Bsi bs en 50341 2 19 2015

Symbol Signification References bemp Minimum clearance between conductors within the span cemp Constant in empirical formula for the minimum clearance between Del1 Minimum clearance r

BSI Standards Publication

Overhead electrical lines

Part 2-19: National Normative Aspects (NNA) for CZECH REPUBLIC

National foreword

This British Standard is the UK implementation of EN 50341-2-19:2015

This standard, together with the following list of National Normative Aspect standards, supersedes BS EN 50423-3:2005 and BS EN 50341-3:2001:

BS EN 50423-3:2005 and BS EN 50341-3:2001 will be withdrawn upon publication of the rest ofthe series

The UK participation in its preparation was entrusted to Technical Committee PEL/11, OverheadLines

A list of organizations represented on this committee can be obtained on request to its secretary

This publication does not purport to include all the necessary provisions of a contract Users areresponsible for its correct application

© The British Standards Institution 2015

Published by BSI Standards Limited 2015ISBN 978 0 580 90341 0

ICS 29.240.20

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy andStrategy Committee on 30 June 2015

Amendments/corrigenda issued since publication

Date Text affected

Compliance with a British Standard cannot confer immunity from legal obligations

NORME EUROPÉENNE

English Version

Overhead electrical lines exceeding AC 1 kV - Part 2-19:

National Normative Aspects (NNA) for CZECH REPUBLIC

(based on EN 50341-1:2012)

