Overhead electrical lines exceeding AC 1 kV - Part 2-13: National Normative Aspects (NNA) for ITALY (based on EN 50341-1:2012)

This NNA (National Normative Annex) is only applicable to all new overhead lines equipped with bare conductors, covered conductors or cables, with voltages above 1kV AC. This standard is not applicable to overhead lines pre-existing before its coming into force and shall not be applied to maintenance or reconductoring; the standard can be applied in case of significant modifications of existing lines.

Lignes électriques aériennes dépassant 1 kV en courant alternatif - Partie 2-13: Aspects normatifs nationaux (NNA) pour l'ITALIE (basés sur l'’EN 50341-1:2012)

Nadzemni električni vodi za izmenične napetosti nad 1 kV - 2-13. del: Nacionalna normativna določila (NNA) za Italijo (na podlagi EN 50341-1:2012)

Ta nacionalna normativna določila (NNA) se uporabljajo samo za nove nadzemne električne vode, opremljene z neizoliranimi vodniki, izoliranimi vodniki ali kabli, z napetostmi nad 1 kV pri izmeničnem toku. Ta standard se ne uporablja za nadzemne električne vode, ki so že obstajali pred začetkom veljavnosti določil, in se ne uporablja za vzdrževanje ali zamenjavo napeljave. Standard je mogoče uporabiti v primeru večjih sprememb obstoječih vodov.

General Information

Status
Published
Publication Date
14-Jan-2018
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
24-Jan-2017
Due Date
31-Mar-2017
Completion Date
15-Jan-2018

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Overhead electrical lines exceeding AC 1 kV - Part 2-13: National Normative Aspects (NNA) for ITALY (based on EN 50341-1:2012)29.240.20DaljnovodiPower transmission and distribution linesICS:Ta slovenski standard je istoveten z:EN 50341-2-13:2017SIST EN 50341-2-13:2018en01-februar-2018SIST EN 50341-2-13:2018SLOVENSKI

STANDARD
SIST EN 50341-2-13:2018
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 50341-2-13
January 2017 ICS 29.240.20
English Version

Overhead electrical lines exceeding AC 1 kV - Part 2-13: National Normative Aspects (NNA) for ITALY (based on EN 50341-1:2012)

Lignes électriques aériennes dépassant 1 kV en courant alternatif - Partie 2-13: Aspects normatifs nationaux (NNA) pour l'ITALIE (basés sur l'EN 50341-1:2012)

This European Standard was approved by CENELEC on 2016-12-13. 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 50341-2-13:2017 E SIST EN 50341-2-13:2018
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Contents

European 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 2.2 Definitions ........................................................................................................... 7 2.3 Symbols ............................................................................................................... 7 3 Basis of design ............................................................................................................... 7 3.1 Introduction ......................................................................................................... 7 3.2 Requirements of overhead lines.......................................................................... 7 4 Actions on lines .............................................................................................................. 7 4.1 Introduction ......................................................................................................... 7 4.3 Wind loads ........................................................................................................... 8 4.5 Ice loads ............................................................................................................ 12 4.6 Combined wind and ice or snow loads .............................................................. 13 4.7 Temperature effects .......................................................................................... 13 4.8 Security loads ................................................................................................... 15 4.9 Safety loads ....................................................................................................... 16 4.11 Other special forces .......................................................................................... 16 4.12 Load cases ........................................................................................................ 17 4.13 Partial factors for actions.................................................................................. 18 5 Electrical requirements ................................................................................................ 18 5.6 Load cases for clearances calculation .............................................................. 18 5.8 Internal clearances within the span and at the top of the tower ....................... 18 5.9 External

clearances .......................................................................................... 20 5.11 Electric and magnetic fields .............................................................................. 23 6 Earthing systems .......................................................................................................... 24 7 Supports ....................................................................................................................... 24 7.3

Lattice steel towers ........................................................................................... 24 7.5 Wood poles ........................................................................................................ 25 7.10 Maintenance facilities........................................................................................ 25 8 Foundations .................................................................................................................. 25 8.1 Introduction ....................................................................................................... 25 8.2 Basis of geotechnical design

