SIST EN 50341-2-7:2016

Overhead electrical lines exceeding AC 1 kV - Part -2-7: National Normative Aspects (NNA) for FINLAND (based on EN 50341-1:2012)

1.1 General
(ncpt)   FI.1   Application of the standard in Finland
In Finland the standard EN 50341-1 (Part 1) can only be applied using this NNA (EN 50341-2-7) containing National Normative Aspects for Finland.
The requirements of the standard are applied also for low voltage (below 1 kV AC) overhead lines. The requirements of the structural design are applicable also for DC overhead lines, where the electrical requirements are given in the Project Specification.
This standard is applicable for new overhead lines only.
(ncpt)  FI.2   Application for existing overhead lines
Overhead lines complying with the mechanical and electrical requirements of its original date of construction can be operated and maintained, if they do not cause obvious danger.
The reparation and overhaul of lines can be done according to the previous requirements. Reparation means that a component which has been damaged is substituted with a similar new one. Overhaul means a wider improvement of the line for extending its lifetime. The basic structure remains same as before.
This standard should be used for all modification works on existing lines. In modification works earlier norms and standards may also be used. In that case it shall especially be verified that changes in actions do not have significant impact on the loads of lines. Modification work means e.g. relocation of some supports or an extension to a line when this supplement has been taken into account in the original design, e.g. addition of a circuit or changing of the conductors to existing supports.
1.2      Field of application
(ncpt)   FI.1   Application to covered conductors and aerial cables
The standard includes requirements for the design and construction of overhead lines equipped with covered conductors and aerial cables. Additionally, the requirements of the equipment standards and manufacturers’ instructions shall be followed.
(ncpt)   FI.2   Application to cables for telecommunication
   The standard includes requirements for the application of telecommunication cables installed on common supports with electrical lines.
(ncpt)   FI.3   Installation of other equipment
Only equipment belonging to the line (electric or telecommunication line) can be installed on the overhead lines. However, equipment serving communal services or environmental protection like telecommunication equipment, road signs, warning signs or warning balls may also be installed with the permission of the owner of the line.
Other equipment than those mentioned above can also be installed on supports equipped with aerial cables with the permission of the owner of the line.  
If other equipment is installed on the supports, the requirements of safe working practices shall be taken into account. The installation height of equipment meant to be installed and maintained by an ordinary person shall be such that the work can be done without climbing the support and the distances of safe electrical work can be followed (see standard SFS 6002).
The additional loads due to other equipment on the line supports shall be taken into account.

Nadzemni električni vodi za izmenične napetosti nad 1 kV - 2-7. del: Nacionalna normativna določila (NNA) za Finsko (na podlagi EN 50341-1:2012)