This European Standard was approved by CENELEC on 2015-04-07

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

Contents

Page

1 Scope 7

1.1 General 7

1.2 Field of application 7

2 Normative references, definitions and symbols 7

2.1 Normative references 7

2.2 Definitions 10

2.3 Symbols 10

3 Basis of design 12

3.2.2 Reliability requirements 12

3.2.5 Strength coordination 12

3.2.6 Additional considerations 12

4 Actions on lines 13

4.3 Wind loads 13

4.3.1 Field of application and basic wind velocity 13

4.3.2 Mean wind velocity 13

4.3.3 Mean wind pressure 13

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 14

4.4.3 Wind forces on lattice towers 15

4.4.4 Wind forces on poles 15

4.5 Ice loads 15

4.5.1 General 15

4.6 Combined wind and ice loads 16

4.6.1 Combined probabilities 16

4.6.2 Drag factors and ice densities 17

4.6.5 Wind forces on support for ice covered conductors 17

4.6.6 Combination of wind velocities and ice loads 17

4.7 Temperature effects 18

4.8 Security loads 18

4.8.1 General 18

4.8.2 Torsional loads 18

4.8.3 Longitudinal loads 19

4.9 Safety loads 19

4.9.1 Construction and maintenance loads 19

4.9.2 Loads related to the weight of linesmen 19

4.10 Forces due to short-circuit currents 19

4.11 Other special forces 20

4.11.1 Avalanches, creeping snow 20

4.11.2 Earthquakes 20

4.12 Load cases 20

4.12.1 General 20

4.12.2 Standard load cases 20

4.13 Partial factors for actions 22

5 Electrical requirements 25

5.3 Insulation coordination 25

5.4 Classification of voltages and overvoltages 25

5.4.2 Representative power frequency voltages 25

5.5 Minimum air clearance distances to avoid flashover 26

5.5.2 Application of the theoretical method in Annex E 26

5.5.3 Empirical method based on European experience 26

5.6 Load cases for calculation of clearances 27

5.6.2 Maximum conductor temperature 27

5.6.3 Wind loads for determination of electric clearances 27

5.6.4 Ice loads for determination of electric clearances 28

5.6.5 Combined wind and ice loads 29

5.7 Coordination of conductor positions and electrical stresses 30

5.8 Internal clearances within the span and at the top of support 30

5.9 External clearances 33

5.9.1 General 33

5.9.2 External clearances to ground in areas remote from buildings, roads, etc 34

5.9.3 External clearances to residential and other buildings 34

5.9.4 External clearances to crossing traffic routes 36

5.9.5 External clearances to adjacent traffic routes 38

5.9.6 External clearances to other power lines or overhead telecommunication lines 38

5.10 Corona effect 40

5.10.1 Radio noise 40

5.11 Electric and magnetic fields 40

5.11.1 Electric and magnetic fields under a line 40

5.11.2 Electric and magnetic field induction 40

5.11.3 Interference with telecommunication circuits 40

6 Earthing systems 41

6.1 Introduction 41

6.1.2 Requirements for dimensioning of earthing systems 41

6.1.3 Earthing measures against lightning effects 41

6.1.4 Transferred potentials 42

6.2 Ratings with regard to corrosion and mechanical strength 43

6.2.1 Earth electrodes 43

6.2.2 Earthing and bonding conductors 43

6.4 Dimensioning with regard to human safety 43

6.4.1 Permissible values for touch voltages 43

6.4.3 Basic design of earthing systems with regard to permissible touch voltage 43

7 Supports 44

7.3 Lattice steel towers 44

7.3.6 Ultimate limit states 44

7.3.7 Serviceability limit states 44

7.3.8 Resistance of connections 44

7.3.9 Design assisted by testing 44

7.4 Steel poles 45

7.4.6 Ultimate limit states (EN 1993-1-1:2005 – Chapter 6) 45

7.4.7 Serviceability limit states (EN 1993-1-1:2005 – Chapter 7) 45

7.4.8 Resistance of connections 45

7.4.9 Design assisted by testing 45

7.5 Wood poles 45

7.5.5 Ultimate limit states 45

7.5.6 Serviceability limit states 45

7.5.7 Resistance of connections 45

7.5.8 Design assisted by testing 46

7.6 Concrete poles 46

7.6.4 Ultimate limit states 46

7.6.5 Serviceability limit states 46

7.6.6 Design assisted by testing 46

7.7 Guyed structures 46

7.7.4 Ultimate limit states 46

7.7.5 Serviceability limit states 47

7.9 Corrosion protection and finishes 47

7.9.1 General 47

7.10 Maintenance facilities 47

7.10.1 Climbing 47

7.10.2 Maintainability 47

7.10.3 Safety requirements 47

8 Foundations 47

8.1 Introduction 47

8.2 Basis of geotechnical design (EN 1997-1:2004 – Section 2) 47

8.2.2 Geotechnical design by calculation 47

8.3 Soil investigation and geotechnical data (EN 1997-1:2004 – Section 3) 47

9 Conductors and earth-wires 48

9.1 Introduction 48

9.2 Aluminium based conductors 48

9.2.2 Electrical requirements 48

9.2.3 Conductor service temperatures and grease characteristics 49

9.2.4 Mechanical requirements 49

9.2.5 Corrosion protection 49

9.2.6 Test requirements 49

9.3 Steel based conductors 50

9.3.1 Characteristics and dimensions 50

9.3.3 Conductor service temperatures and grease characteristics 50

9.3.4 Mechanical requirements 50

9.3.5 Corrosion protection 51

9.3.6 Test requirements 51

9.4 Copper base conductors 51

9.5 Conductors and ground wires containing optical fibre telecommunication circuits 51

9.5.1 Characteristics and dimensions 51

9.5.2 Electrical requirements 51

9.5.3 Conductor service temperatures 51

9.5.4 Mechanical requirements 51

9.6 General requirements 52

9.6.2 Partial factor for conductors 52

9.6.3 Minimum cross-sections 52

9.6.4 Sag – tension calculations 52

10 Insulators 52

10.1 Introduction 52

10.4 Pollution performance requirements 52

10.5 Power arc requirements 53

10.7 Mechanical requirements 53

10.10 Characteristics and dimensions of insulators 53

10.11 Type test requirements 54

10.11.1 Standard type tests 54

10.11.2 Optional type tests 54

11 Hardware 54

11.1 Introduction 54

11.6 Mechanical requirements 54

12 Quality assurance, checks and taking-over 55

Annex H/CZ (informative) 55

Installation and measurements of earthing systems 55

H.2 Basis for the verification 55

H.2.2 Resistance to earth 55

H.3 Installation of earth electrodes and earthing conductors 55

H.3.1 Installation of earth conductors 55

H.4 Measurements for and on earthing systems 55

H.4.4 Determination of the earth potential rise 55

H.4.5 Reduction factor related to earth wires of overhead lines 56

Annex M/CZ (informative) 56

Geotechnical and structural design of foundations 56

M.1 Typical values of the geotechnical parameters of soils and rocks 56

M.1.3 Symbols, definitions and units of some ground parameters 56

M.3 Sample semi-empirical models for resistance estimation 62

M.3.1 Geotechnical design by calculation 62

Annex S/CZ (informative) 63

Map of icing zones in the Czech Republic 63

Foreword

1 The Czech National Committee (NC) is identified by the following address :

CZECH OFFICE FOR STANDARDS, METROLOGY AND TESTING email: unmz@unmz.cz

Czech Republic

2 The Czech National Committee has prepared this Part 2−19 (EN 50341-2-19) listing the Czech National Normative Aspects (NNA) under its sole responsibility and duly passed this document through the CENELEC and CLC/TC11 procedures

co-ordination of this EN 50341-2-19 with EN 50341-1 It has performed the necessary checks in the frame of quality assurance/control However, it is noted that this quality assurance/control has been made in the

laws/regulations

3 This EN 50341-2-19 is normative in the Czech Republic and informative for other countries

4 This EN 50341-2-19 has to be read in conjunction with EN 50341-1, hereinafter referred as Part 1 All clause numbers used in Part 2−19 correspond to those of Part 1 Specific subclauses which are prefixed CZ are to be read as amendments to the relevant text in Part 1 Any necessary clarification regarding the application of Part 2−19 in conjunction with Part 1 shall be referred to the Czech Office for Standards, Metrology and Testing that will, in co-operation with CLC/TC11, clarify the requirements When no reference is made in Part 2−19 to a specific subclause, then Part 1 applies

5 In the case of “boxed values“ defined in Part 1, amended values (if any) which are defined in Part 2−19 shall be taken into account in the Czech Republic

However, any “boxed values” whether in Part 1 or Part 2-19, shall not be amended in direction of greater risk in the Project Specification

6 The national Czech standards/regulations, regarding overhead lines exceeding 1 kV AC, are listed

in 2.1/CZ.2 and 2.1/CZ.3

Standards as soon as they become available and are declared by the Czech Office for Standards, Metrology and Testing to be applicable and thus reported to the secretary of CLC/TC11

1 Scope

1.1 General

The new overhead line is considered a brand new electric overhead line with nominal voltage exceeding 1 kV AC, between the points A and B

The new branch line of the existing overhead line shall be considered a new overhead line except for a junction support for which the specific requirements shall be defined in the Project Specification

The extent of application of this standard in respect of reconstruction, relaying and extension

of existing overhead lines shall be determined in the Project Specification Simultaneously, the Project Specification shall determine, which of the previous national standards shall be used and to what extent they shall be used for the project in question

Provisions of this standard also apply to the telecommunication equipment and devices (aerials, dish antennas, etc.) which are installed on individual supports of overhead power lines, especially in terms of wind and ice loads on such installed equipment Design and installation has to respect requirements of the utility operating the line in question The design of such telecommunication equipment has to incorporate such technical solutions and such precautions, which shall allow safe access and maintenance of both a power line and telecommunication equipment, and which shall provide protection of persons performing repairs or maintenance of the power line and/or telecommunication equipment against electric shock and protection of telecommunication equipment and attached installations against the influence of the power line (short-circuits, switching and lightning overvoltages etc.)

2 Normative references, definitions and symbols

2.1 Normative references

National laws, Government regulations and other binding regulations are included in following 2.1/CZ.2 International and national standards quoted in EN 50341-2-19 and not included in 2.1 EN 50341-1 are included in 2.1/CZ.3

The set of standards included in 2.1 EN 50341-1 under a common title of Eurocodes is valid

in the Czech Republic including the Czech National Application documents related to relevant standards, unless EN 50341-1 and/or these Czech National Normative Aspects (EN 50341-2-19) specify otherwise

NOTE Some EN, IEC, ISO and CISPR International Standards and publications implemented as Czech National Standards – ČSN EN, ČSN IEC, ČSN ISO and ČSN CISPR – include informative notes and informative annexes useful in the Czech Republic

(A-dev) CZ.2 National laws, government decrees and other binding rules of law

Inland Navigation Act

provozu v přístavech, společné havárii a dopravě nebezpečných věcí

Regulation of the Ministry of Transport on Waterways, Navigable operation in Harbors, Common collapse and the transport of dangerous goods

Decree of the government on health protection against ionizing radiation

v energetických odvětvích a o změně některých zákonů (energetický zákon)

Act on Conditions of Enterprise and on Performance of State Administration in Power Industries and on Alteration of Certain Acts (Energy Act)

Eurocode 1: Action on structures Part 1-4: General actions – Wind Actions (National Annex NA for the Czech Republic, Wind zone map)

ČSN 33 2040:1993 Elektrotechnické předpisy Ochrana před účinky

elektro-magnetického pole 50 Hz v pásmu vlivu zařízení elektrizační soustavy

Electric engineering regulations Protection against effects of the electromagnetic fields 50 Hz in the zone of influence of electric power system device

ČSN 33 2160:1993 Elektrotechnické předpisy Předpisy pro ochranu sdělovacích

vedení a zařízení před nebezpečnými vlivy trojfázových vedení

vn, vvn a zvn

Electric engineering regulations Rules for the protection of telecommunication lines and equipment against dangerous influences of three-phase high voltage, very high voltage and ultra high voltage lines

ČSN 33 2165 ed.2:2014 Elektrotechnické předpisy Zásady pro ochranu ocelových

izolovaných potrubí uložených v zemi před nebezpečnými vlivy venkovních trojfázových vedení a stanic vvn a zvn

