Overhead electrical lines exceeding AC 1 kV - Part 2-9: National Normative Aspects (NNA) for Great Britain and Northern Ireland (based on EN 50341-1:2012)

This NNA is only applicable to all new overhead lines above A.C. 1kV.
This Euronorm is only applicable to new overhead lines and shall not be applied to maintenance, reconductoring, tee-offs, extensions or diversions to existing overhead lines unless specifically required by the Project Specification.
For details of the application of this standard for overhead lines constructed with covered conductor refer to the Project Specification.
For details of the application of this standard to telecommunication systems involving optical fibres either incorporated in or wrapped around earthwires or conductors or suspended from overhead line supports, reference should be made to the Project Specification.

Nadzemni električni vodi za izmenične napetosti nad 1 kV - 2-9. del: Nacionalna normativna določila (NNA) za Veliko Britanijo in Severno Irsko (na podlagi EN 50341-1:2012)

To nacionalno normativno določilo velja le za vse nove nadzemne vode za izmenično napetost nad 1kV.
Ta normativ Euronorm velja le za nove nadzemne vode in ne velja za vzdrževanje, zamenjavo napeljave, odcepne prenosne tokokroge, podaljške ali preusmeritve v zvezi z obstoječimi nadzemnimi vodi, razen če tega izrecno ne zahteva projektna specifikacija.
Za podrobnejše informacije o uporabi tega standarda za nadzemne vode, izdelane z izoliranim vodnikom, glej projektno specifikacijo.
Za podrobnejše informacije o uporabi tega standarda za telekomunikacijska omrežja, ki vključujejo optična vlakna, vgrajena v zaščitne vrvi ali vodnike ali so ovita vanje oziroma visijo z nosilcev nadzemnih vodov, glej projektno specifikacijo.

General Information

Status
Published
Publication Date
11-Mar-2019
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
22-Dec-2017
Due Date
26-Feb-2018
Completion Date
12-Mar-2019

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SLOVENSKI STANDARD
SIST EN 50341-2-9:2019
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Overhead electrical lines exceeding AC 1 kV - Part 2-9: National Normative Aspects

(NNA) for Great Britain and Northern Ireland (based on EN 50341-1:2012)
Ta slovenski standard je istoveten z: EN 50341-2-9:2017
ICS:
29.240.20 Daljnovodi Power transmission and
distribution lines
SIST EN 50341-2-9:2019 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 50341-2-9:2019
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SIST EN 50341-2-9:2019
EUROPEAN STANDARD
EN 50341-2-9
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2017
ICS 29.240.20 Supersedes EN 50341-2-9:2015
English Version
Overhead electrical lines exceeding AC 1 kV - Part 2-9: National
Normative Aspects (NNA) for Great Britain and Northern Ireland
(based on EN 50341-1:2012)
This European Standard was approved by CENELEC on 2017-04-26.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,

Switzerland, Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN 50341-2-9:2017 E
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EN 50341-2-9:2017 -2/35- Great Britain and Northern Ireland
CONTENTS

1 Scope ...................................................................................................................................................... 6

1.1 General ................................................................................................................................................ 6

2 Normative References, definitions and symbols ................................................................................. 6

2.1 Normative references ......................................................................................................................... 6

2.3 Symbols ............................................................................................................................................... 7

3 Basis of design ........................................................................................................................................ 7

3.2 Requirements of overhead lines ....................................................................................................... 7

3.2.2 Reliability requirements .................................................................................................................... 7

3.2.5 Strength coordination ....................................................................................................................... 7

3.2.6 Additional considerations .................................................................................................................. 7

3.3 Limit states ................................................................................................................................................. 7

3.3.3 Serviceability limit states .................................................................................................................. 7

4 Actions on lines ...................................................................................................................................... 8

4.1 Introduction ......................................................................................................................................... 8

4.3 Wind loads ........................................................................................................................................... 8

4.3.1 Field of application and basic wind velocity ...................................................................................... 8

4.3.2 Mean wind velocity ........................................................................................................................... 9

4.3.3 Mean wind pressure ......................................................................................................................... 9

4.4 Wind forces on overhead line components ..................................................................................... 9

4.4.1 Wind forces on conductors ............................................................................................................. 10