1.1 Splošno
(ncpt) FI.1 Uporaba standarda na Finskem
Na Finskem je standard EN 50341-1 (1. del) mogoče uporabljati le ob uporabi teh nacionalnih normativnih določil (NNA) (EN 50341-2-7), ki obravnavajo nacionalna normativna določila za Finsko.
Zahteve standarda veljajo tudi za nadzemne vode z nizko napetostjo (pod 1 kV pri izmeničnem toku). Zahteve statičnega izračuna veljajo tudi za nadzemne vode z enosmernim tokom, pri čemer so električne zahteve obravnavane v projektni specifikaciji.
Ta standard velja le za nove nadzemne vode.
(ncpt) FI.2 Uporaba za obstoječe nadzemne vode
Nadzemne vode, ki so skladni z mehanskimi in električnimi zahtevami, določenimi na dan njihove konstrukcije, je mogoče upravljati in vzdrževati, če ne povzročajo očitne nevarnosti.
Popravilo ali obnovo vodov je mogoče izvesti v skladu s prejšnjimi zahtevami. Popravilo pomeni, da se poškodovano komponento zamenja z ustrezno novo komponento. Obnova pomeni obsežnejšo izboljšavo voda za podaljšanje njegove življenjske dobe. Osnovna struktura ostane ista.
Ta standard naj bi se uporabljal za vse spremembe na obstoječih vodih. Za spremembe se lahko uporabljajo tudi prejšnje norme in standardi. V tem primeru je treba zlasti preveriti, ali spremembe ne bodo pomembno vplivale na obremenitve vodov. Spremembe se nanašajo npr. na premestitev nekaterih podpor ali podaljšanje voda, če se v izvirnem načrtu upošteva to dopolnilo, npr. dodatek tokokroga ali zamenjava vodnikov na obstoječih podporah.
1.2 Področje uporabe
(ncpt) FI.1 Uporaba z izoliranimi vodniki in nadzemnimi kabli
Ta standard vključuje zahteve za obliko in izdelavo nadzemnih vodov, opremljenih z izoliranimi vodniki in nadzemnimi kabli. Poleg tega je treba upoštevati tudi zahteve standardov za opremo in navodila proizvajalcev.
(ncpt) FI.2 Uporaba s telekomunikacijskimi kabli
Ta standard vključuje zahteve za uporabo telekomunikacijskih kablov, napeljanih na običajne podpore z električnimi vodi.
(ncpt) FI.3 Montaža druge opreme
Na nadzemne vode je mogoče montirati le opremo, ki pripada vodu (električni ali telekomunikacijski vod). Vendar je z dovoljenjem lastnika voda lahko montirana tudi oprema, ki se uporablja za skupne storitve ali za zaščito okolja, kot so telekomunikacijska oprema, prometni znaki, opozorilni znaki ali opozorilne krogle.
Z dovoljenjem lastnika voda je mogoče na podpore, opremljene z nadzemnimi kabli, montirati tudi drugo opremo, ki ni navedena zgoraj.  
Če je na podpore montirana druga oprema, je treba upoštevati zahteve za varne delovne postopke. Opremo, ki naj bi jo montirali in vzdrževali laiki, je treba montirati na višini, ki omogoča izvajanje del brez plezanja na podporo in upošteva razdalje za varno izvajanje električnih del (glej standard SFS 6002).
Upoštevati je treba dodatne obremenitve na podporah voda zaradi druge opreme.

General Information

• Status: Published
• Publication Date: 03-Mar-2016
• ICS: 29.240.20 - Power transmission and distribution lines
• Technical Committee: NVV - Overhead lines and overhead electrical conductors
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 23-Sep-2015
• Due Date: 28-Nov-2015
• Completion Date: 04-Mar-2016
• Ref Project: EN 50341-2-7:2015 - Overhead electrical lines exceeding AC 1 kV - Part -2-7: National Normative Aspects (NNA) for FINLAND (based on EN 50341-1:2012)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 50341-2-7:2016
01-april-2016
1DG]HPQLHOHNWULþQLYRGL]DL]PHQLþQHQDSHWRVWLQDGN9GHO1DFLRQDOQD
QRUPDWLYQDGRORþLOD11$]D)LQVNRQDSRGODJL(1
Overhead electrical lines exceeding AC 1 kV - Part -2-7: National Normative Aspects
(NNA) for FINLAND (based on EN 50341-1:2012)
Ta slovenski standard je istoveten z: EN 50341-2-7:2015
ICS:
29.240.20 Daljnovodi Power transmission and
distribution lines
SIST EN 50341-2-7:2016 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 50341-2-7:2016

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SIST EN 50341-2-7:2016


EUROPEAN STANDARD
EN 50341-2-7

NORME EUROPÉENNE

EUROPÄISCHE NORM
September 2015
ICS 29.240.20

English Version
Overhead electrical lines exceeding AC 1 kV -
Part -2-7: National Normative Aspects (NNA) for FINLAND
(based on EN 50341-1:2012)
This European Standard was approved by CENELEC on 2015-08-11.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.