(EN 1997-1:2004 – Section 2) ............................ 25 9 Conductors and earth-wires......................................................................................... 26 9.1 Introduction ....................................................................................................... 26 9.2 Aluminium based conductors ........................................................................... 26 SIST EN 50341-2-13:2018

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9.3 Steel based conductors ..................................................................................... 26 9.4 Copper based conductors ................................................................................. 26 9.6 General requirements ........................................................................................ 27 10 Insulators ...................................................................................................................... 27 10.7 Mechanical requirements .................................................................................. 27 11 Hardware ....................................................................................................................... 28 11.6 Mechanical requirements .................................................................................. 28 12 Quality assurance, checks and taking-over ................................................................ 28 Annex J ............................................................................................................................... 30 J.4

Buckling resistance of angle in compression (see 7.3.6.4) ........................................ 30 J.5 Design resistance for bolted connections (see 7.3.8) ................................................ 32 J.5.1

General ................................................................................................................... 32 SIST EN 50341-2-13:2018

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European foreword
1. The Italian National Committee (NC) is identified by the following address:
Italian Electrotechnical National Committee
Via Saccardo 9
20134 Milano
Italy
Phone n°. ++39 02 21006.1
Fax n°. ++39 02 21006210
Committee 11/7 – Overhead electrical lines
E-Mail cei@ceinorme.it.

2. The Italian NC has prepared this Part 2-13 (EN 50341-2-13) listing the Italian National Normative Aspects

(NNA) under its sole responsibility and duly passed it through the CENELEC and CLC/TC 11 procedures.

NOTE: The Italian NC 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 already made in the framework of the general responsibility of a standards committee under the national laws/regulations.

This NNA is normative in Italy 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 subclauses, which are prefixed “IT”, 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 Italian NC who will, in co-operation with CLC/TC 11, clarify the requirements.

When no reference is made in this NNA 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 this NNA, shall be taken into account in Italy.

However, any boxed value, whether defined in Part 1 or in this NNA, shall not be amended in the direction of greater risk in a Project Specification.

6. The national Italian standards/regulations related to overhead electrical lines exceeding 1 kV (AC) are listed in subclause 2.1/IT.1 and 2.1/IT.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 Italian NC to be applicable and thus reported to the secretary of CLC/TC 11. SIST EN 50341-2-13:2018

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1 Scope 1.1 General (ncpt) IT.1

New overhead line This NNA (National Normative Annex) is only applicable to all new overhead lines equipped with bare conductors, covered conductors or cables, with voltages above 1kV AC. This standard is not applicable to overhead lines pre-existing before its coming into force and shall not be applied to maintenance or reconductoring; the standard can be applied in case of significant modifications of existing lines.

1.2 Field of application (ncpt) IT.1
Field of application

This standard specifies the general safety requirements, clarifies the actions that shall be carried out in the project and their relevant combinations, defines the characteristics of materials, products and any other aspects relevant to safety of electrical overhead lines as reported in the following clause 2. With reference to structural safety aspects, in absence of specific indications, and as an integration to this standard, the dispositions reported in “Norme tecniche sulle costruzioni” apply (see subclause 2.1). For what concerns structural aspects this standard applies also to D.C. overhead lines. For details concerning the application of this standard to telecommunication systems involving optical fibres either incorporated in or wrapped around earth-wires or conductors or suspended from overhead line supports, reference should be made to the Project Specifications.

2 Normative references, definitions and symbols 2.1 Normative references (A-dev) IT.1 National normative laws, government regulations

List of Law Decrees, Ministerial Decrees, Decrees of the President of the Minister’s Council: − In the following text the new Italian Technical Standard, reported in the Ministerial Decree 14.01.2008 promulgated in force of article 5, subsection 2 of Law Decree 28 May 2004 n. 136 turned into law 27.07.2004 n. 186 and the articles 52 e 83 of D.P.R. 06.06.2001, n. 380, contained the “Testo Unico delle disposizioni legislative e regolamentari in materia edilizia” will be referred as “Norme tecniche sulle costruzioni”. − Decree of the President of the Ministers’ Council, 23 April 1992.

