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 con
General
(ncpt) IT.1 New overhead line
The National Normative Annex (NNA) applies exclusively to new overhead lines using bare conductors, covered conductors, or cables with voltages exceeding 1kV AC It does not pertain to overhead lines that existed prior to its implementation and is not intended for maintenance or reconductoring activities However, the standard may be applied in instances of significant modifications to existing lines.
Field of application
(ncpt) IT.1 Field of application
This standard outlines the essential safety requirements for electrical overhead lines, detailing the necessary actions and their combinations, as well as defining the characteristics of materials and products relevant to safety For structural safety aspects, in the absence of specific guidelines, the provisions outlined in the "Norme tecniche sulle costruzioni" are applicable.
For what concerns structural aspects this standard applies also to D.C overhead lines
For information on the application of this standard to telecommunication systems that utilize optical fibers, whether integrated with or encased in earth wires, conductors, or suspended from overhead line supports, please consult the Project Specifications.
2 Normative references, definitions and symbols
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:
The new Italian Technical Standard, established by Ministerial Decree 14.01.2008 under article 5, subsection 2 of Law Decree 28 May 2004 n 136, which was later enacted as law on 27.07.2004 n 186, along with articles 52 and 83 of D.P.R 06.06.2001, n 380, is referred to as the "Norme tecniche sulle costruzioni" or Technical Standards for Construction.
− 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
Technical standard related to “Criteri generali per la verifica di sicurezza delle costruzioni e dei carichi e sovraccarichi”
1 The Italian National Committee (NC) is identified by the following address:
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
The Italian NC is solely responsible for ensuring the technical accuracy of this NNA in accordance with EN 50341-1, having conducted the required quality assurance and control checks.
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
3 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
The amendments to the relevant text in Part 1 are referred to as "IT." For any necessary clarifications regarding the application of this NNA alongside Part 1, inquiries should be directed to the Italian NC, which will work in collaboration with CLC/TC 11 to 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
(ncpt) IT.1 New overhead line
The National Normative Annex (NNA) applies exclusively to new overhead lines using bare conductors, covered conductors, or cables with voltages exceeding 1kV AC It does not pertain to overhead lines that existed prior to its implementation and is not intended for maintenance or reconductoring activities However, the standard may be applied in instances of significant modifications to existing lines.
(ncpt) IT.1 Field of application
This standard outlines the essential safety requirements for electrical overhead lines, detailing the necessary actions and their combinations, as well as defining the characteristics of materials and products relevant to safety In terms of structural safety, in the absence of specific guidelines, the provisions outlined in the "Norme tecniche sulle costruzioni" will apply as an addition to this standard.
For what concerns structural aspects this standard applies also to D.C overhead lines
For information on the application of this standard to telecommunication systems using optical fibers integrated with or wrapped around earth wires, conductors, or suspended from overhead line supports, please consult the Project Specifications.
2 Normative references, definitions and symbols
(A-dev) IT.1 National normative laws, government regulations
List of Law Decrees, Ministerial Decrees, Decrees of the President of the Minister’s Council:
The new Italian Technical Standard, outlined in Ministerial Decree 14.01.2008 and established under article 5, subsection 2 of Law Decree 28 May 2004 n 136, which was converted into law on 27.07.2004 n 186, along with articles 52 and 83 of D.P.R 06.06.2001, n 380, is referred to as the "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
Technical standard related to “Criteri generali per la verifica di sicurezza delle costruzioni e dei carichi e sovraccarichi”
− Decree of the President of the Ministers’ Council, 8 July 2003
Establishing exposure limits, attention values, and quality objectives is essential for protecting the population from electric and magnetic fields generated by power lines at a frequency of 50 Hz.
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
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
Norme per conduttori di rame e leghe di rame per linee elettriche aeree
Requirements for copper and copper-alloy conductors for electrical overhead lines
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
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
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
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
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
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.
Definitions
(A-dev) IT.1 Reference wind speed V b
In this standard, the reference wind speed is referenced as V b and is in agreement with Eurocodice 1991-1-4 and “Norme tecniche sulle costruzioni”.