Electric engineering regulations Principles for protection of buried insulated steel pipelines against dangerous effects of very high voltage overhead lines and very high voltage stations

Reference Title

ČSN 34 1530:2010 Drážní zařízení − Elektrická trakční vedení železničních drah

celostátních, regionálních a vleček Railway applications – The catenary for electrified railways

Fire protection of buildings - General requirements

Road earthwork - Design and execution

EN 13501-1:2007

+A1:2009 Požární klasifikace stavebních výrobků a konstrukcí staveb – Část 1: Klasifikace podle výsledků zkoušek reakce na oheň

Fire classification of construction products and building elements

- Part 1:Classification using data from reaction to fire tests

Earthing of power installations exceeding 1 kV AC

ČSN EN 61936-1:2011 Elektrické instalace nad AC 1 kV − Část 1: Všeobecná pravidla

(Národní příloha NA – odrušení vedení a rozvoden vn, vvn a zvn – přípustné meze vf šumu)

Power installations exceeding 1 kV AC – Part 1: Common rules (National Annex NA – Disturbance elimination for lines and substations of high voltage, extra high voltage and ultra high voltage – allowed high-frequency noise limits

nebezpečí života

Protection against lightning – Part 3: Physical damage to structures and life hazard

EN ISO 14688-1:2002

+A1:2013 Geotechnický průzkum a zkoušení − Pojmenování a zatřiďování zemin−Část 1: Pojmenování a popis

Geotechnical investigation and testing - Identification and classification of soil - Part 1: Identification and description

EN ISO 14688-2:2004

+A1:2013 Geotechnický průzkum a zkoušení - Pojmenování a zatřiďování zemin - Část 2: Zásady pro zatřiďování

Geotechnical investigation and testing - Identification and classification of soil - Part 2: Principles for a classification

EN ISO 14689-1:2003 Geotechnický průzkum a zkoušení - Pojmenování a zatřiďování

hornin - Část 1: Pojmenování a popis

Geotechnical investigation and testing - Identification and classification of rock - Part 1: Identification and description

Concrete - Specification, performance, production and conformity

ČSN 73 1001:1988

(withdrawn 1.4.2010) Zakládání staveb Základová půda pod plošnými základy Foundation of structures Subsoil under shallow foundations

ČSN 73 3050:1987

(withdrawn 1.3.2010) Zemné práce Všeobecné ustanovenia Earth works General requirements

CIGRE TB 207:2002 CIGRÉ technical brochure No 207 “Thermal behaviour of

overhead conductors”

CIGRE TB 273:2005 CIGRÉ technical brochure No 273 “Overhead conductor safe

design tension with respect to Aeolian vibrations”

2.2 Definitions

part of a line between attachment points of a conductor on two consecutive supports

(IEV 466-03-01)

Czech conversion used in ČSN IEC 50 (466) which means “a span length”

wire or cable line and telecommunication equipment leading above ground and outside buildings and transmitting information via electromagnetic waves

bare conductor made of round or shaped wires being concentric lay stranded with alternating

directions of stranding, with grease or not, produced of materials or various materials according to one of following alternatives

− aluminium wires

− aluminium alloy wires

− combination of aluminium wires and aluminium alloy wires

− combination of aluminium wires and steel zinc coated wires

− combination of aluminium wires and aluminium clad steel wires

− combination of aluminium alloy wires and steel zinc coated wires

− combination of aluminium alloy wires and aluminium clad steel wires

bare conductor made of round or shaped wires being concentric lay stranded with alternating

directions of stranding, with grease or not, produced of materials or various materials according to one of following alternatives

− steel zinc coated wires

− aluminium clad steel wires

Symbols which are contained in EN 50341-2-19 and are not contained in EN 50341-1, or which are contained in EN 50341-2-19 also with a different meaning than in 2.3 EN 50341-1, are included below

Symbol Signification References

bemp Minimum clearance between conductors within the span

cemp Constant in empirical formula for the minimum clearance between

Del1 Minimum clearance required to prevent a disruptive discharge

between phase conductor and external object at earth potential during fast front and slow front overvoltages (external clearance)

5.5.3/CZ.1

Del2 Minimum clearance required to prevent a disruptive discharge

between phase conductor and support structure during fast front and slow front overvoltages (internal clearance)

5.5.3/CZ.1

Del3 Minimum clearance required to prevent a disruptive discharge

between phase conductor in window of a support and support structure during fast front and slow front overvoltages (internal clearance)

5.5.3/CZ.1

Del4 Minimum clearance required to prevent a disruptive discharge

between phase conductor and earth wire during fast front and slow front overvoltages (internal clearance)

5.5.3/CZ.1

Dtr Horizontal distance of a tree trunk from the most endangered

hc_tr Height of the most endangered conductor above the horizontal

hpc Mean height of phase conductors of a given circuit on a support 4.4.1.1/CZ.2

IR50 Extreme reference ice load per conductor unit length at 10 m

kemp,

kemp_r

Factor depending on weight and diameter of a conductor and on

Lins Vertical length of that part of insulator set which may swing

r Horizontal distance between the attachment point of a shorter

insulator set and the point in a span, where the distance between conductors is checked

5.8/CZ.1

tI Ice thickness on a conductor with a diameter of 30 mm according to

Urw50Hz Required withstand voltage for power frequency overvoltage 5.3.1/CZ.1

za Depth of geotechnical soil investigation below the foundation base 8.3/CZ.1

αLSL Reduction factor of ice load for longitudinal security loads 4.8.3/CZ.2

3 Basis of design

3.2.2 Reliability requirements

Reliability level 1 (Return period of climatic action 50 years) is considered, unless a higher reliability level is specified in the Project Specification

Depending on their life duration, the return period of climatic actions for temporary lines, with duration less than 1 year, may be reduced due to the shorter exposure to climatic effects Return periods of climatic loads and additional information is given in the following Table 3/CZ.1

Table 3/CZ.1 – Return periods for temporary lines

NOTES

meteorological forecast for the given site

wind speed lower than 20 m/s

3.2.5 Strength coordination

Only strength coordination for the above-ground part of steel structure of lattice tower stub is specified in this standard (see 7.3.6.1/CZ.3) Additional requirements may be given in the Project Specification

3.2.6 Additional considerations

Any further specific requirements, e.g installation of aircraft warning spheres, night aircraft warning markers, fittings preventing biological pollution of insulators, fittings for bird protection etc., shall be specified in the Project Specification

4 Actions on lines

4.3 Wind loads

4.3.1 Field of application and basic wind velocity

The territory of the Czech Republic is divided into five wind zones, for which different basic

wind velocities Vb,0 are defined, as shown in Table 4/CZ.1 Wind zones are shown on Wind zone map of the Czech Republic, that is a part of the National Annex of ČSN EN 1991-1-4:2007 and a part of English version of the National Annex of ČSN EN 1991-1-4 NA ed.A:2013 More accurate information on wind zone borders may be provided by Czech Hydrometeorological Institute