4.4.3 Wind forces on lattice towers ......................................................................................................... 11

4.5 Ice loads ............................................................................................................................................ 11

4.6 Combined Wind and Ice loads ........................................................................................................ 12

4.7 Temperature effects ......................................................................................................................... 13

4.8 Security loads ................................................................................................................................... 13

4.9 Safety loads ....................................................................................................................................... 14

4.9.1 Construction and maintenance loads ............................................................................................. 14

4.9.2 Loads related to the weight of linesmen ......................................................................................... 14

4.10 Forces due to short-circuit currents ............................................................................................... 14

4.11 Other special forces ......................................................................................................................... 14

4.12 Load cases ........................................................................................................................................ 15

4.12.2 Standard load cases ....................................................................................................................... 15

4.13 Partial factors for actions ................................................................................................................ 16

5 Electrical requirements ........................................................................................................................ 19

5.2 Currents ............................................................................................................................................. 19

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5.2.1 Normal current ................................................................................................................................ 19

5.2.2 Short circuit current ........................................................................................................................ 19

5.5 Minimum air clearance distances to avoid flashover ................................................................... 20

5.5.3 Empirical method based on European experience......................................................................... 20

5.6 Load cases for calculation of clearances....................................................................................... 20

5.6.1 Load cases for calculation of clearances ....................................................................................... 20

5.6.3 Wind load for determination of electric clearances ........................................................................ 20

5.6.4 Ice load for determination of electric clearances ............................................................................ 20

5.6.5 Combined wind and ice loads......................................................................................................... 20

5.8 Internal clearances within the span and at the top of support .................................................... 20

5.9 External clearances .......................................................................................................................... 21

5.9.1 General ........................................................................................................................................... 21

5.9.4 External clearances to crossing traffic routes ................................................................................ 21

5.9.6 External clearances to other power lines or overhead telecommunication lines ............................ 22

5.9.7 External clearances to recreational areas (playgrounds, sports areas, etc.) ................................. 22

5.10 Corona effect ..................................................................................................................................... 22

5.10.2 Audible noise .................................................................................................................................. 22

5.10.3 Corona loss .................................................................................................................................... 22

5.11 Electrical and magnetic field ........................................................................................................... 22

5.11.1 Electrical and magnetic fields under a line ..................................................................................... 22

6 Earthing Systems .................................................................................................................................. 22

6.2 Ratings with regard to corrosion and mechanical strength................................................................ 22

6.2.1 Earth electrodes ............................................................................................................................ 22

6.4 Dimensioning with regard to human safety ................................................................................... 22

7 Supports ................................................................................................................................................ 23

7.3 Lattice steel towers .......................................................................................................................... 23

7.3.6 Ultimate limit states .............................................................................................................................. 23

7.4 Steel poles ......................................................................................................................................... 23

7.4.5 Structural analysis .......................................................................................................................... 23

7.4.6 Ultimate limit states ........................................................................................................................ 23

7.5 Wood Poles ....................................................................................................................................... 24

7.5.1 General ........................................................................................................................................... 24

7.5.5 Ultimate limit states ........................................................................................................................ 24

7.7 Guyed structures .............................................................................................................................. 25

8. Foundations........................................................................................................................................... 25

8.2 Basis of geotechnical design .......................................................................................................... 25

8.2.2 Geotechnical design ........................................................................................................................... 25

8.2.3 Design by prescriptive measures ................................................................................................... 25

8.2.4 Load tests and tests on experimental models ................................................................................ 25

8.4 Supervision of construction, monitoring and maintenance ........................................................ 25

9. Conductor and earth wires .................................................................................................................. 26

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10. Insulators ............................................................................................................................................... 26

10.10 Characteristics and dimensions of insulators .......................................................................... 26

11 Line equipment – overhead line fittings ............................................................................................. 27

11.9 Characteristics and dimensions of insulator fittings .................................................................... 27

12 Quality assurance, checks and taking-over ....................................................................................... 27

Annex J Angles in lattice steel towers ......................................................................................................... 27

J.4 Buckling resistance of angles in compression (see 7.3.6.4) ............................................................... 27

J.4.2 Effective non-dimensional slenderness for flexural buckling .............................................................. 27