Symbols
(A-dev) IT.1 Reference wind speed V b
V b mean wind speed in agreement with Eurocodice 1991-1-4 and “Norme tecniche sulle costruzioni” Reference 4.3 IT1 (A-dev)
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.
Requirements of overhead lines
(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:
Higher reliability levels can be indicated in the Project Specifications
Introduction
(ncpt) IT.1 Action on overhead lines
Wind load and tensile forces from conductors and earth-wires on angle supports impact overhead lines Additionally, in the event of conductor or earth-wire breakage, the weight of these components and ice accumulation also contribute to the overall load.
− Decree of the President of the Ministers’ Council, 8 July 2003
Establishing exposure limits, attention values, and quality objectives is essential for protecting the population from electric and magnetic fields generated by power lines at a frequency of 50 Hz.
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
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
Norme per conduttori di rame e leghe di rame per linee elettriche aeree
Requirements for copper and copper-alloy conductors for electrical overhead lines
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
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
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
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
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
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
(A-dev) IT.1 Reference wind speed V b
In this standard, the reference wind speed is referenced as V b and is in agreement with Eurocodice 1991-1-4 and “Norme tecniche sulle costruzioni”
(A-dev) IT.1 Reference wind speed V b
V b mean wind speed in agreement with Eurocodice 1991-1-4 and “Norme tecniche sulle costruzioni” Reference 4.3 IT1 (A-dev)
(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:
Higher reliability levels can be indicated in the Project Specifications
(ncpt) IT.1 Action on overhead lines
Actions affecting overhead lines arise from various factors, including wind load, tensile load from conductors and earth-wires on angle supports, and the weight of components in the event of conductor or earth-wire breakage Additional influences include ice or snow accumulation, temperature variations, erection and maintenance loads, and seismic events To ensure the required reliability of the lines, these actions are combined according to specified criteria.
In the Project Specification, actions on lines resulting from ice, snow, and wind loads that exceed the values outlined in the subsequent paragraphs may be specified based on experimental data derived from field observations with adequate statistical significance.
Wind loads
4.3.1 Field of application and basic wind velocity
(A-dev) IT1 Wind load acting on overhead line
Wind load on overhead line components is determined by the reference wind speed, incorporating factors that account for gust wind effects, terrain roughness, and elevation above ground.
(A-dev) IT.2 Reference wind speed
The reference wind speed, denoted as V b, represents the maximum mean wind speed measured in meters per second (m/s) over a 10-minute period at a height of 10 meters above ground level This value is based on a return period of 50 years and is applicable to terrain classified under exposure category II, as outlined in the "Norme tecniche sulle costruzioni" and detailed in table 4.1.
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:
V T is the extreme wind speed with return period T;
V 50 is the extreme wind speed with return period of 50 years
The reference wind speed V b 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:
Where a s is the effective height above sea level in [m]
Values for V b,0 , K a and a 0 are reported in Table 3.3.I of “Norme tecniche sulle costruzioni” For altitudes a s > 1500 m, except for local conditions, properly documented and proven, it is assumed a s = 1500 m
The zoning is represented in Figure 4.3/IT.2 (equivalent to Figure 3.3.1 of
(A-dev) IT.3 Exposition category of the site
The assessment of terrain roughness and the parameters required for calculating wind action will refer to the "Technical Standards for Construction."
Referring to 3.3.7 of “Norme tecniche sulle costruzioni”, the calculation of the exposure coefficient C e 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 C t ;
- the exposition category of the site
In the absence of specific analyses considering wind direction, effective roughness, and terrain topography, structures with heights up to 200 m are evaluated using defined formulas based on their height compared to a minimum threshold Additionally, factors such as snow accumulation on conductors, temperature effects, erection and maintenance loads, and seismic events must be considered The combination of these factors is crucial to ensure the 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
4.3.1 Field of application and basic wind velocity
(A-dev) IT1 Wind load acting on overhead line
Wind load on overhead line components is determined by the reference wind speed, incorporating factors that account for gust wind effects, terrain roughness, and elevation above ground.
