EN 50341-2-7:2015

SLOVENSKI STANDARD
01-april-2016
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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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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

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

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. +358-9-696391
Fax. +358-9-677059
Email palaute@sesko.fi
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

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
U > AC 45 kV Temporary or unimportant lines
n
U ≤ AC 45 kV Special lines
n
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,
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.

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.
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 transversal loads from conductors will stay inside the angle
between the two arms of the insulator set in the following service conditions (without partial
load factors):
• Extreme wind load (mean wind with 50 year return period)
• Minimum temperature (3 year return period value, see Table 4.7/FI.1)

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4.4.3 Wind forces on lattice towers
4.4.3.1 General
(ncpt)  FI.1 Calculation method of wind loads
Wind loads shall be calculated by dividing the tower into sections (Method 1 in Part 1).
4.4.3.2 Method 1
(ncpt)  FI.1 Structural factors
Structural factor shall be G = 1,0 for tower body and G = 1,0 for cross-arms.
t tc
(ncpt)  FI.2 Drag factors
Wind forces on rectangular towers shall be calculated according to Part 1. Drag factors of other
types of lattice towers (towers with triangular body or towers containing mixed profile shapes,
i.e. tubular legs and angle bracings) shall be calculated according to SFS-EN 1993-3-1.
4.4.4  Wind forces on poles
(ncpt)  FI.1 Calculation of wind loads on poles
Wind loads on poles shall be calculated by dividing the pole into sections (Method 1 in Part 1).
Structural factor shall be G = 1,0.
pol
4.5 Ice loads
4.5.1 General
(snc)  FI.1 Icing categories and ice load parameters
The philosophy in defining ice loads is based on ISO 12494. The characteristic ice load on a
conductor depends on the relative altitude, which is defined as the altitude difference between
the conductor and the average level of the surrounding terrain within a distance of 10 km from
the site. Values for characteristic ice loads are given in Table 4.5/FI.1.
If higher load values based on long term statistics or experience on the local conditions are
available, they shall be applied and given in the Project Specification.
(snc)  FI.2 Ice loads on conductors
Values for ice load parameters for conductors are given in Table 4.5/FI.1. In categories II and III
intermediate values based on linear interpolation shall be used.
For spans in the same tension section, ice load value based on the uppermost height level of
the spans concerned shall be used in conductor tension calculations. Ice load parameters in
icing category IV should be evaluated by meteorological specialists.
Table 4.5/FI.1 - Conductor ice load
Relative Characteristic
Icing Density Drag Type
altitude ice load I
50 3
category [kg/m ] factor of ice
[m] [N/m]
I 0 - 50 10 500 1,15 rime
II 50 - 100 10-25 500 1,15 rime
III 100 - 200 25-50 500 1,15 rime

IV > 200 >50 500 1,15 rime
(ncpt)  FI.3 Ice loads on structures and insulators
No ice needs to be considered on structures or insulators, if not otherwise specified in the
Project Specification.
4.6 Combined wind and ice loads
4.6.2 Drag factors and ice densities
(ncpt)  FI.1 Drag factors of iced conductors and ice densities
Drag factors for iced conductors as well as ice densities are given in Table 4.5/FI.1.
4.7 Temperature effects
(snc)  FI.1 Reference condition (EDS-condition)
o
Reference condition is specified as still air condition with no ice at temperature 0 C. The
temperatures in different load conditions are given in Table 4.13/FI.1.