European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. EN 50341-2-7:2015 E

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Contents
Page
Foreword . 4
1 Scope . 5
1.1 General . 5
1.2 Field of application . 5
2 Normative references, definitions and symbols . 5
2.1 Normative references . 5
3 Basis of design . 6
3.2 Requirements of overhead lines . 6
3.2.2 Reliability requirements . 6
3.2.5 Strength coordination . 6
4 Actions on lines . 7
4.3 Wind loads . 7
4.3.1 Field of application and basic wind velocity . 7
4.3.2 Mean wind velocity . 7
4.3.3 Mean wind pressure . 8
4.4 Wind forces on overhead line components . 8
4.4.1 Wind forces on conductors . 8
4.4.1.1 General . 8
4.4.1.2 Structural factor . 8
4.4.1.3 Drag factor . 8
4.4.2 Wind forces on insulator sets. 8
4.4.3 Wind forces on lattice towers . 9
4.4.3.1 General . 9
4.4.3.2 Method 1 . 9
4.4.4  Wind forces on poles . 9
4.5 Ice loads . 9
4.5.1 General . 9
4.6 Combined wind and ice loads . 9
4.6.2 Drag factors and ice densities . 9
4.7 Temperature effects . 9
4.8 Security loads. 10
4.9 Safety loads . 10
4.9.1 Construction and maintenance loads . 10
4.12 Load cases . 11
4.12.1 General . 11
4.12.2 Standard load cases . 11
4.13 Partial factors for actions . 13
5 Electrical requirements . 14
5.4 Classification of voltages and overvoltages . 14
5.4.1 General . 14
5.6 Load cases for calculation of clearances . 14
5.6.1 Load conditions . 14
5.6.2 Maximum conductor temperature . 15
5.6.3 Ice loads for determination of electric clearances . 15
5.8 Internal clearances within the span and at the top of support . 15
5.9 External clearances . 15
5.9.1 General . 15
5.9.2 External clearances to ground in areas remote from buildings, roads etc. . 15
5.9.3 External clearances to residential and other buildings . 16
5.9.4 External clearances to crossing traffic routes . 16
5.9.6 External clearances to other power lines or telecommunication lines . 17
6 Earthing systems . 19
6.1 Introduction . 19
6.1.4 Transferred potentials . 19
6.4 Dimensioning with regard to human safety . 19
6.4.3 Design of earthing systems with regard to permissible touch voltage . 19

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7 Supports . 19
7.3 Lattice steel towers . 19
7.3.1 General . 19
7.3.6 Ultimate limit states . 19
7.3.6.1 General . 19
7.5 Wood poles . 20
7.5.3 Materials . 20
7.5.5 Ultimate limit states . 20
7.5.5.1 Basis. 20
7.5.5.2 Calculation of internal forces and moments . 20
7.5.5.3 Resistance of wood elements . 20
7.5.5.4 Decay conditions . 20
7.7 Guyed structures . 21
7.7.4 Ultimate limit states . 21
7.7.4.1 Basis. 21
7.7.4.3 Second order analysis . 21
7.7.6 Design details for guys . 21
7.10 Maintenance facilities . 22
7.10.3 Safety requirements . 22
8 Foundations . 22
8.1 Introduction . 22
8.2 Basis of geotechnical design . 23
8.2.1 General . 23
8.2.2 Geotechnical design by calculation . 23
8.2.3 Design by prescriptive measures . 24
9 Conductors and earth wires . 25
9.1 Introduction . 25
9.6 General requirements . 26
9.6.2 Partial factor for conductors . 26
10 Insulators . 26
10.2 Standard electrical requirements . 26
10.11 Type test requirements . 26
11 Hardware . 27
11.6 Mechanical requirements . 27
11.8 Material selection and specification . 27
12 Quality assurance, checks and taking over . 27

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EN 50341-2-7:2015 - 4/27 - Finland


Foreword

1 The Finnish National Committee (NC) is identified by the following address:
SESKO Standardization in Finland
Standardization committee SK11, High Voltage Overhead Lines
Addr. P.O. Box 134, 00211 Helsinki, Finland
Tel. [phone]
Fax. [phone]
Email [e-mail]

2 The Finnish NC has prepared this Part 2-7 of EN 50341 listing the Finnish national normative aspects
(NNA), under its sole responsibility, and duly passed it through the CENELEC and CLC/TC 11
procedures.
NOTE:  The Finnish 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 NNA is normative in Finland and informative for other countries.