(A-dev) IT.2 Reference wind speed
The reference wind speed, denoted as V b, represents the maximum mean wind speed measured in meters per second (m/s) over a 10-minute period at a height of 10 meters above ground level This value is based on a return period of 50 years and is applicable to terrain classified under exposure category II, as outlined in the "Norme tecniche sulle costruzioni" and detailed in table 4.1.
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:
V T is the extreme wind speed with return period T;
V 50 is the extreme wind speed with return period of 50 years
The reference wind speed V b 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:
Where a s is the effective height above sea level in [m]
Values for V b,0 , K a and a 0 are reported in Table 3.3.I of “Norme tecniche sulle costruzioni” For altitudes a s > 1500 m, except for local conditions, properly documented and proven, it is assumed a s = 1500 m
The zoning is represented in Figure 4.3/IT.2 (equivalent to Figure 3.3.1 of
(A-dev) IT.3 Exposition category of the site
The assessment of terrain roughness and the parameters required for calculating wind action will refer to the "Technical Standards for Construction."
Referring to 3.3.7 of “Norme tecniche sulle costruzioni”, the calculation of the exposure coefficient C e 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 C t ;
- the exposition category of the site
In the absence of detailed analyses considering wind direction, effective roughness, and the surrounding terrain's topography, the height of a structure, not exceeding 200 m, can be evaluated using specific formulas These formulas are applied based on a comparison between the structure's height and the minimum height, denoted as \( z_{min} \).
≥ where: z is height above ground of the structure (of the related component),
The topography coefficient, denoted as \$C_t\$, is usually set to 1 The coefficients \$k_r\$, \$z_0\$, and \$z_{min}\$ are defined based on the site's exposition category, which takes into account the exposure area and terrain roughness class, as outlined in Table 3.3.II of the "Norme tecniche sulle costruzioni." Specifically, \$z_{min}\$ represents the minimum height of a construction for a specified 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 − Characteristics of exposition category II
Exposition category of the site k r z 0
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
By multiplying V b by square root of C e it is possible to obtain the peak speed (extreme wind) at the height of the structure
(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/m 2 ] is: q b = ρ V b 2 where the air density is ρ = 1,25 kg/m 3 and
V b 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:
Q w = q b⋅ C e ⋅ G x ⋅ C x ⋅A where q b is the dynamic pressure of wind
C e is the exposition coefficient according to “Norme tecniche sulle costruzioni”
The dynamic factor \( G_x \) accounts for the reduction effects due to the non-contemporaneous occurrence of maximum local pressures, as outlined in the "Norme tecniche sulle costruzioni." For overhead lines, it is essential to refer to EN 50341-1, especially when calculating wind action on conductors or earth-wires, where the coefficient \( G_x \) should be substituted with the appropriate coefficient.
C x is the dynamic factor of drag resistance, which depends on the shape of the element considered; the following values can be considered:
− 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
− 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
≥ where: z is height above ground of the structure (of the related component),
The topography coefficient, denoted as \$C_t\$, is generally set to 1 The coefficients \$k_r\$, \$z_0\$, and \$z_{min}\$ are defined based on the site's exposure category, which takes into account the exposure area and terrain roughness class, as outlined in Table 3.3.II of the "Norme tecniche sulle costruzioni." Specifically, \$z_{min}\$ represents the minimum height required for a construction based on its exposure 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 − Characteristics of exposition category II
Exposition category of the site k r z 0
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
By multiplying V b by square root of C e it is possible to obtain the peak speed (extreme wind) at the height of the structure
(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/m 2 ] is: q b = ρ V b 2 where the air density is ρ = 1,25 kg/m 3 and
V b 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:
Q w = q b⋅ C e ⋅ G x ⋅ C x ⋅A where q b is the dynamic pressure of wind
C e is the exposition coefficient according to “Norme tecniche sulle costruzioni”
The dynamic factor \( G_x \) accounts for the reduction effects due to the non-contemporaneous occurrence of maximum local pressures, as outlined in the "Norme tecniche sulle costruzioni." For overhead lines, it is essential to refer to EN 50341-1, especially regarding the calculation of wind action on conductors or earth-wires, where the coefficient \( G_x \) should be substituted with the appropriate coefficient.