Based on long-term experience of transmission or distribution system operators, certain locations may be in the Project Specification classified into a wind zone with higher basic

wind velocity Vb,0

Table 4/CZ.1 – Basic wind velocities Vb,0

Basic wind velocity

a) Basic wind speed in a given location inside wind zone V shall be specified by a corresponding branch office of Czech Hydrometeorological Institute

4.3.2 Mean wind velocity

Mean wind velocity in the Czech Republic is independent of wind direction The value of

wind directional factor cdir = 1,0 shall be used

The value of orography factor co = 1,0 shall be used, unless otherwise specified in the Project Specification

For elements associated with supports with nominal voltage up to 45 kV and with a

maximum height of 24 m, the value of mean wind velocity Vh(h), calculated at 10 m height

above ground is considered

4.3.3 Mean wind pressure

The air density ρ in formula for calculation of mean wind pressure at a reference height h

according to 4.3.3 is taken as 1,25 kg/m3 independently of air temperature and altitude H

4.4 Wind forces on overhead line components

4.4.1 Wind forces on conductors

4.4.1.1 General

When calculating the wind force on conductor, apart from using a method given in 4.4.1.1, it

is possible to use an alternative calculation method, where the total wind force on conductor, transferred to a support, is specified as a sum of halved wind forces acting on conductor in

both adjacent spans The values of peak pressure qp(h) and structural factor for the conductor Gc are calculated separately for both adjacent spans, while reference height of

conductor above ground h for corresponding span is given as an arithmetic average of the reference heights h on supports, delimiting the span, specified in 4.4.1.1/CZ.2

(ncpt) CZ.2 Reference height of conductor above ground

When calculating the transversal wind forces on conductors, transferred to individual

supports, and when calculating the tensions in conductors, reference heights of conductors h

above ground shall be specified by the method 4 according to 4.4.1.1 or by the alternative method, given below Unless otherwise specified in the Project Specification, the reference heights of conductors may also be determined by the more conservative method 7 according

to 4.4.1.1 or by the alternative method, given below, where the heights of attachment points

of insulator sets at the support are considered instead of the heights of attachment points of conductors For the lines with a nominal voltage up to 45 kV and with supports with a maximum height of 24 m, it is possible to consider for all conductors the same reference height of 10 m

The alternative method

The reference height of conductor above ground h for all phase conductors of the same circuit is considered to be the mean height hpc of the phase conductors of the circuit on a support above ground according to a formula:

hpc = (h1 + h2 + h3)/3 where

h1, h2, h3 are heights of individual conductor attachment points of the circuit on

a support above ground Unless otherwise specified in the Project Specification, the heights of attachment points of insulator sets at the support may be considered instead of the heights of attachment points

of conductors

For the earth wires and for the different circuits, placed one above the other, reference

heights h above ground are calculated separately

If insulator sets on suspension supports allow for equalizing the conductor tensions in adjacent spans, it is possible, when calculating conductor tensions in the line section, to

consider the same reference height h for all conductors of a circuit in all spans of the line section or the same reference height h of an individual conductor in all spans of the line

section However, the chosen reference height h of phase conductors of a considered circuit

shall not be lower than the arithmetic average of the mean heights hpc of phase conductors

of the circuit on all supports of the line section and the chosen reference height h of an individual conductor shall not be lower than the arithmetic average of heights h of the

conductor on all supports of the line section For the lines with a nominal voltage up to 45 kV and with supports with a maximum height of 24 m, it is possible to consider for all conductors the same reference height of 10 m

4.4.1.2 Structural factor

If insulator sets on suspension supports allow for equalizing the conductor tensions in

adjacent spans, structural factor Gc for conductors, when calculating conductor tensions in a line section under wind load, is specified according to 4.4.1.2, where in the formula for the

background factor B2, L m is the length of a line section (but not more than 3 km), and h is the

reference height of a conductor (or conductors) in the line section according to 4.4.1.1/CZ.2

4.4.1.3 Drag factor

The value of drag factor Cc = 1 (Method 1 according to 4.4.1.3) shall be used for commonly used bare stranded conductors, when calculating the wind forces on conductors

The value of drag factor Cc = 1 shall also be used for covered conductors and overhead insulated cable systems

4.4.2 Wind forces on insulator sets

When calculating the loads on supports, wind force on insulator sets without ice load is considered according to 4.4.2 for lines with nominal voltage exceeding 45 kV Unless

otherwise specified in the Project Specification, wind forces on insulator sets may be neglected, provided that the reference heights of conductors are determined by the method 7 according to 4.4.1.1 or by the alternative method given in 4.4.1.1/CZ.2, where the heights of the attachment points of insulator sets at the support are considered

For lines with nominal voltage up to 45 kV, wind force on insulator sets is not considered

4.4.3 Wind forces on lattice towers

4.4.3.1 General

Wind force on lattice towers shall be specified by Method 1 according to 4.4.3.2

4.4.3.2 Method 1

The value of structural factor Gt = 0,9 shall be used when calculating wind forces on lattice towers (tower body as well as crossarms)

For towers of lines with nominal voltage exceeding 45 kV, the reference height above ground

h is equal to the height of the geometrical center of the considered tower section above

ground If the height of the geometrical center of the considered tower section above ground

is less than 10 m, the height of 10 m is taken instead

For towers of lines with nominal voltage up to 45 kV, the reference height of all tower sections is considered to be the same, equal to 60% of the total tower height For towers with the total height up to 24 m, reference height of 10 m is considered for the whole tower Drag factor for a section of a lattice tower with rectangular cross-section shall be specified by

4.4.3.2 However, for towers of lines with nominal voltage up to 45 kV, the value Ct1 = Ct2 = 2,6 shall be used

4.4.4 Wind forces on poles

The value of structural factor Gt = 0,9 and the value of drag factor according to 4.4.4 shall be used when calculating wind forces on poles

For lines with nominal voltage exceeding 45 kV, the reference height above ground shall be determined by Method 1 according to 4.4.4, when calculating wind force on poles

For towers of lines with nominal voltage up to 45 kV, the reference height shall be determined by Method 2 according to 4.4.4 For poles with the total height up to 24 m, reference height of 10 m is considered for the whole pole

For the lines where ice removal during its accretion is expected (e.g wiping, heating, etc.), it

is possible to adequately decrease the ice load

Unless otherwise specified in the Project Specification, the ice load on supports and insulator sets is not considered

For the accessories of larger dimensions, located on conductors, the ice load with a thickness corresponding to the design thickness of ice on the conductor with a diameter of

30 mm in the relevant icing zone is considered

Extreme reference ice load on conductors IR50 with diameter d at height of 10 m above ground is given in the following Table 4/CZ.2

Table 4/CZ.2 – Extreme reference ice load on conductors

Icing zone

Extreme reference ice load IR50 (N/m) per unit length of a conductor with

NOTE 1 For lines with nominal voltage exceeding 45 kV, the ice load in zone I-0 is considered the same as in zone I-1