4 This NNA has to be read in conjunction with Part 1 (EN 50341-1). All clause numbers used in this NNA
correspond to those of Part 1. Specific sub-clauses, which are prefixed "FI", are to be read as
amendments to the relevant text in Part 1. Any necessary clarification regarding the application of this
combined NNA in conjunction with Part 1 shall be referred to the Finnish NC who will, in co-operation
with CLC/TC 11, clarify the requirements.
When no reference is made in this NNA to a specific sub-clause, then Part 1 applies.

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 Finland.
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 national Finnish standards/regulations related to overhead electrical lines exceeding 1 kV AC are
listed in 2.1/FI.1-2.

NOTE:  All national standards referred to in this NNA will be replaced by the relevant European Standards as
soon as they become available and are declared by the Finnish NC to be applicable and thus reported
to the secretary of CLC/TC 11.

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1 Scope
1.1 General
(ncpt)  FI.1 Application of the standard in Finland
In Finland the standard EN 50341-1 (Part 1) can only be applied using this NNA (EN 50341-
2-7) containing National Normative Aspects for Finland.
The requirements of the standard are applied also for low voltage (below 1 kV AC) overhead
lines. The requirements of the structural design are applicable also for DC overhead lines,
where the electrical requirements are given in the Project Specification.
This standard is applicable for new overhead lines only.
(ncpt)  FI.2 Application for existing overhead lines
Overhead lines complying with the mechanical and electrical requirements of its original date
of construction can be operated and maintained, if they do not cause obvious danger.
The reparation and overhaul of lines can be done according to the previous requirements.
Reparation means that a component which has been damaged is substituted with a similar
new one. Overhaul means a wider improvement of the line for extending its lifetime. The
basic structure remains same as before.
This standard should be used for all modification works on existing lines. In modification
works earlier norms and standards may also be used. In that case it shall especially be
verified that changes in actions do not have significant impact on the loads of lines.
Modification work means e.g. relocation of some supports or an extension to a line when this
supplement has been taken into account in the original design, e.g. addition of a circuit or
changing of the conductors to existing supports.
1.2 Field of application
(ncpt)  FI.1 Application to covered conductors and aerial cables
The standard includes requirements for the design and construction of overhead lines
equipped with covered conductors and aerial cables. Additionally, the requirements of the
equipment standards and manufacturers’ instructions shall be followed.
(ncpt)  FI.2 Application to cables for telecommunication
The standard includes requirements for the application of telecommunication cables installed
on common supports with electrical lines.
(ncpt)  FI.3 Installation of other equipment
Only equipment belonging to the line (electric or telecommunication line) can be installed on
the overhead lines. However, equipment serving communal services or environmental
protection like telecommunication equipment, road signs, warning signs or warning balls may
also be installed with the permission of the owner of the line.
Other equipment than those mentioned above can also be installed on supports equipped
with aerial cables with the permission of the owner of the line.
If other equipment is installed on the supports, the requirements of safe working practices
shall be taken into account. The installation height of equipment meant to be installed and
maintained by an ordinary person shall be such that the work can be done without climbing
the support and the distances of safe electrical work can be followed (see standard SFS
6002).
The additional loads due to other equipment on the line supports shall be taken into account.

2 Normative references, definitions and symbols
2.1 Normative references
(A-dev) FI.1 National normative laws, government regulations
Sähköturvallisuuslaki (410/1996)
Electrical Safety Act
Sähköturvallisuusasetus (498/1996)
Electrical Safety Decree
Kauppa- ja teollisuusministeriön päätös sähkölaitteistojen turvallisuudesta (1193/1999)
Decision of Ministry of Trade and Industry on Safety of electrical installations
Viestintäviraston määräys M 43 tietoliikenneverkon sähköisestä suojaamisesta

