,
3 kN, should be added to the weight of the conductor without ice, insulators, and
fittings.
The loads mentioned in items 1 and 2 shall be applied simultaneously to a phase or to an
earth-wire. The partial factor for maintenance load γ (equal to 1,5) shall be applied to the
P
conductor tension corresponding to the mounting tables.

Estonia 13 / 42 EN 50341-2-20:2015
Additional vertical load due to anchorage to the ground of installed conductors mentioned
in item 3 shall be applied simultaneously to all attachment points of the phase conductors
and earth wires. Conductor tension shall be calculated at the wind load with a return
period of 3 years at –15 °C. The partial factor γ (equal to 1,5) shall be applied to the
P
conductor tension.
4.9.2 Loads related to the weight of linesmen
(snc) EE.1 Weight of linesmen
The weight of linesmen and erection facilities should be taken as 2 kN.
4.10 Forces due to short-circuit currents
(NCPT) EE.1 Consideration forces due to short-circuit currents
Forces due to short-circuit currents should to be considered, if the level of short-circuit
currents (three phase short-circuit current I ) exceeds 31,5 kA for lines with 330 kV and
SC3φ
20 kA for lines with a lower nominal voltage.
4.11 Other special forces
4.11.1 Avalanches, creeping snow
(snc) EE.1 Consideration of loads
Possible additional loads due to avalanches or creeping snow are neglected.
4.11.2 Earthquakes
(snc) EE.1 Loads related to earthquakes
Possible additional loads due to earthquakes are not considered.
Additional Clauses:
4.11.3 Floating of ice, accidents of vessels
(snc) EE.1 Consideration of loads
Loads caused by floating ice or accidents of vessels shall be taken into account if
supports are located in rivers, including river foreland, or lakes. Determination of these
loads shall be specified in the Project Specification.
4.11.4 Mining out areas
(snc) EE.1 Supports on mining out areas
When overhead lines are to be constructed in the mining out areas they should be built
on the place of pillars if possible. Special considerations shall be defined in the Project
Specification.
4.12 Load cases
4.12.1 General
(NCPT) EE.1 Supports of special types
Additional load cases for supports of special types should be defined in the Project
Specification if needed.
(NCPT) EE.2 Partial installation of circuits or subconductors
Partial installation of circuits or subconductors should be specified in the Project
Specification if needed.
4.12.2 Standard load cases
(snc) EE.1 Definition of load cases
Standard load cases, partial factors and combination factors are defined in
Table 4.13/EE.1.
(snc) EE.2 Minimum temperature
For minimum temperature wind and ice loads are not considered. According to 4.7/EE.1
the minimum temperature is –40 °C; on Western Estonian islands: -30 °C.
(snc) EE.3 Dropped ice
In addition to the normal ice load case the dropped ice case on one span can be
specified in the Project Specification: uniform extreme ice loads (without wind) in all
spans of the phase conductors and earth wires except for one span of any phase
conductor or earth wire, which is non-iced.
(snc) EE.4 Security loads – Torsion
Tension supports shall be checked for interruption of all subconductors of a phase or
earth wire.
Intermediate supports shall be checked to interruption of one subconductor of a phase or
earth wire.
(snc) EE.5 Construction loads – Installation of conductors
One phase conductor or earth wire shall be installed at the same time, the remaining
wires either already installed or uninstalled. The least favoured installation order of
conductors and earth wires should be considered for a specific line element. Conductor
tension shall be taken according to mounting tables. For the conductor to be installed, the
partial factor γ equal to 1,5 shall be applied. The partial factor shall not be applied to
P
conductors already installed.
On tension supports the loads 1 and 2 on the conductor under installation from
4.9.1/EE.3 as well as load 3 on already installed conductors from the same clause shall
be applied. On intermediate supports load 2 on the conductor under installation from
4.9.1/EE.3 and load 3 on already installed conductors from the same clause shall be
applied.
(snc) EE.5 Construction loads – Partially installed conductors
In one span of the line all the conductors and earth wires are installed and anchored,
leading to load 3 on supports from 4.9.1/EE.3. Conductor tension shall be calculated in
load cases during construction, as mentioned in 4.9.1/EE.3. The partial factor for
maintenance loads shall not be applied to conductor tension.
4.13 Partial factors for actions
(snc) EE.1 Partial factors, combination factors and reduction factors
Partial factors γ and combination factors Ψ as well as load reduction factors are given in
Table 4.13/EE.1. The following definitions are used:
Extreme wind load − wind load with a return period corresponding to the reliability level,
taking into account terrain category, height from ground, height from sea level, and
temperature impact.
High wind load − extreme wind load multiplied by the reduction factor 0,70 (i.e. load at the
wind speed with low probability).
Nominal wind load − Extreme wind load with a return period of 50 years, Q , multiplied
W50
by the combination factor 0,40.
Extreme ice load – ice load with a return period corresponding to the reliability level (i.e.
ice load with low probability).
Nominal ice load − ice load with a return period of 3 years (or ice load with high
probability), i.e. extreme ice load with a return period of 50 years multiplied by the
combination factor 0,35.
Estonia 15 / 42 EN 50341-2-20:2015
Table 4.13/EE.1 — Load cases, temperatures, partial factors γ, combination factors Ψ
and reduction factors
Reliability level
Tempera- Reduction
Weight
ture factors
1 2 3
No. Load case
γ γ γ γ γ γ
W I W I W I
Wind Ice
°C or or or or or or γ
G
load load
Ψ Ψ Ψ Ψ Ψ Ψ
W I W I W I
1a Extreme wind load -5  1,0 1,2 1,4 1,0
1b Minimum temperature –40     1,0
(–30**)
2a Uniform extreme ice load –5  1,0 1,25 1,5 1,0
2b* Uniform extreme ice load, transversal –5 α = 0,5 1,0 1,25 1,5 1,0
bend (4.12.2 b)
2c* Unbalanced extreme ice load, –5 α = 0,3 1,0 1,25 1,5 1,0
longitudinal bend (4.12.2 c)
α = 0,7
2d* Unbalanced extreme ice load, –5 α = 0,3 1,0 1,25 1,5 1,0
torsional bend (4.12.2 d)
α = 0,7
3a Extreme ice load with nominal wind –5  0,4 1,0 0,4 1,25 0,4 1,5 1,0
load (4.6.6.1)
3b High wind load with nominal ice load –5 0,7 1,0 0,35 1,2 0,35 1,4 0,35 1,0
(4.6.6.2)
5a Security loads, torsional loads +5  γ = 1,0 1,0
A
5b Security loads, longitudinal loads +5  γ = 1,0 1,0
A
6a Construction and maintenance loads –15 0,4 γ = 1,5 1,0
P
6b Loads due to the weight of linesmen –15 0,4 γ = 1,5 1,0
P
NOTE 1 The partial load factors shall be applied on the loads prior to the conductor tension
analysis.
NOTE 2 The cases marked with an asterisk (*) shall be checked only if so required in the Project
Specification.
NOTE 3 Temperature on Western Estonian islands is marked with two asterisks (**).
NOTE 4 Load cases 2b*, 2c*, 2d*, 2e* and 3b shall not be investigated for lines with nominal
voltage exceeding AC 1 kV up to and including 20 kV.
(NCPT) EE.2 Modified factors
Modified factors may appear in the Project Specification.