Extreme ice load per unit length of a conductor I50 (N/m) at height h above ground is

determined by the following formula:

I50 = Klc Kh(h) IR50, where

IR50 extreme reference ice load per unit length of a conductor with diameter d

at height 10 m above ground with return period T = 50 years according to

the table 4/CZ.2;

Klc local condition factor for ice load;

Kh(h) height factor for ice load

For a defined area, it is possible to specify the value of local condition factor for ice load

Klc ≠ 1 in the Project Specification, expressing the deviation from extreme reference ice load

in a given area, based on long-term experience of transmission or distribution system

operator in a given area Unless otherwise specified in the Project Specification, Klc = 1,0

For a defined area, it is possible to specify the value of height factor for ice load Kh(h) > 1 in

the Project Specification, expressing the dependence of extreme ice load on a height above ground, based on long-term experience of transmission or distribution system operator in a

given area Unless otherwise specified in the Project Specification, Kh(h) = 1,0

4.6 Combined wind and ice loads

4.6.1 Combined probabilities

Unless otherwise specified in the Project Specification, only the combination of extreme ice

load IT combined with a high probability wind velocity VIH according to 4.6.6.1 and 4.6.6.1/CZ.1 is considered for lines with nominal voltage up to 45 kV

4.6.2 Drag factors and ice densities

When determining ice loads on line components according to this standard, only in-cloud ice

in the form of rime with a density of ρI = 500 kg/m3 is considered

The value of drag factor for ice covered conductors CIc = 1,1, independently of conductor diameter and the size of ice

When calculating wind forces on iced conductor accessories, the projected area of an

accessory is assumed to be increased by the ice thickness, corresponding to ice thickness tI

on a conductor with a diameter of 30 mm, under the same combination of wind and ice loads and the same conditions, which apply to a conductor, on which the accessory is located, and

the corresponding drag factor CIx for an iced accessory shall be used

4.6.5 Wind forces on support for ice covered conductors

Analogically as with the calculation of wind force on ice-free conductor according to 4.4.1.1/CZ.1, when calculating wind force on ice covered conductor, apart from using a method given in 4.6.5, it is possible to use an alternative calculation method, where the total wind force on ice covered conductor, transferred to a support, is specified as a sum of halved wind forces acting on an iced conductor in both adjacent spans The values of peak

pressure qIp(h) and structural factor for the conductor Gc are calculated separately for both

adjacent spans, while reference height of conductor above ground h for corresponding span

is given as an arithmetic average of the reference heights h on supports, delimiting the span,

specified in 4.4.1.1/CZ.2

4.6.6 Combination of wind velocities and ice loads

4.6.6.1 Extreme ice load I T combined with a high probability wind velocity VIH

associated with icing BI

The values of combination factors for wind loads ΨW

− Permanent lines with nominal voltage exceeding 110 kV ΨW = 0,29;

− Permanent lines with nominal voltage up to and including 110 kV and temporary lines with life duration exceeding 3 days ΨW = 0,25;

− Temporary lines with life duration up to and including 3 days ΨW = 0,22

For permanent lines with nominal voltage exceeding 110 kV, the factor ΨW includes the

effect of reduction factor of wind velocity associated with icing BI = 0,707 (BI2 = 0,50) and the

ratio of nominal wind pressure with the return period T = 3 years to extreme wind pressure with the return period T = 50 years (V3/V50)2 = 0,58

For permanent lines with nominal voltage up to and including 110 kV and for temporary lines with life duration exceeding 3 days, the factor ΨW includes the effect of reduction factor of

wind velocity associated with icing BI = 0,656 (BI2 = 0,43) and the ratio of nominal wind

pressure with the return period T = 3 years to extreme wind pressure with the return period T

= 50 years (V3/V50)2 = 0,58

For temporary lines with life duration up to and including 3 days, the factor ΨW includes the

effect of reduction factor of wind velocity associated with icing BI = 0,656 (BI2 = 0,43) and the

ratio of wind pressure with the return period T = 2 years to extreme wind pressure with the return period T = 50 years (V2/V50)2 = 0,52

Higher values of reduction factor of wind velocity associated with icing BI and combination factor for wind loads ΨW may be specified in the Project Specification

4.6.6.2 Nominal ice load I3 combined with a low probability wind velocity VIL

The value of combination factor for ice loads, corresponding to nominal ice load with return

period T = 3 years, ΨI = 0,35

When combined with nominal ice load I3, low probability wind velocity VIL is equal to the

extreme wind velocity with the return period T according to a selected reliability level VT,

multiplied by the reduction factor of wind velocity associated with icing BI For the values of

(a) The minimum temperature with no other climatic loads is −30 °C for reliability level 1,

−35 °C for reliability level 2 and −40 °C for reliability level 3, unless a different temperature with respect to local conditions is given in the Project Specification

(b) A temperature of −5 °C is assumed under extreme wind speed

(c) Nominal wind speed combined with minimum temperature is not considered, unless otherwise specified in the Project Specification If this design situation is required, the Project Specification shall also specify the respective minimum temperature

(d) A temperature of −5 °C is assumed under ice load

(e) A temperature of −5 °C is assumed under combined wind and ice loads

(f) Average temperature in the coldest month of the year is taken as −5 °C

Relevant temperatures to check clearances are specified in Clause 5 of this part of the Standard

4.8 Security loads

4.8.1 General

Security loads for supports of lines with nominal voltage up to 45 kV are not considered, unless otherwise specified in the Project Specification If security loads for supports are required, conditions for their calculation shall also be specified in the Project Specification

4.8.2 Torsional loads

The residual static load at any one earth wire or phase conductor attachment point, resulting from the release of the tension of a phase conductor or sub-conductor or of an earth wire in

an adjacent span shall be applied Tension release in such conductor and in such span of the two adjacent spans giving the maximum loading effect in any individual member of the structure and/or foundation shall be considered

For circuits with bundle conductors, tension release in one sub-conductor of a bundle is considered for suspension and non-section tension supports, and tension release in all sub-conductors of a bundle for section and terminal (dead-end) supports is considered

The Project Specification may define more severe requirements, i.e tension release in several sub-conductors of a bundle, or simultaneous release of tension in several conductors

Loads on supports and conductor tensions are calculated at the conductor temperature

of −5 °C, no wind load, and with loads on conductors by reduced ice, which for permanent

lines corresponds to the extreme ice load with the return period 50 years I50 according to 4.5.1/CZ.3, multiplied by reduction factor αTSL For lines with nominal voltages up to and

including 110 kV, the value of the reduction factor is αTSL = 0,4, for lines with rated voltages

of 220 and 400 kV, the value of the reduction factor is αTSL = 0,5 The weight of the ice deposit on insulator sets is not considered The same conditions apply to other unreleased conductors

When calculating torsional security loads for supports of temporary lines, extreme ice load

with a return period T years IT = γI I50, where the partial factor for an ice action γI depends on the life duration of a temporary line according to 4.13/CZ.2, is multiplied by a reduction factor

exceeding 45 kV

Longitudinal loads for section supports are based on one-sided release of tension in all conductors in that of the adjacent spans, leading to higher loads