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Decree nr M 43 of the Finnish Communications Regulatory Authority on the electrical
protection of a telecommunication network
Liikenteen turvallisuusviraston määräys AGA M3-6, Lentoesterajoitukset ja lentoesteiden
merkitseminen. Aviation regulation AGA M3-6 of the Finnish Transport Safety Agency on the
Aviation obstacle limitations and marking of objects.
Liikenneviraston ohje 23/2014 Ilmajohtojen sekä kaapeleiden ja putkijohtojen asettaminen ja
merkitseminen vesialueella. Publication 23/2014 of the Finnish Transport Agency: Installation
and marking of overhead lines, cables and pipelines in waterways.
(ncpt)  FI.2 National normative standards
SFS 2662 Ilmajohtotarvikkeet. Puupylväs
Overhead line materials. Wood pole
SFS 5717 Maakaasun siirtoputkiston sijoittaminen suurjännitejohdon tai kytkinlaitoksen
läheisyyteen
Placing of the natural gas transmission pipeline close to a high-voltage line or
substation
SFS 6000 Pienjännitesähköasennukset
Low voltage electrical installations
SFS 6001 Suurjännitesähköasennukset
High voltage electrical installations
SFS 6002 Sähkötyöturvallisuus (perustuu standardiin EN 50110-1/2)
Safety at electrical work (based on standard EN 50110-1/2)
RIL 202/by 61 Betonirakenteiden suunnitteluohje (perustuu standardiin SFS-EN 1992-1-1)
Design guide for concrete structures (based on standard SFS-EN 1992-1-1)
RIL 207  Geotekninen suunnittelu (perustuu standardiin SFS-EN 1997-1)
Geotechnical design (based on standard SFS-EN 1997-1)
RIL 254 Paalutusohje
Piling instructions

3 Basis of design
3.2 Requirements of overhead lines
3.2.2 Reliability requirements
(ncpt)  FI.1 Selection of reliability levels
The minimum reliability levels based on the nominal voltage and importance of the lines are
defined in Table 3.1/FI.1 below. The level shall be given in the Project Specification.
Table 3.1/FI.1 - Reliability levels of overhead lines in Finland
Level Nominal voltage Type of line
≤ AC 45 kV Normal lines
U
n
1
U > AC 45 kV Temporary or unimportant lines
n
U ≤ AC 45 kV Special lines
n
2
U > AC 45 kV Normal lines
n
3 all Very important lines, i.e. all 400 kV lines

3.2.5 Strength coordination
(ncpt)  FI.1 Angle and tension supports
for the resistance of the structural elements of angle (angle ≥ 10 degrees),
The partial factors γ
M
tension and terminal supports shall be multiplied by an additional factor γ = 1,1. This
S
requirement needs not to be applied at construction load cases.
In these cases, when determining the structural design resistance R in the basic design
d
formula E < R , the design value X of a material property shall be calculated from formula:
d d d
X = X / (γ γ )  See Clauses 3.6.3 and 3.7.2 of Part 1.
d K M S
This clause shall be applied only for lines with nominal voltages > 45 kV, if not otherwise
required in the Project Specification.

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(ncpt)  FI.2 Foundations
As the foundation should be 10 % stronger than the support, the loads from the support to
foundations shall be multiplied by the factor 1,1.
At angle, tension and terminal supports of lines with nominal voltage > 45 kV the loads shall be
multiplied by an additional factor 1,1. Thus, in these cases the total factor will be 1,21. This
requirement needs not to be applied at construction load cases.
Alternatively, the strength coordination of the foundations can be executed by applying the
factors 1,1 and 1,21 to the partial factors of the resistances and properties of materials.