5 ELECTRICAL REQUIREMENTS
5.1 Introduction
(snc) EE.1 Galloping of conductors
For calculation of clearances the galloping of conductors and earth wires shall be taken
into account only when specified in the Project Specification. The method of calculation
shall be given in the Project Specification.
5.2 Currents
5.2.1 Nominal current
(snc) EE.1 Conditions for the determination of maximum design temperature of the
conductor
The maximum design temperature of conductors shall be determined at an ambient
temperature of +35 °C at wind speed of 0 m/s.
5.2.2 Short-circuit currents
(NCPT) EE.1 Magnitude of short-circuit currents
The magnitude and duration of short-circuit currents shall be given in the Project
Specification.
5.4 Classification of voltages and overvoltages
5.4.1 General
(A-dev) EE.1 Nominal voltages in Estonia
Nominal system voltages and the corresponding highest system voltages preferably used
or to be used in Estonia are given in Table 5.1/EE.1.
Table 5.1/EE.1 — Nominal voltages and corresponding highest system voltages
Nominal system voltage, kV Highest system voltage, kV
6 7,2
10 12
15 17,5
20 24
35 40,5
110 123
220 245
330 *) 362 *)
400 420
*) These values are taken from EVS-EN 60071-1, as they are absent from EN 50341.
(NCPT) EE.2 Co-ordination of overhead line insulation and substation insulation
Guidelines for the co-ordination of overhead line insulation and connected substations
insulation may be given in the Project Specification.

Estonia 17 / 42 EN 50341-2-20:2015
5.5 Minimum air clearance distances to avoid flashover
5.5.2 Application of the theoretical method in Annex E
(NCPT) EE.1 Derivation of minimum clearances
The method described in Annex E of Part 1 is used for the derivation of D and D or
el pp
D and D .
50Hz_p_e 50Hz_p_p
5.5.3 Empirical method based on European experience
(NCPT) EE.1 Rough evaluation of minimum air clearances
For rough evaluation of D and D for lines > 45 kV the empirical values in
50Hz_p_e 50Hz_p_p
Table 5.5/EE.1 can be used.
Table 5.5/EE.1 — Minimum air clearances necessary to withstand
the power frequency voltage (to be used in extreme wind conditions)
D [m] D [m]
50Hz_p_e 50Hz_p_p
K = 1,45 K = 1,60
g g
conductor-structure conductor-conductor
123 0,23 0,37
245 0,43 0,69
362 0,62 1,02
420 0,70 1,17
For rough evaluation of D and D the empirical values in Table 5.6/EE.1 can be used.
el pp
Table 5.6/EE.1 — Clearances D and D
el pp
Highest system voltage
D D
el pp
U
s
[m] [m]
[kV]
7,2 0,09 0,10
12 0,12 0,15
17,5 0,16 0,20
24 0,22 0,25
40,5 0,41 0,50
123 1,00 1,15
245 1,70 2,00
362 2,50 2,85
420 2,80 3,20
5.6 Load cases for calculation of clearances
5.6.2 Maximum conductor temperature
(snc) EE.1 Maximum temperature
The following maximum continuous service temperatures of conductors shall be used
unless specified otherwise in the Project Specification:
Phase conductors +60 °C,
Earth wires +40 °C.
(NCPT) EE.2 Temperature at short circuit conditions
The maximum temperature for aluminium and aluminium-alloyed conductors in aerial
insulated cable systems or covered conductor systems shall not exceed the maximum
permitted temperature of the insulation material. The overhead line fittings shall not be
affected by this maximum temperature.

5.6.3 Wind loads for determination of electric clearances
5.6.3.1 Wind load cases
(snc) EE.1 Temperatures of conductor under wind load
The design temperatures of the conductor under nominal wind load and under extreme
wind load shall be taken as –5 °C and +15 °C.
5.6.4 Ice loads for the determination of electric c
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