Loads on supports and conductor tensions are calculated at a conductor temperature of

−5 °C, without any wind load, and with loads on conductors by reduced ice, which for

permanent lines corresponds to the extreme ice load with the return period 50 years I50

according to 4.5.1/CZ.3, multiplied by a reduction factor αLSL = 0,5 The weight of the ice deposit on insulator sets is not considered Higher ice load may be specified in the Project Specification

When calculating longitudinal security loads for section supports of temporary lines, extreme

ice load with a return period T years IT = γI I50, where the partial factor for an ice action γI

depends on the life duration of a temporary line according to 4.13/CZ.2, is multiplied by a reduction factor αLSL = 0,5

The vertical loads on the support do not include the weight of insulator sets, conductors and ice on the conductors from the span, where the release of conductor tensions is considered

4.9 Safety loads

4.9.1 Construction and maintenance loads

Requirements for construction and maintenance loads shall be specified in the Project Specification

4.9.2 Loads related to the weight of linesmen

Characteristic construction and maintenance loads, acting on crossarms for single conductors and earth wires shall not be less than 1,0 kN, on crossarms for bundled conductors less than 2,0 kN

Concurrent permanent load is considered at temperatures of −20 °C and +40 °C

More severe conditions may be specified in the Project Specification

4.10 Forces due to short-circuit currents

Unless otherwise specified in the Project Specification, forces due to short-circuit currents are not considered

4.11 Other special forces

4.11.1 Avalanches, creeping snow

Unless otherwise specified in the Project Specification, forces acting on lines, due to avalanches or creeping snow, are not considered

4.11.2 Earthquakes

Additional loads resulting from an earthquake or seismic tremors, may occur only in seismically very active or undermined areas They are considered only if required in the Project Specification

4.12 Load cases

4.12.1 General

Standard load cases are listed in 4.12.2/CZ.1

In cases where an external load component decreases the stress in a particular member or a cross-section (e.g ice load on the middle conductor in the gantry of a support with horizontal arrangement of phase conductors), special load case(s) with a reduced component of that load shall be defined in the Project Specification

If a double or a multiple insulator set is to be attached to the support structure of line with nominal voltage exceeding 45 kV at two or more attachment points, the release of load from one attachment point of the insulator set shall be investigated In this case, all remaining attachment points of the insulator set are considered to be loaded by forces transferred from the phase conductor and the insulator set itself at the maximum load resulting from the load cases 1, 3a and 4 according to Table 4/CZ.3 Neither reduction of static tension in the conductor nor dynamic effects from the string failure are considered Forces resulting from the same load cases are acting at attachment points of other insulator sets

Conditions for the verification of strength of insulators and insulator sets fittings for the failure

of one string of a multiple set are specified in 10.7/CZ.3 and 11.6/CZ.2

Where criteria for the verification of serviceability limit states are given in clause 7 of this standard or in the Project Specification, load cases selected from the load cases specified in 4.12.2/CZ.1 are used for the verification Climatic loads and temperatures, specified for the reliability level 1, are used for the verification of serviceability limit states It shall also be determined in Clause 7 and in the Project Specification, which of the specified load cases shall be used for such verification

4.12.2 Standard load cases

Standard load cases are given in table 4/CZ.3, which replaces table 4.6 in 4.12.2 All specified load cases shall be used for supports, unless otherwise specified in notes in Table 4/CZ.3

Characteristic ice load is replaced by extreme ice load in items (b), (c) and (d) in 4.12.2 Unbalanced wind load according to item (a) and combined unbalanced wind and ice load according to item (e) is not considered, unless otherwise specified in the Project Specification

Load cases for junction supports are based on standard load cases given in Table 4/CZ.3 Additional information on load arrangement and specific requirements shall be given in the Project Specification

If special supports are required, requirements shall be specified in the Project Specification

Table 4/CZ.3 – Standard load cases

2a Uniform extreme ice load (IT)

2b Uniform ice load, transversal bending

− Uniform extreme ice load (IT)

− Wind load with high probability wind velocity VIH

(for the values of ΨW see 4.6.6.1/CZ.1 and tables 4/CZ.4 and 4/CZ.5)

− Uniform nominal ice load (I3 = 0,35 I50)

− Wind load with low probability wind velocity VIL

(for the values of BI and BI2 see 4.6.6.2/CZ.1)

3)

4 Minimum temperature without other climatic loads

5a Security loads, torsional bending

− Tension release in conductor or bundle sub-conductor under reduced ice load according to 4.8.2/CZ.1

(for permanent lines αTSL I50, for temporary lines αTSL γI I50)

3)

5b Security loads, longitudinal bending

− Unbalanced tensions of all conductors resulting from fictitious overload equal to the self-weight of conductors in all spans in one direction from the support according to 4.8.3/CZ.1

4)

5c Security loads, longitudinal bending

− Tension release in all conductors in one direction from the support under reduced ice load according to 4.8.3/CZ.2

(for permanent lines αLSL I50, for temporary lines αLSL γI I50)

5)

6a Safety loads, construction and maintenance loads

6b Safety loads, loads due to the weight of linesmen Temperature of −5 °C is considered for all load cases, except for load case 4

NOTES

1) Considered only when required in the Project Specification

2) Considered for lines with bundle conductors, for lines with single conductors only considered

when required in the Project Specification

3) For lines with nominal voltage up to 45 kV only considered when required in the Project

In load cases with unbalanced ice load (2c, 2d), the relevant reduced ice loads α1 IT and α3 IT

are always considered in all spans in one direction from the support

4.13 Partial factors for actions

for permanent lines

Values of partial factors for actions γF, combination factors for wind actions ΨW and ice actions ΨI, squared value of reduction factor for wind velocity associated with icing BI2 and values of reduction factors α for ice loads for verification of permanent lines in ultimate limit states, are given in Table 4/CZ.4, which replaces table 4.7

for temporary lines

Values of partial factors for actions γF, combination factors for wind actions ΨW and ice actions ΨI, squared value of reduction factor for wind velocity associated with icing BI2 and values of reduction factors α for ice loads for verification of temporary lines in ultimate limit states, are given in Table 4/CZ.5, which replaces table 4.7

5 Electrical requirements

5.3 Insulation coordination

Required withstand voltages are given in Table 5/CZ.1

Table 5/CZ.1 – Required withstand voltages

Highest system voltage

Us

(kV)

Urw50Hz

wet (kV)

UrwLI

dry (kV)

UrwSI

wet (kV)

the line for reduction of atmospheric and switching overvoltages

exceeding 45 kV

For insulator strings, selected in terms of heavy pollution, that are longer than the ones

selected in terms of insulation co-ordination, the co-ordination spark gaps shall be used to

hold the withstand voltages in required limits, according to Table 5/CZ.2, or external

clearances to persons or objects shall be greater than 1,1⋅asom (see 5.9.1/CZ.4)