(snc)  FI.2 Minimum temperatures
o
Minimum temperatures T [ C] have been calibrated to correspond the region and return
min
period of the reliability level concerned. They are given in Table 4.7/FI.1. The proper region and
possible deviations from the values in the table shall be specified in the Project Specification.
o
Table 4.7/FI.1 - Minimum temperatures T [ C]
min
Reliability level
3-year
Temperature region
value
1 2 3
Southern Finland - 40 - 45 - 50 - 30
Middle Finland - 45 - 50 - 55 - 36
Northern Finland - 50 - 55 - 60 - 42
4.8 Security loads
(ncpt)  FI.1 Security loading definition
All conductors are assumed intact. The transversal and vertical forces are the same as those
in the reference condition. It is assumed that the possible hinged dropper is not inclined in the
direction of the line.
The value of the longitudinal security load (acting in the direction of the line) is the force of
one sub-conductor of any one phase conductor or earth wire at the reference condition. The
point of action of the force is the attachment point of the insulator at the structure.
In case of V-insulator sets the longitudinal force shall be evenly distributed between the
attachment points of the strings. In case of V-insulator sets with hinged dropper for the outer
string, the point of action of the longitudinal force component concerned is the outermost
attachment point of the dropper at the cross-arm.
(ncpt)  FI.2 Application of security loads on lines with nominal voltages ≤ 45 kV
Security loads need to be applied on lines with nominal voltages ≤ 45 kV only, if required in
the Project Specification.
(ncpt)  FI.3 Other longitudinal loads
In other load cases than the security case, all load components including the possible
longitudinal loads shall be placed in their correct locations at conductor attachment points.
Insulators and hinged droppers are assumed to be properly inclined due to the longitudinal
force. This fact together with possible simultaneous transversal load component may cause
significant secondary bending and torsional effects especially on angle supports.
(ncpt)  FI.4 Anti-cascade supports
Suspension supports may be assumed to act also as anti-cascade supports, if so specified in
the Project Specification. See the load definitions for anti-cascade supports in Clause
4.12.2/FI.2.
4.9 Safety loads
4.9.1 Construction and maintenance loads
(ncpt)  FI.1 Temporary anchoring of conductors at suspension supports
Should conductors be anchored at a suspension support during the stringing process, the slope
of the anchored conductors shall not exceed 25 %. The support shall be designed for extra
vertical loads placed at the fixing points of the conductors on the support. These vertical loads
shall be taken as 1/3 of the design loads of the conductors in the stringing condition.
(ncpt)  FI.2 Stringing conditions on tension supports
All relevant stringing conditions shall be taken into account in the design of tension supports.
The principal stringing cases are shown in Fig. 4.12/FI.1.
Temporary guying can be used at guyed tension supports to relax the effects of unsymmetrical
or unbalanced loads which may take place during the stringing process. The utilization of the
relaxing effect shall not exceed 25 % of the strength in the condition where temporary guys are
not used. The above mentioned relaxing effects can be taken into account at self-supporting
lattice towers or steel poles only, if so allowed in the Project Specification.
The support shall resist the final design stringing loads at the condition after the completion of
the stringing works with all relevant conductors intact and temporary guys removed. Additional
requirements may be given in the Project Specification.

Finland - 11/27 - EN 50341-2-7:2015

The use of temporary guying shall be properly documented for possible later detachment of
conductors due to maintenance or dismantling works.
4.12 Load cases
4.12.1 General
(ncpt)  FI.1 Conductor sag and tension calculations
Partial load and combination factors shall be applied on loads prior to the conductor tension
analysis.
In calculations the conductor shall be treated as a catenary curve (hyperbolic formula).
Parabola formula can be used for span lengths not exceeding 500 m. The calculations shall
be done using either a non-linear stress-strain curve of the conductor based on the
specification of the conductor manufacturer or using a linear approach based on the initial
and final values of the modulus of elasticity of the conductor.
Normally sag and tension calculations shall be done for each load case by using the ruling
span method. The calculations shall be based on the reference condition after the over-
stress due to the creep compensation has ceased.
The main assumption for the validity of the ruling span method is that the variation of the
span length from span to span is reasonable. In earth wires and in phase conductors
installed at post insulators on lines with nominal voltages > 45 kV, the ruling span shall be
taken as equal to the actual span length.
NOTE: When using an iterative stress balancing method for calculating conductor tensions in
cases with unbalanced ice at suspension supports (in icing categories III and IV),
reasonable number of spans on both sides of the support concerned should be taken into
account.
(ncpt)  FI.2 Effect of unequal span lengths
Large variations in span lengths, especially between two adjacent spans, will cause variation
in the conductor stress from span to span and thus, result in longitudinal loads. The shorter
the insulator string the bigger is the effect of this variation. The effect is often significant in the
case of earth wires (short clamps) and during loads where ice is present. If the span ratio
between the adjacent spans is large enough, also other load cases may cause longitudinal
loads, which shall be taken into account in the loads at the support.
In these cases the ruling span method cannot be used directly. In load calculations for
suspension supports the tensions of the phase conductors should be calculated by using a
global complete line analysis technique for a line section taking into account the effects of
sufficient number of spans on both sides of the support concerned.
More conservative simplified methods can be used as well.
NOTE 1: Also the relaxing effect of the displacements of the supports can be taken into account,
when calculating conductor stresses and longitudinal forces. However, in the case of
self-supporting lattice towers this effect is not significant.
NOTE 2: Exact rules for judging, when the longitudinal loads due to unequal spans shall be taken
into account, cannot be given. The designer should verify this case by case. Based on
the experience, the effect of the longitudinal load is considered to be significant, if its
value exceeds 5% of the force of one sub-conductor in the reference condition.
(ncpt)  FI.3 Creep compensation
Due to the creep phenomenon, the conductor will be over-tensioned in the stringing phase.
Nominal reference stress is supposed to be achieved within one year's time from the
installation. Extreme load conditions are not assumed to occur during this time. The correct
stringing tension depends on the type of the conductor.
NOTE: In the stringing load cases the over-tensioning can be taken into account by deducting the
compensation temperature of the conductor concerned to the temperature value in the
stringing load case. Detailed parameters can be acquired from the Project Specification or
conductor manufacturer.
(ncpt)  FI.4 Guying effect of conductors
Guying effect of conductors shall not be taken into account at security loads in designing
supports in lines of reliability levels 2 and 3. It can be taken into account in other cases, if not
otherwise specified in the Project Specification,
4.12.2 Standard load cases
(ncpt)  FI.1 Load case definitions
Load cases, partial load factors and temperatures in each case are specified in Table 4.13/FI.1.