Limiti massimi di esposizione ai campi elettrico e magnetico generati alla frequenza industriale nominale (50 Hz) negli ambienti abitativi e nell’ambiente esterno. Maximum limits of exposure to power frequency (50 Hz) electric and magnetic fields in inhabited buildings and external environment. − Decree of the Ministers of Public Works and of Internal Affairs, 16 January 1996.

Technical standard related to “Criteri generali per la verifica di sicurezza delle costruzioni e dei carichi e sovraccarichi”.

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− Decree of the President of the Ministers’ Council, 8 July 2003.

“Fissazione dei limiti di esposizione, dei valori di attenzione e degli obiettivi di qualità per la protezione della popolazione dalle esposizioni ai campi elettrici e magnetici alla frequenza di rete (50 Hz) generati dagli elettrodotti”.

Prescription of the exposition limits, attention values and quality objectives for the protection of people from the expositions to electrical and magnetic fields at power frequency (50 Hz). (ncpt) IT.2 National technical standards

List of Standard: − CEI 103-6 (1997-12) Protezione delle linee di telecomunicazione agli effetti dell’induzione elettromagnetica provocata dalle linee elettriche vicine in caso di guasto. Protection of telecommunication lines against harmful effects produced by power lines in fault conditions − CEI 7-1 (1997-09) Norme per conduttori di rame e leghe di rame per linee elettriche aeree. Requirements for copper and copper-alloy conductors for electrical overhead lines. − CEI 7-2 (1997-09) Norme per conduttori di alluminio, alluminio-acciaio, lega di alluminio, e lega di alluminio-acciaio per linee elettriche aeree. Requirements for all aluminium, aluminium-steel reinforced, all aluminium alloy and aluminium alloy-steel reinforced conductors for electrical overhead lines. − CEI 7-6 (1997-04) Norme per il controllo della zincatura a caldo per immersione su elementi di materiale ferroso destinati a linee e impianti elettrici.

Requirements for checking hot galvanizing by immersion on ferrous components used in lines and electrical installations.

− CEI 7-10 (1997-09) Norme per conduttori di acciaio rivestito di rame a filo unico ovvero cordati destinati a linee di telecomunicazione ed a linee di trasporto energia.

Requirements for copper clad steel conductors, single wire and stranded, for telecommunication and power lines.

− CEI 7-11 (1997-09) Norme per conduttori di acciaio rivestito di alluminio a filo unico e a corda per linee elettriche aeree.

Requirements for aluminium clad steel conductors, single wire and stranded, for electrical overhead lines.

− Guida CEI 36 (1997-10) Resistenza meccanica residua di elementi di catene di isolatori di vetro o di ceramica per linee aeree dopo il danneggiamento meccanico della parte isolante.

Residual strength of insulators units of glass or ceramic materials for overhead lines after mechanical damage of dielectric.

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− CEI EN 50443 (2012-12)

Effetti delle interferenze elettromagnetiche sulle tubazioni causate da sistemi di trazione elettrica ad alta tensione in corrente alternata e/o da sistemi di alimentazione ad alta tensione in corrente alternata.

Effects of electromagnetic interference on pipelines caused by high voltage a.c. electric traction system and/or high voltage a.c. power supply system.

− CEI UNI EN ISO/IEC 17065 (2012-12) (CEI 501-22) ex EN 45011

Valutazione della conformità - Requisiti per organismi che certificano prodotti, processi e servizi.

Conformity assessment – Requirements for bodies certifying products, processes and services.

2.2 Definitions (A-dev)
IT.1 Reference wind speed Vb

In this standard, the reference wind speed is referenced as Vb and is in agreement with Eurocodice 1991-1-4 and “Norme tecniche sulle costruzioni”.

2.3 Symbols (A-dev)
IT.1 Reference wind speed Vb

Vb mean wind speed in agreement with Eurocodice 1991-1-4 and “Norme tecniche sulle costruzioni”. Reference 4.3 IT1 (A-dev).

3 Basis of design 3.1 Introduction
(ncpt)
IT.1 Design philosophy and approach

The design philosophy of the Italian overhead lines shall be based on the limit state criterion of Eurocodes 1, 2, 3, 5, 7, 8.

The specific design approach to be used shall be specified in the Project Specifications.