Table 5/CZ.2 – Required withstand voltages of insulator sets

Highest system voltage

Us

(kV)

Urw50Hz

wet (kV)

UrwLI

dry (kV)

UrwSI

wet (kV)

reduction of atmospheric and switching overvoltages

5.4 Classification of voltages and overvoltages

5.4.2 Representative power frequency voltages

equipment

Nominal system voltages, highest system voltages and highest voltages for equipment are

given in Table 5/CZ.3

Table 5/CZ.3 Nominal system voltages, highest system voltages and highest voltages

for equipment Nominal system voltage Highest system voltage Highest voltage for

5.5 Minimum air clearance distances to avoid flashover

5.5.2 Application of the theoretical method in Annex E

For the determination of minimum clearances, the method based on the long-term experience with clearances verified in operation, calculation analyses according to Annex E and results of experiments was used Clearances are considered to be empirical

5.5.3 Empirical method based on European experience

Minimum clearances Del and Dpp are given in Table 5/CZ.4, which replaces Table 5.6

Table 5/CZ.4 – Minimum clearances Del and Dpp

Highest system voltage

U S

(kV)

Del1

(m) external

Del2

(m) internal conductor − structure

Del3

(m) internal conductor − structure (in window)

Del4

(m) internal conductor − earth wire

Dpp 1)

(m) internal and external conductor − conductor

line of electrical system For electric circuits of different utilities, greater clearances might be determined

required withstand voltages levels, given in Table 5/CZ.1 and Table 5/CZ.2, or if appropriate measures are adopted to lower maximum overvoltage values to the values of withstand voltages

NOTE

according to this table

For lines with nominal voltage up to 45 kV, Del = 0,6 m shall be used for the verification of

clearances to ground and crossed objects and Dpp = 0,7 m for the crossings with other lines

with nominal voltage up to 45 kV

Minimum air clearances to withstand power frequency voltages at extreme wind load are

specified in Table 5/CZ.5, which replaces Table 5.5

Table 5/CZ.5 Minimum clearances D50Hz_p_e and D50Hz_p_p

5.6 Load cases for calculation of clearances

5.6.2 Maximum conductor temperature

Maximum design temperature of phase conductors for the verification of minimum internal

and external clearances shall be given in the Project Specification Conditions for the

determination of maximum design temperature of phase conductors are given in 9.2.2/CZ.1

When checking internal and external clearances under maximum conductor temperature,

temperature of conductors of other circuits or other lines (including earth wires and other

conductors) is assumed to be +40 °C, unless a lower temperature is specified in the Project

Specification

(e.g short-circuit), unless otherwise specified in the Project Specification

Conditions for the verification of clearances under minimum conductor temperature:

− conductor temperature −30 °C,

− no wind action,

− no ice

This load case is used to check internal clearances on a support and to check external

clearances in case of undercrossing

5.6.3 Wind loads for determination of electric clearances

5.6.3.1 Wind load cases

Conditions for the verification of clearances under still air:

− conductor temperatures −5 °C and maximum design temperature

5.6.3.2 Nominal wind loads for determination of internal and external clearances

Conditions for the verification of clearances under nominal wind load according to 5.6.3.2:

− conductor temperatures −5 °C and +40 °C,

− no ice

Minimum external clearances under wind actions from still air to nominal wind load shall comply with the values of minimum external clearances specified in the following subclauses

Conditions for the verification of clearances under unequal wind load:

− conductor temperatures −5 °C and +40 °C,

− no ice,

perpendicular to the conductor, corresponding to wind pressure from 0 to mean wind pressure with a three year return period (qh CT2),

− simultaneously, wind force acting on the other conductor due to wind, blowing in the same direction as on the first conductor, corresponding to mean wind pressure, always by 36 % lower than the wind pressure acting on the first conductor

This load case is used to check internal clearances between conductors and external clearances in case of crossing and parallel lines

account the influence of angle of incidence between the wind direction and the normal to the conductor, to which wind direction is not perpendicular, when calculating wind load on this conductor

5.6.3.3 Extreme wind loads for determination of internal clearances

Conditions for the verification of clearances under extreme wind load according to 5.6.3.3:

− conductor temperatures −5 °C and +40 °C,

− no ice, This load case is used to check internal clearances within the span and at the top of support according to 5.8

5.6.4 Ice loads for determination of electric clearances

Conditions for the verification of clearances under uniform ice load:

− conductor temperature −5 °C,

− no wind action,

− extreme ice load with 50-year return period

Conditions for the verification of clearances under non-uniform ice load :

When checking internal clearances between conductors (if required in the Project Specification) and when checking external clearances in case of parallel lines, required clearance shall be kept under 50% of extreme ice load on upper conductor in any single span, while bottom conductor is without ice

When checking external clearances, this load case is only applicable in spans, where

conductor is at least on one end of the span attached to a suspension insulator set, capable

of swinging in the line direction

Case B

The load case is used for checking external clearances in case of crossing and parallel lines

and for checking internal clearances between conductors of the same circuit or different

circuits (if required in the Project Specification) When checking external clearances, the load

case is only applicable for a span, where bottom conductor is at least on one end of the span

attached to a suspension insulator set, capable of swinging in the line direction

In case of crossing, 50% of extreme ice load on upper line’s conductors is considered in all

spans and simultaneously 50% of extreme ice load on bottom line’s conductors is

considered in all but the crossing span, where ice is not considered

When checking internal clearances between conductors (if required in the Project

Specification) and when checking external clearances in case of parallel lines, required

clearance shall be maintained under 50% of extreme ice load on upper conductor in all

spans and simultaneously under 50% of extreme ice load on lower conductor in all spans

except any one span of the line section, where ice is not considered

kV

If required in the Project Specification, this load case is considered for lines with suspension

insulators Conditions and requirements on minimum external clearances shall be specified

in the Project Specification if such verification is required

5.6.5 Combined wind and ice loads

Conditions for the verification of clearances under combined wind and ice load:

− conductor temperature −5 °C,

− extreme ice load on conductors with return period 50 years,

− wind load on ice covered conductors with wind velocity from 0 up to the high

probability mean wind velocity combined with ice (Vh CT Bl), while structural factor for

conductors Gc is taken equal to 1

This load case is used for the verification of external clearances when the sag of conductors

under considered ice is greater than the sag under conductor temperature +40 °C The same

minimum clearances from the surface of iced conductors as under nominal wind load apply

for this load case

Conditions for the verification of clearances under combined ice and unequal wind load:

− conductor temperature −5 °C,

− extreme ice load with return period 50 years on conductors of upper line, conductors

of bottom line without ice,

− wind force acting on one conductor due to wind, blowing in direction perpendicular to the conductor, corresponding to wind speed from 0 to the high probability mean wind

velocity combined with ice (Vh CT Bl), while structural factor for conductors Gc is taken equal to 1,