J.4.3 Slenderness of members ..................................................................................................................... 27

J.4.3.3 Primary bracing patterns.................................................................................................................. 27

J.5 Design resistance of bolted connections (see 7.3.8) ........................................................................... 28

J.5.1 General ............................................................................................................................................... 28

Figure NA.1 10-Minute mean wind speeds for GB, v in metres per second ................................ 29

b, map

Figure NA.2 Ice thickness for GB, r and (r ) in millimetres ................................................................. 30

o w

Figure NA.3 Weather Zones for site heights of 0 to 100m .................................................................... 31

Figure NA.4 Weather Zones for site heights of 100 to 200m ................................................................ 32

Figure NA.5 Weather Zones for site heights of 200 to 300m ................................................................ 33

Figure NA.6 Weather Zones for site heights of 300 to 400m ................................................................ 34

Figure NA.7 Weather Zones for site heights of 400 to 500m ................................................................ 35

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European foreword
1. The British National Committee is identified by the following address:
British Standards Institution
389 Chiswick High Road
London W4 4AL
Tel: + 44 20 8996 9000
Fax: + 44 20 8996 7799
email: info@bsi.org.uk
Attention: Secretary of PEL/11 Overhead lines – Standards Development

2. The British National Committee has prepared this NNA (part 2-9 of EN 50341) listing the GB National

Normative Aspects under its sole responsibility and duly passed this document through the CENELEC

and CLC/TC 11 procedures.

NOTE: The British National 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 2-9 is normative in GB and informative for other countries.

4. This document shall be read in conjunction with Part 1 (EN 50341-1). All clause numbers used in this

NNA correspond to those in Part 1. Specific sub-clauses that are prefixed “GB” are to be read as

amendments to the relevant text in Part 1. Any necessary clarification regarding the application of this

NNA in conjunction with Part 1 shall be referred to the British NC who will, in co-operation with CLC/TC

11, clarify the requirements.

Where no reference is made in this NNA to a specific sub-clause, then Part 1 shall apply.

5. In the case of “boxed values” defined in Part 1, amended values (if any), which are defined in this NNA,

shall be taken into account in GB and Northern Ireland.

However any boxed value whether in Part 1 or in this NNA, shall not be amended in the direction of

greater risk in a Project Specification.

6. The GB and Northern Ireland standards/ regulations relating to overhead electrical lines exceeding

A.C. 1 kV are listed in subclause 2.1.

7. The British NC declares in accordance with clause 4.1 of Part 1 that this NNA follows both design

“Approach 1” and design “Approach 3”. The specific design Approach to be used shall be specified in the

Project Specification.
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1 SCOPE
1.1 General
(ncpt) GB.1 General
This NNA is only applicable to all new overhead lines above A.C. 1kV.

This Euronorm is only applicable to new overhead lines and shall not be applied to maintenance,

reconductoring, tee-offs, extensions or diversions to existing overhead lines unless specifically

required by the Project Specification.

For details of the application of this standard for overhead lines constructed with covered

conductor refer to the Project Specification.

For details of the application of this standard to telecommunication systems involving optical

fibres either incorporated in or wrapped around earthwires or conductors or suspended from

overhead line supports, reference should be made to the Project Specification.
2 NORMATIVE REFERENCES, DEFINITIONS AND SYMBOLS
2.1 Normative references
(A-dev) GB.1 National statutes
Reference Name and Date of GB and NI Statute
Electricity Act 1989, Chapter 29,
Health and Safety at Work Act 1974 and subsequent amendments
SI 635 The Electricity at Work Regulations 1989 (Northern Ireland) 1991
SI 1355 The Electricity (Overhead Lines) Regulations 1970
SI 2035 The Overhead Lines (Exemption) Regulations 1990
SI 2665 The Electricity Safety, Quality and Continuity Regulations 2002

SI 381 The Electricity Safety, Quality and Continuity Regulations (Northern Ireland) 2012

SI 3074 The Overhead Lines (Exemption) Regulations 1992
SI 320 The Construction (Design & Management) Regulations 2007
SI 231(NI) Electricity (Northern Ireland) Order 1992

SR 142 The Construction (Design & Management) (Amendment) Regulations (Northern Ireland) 2001