3.2 Requirements of overhead lines
3.2.2 Reliability requirements (ncpt)
IT.1 Reliability of overhead lines

In compliance with EN 50341-1 and in accordance with past experiences, the reliability of overhead lines shall be as follows:

− Level 1: 50-years return period.
Higher reliability levels can be indicated in the Project Specifications.
4 Actions on lines

4.1 Introduction (ncpt) IT.1 Action on overhead lines Actions on overhead lines are due to the wind load, to the tensile load of conductors and earth-wires on angle supports, or, in case of breakage of conductors or earth-wires, to the weight of the components, to the weight of ice SIST EN 50341-2-13:2018

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or snow formations on conductors or earth-wires, to the temperature effects, to erection and maintenance loads and to seismic events. The combination of the above actions is made according to the criteria indicated in the following in order to meet the required reliability of the lines.

Actions on lines due to ice, snow and wind loads with higher values than those reported in the following paragraphs can be prescribed in the Project Specification on the base of experimental data due to field observations with sufficient statistical numerosity.

4.3 Wind loads 4.3.1 Field of application and basic wind velocity (A-dev) IT1

Wind load acting on overhead line Wind load acting on overhead line components is based on the reference wind speed, defined in the following subclause, by applying factors that take into account gust wind phenomena, the terrain roughness and the height above ground.

(A-dev)
IT.2 Reference wind speed

The reference wind speed, Vb, is defined as the maximum value, with a return period of 50 years, of the mean wind speed, in m/s, over a period of 10 min at a height of 10 m above the ground, on a terrain with exposition category II, as defined in “Norme tecniche sulle costruzioni” and according to table 4.1 of EN 50341-1.

The reference wind speed, as a function of site and of altitude above sea level shall be evaluated according to the specifications in the “Norme tecniche sulle costruzioni”.

In order to calculate the wind speed for different return periods “Table B.1 - Conversion factors for different return periods of wind speed” of EN 50341-1 shall be applied, where:

is the extreme wind speed with return period T;
V50
is the extreme wind speed with return period of 50 years.

The reference wind speed Vb is obtained from maps in 3.3.2 of “Norme tecniche sulle costruzioni”.

Each zone is characterized by maximum mean wind speed per hour, defined as follow:

Vb = Vb,0
for as ≤ a0
Vb = Vb,0 + ka(as – a0) for as > a0
Where as is the effective height above sea level in [m].

Values for Vb,0, Ka and a0 are reported in Table 3.3.I of “Norme tecniche sulle costruzioni”. For altitudes as > 1500 m, except for local conditions, properly documented and proven, it is assumed as = 1500 m.

The zoning is represented in Figure 4.3/IT.2 (equivalent to Figure 3.3.1 of “Norme tecniche sulle costruzioni”).

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Figure 4.3/IT.2

(A-dev) IT.3 Exposition category of the site For the evaluation of the terrain roughness of the site and of the necessary parameters for the calculation of wind action, reference shall be made to “Norme tecniche sulle costruzioni”.

(A-dev) IT.4 Exposure coefficient Ce Referring to 3.3.7 of “Norme tecniche sulle costruzioni”, the calculation of the exposure coefficient Ce

is made on the base of the following parameters: - the height above ground of the construction. For overhead lines “z” means the height above ground of the different components (such as supports, fitting, insulators, conductors, earth-wires);

- the terrain topography, with the related topography coefficient Ct;
- the exposition category of the site.

In the absence of specific analyzes which take into account the wind direction and the effective roughness and topography of the terrain surrounding the structure, for heights above ground of the structure no more than z = 200 m, it is given by the following formulas to be applied based on a comparison between the height of the structure and zmin as defined below:

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()()()=⋅⋅+⋅⋅=min002lnln7zCzCzzzzCCkzCeettre
minminzzzz<≥==where:==z
is height above ground of the structure (of the related component), Ct
is topography coefficient, typically set to 1,

kr, z0, zmin are coefficients defined as function of exposition category of site, depending on exposure area and terrain roughness class according to Table 3.3.II of “Norme tecniche sulle costruzioni”. In particular zmin indicates the minimum height of the construction for a given exposition category.

According to 4.2 of EN 1991-1-4, reference is made to exposition category of site II, whose characteristics are reported in Table 4.3/IT.4, conforming to Table 3.3.II of “Norme tecniche sulle costruzioni”.