4 Actions on lines
4.3 Wind loads
4.3.1 Field of application and basic wind velocity
(snc)  FI.1 Basic wind velocity
The basic wind velocity V = 21 m/s is normally applied in all areas of Finland.
b,0
Other basic wind velocity values may be used, if they are based on the local conditions and
reliable statistics. These values shall be given in the Project Specification.
NOTE: Local values are given e.g. in the research report ”Mitoitustuuli Suomessa, 2007” by the
Finnish Meteorological Institute.
4.3.2 Mean wind velocity
(snc)  FI.1 Terrain categories
The terrain categories in Finland are specified in Table 4.1/FI.1.
Table 4.1/FI.1 - Terrain categories, roughness length z and terrain factor k
0 r
Terrain
Description z [m] k
0 r
category
0 Open sea, outer archipelago and open coastal areas 0,003 0,180
0+ Scattered inner archipelago and sheltered coastal areas 0,003 0,167
Dense inner archipelago, large lake districts and wide
I 0,010 0,169
agricultural areas
Reference terrain: Area with low vegetation and isolated
II 0,050 0,189
obstacles (trees, buildings)
Variable inland terrain (forests, forest-openings, small fields
II+ 0,095 0,195
and lakes, single buildings or building-groups)
Area with regular vegetation or with isolated obstacles (such
III 0,300 0,214
as buildings, villages, suburban terrain, permanent forest)
Cities and towns, i.e. area in which at least 15 % is covered
IV with buildings with average height > 15 m. This category 1,000 0,233
shall not be applied in Finland.
NOTE 1:  Typical Finnish inland terrain with forests and small hills can be considered as category III. If
possible tree cuttings or storms can have impact on this assumption, then category II or II+
should be applied.
NOTE 2:  In mountainous areas category II should be applied, unless otherwise specified in the
Project Specification.
NOTE 3:  The table values of the constants z0 and kr deviating from those given in SFS-EN 1991-1-4
are marked in italics.
(ncpt)  FI.2 Terrain orography
If the slope of a single hill or ridge exceeds 5 % and its height from the level of the
surrounding flat terrain exceeds 10 m, the effect of terrain orography (hill effect) shall be
taken into account.
The orography factor c for wind speed can be calculated according to SFS-EN 1991-1-4,
0
Annex A.3.
Alternatively, the hill effect can be taken into account by taking the wind speed at the height H
measured from the level of the surrounding flat terrain in the direction of the coming wind.

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However, the gust effect shall be determined by using the height h measured from the level
of the top of the hill. For heights h < 10 m the gust factor at height h = 10 m shall be used.
Additional guidance and requirements on the effects of the topography on the determination
of the wind loads can be given in the Project Specification.
NOTE: The terrain category and the local wind velocity may depend on the direction of the wind. If
necessary, meteorological specialists should be consulted in assessing the terrain category,
orography and wind velocity.
4.3.3 Mean wind pressure
(ncpt)  FI.1 Effects of altitude and temperature
When calculating the wind pressure, the effects of temperature and altitude on the air density
shall be taken into account.
3
At the reference condition the temperature is 0 °C and air density 1,292 kg/m at sea level.
4.4 Wind forces on overhead line components
4.4.1 Wind forces on conductors
4.4.1.1 General
(ncpt)  FI.1 Effective height of conductor
The effective height of a conductor shall be taken as the height of the centre of gravity of the
conductor (Method 1 in Part 1). In cases, where the shape of the terrain is uneven or, if so
required in the Project Specification, the height of the attachment point of the conductor at
the insulator shall be used (Method 4 in Part 1). In the sag and tension analyses the average
height of each tension section shall be used.
Additionally, the terrain orography shall be taken into account, if the wind speed will be
determined from the level of the surrounding flat terrain (see Clause 4.3.2/FI.2).
If the same constant height will be used for all conductors and earth wires, it shall be
calculated according to the height of the uppermost phase conductor.
4.4.1.2 Structural factor
(ncpt)  FI.1 Span factor
When calculating the span factor for the sag and tension analysis, the ruling span shall be used
as the span length. When calculating the span factor for the tower load analysis, the average
length of the adjacent spans of the support concerned shall be used as the span length.
4.4.1.3 Drag factor
(ncpt)  FI.1 Drag factor of conductors
In the case of conductors or earthwires the drag factor shall be taken as 1,0 for each sub-
conductor (Method 1 in Part 1).
In the case of bundled aerial cables the drag factor shall be taken as 1,2 for the average
diameter of the bundled cable.
4.4.2 Wind forces on insulator sets
(ncpt)  FI.1 Wind load of insulator
The recommended values in Part 1 for height, structural and drag factors shall be used. The
wind load of an insulator set shall be calculated according to Part 1. The projected wind area of
the insulator shall be calculated from:
A = L D sinα
ins
L = Effective length of the insulator string
D = Outer diameter of the insulator unit
α = Angle between the directions of the insulator and wind at the loaded position. A
conservative value α = 90º may also be used.
(ncpt)  FI.2 V-insulator set dimensions
The dimensions of a V-insulator set configuration shall be such that the direction of the
resulting force due to the tra
...