C x is the dynamic factor of drag resistance, which depends on the shape of the element considered; the following values can be considered:
− 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
− 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
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.
Ice loads
(snc) IT.1 Ice loads evaluation
Ice and snow loads are classified as variable loads, defined by their return period and thickness, which vary based on location and altitude These loads typically have a cylindrical shape, with specific values determined for different zones.
(snc) IT.2 Ice and snow reference thickness
This clause specifies the ice and snow reference thickness (Sk) for conductors and earth-wires, based on a 50-year return period It represents an extreme value of thickness used to assess overloads on these components, assuming a cylindrical shape with a circular cross-section sleeve.
For all altitudes, as, above sea level higher than 1500 m, as shall be assumed equal to 1500 m
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.) a s > 600 m:
The regions of Italy include Valle d’Aosta, Piemonte, Liguria, Lombardia, Trentino Alto Adige, Emilia Romagna, Friuli Venezia Giulia, Veneto, Marche, Abruzzo, Molise, and Toscana, excluding the provinces of Livorno and Grosseto Additionally, Umbria, Lazio (excluding Viterbo, Roma, and Latina), Campania (excluding Napoli and Caserta), Puglia (excluding Brindisi and Lecce), Basilicata, and Calabria (excluding Reggio Calabria) are also part of this list.
Sk $ + 20 (as - 600)/1000 mm for as > 600 m
The regions of Italy include Toscana, encompassing the provinces of Livorno and Grosseto; Lazio, which consists of Viterbo, Roma, and Latina; Campania, featuring Napoli and Caserta; Puglia, with the provinces of Brindisi and Lecce; Sardegna; Calabria, represented by the province of Reggio Calabria; and Sicilia.
Sk = 20 + 15 (as - 600) /1000 mm for as > 600 m
(snc) IT.1 Ice and snow loads on conductors and earth-wires
The ice and snow load I T (N/m) is calculated using the thicknesses and densities indicated in 4.5, and represents the extreme ice or snow load with return period
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 factors for different return periods for ice or snow loads
I T is the extreme ice or snow load with a return period T;
I mm is the mean value of maximum ice or snow loads in a year;
I 50 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
MV cables feature a helical design that enhances the torsional rigidity of the single core, effectively minimizing the accumulation of ice or snow The smooth polyethylene sheath aids in the easy shedding of ice or snow deposits For calculating the ice or snow load, a reduction factor of 0.8 should be applied.
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.
Temperature effects
For calculating the tensile load on conductors and earth-wires, as well as the forces transmitted to supports, specific temperatures must be considered for geometrical verifications of height above ground, electrical clearances, and insulating distances.
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
(snc) IT.1 Ice loads evaluation
Ice and snow loads are classified as variable loads, defined by their return period and thickness, which vary based on location and altitude These loads typically have a cylindrical shape and are influenced by specific regional factors.
(snc) IT.2 Ice and snow reference thickness
This clause specifies the ice and snow reference thickness (Sk) for conductors and earth-wires, based on a 50-year return period It represents an extreme thickness value used to assess overloads on these components, assuming a cylindrical shape with a circular cross-section sleeve.
For all altitudes, as, above sea level higher than 1500 m, as shall be assumed equal to 1500 m
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.) a s > 600 m:
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, excluding the provinces of Viterbo, Roma, and Latina; Campania, excluding Napoli and Caserta; Puglia, excluding Brindisi and Lecce; along with Basilicata and Calabria, excluding Reggio Calabria, are the regions of focus.
Sk $ + 20 (as - 600)/1000 mm for as > 600 m
The regions of Italy include Toscana, encompassing the provinces of Livorno and Grosseto; Lazio, which consists of the provinces of Viterbo, Roma, and Latina; Campania, featuring the provinces of Napoli and Caserta; Puglia, comprising the provinces of Brindisi and Lecce; as well as Sardegna and Calabria, represented by the province of Reggio.