SR 209 The Construction (Design & Management) Regulations (Northern Ireland) 1995

SR 536 Electricity Supply Industry Regulations (Northern Ireland) 1991
SR 21 Electricity Supply (Amendment) Regulations (Northern Ireland) 1993
SI 1039 (NI9) Health and Safety at Work (Northern Ireland) Order 1978
SI 2448 (S.165) The Electricity Act 1989 (Scotland)
(ncpt) GB.2 National normative standards

BSEN 1991-1-4:2005 Actions on Structures - Part 1-4: General Actions – Wind actions

BSEN 1995-1-1:2008 Design of Timber Structures – Part 1-1 General – Common rules and rules for buildings

BS 7354:1990 Design of high-voltage open-terminal stations
BSEN 10025 Hot rolled products of structural steels
BSEN 14229:2010 Structural timber – wood poles for overhead lines

BSEN 50182:2001 Conductors for overhead lines – round wire concentric lay stranded conductors

Electricity Association Technical Report (EATR) 111 - High Voltage Single Circuit Overhead Lines on Wood Poles

(1991)
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2.3 Symbols
(ncpt) GB.1 Additional symbols
A altitude of the site above mean sea level
SITE
a altitude in metres above sea level of the conductor
c altitude factor
alt
cdir wind direction factor
Dc diameter of the conductor, mm
f yield strength for bolt
Ki ice thickness coefficient
K shape factor
L length of conductor span, m
Nc number of phases and earthwires
q wind pressure on conductor, N/m²
qx wind pressure on structural element, N/m²
r basic radial thickness of ice, mm
ro radial ice thickness in mm in the absence of wind, mm
rr reference ice thickness, mm
r radial ice thickness in mm in the presence of wind
vb,0 fundamental basic wind velocity, m/sec
v 10-minute wind velocity at sea level taken from a GB map, m/sec
b,map
z height above ground, m

γ partial safety factor on wind speed and ice thickness (partial factors on actions)

γm partial factor on strength of structural materials
γ partial factors on permanent actions
3 BASIS OF DESIGN
GB.1 Basic Requirements
3.2 Requirements of overhead lines
Design Approach 1
3.2.2 Reliability requirements
(ncpt) GB.1 Reliability levels

The partial coefficients to be used for the reliability levels are shown in Table 4.13.1/GB.1.

The required reliability level shall be stated in the Project Specification. For temporary loading

conditions reduced reliability levels may be specified.
3.2.5 Strength coordination
(ncpt) GB.1 Strength coordination

The required degree of strength coordination shall be stated in the Project Specification.

3.2.6 Additional considerations
(ncpt) GB.1 Additional considerations

Higher partial factors than those shown within this NNA may be specified in the Project

Specification. Any additional considerations shall also be stated in the Project Specification.

3.3 Limit states
3.3.3 Serviceability limit states
(ncpt) GB.1 Specific requirement
These shall be defined in the Project Specification.
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4 ACTIONS ON LINES
4.1 Introduction
Design Approach 1
(ncpt) GB.1 Peak factor equation

The formulation in the UK National Annex to BS EN 1991-1-4 modifies the parameter to define

peak pressures by adopting a “peak factor” of 3,0 with a quadratic equation, rather than 3,5 with

a linear equation, as used in BS EN 1991-1-4. The decision to change the formulation was due

to the use of the ten minute wind speed in BS EN 1991-1-4 and the greater accuracy in the

quadratic expression. As a consequence of this, equations included in clauses 4.3.4, 4.4.1.2,

4.4.3.2, 4.4.3.3 need to be amended as follows for use in the UK:
Replace the expression: [1 + 7Iv(z)]
with: [1 + 3,0Iv(z)]²
(ncpt) GB.2 Design approach definition

Approach 1 (as detailed in BS EN 50341-1:2012 Clause 4.1) shall be adopted for all new

overhead lines supported on steel poles or lattice steel towers.

Approach 2 (as detailed in BS EN 50341-1:2012 Clause 4.1) may be used subject to the

availability of suitable statistical data, and the agreement of the client. Before doing so, the

proposed methodology for design, and the quality of the statistical data, shall be subject to a

rigorous review by an independent expert to confirm that Reliability Levels equivalent to those

provided by Design Approach 1 would be achieved with the proposed Design Approach 2.