Table 4.3/IT.4 −=Charac≥eris≥ics=of exposition category II Exposition category

of the site kr z0 [m] zmin [m] II 0,19 0,05 4 In Figure 4.3/IT.4 (corresponding to figure 3.3.3 of “Norme tecniche sulle costruzioni”) the exposition coefficient trend for each exposition category is indicated as a function of the height of the construction.

Figure 4.3/IT.4

By multiplying Vb by square root of Ce it is possible to obtain the peak speed (extreme wind) at the height of the structure.

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(A-dev)
IT.5 Wind speed at arbitrary height above ground
It is calculated according to clause IT.4 above.
(A-dev)
IT.6 Dynamic pressure of the wind
The dynamic pressure of the wind [N/m2] is:
ρ Vb2 where
the air density is ρ = 1,25 kg/m3 and
Vb is the reference wind speed.
(A-dev)
IT.7 Dynamic wind force on any element of lines

The force value Qw of the wind which blows horizontally or at right angle on any element of lines is:

= qb ⋅ Ce ⋅ Gx ⋅ Cx ⋅ A where
qb is the dynamic pressure of wind.
is the exposition coefficient according to “Norme tecniche sulle costruzioni”.

Gx is the dynamic factor which considers the effects of reduction due to the not contemporaneousness of the maximum local pressures, as defined in “Norme tecniche sulle costruzioni”; for what concerns aspects that are peculiar to overhead lines, reference shall be made to EN 50341-1, in particular when calculation is referred to wind action on conductors (or earth-wires), the coefficient Gx shall be replaced by the coefficient Gc of EN 50341-1 4.4.1.2.

is the dynamic factor of drag resistance, which depends on the shape of the element considered; the following values can be considered:

− conductors
C = 1,00
− overhead stranded conductors
C = 1,00
− overhead cables
C = 1,00
− cylindrical objects (bars, tubular poles)
C = 0,80
− bar, tubular poles with more than six sides
C = 1,20
− bar, tubular poles with six sides
C = 1,40
− flat surfaces normal to wind direction
(angles, rectangular poles)
C = 1,80
spherical objects
C = 0,35
− insulators
C = 1,20

for additional information on lattice structures, reference shall be made to EN 50341-1.

A is the area of considered element, projected on a plane perpendicular to the wind direction.

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For the definition of height above ground for dynamic pressure of the wind on conductor calculation reference may be made to subclause 4.4.1.1 of EN 50341-1.

The wind pressure on conductors or earth-wires, which are not right angled to wind direction, can be calculated considering the actual angle of incidence.

4.5 Ice loads 4.5.1 General
(snc) IT.1 Ice loads evaluation

The ice or snow loads are valuated as variable loads, characterized by the return period and thickness which assumes conventionally different values, having cylindrical shape, depending on the zone, and altitude above sea level, as specified in the following.

(snc) IT.2 Ice and snow reference thickness

This clause reports the ice and snow reference thickness (Sk) on conductors and earth-wires with a return period of 50 years; it is an extreme value of thickness with which to evaluate the overloads on conductors and earth-wires, assuming a cylindrical shape with circular cross section sleeve.

For all altitudes, as, above sea level higher than 1500 m, as shall be assumed equal to 1500 m.

Load type 1 (ice)

Regions: Valle d’Aosta, Piemonte, Liguria, Lombardia, Trentino Alto Adige, Emilia Romagna, Friuli Venezia Giulia, Veneto, Abruzzo and Molise, with altitude above sea level (a.s.l.) as > 600 m:

Ice density ρi = 900 kg/m³
Sk = 0 mm
for as ≤ 600 m
Sk = 18 + 16 (as- 600)/1000 mm
for as > 600 m
Load type 2 (snow)

Regions: Valle d’Aosta, Piemonte, Liguria, Lombardia, Trentino Alto Adige, Emilia Romagna, Friuli Venezia Giulia, Veneto e Marche, Abruzzo, Molise, Toscana (with exclusion of the provinces of Livorno and Grosseto), Umbria, Lazio (with exclusion of the provinces of Viterbo, Roma and Latina), Campania (with exclusion of the provinces of Napoli and Caserta), Puglia (with exclusion of the provinces of Brindisi and Lecce), Basilicata, Calabria (with exclusion of the province of Reggio Calabria):

Snow density ρi = 500 kg/m³
Sk =24 mm
for as ≤ 600 m
Sk =24 + 20 (as - 600)/1000 mm for as > 600 m.