Sk = 20 + 15 (as - 600) /1000 mm for as > 600 m
(snc) IT.1 Ice and snow loads on conductors and earth-wires
The ice and snow load I T (N/m) is calculated using the thicknesses and densities indicated in 4.5, and represents the extreme ice or snow load with return period
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 factors for different return periods for ice or snow loads
I T is the extreme ice or snow load with a return period T;
I mm is the mean value of maximum ice or snow loads in a year;
I 50 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
MV cables feature a helical design that enhances the torsional rigidity of the single core and minimizes the accumulation of ice or snow The smooth polyethylene sheath aids in the easy shedding of ice or snow deposits For calculating the ice or snow load, a reduction factor of 0.8 should be applied.
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
For calculating the tensile load on conductors and earth-wires, as well as the forces transmitted to supports and verifying the height above ground for electrical clearances and insulating distances, the following temperatures should be considered: the Every Day Stress (EDS) temperature is set at 15°C Under these conditions, and in the absence of wind, the tensile load on conductors must not exceed 25% of the breakage load.
To mitigate wind vibration effects based on specific project conditions, it is crucial to pay special attention to laying conditions when the parameter value (the ratio of horizontal tension to mass per linear meter of conductor) exceeds 2000 m Project specifications should clearly define the criteria and conditions for installation Additionally, the minimum temperature to be considered varies depending on the designated 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 encompasses territories in central, southern, and insular Italy with altitudes over 800 m a.s.l., including northern Italy The minimum recorded temperature in this region is –20°C, while extreme wind conditions are noted at –7°C Additionally, the temperature for assessing wind combined with ice or snow loads is –2°C For detailed temperature and wind action combinations, refer to Table 4.7/IT.1.
For both icing and snow deposits, a temperature of -2°C is assumed for verifying electrical clearances Two methods can be applied for this verification process.
The electrical clearances on cross structures must be assessed at the maximum reference temperature specified in the project for normal service, applicable to both zone A and zone B of the Italian territory.
The maximum temperature during normal service is defined in 9.1, 9.2.3, 9.3.3 and 9.4
The electrical clearances over cross structures must be verified at reference temperatures of 55°C for zone A and 48°C for zone B in Italy Additionally, the current carrying capacity of the line is determined by the risk of discharge over these cross structures.
For high thermic limit conductors, project specifications must define reference temperatures and current capacity For lines with voltages exceeding 45kV, it is essential to verify electrical clearances over cross structures under both standard and extreme temperature conditions This includes adjustments to the electrical clearances as specified in sections 9.1, 9.2.3, 9.3.3, and 9.4, where terms D el and D pp are replaced with D 50Hz_p_e and D 50Hz_p_p, respectively This verification process is crucial for assessing the current capacity based on discharge risks Additionally, the temperature for checking electrical clearances in swung catenary conditions is set at 55°C for zone A and 48°C for zone B in Italy.
The Table 4.7/IT.1 summarizes temperature, wind and ice/snow combinations
Table 4.7/IT.1 − Temperature, wind and ice/snow combinations
(°C) Extreme wind Ice/snow a) Every Day Stress 15 0 0 b) Minimum temperature Zone A –7
Co-existence of wind and ice or snow (*) actions –2 0,6 V b Sk f1) Verification of design clearances – Method of maximum reference temperature
0 0 f2) Verification of design clearances – Method at limit states
0 0 f3) Verification of clearances at extreme temperature conditions – Method at limit states
96 0 0 g) Check of electrical clearances in conditions of swung catenary
(*) This verification is not applicable to zones where S k = 0 (zone where the type 3 load per a s
In zone where the type 1 and type 2 loads can be expected, both verifications are required
The temperature values for verifications of f1), f2), f3), g) on high temperature conductors shall be indicated in project specifications
In scenarios involving a series of suspended spans with uniform loads, the calculation of tensile loads on conductors can effectively utilize the concept of equivalent span.
Security loads
(ncpt) IT.1 Breaking of conductors case
The loads shall be calculated:
In regions prone to ice or snow sleeve formation, particularly where such conditions are anticipated every three years, it is crucial to consider the wind load generated by a wind velocity of 0.6 times the basic wind speed (Vb) This load acts on a cylinder with a diameter that corresponds to the ice or snow overload.