− simultaneously, wind force acting on the other conductor due to wind, blowing in the same direction as on the first conductor, corresponding to mean wind speed, always

by 20 % lower than the wind speed acting on the first conductor

This load case is used for the verification of external clearances between conductors of

different lines in a case of crossing or parallel lines The same minimum clearances from the

surface of iced conductors as under nominal wind load apply for this load case

5.7 Coordination of conductor positions and electrical stresses

Subclause 5.7 does not apply to lines with nominal voltage up to 45 kV, where internal

clearances are derived from values Dpp and Del even under extreme wind load

5.8 Internal clearances within the span and at the top of support

The value of reduction factor k1 in 5.8 in Tables 5.8 and 5.9 is 0,7, unless a higher value is specified in the Project Specification for clearances between phase conductors of different circuits of the same utility

Internal clearances Del and Dpp in Tables 5.8 and 5.9 are represented by relevant clearances

Del1, Del2, Del3, D el4 and Dpp given in 5.5.3/CZ.1 in Table 5/CZ.4

clearances

For lines with nominal voltage exceeding 45 kV, clearances for still air without ice shall be applied even under wind with mean speed up to 10 m/s

Unless otherwise specified in the Project Specification, minimum internal clearances Del,

specified in Table 5.8, are reduced by reduction factor k1= 0,7 under minimum conductor temperature according to 5.6.2/CZ.2

For load case Unequal wind load according to 5.6.3.2/CZ.2, the same reduced clearances

k1 Del and k1 Dpp with value k1=0,7 as for load case Nominal wind load apply, unless more strict requirements on clearances between phase conductors of different circuits are

specified in the Project Specification, i.e 0,7 < k1 ≤ 1

If internal clearances between phase conductors and earth wires, between phase conductors

of the same circuit, or phase conductors of different circuits of the same utility are required to

be checked under non-uniform ice load according to 5.6.4/CZ.2 in the Project Specification,

minimum internal clearances Dpp and Del4 may be lowered by reduction factors k1, whose values shall be specified in the Project Specification

This subclause replaces subclause F.1 of annex F

Minimum clearance between two conductors with equal cross-sections, composition and sags under still air, calculated according to the following method ensures, that clearances between conductors under wind action would not be violated

Between bare phase conductors, between bare phase conductors and earth wires, and

between bare phase conductors of different circuits, at least a distance bemp according to the following equations has to be maintained in mid-span:

pp ins

f is the conductor sag (m) at temperature + 40 °C,

Lins is the vertical length of the suspension insulator set which may swing in the direction perpendicular to the line (m) If lengths of insulator sets on both supports

of the span are different, their arithmetic mean is put into the equation For insulator sets, which cannot swing in the direction perpendicular to the line axis, for

tension insulator sets, insulator crossarms and line post insulators Lins = 0 is taken

If values of Lins are different for the two conductors, higher value of Lins shall be used,

Dpp according to Table 5/CZ.4 When checking clearances between phase conductors

of different circuits operating at different nominal voltages, the distance Dpp

corresponding to the higher voltage shall be taken,

Del4 according to Table 5/CZ.4,

cemp is a constant For verification of internal clearances cemp = 0,6 A higher value may

be specified in the Project Specification (e.g for clearances between conductors of different circuits),

kemp is a factor depending on conductor weight and mutual position of both conductors according to a formula:

= δ cos 2 δ 0 , 5 sin 2 δ

50 1 1 , 2 7 , 5 200

/ 1 54 ,

Figure 5/CZ.1 Angle between conductors

according to the above-specified empirical relations, may not be lower than the minimum

clearance between conductors Dpp, or Del4 according to Table 5/CZ.4

Minimum clearances between covered conductors within the span are specified as 1/3 of the

distance bemp, calculated for a line with bare conductors

with different cross-sections, materials, sags or mutual positions on supports

In case of conductors with different cross-sections, materials or sags, it is possible to

calculate the clearances between the two conductors according to 5.8/CZ.3 Clearances bemp

are calculated separately for each conductor with corresponding values kemp and (f + Lins)

Higher of the two values bemp calculated for both conductors is selected

If horizontal and/or vertical distances between both conductors on both supports of the span

are not the same, it is necessary to verify, that in every location within the span the

clearances between the conductors are not less than the ones calculated according to

5.8/CZ.3 In this case, it is necessary to input into equation sag fr in the checked point of the

span, factor kemp_r, calculated for the angle δr in checked point of the span, and in the case

that lengths of suspension insulator sets on both supports are not the same, the equivalent

length Lins_r, calculated from the following equation:

Lins_r = Lins1 + (Lins2 – Lins1) r / L where Lins1 is the length of a shorter insulator set (m),

Lins2 is the length of a longer insulator set (m),

L is the span length (m),

r is the horizontal distance between the attachment point of the shorter insulator set and the point in the span, where the distance between conductors is checked (m)

If insulator sets, which cannot swing in the direction perpendicular to the line (e.g tension insulator sets, insulator crossarms or line post insulators) are installed on one of the supports

(or on both supports) of the checked span, then Lins1 (or also Lins2) = 0

according to the above-specified method, may not be lower than the minimum clearance

between conductors Dpp, or Del4 according to Table 5/CZ.4

Minimum clearances between covered conductors within the span are specified as 1/3 of the

distance b emp, calculated for a line with bare conductors

When using the method given in this subclause, it is also necessary to verify internal clearance between conductors swung due to wind under the conditions of Unequal wind load according to 5.6.3/CZ.2 It shall be proven, that the clearance between conductors not lower

than k1 Dpp according to 5.8/CZ.2 is secured under these conditions

This subclause replaces subclause F.3 of annex F

When assessing clearances at support according to 5.8 and 5.8/CZ.1, swing angle of the

insulator set determined by a ratio of horizontal wind force QWc acting on conductor and

vertical self-weight of conductor GK, based on the weight span, shall be considered

The swing angle of insulator set is calculated by a formula:

ϕ = arctg (CT2 QWc / GK)

where QWc is the wind force on conductor (N) according to 4.4.1 and national provisions

4.4.1.1/CZ.1, 4.4.1.1/CZ.2 and 4.4.1.3/CZ.1, where in the formula for QWc,

peak wind pressure qp(h) is replaced by mean wind pressure qh(h) according

to 4.3.3 and 4.3.3/CZ.1 and a conservative value Gc = 1 and angle φ = 0° shall be used,

CT is conversion factor for wind velocity with return period T years For extreme wind load with return period 50 years, CT2 = 1, for nominal wind load with

return period 3 years, CT2 = 0,58,

G K is self-weight of conductor (N), determined by equation:

GK = gc (LW1 + LW2) where

gc is weight of conductor per 1 m length (N/m),

LW1, LW2 are contributions of weight span (m) from both adjacent spans

under considered temperature (−5 °C and +40 °C) and wind load For a more accurate calculation with consideration of wind force on insulator set and weight

of insulator set, swing angle of insulator set is calculated by equation:

Wins Wc

2 T

9,81 2

1 2

1 arctg

m G

Q Q

C

φ