(ncpt)  FI.2 Load cases for different support types
The following load cases shall be applied to different support types. See details of the cases in
Table 4.13/FI.1 and figures for stringing case examples for lines with nominal voltages > 45 kV
in Figure 4.12/FI.1. Additional requirements may be given in the Project Specification.
Suspension support
• Case 1a, Extreme wind
• Case 1b, Minimum temperature
• Case 2a, Extreme ice + snow
• Cases 2b-e, Special icing cases (only in icing categories III and IV)
• Case 3a, Extreme ice + nominal wind
• Case 3b, High wind + nominal ice
• Case 4, Temporary construction condition (stringing condition with temporary anchoring
and extra vertical force at each conductor attachment point), see Clause 4.9.1/FI.1.
• Case 5, Security load at any of the conductor attachment points
Tension support
• Cases 1-3 as at suspension support
• Cases 4, Construction loads in all required stringing conditions S1-S5 (see Figure
4.12/FI.1) in the project concerned with and without optional temporary guying. The most
unfavourable arrangements for conductors shall be considered in unbalanced conditions.
Anti-cascade support
• Cases 1-3 as at suspension support
• Case 5, Accidental case with all conductors in one span detached (cases S2-S3 in Figure
4.12/FI.1). For other conductors the conductor tensions in the reference condition shall
be used. The dynamic effects are assumed to be covered by the relaxing of the
conductor tension.
Terminal support or gantry
• Cases 1-3 as at suspension support
• Cases 4, Construction loads in the required stringing conditions (cases S2, S4-S6 in
Figure 4.12/FI.1).
Double circuit tower   Single circuit portal tower

Case S1
Case S2
Case S3
Case S4
Case S5   Case S6
Case S1, Stringing with all conductors installed
Case S2, One sided stringing with conductors installed only in one span
Case S3, Unbalanced stringing with conductors installed in one span and partly in the other span
Case S4, Unbalanced stringing with conductors installed partly in one span
Case S5, One-sided stringing of center phase conductor
Case S6, One-sided stringing of outer phase conductors

Figure 4.12/FI.1 – Examples of stringing conditions for lines with nominal voltages > 45 kV
(case 4 in Table 4.13/FI.1)
Finland - 13/27 - EN 50341-2-7:2015

4.13 Partial factors for actions
(ncpt)  FI.1 Load and combination factors
Partial load factors γ and combination factors Ψ for different actions are given in Table
F
4.13/FI.1. The following definitions are used:
Extreme wind = 50 years return period wind load based on the basic wind speed value
including gust, terrain, height, altitude and temperature effects
High wind = Extreme wind load x 0,70.
In special cases the factor 0,45 can be used.
Nominal wind = Extreme wind load x 0,40.
In special cases the factor 0,25 can be used.
Extreme ice = 50 years return period ice load (= characteristic ice load I ), see Table
4.5.1/FI.1.
Extreme ice+snow = Extreme ice x Ψ , where 1,0 < Ψ < 3,0 (see Clause 4.13/FI.2).
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