For overhead lines supported on timber poles, the project specification shall specify either design

Approach 3 or 1.

NOTE Approaches 1 and 3 are based on different design philosophies and care should be taken not to combine

elements of the two when undertaking calculations. The parts of this standard which apply only to Approach 3 are shown

shaded grey in this document.
4.3 Wind loads
4.3.1 Field of application and basic wind velocity
Design Approach 1
(snc) GB.1 Calculation of basic wind velocity

Partial factor (γv) taken from Table 4.13.1/GB.1 for the specified Reliability Level shall be applied

to the basic wind velocity (v ) instead of applied to wind loading as given in Table 4.7 of

b,0
BSEN 50341-1. The partial factor Ψw shall not be used.
The fundamental basic wind velocity, v should be determined by the equation:
b,0
v = γ v c
b,0 v b,map alt

Where, vb,map is the fundamental velocity indicated in Figure NA.1 and calt is the altitude factor

calculated as follows:
c = 1 + 0,001 A
alt SITE
where: ASITE is the altitude of the site in metres above mean sea level

The above may be used for all site altitudes, but may be considered over-conservative at high

altitudes, in which case c may be calculated for each element greater than 10m above ground

alt
using the modified formula:
0.2
c = 1 + 0,001 A (10/h)
alt SITE

Where h is the height above ground level in metres at the point of application of the wind load.

For calculation of wind loading on conductors and insulators, h may be taken as the mean height

of the conductor attachment points. For calculation of wind on towers, structures may be divided

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in a number of panels of up to 10m in height, and h taken as the mean height of each panel.

4.3.2 Mean wind velocity
(ncpt) GB.1 Wind Direction

Wind direction factor C may conservatively be taken as 1,0 or from Table 4.3.2/GB.1 below.

dir
Table 4.3.2/GB.1 Wind direction factors
Direction 0 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330°
C 0,78 0,73 0.73 0,74 0,73 0,80 0,85 0,93 1,00 0,99 0,91 0,82
dir
NOTE 1 Interpolation may be used

NOTE 2 The directions are defined by angles from due North in a clockwise direction, for wind from the

specified direction (eg. 0° means wind from due North)

NOTE. Unless stated otherwise in the project specification, wind from every direction from 0 to 345° shall

be considered for the design in 15° increments.
(ncpt) GB.2 Seasonal factor, c
season

Where a temporary loading condition will remain in place for less than 1 year, the appropriate

c factor may be applied in the calculation of mean wind speed as indicated in Table NA.2.7

season

in National Annex to BSEN 1991-1-4:2005. Note that the appropriate factor will not be applied in

conjunction with wind speeds of less return period than 50 years.
(ncpt) GB.3 Orography factor, co

The orography factor, c shall be taken as 1,0 where the average ground slope is not greater

than 5% (1:20), measured over a distance of 10 times the height of the supports from the line.

For greater slopes, reference shall be made to Figure NA.2 in National Annex to BSEN 1991-1-

4:2005+A1, “Definition of significant orography [definition of symbols given in A.3(3)]”. For sites

lying within the shaded area of that figure, the method given in BSEN 1991-1-4 A.3 for

calculation of c may be used. As an alternative, or if the topography is complex, calculation by

wind engineering specialists using digital terrain models may be less labour intensive and give

more accurate results.
(ncpt) GB.4 Loading on conductors

For calculation of the load on supports due to wind loading on conductors (excluding those

indirect effects due to conductor tension) the magnitude of the height above ground (h) adopted

for the calculation of V (h) shall generally be taken as the average height to the attachment of the

support considered except in the case of spans crossing deep valleys, river estuaries or hills

where the attachment heights would not be representative of the actual heights to the conductors

away from the supports. In these cases, the value of h adopted shall be adjusted to

approximately represent the mean height from the ground or water level to the attachment points

on the supports. Alternatively, advice from a wind engineering specialist may be sought.

4.3.3 Mean wind pressure
(snc) GB.1 Air density

Air density in Great Britain shall be taken as 1,226 kg/m³. Table 4.2 in BSEN 50341-1:2012 shall

not be used.
4.4 Wind forces on overhead lin
...

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