Load type 3 (snow) Regions: Toscana (provinces of Livorno e Grosseto), Lazio (provinces of Viterbo, Roma and Latina); Campania (provinces of Napoli and Caserta), Puglia (provinces of Brindisi and Lecce), Sardegna, Calabria (province of Reggio Calabria), Sicilia:

Snow density ρi = 500 kg/m³
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Sk = 0 mm
for as ≤ 600 m
Sk = 20 + 15 (as - 600) /1000 mm
for as > 600 m
4.5.2 Ice forces on conductors
(snc) IT.1 Ice and snow loads on conductors and earth-wires

The ice and snow load IT (N/m) is calculated using the thicknesses and densities indicated in 4.5, and represents the extreme ice or snow load with return period T = 50 years.

In order to obtain the ice or snow load for a different return period, Table 4.5.2/IT.1 (corresponding to Table B.2 of EN 50341-1) shall be applied.

Table 4.5.2/IT.1 −=Conversion=fac≥ors=for=≤ifferen≥=re≥urn=perio≤s=for=ice=or=snow=loa≤s==Return period

T [years]
Extreme ratio
IT/Imm
Conversion factor
CT = IT/I50
3 1,30 0,37 50 3,51 1,00 150 4,33 1,23 500 5,22 1,49 where:
is the extreme ice or snow load with a return period T;
Imm
is the mean value of maximum ice or snow loads in a year;
I50
is the extreme ice or snow load with a return period of 50 years.

(snc) IT.2 Ice or snow loads on helically wound cores For MV cables, having helically shape that gives stronger torsional rigidity to the single core and limits ice or snow sleeve increase, with a smooth polyethylene sheath which facilitates the slipping away of any deposits of ice or snow, for the ice or snow load, IT , a reduction factor equal to 0,8 shall be used.

4.6 Combined wind and ice or snow loads
(snc) IT.1 Coincidence of wind and ice or snow loads

In presence of ice or snow thicknesses, the combined wind, ice and snow actions are defined in Table 4.7/IT.1.

4.7 Temperature effects (snc) IT.1 Temperature effects

For the calculation of the tensile load on conductors and earth-wires, and of related forces transmitted to supports, as well as for geometrical verifications of height above ground for electrical clearances and insulating distances, the temperatures below reported shall apply:

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a) EDS temperature (Every Day Stress) is 15°C: in this condition, in absence of wind, the tensile load of conductors shall not be greater than 25 % of the breakage load.

On the basis of specific project conditions, to limit wind vibration effects, special attention should be paid to laying conditions when the parameter value (the ratio, between the horizontal tension and the mass per linear meter of conductor = 2000 m ) is exceeded. Criteria and conditions of installation should be defined in project specifications. b) The minimum temperature to be considered depends on the following zones A and B of the Italian territory:

Zone A Territory with an altitude not exceeding 800 m a.s.l. in the central, southern and insular areas of Italy (zones 3, 4, 5, 6, 9); the minimum temperature is – 7°C;

Zone B Territory with an altitude exceeding 800 m a.s.l in the central, southern and insular part of Italy (zones 3, 4, 5, 6, 9) plus all the territory of northern Italy (zones 1, 2, 7, 8); the minimum temperature is – 20°C.

c) The extreme wind speed condition temperature is – 7°C.
d) The temperature for the combination of wind and ice or snow loads is – 2°C.

e) Temperature and wind actions are combined, as shown in Table 4.7/IT.1. Both for icing and snow deposits it can be assumed a temperature of – 2°C.

f) Temperature to be used for verifying the electrical clearances. Both the two following methods can be applied as follows:

Method of maximum reference temperature

f1) The electrical clearances on cross structures shall be verified at the maximum reference temperature during normal service indicated in project specifications for both zone A and zone B of Italian territory. The maximum temperature during normal service is defined in. 9.1, 9.2.3, 9.3.3 and 9.4.

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