- In areas where is not expected any ice or snow sleeve formation: in presence of extreme wind with return period of 3 years
The following load conditions will be considered:
For lines with voltages not exceeding 45 kV, each support must be evaluated individually, focusing on members connected to up to four conductors Under conditions of Every Day Stress (EDS) at a temperature of 15°C and in the absence of wind, the tensile load on the conductors should not exceed 25% of the breakage load.
To mitigate wind vibration effects, it is crucial to pay special attention to laying conditions when the horizontal tension-to-mass ratio of the conductor exceeds 2000 m Project specifications should clearly define the criteria and installation conditions Additionally, the minimum temperature considerations will vary based on specific 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 encompasses territories in central, southern, and insular Italy with altitudes over 800 m a.s.l (zones 3, 4, 5, 6, 9), as well as all of northern Italy (zones 1, 2, 7, 8) The minimum recorded temperature in this region is –20°C Additionally, extreme wind conditions are noted at –7°C, while the temperature for combined wind and ice or snow loads is –2°C The interplay of temperature and wind actions is detailed in Table 4.7/IT.1.
For both icing and snow deposits, a temperature of -2°C is assumed for verifying electrical clearances Two methods can be applied for this verification process.
The electrical clearances on cross structures must be assessed at the maximum reference temperature specified in the project for both zone A and zone B of Italy during normal service.
The maximum temperature during normal service is defined in 9.1, 9.2.3, 9.3.3 and 9.4
The electrical clearances over cross structures must be verified at reference temperatures of 55°C for zone A and 48°C for zone B in Italy Additionally, the current carrying capacity of the line is determined by the risk of discharge over these cross structures.
For high thermic limit conductors, project specifications must define reference temperatures and current capacity For lines with voltages exceeding 45kV, it is essential to verify electrical clearances over cross structures under both standard and extreme temperature conditions, as outlined in sections 9.1, 9.2.3, 9.3.3, and 9.4 This verification involves replacing the term \(D_{el}\) with \(D_{50Hz_{p_e}}\) and \(D_{pp}\) with \(D_{50Hz_{p_p}}\), as it impacts the current capacity based on discharge risk Additionally, the temperature for assessing electrical clearances in swung catenary conditions is set at 55°C for zone A and 48°C for zone B in Italy.
The Table 4.7/IT.1 summarizes temperature, wind and ice/snow combinations
Table 4.7/IT.1 − Temperature, wind and ice/snow combinations
(°C) Extreme wind Ice/snow a) Every Day Stress 15 0 0 b) Minimum temperature Zone A –7
Co-existence of wind and ice or snow (*) actions –2 0,6 V b Sk f1) Verification of design clearances – Method of maximum reference temperature
0 0 f2) Verification of design clearances – Method at limit states
0 0 f3) Verification of clearances at extreme temperature conditions – Method at limit states
96 0 0 g) Check of electrical clearances in conditions of swung catenary
(*) This verification is not applicable to zones where S k = 0 (zone where the type 3 load per a s
In zone where the type 1 and type 2 loads can be expected, both verifications are required
The temperature values for verifications of f1), f2), f3), g) on high temperature conductors shall be indicated in project specifications
In scenarios involving a series of suspended spans with uniform loads, the calculation of tensile loads on conductors can effectively utilize the concept of equivalent span.
(ncpt) IT.1 Breaking of conductors case
The loads shall be calculated:
In regions prone to ice or snow sleeve formation, particularly where such conditions are anticipated every three years, it is crucial to consider a wind load based on a wind velocity of 0.6 times the basic wind speed (Vb) This load should be applied to a cylinder with a diameter that corresponds to the ice or snow overload.
- In areas where is not expected any ice or snow sleeve formation: in presence of extreme wind with return period of 3 years
The following load conditions will be considered:
For lines with voltages not exceeding 45 kV, it is essential to evaluate the supports based on their connections: a) those connected to up to four conductors, and b) those connected to more than four conductors.
For lines with voltages exceeding 45 kV, it is essential to evaluate the supports based on the number of conductors they connect Specifically, supports should be categorized into two groups: those connected to up to six conductors and those connected to more than six but fewer than eighteen conductors.
The conductors to be considered broken shall be selected, depending on the support member concerned, on the basis of the following criterion:
- Each of the member specified in a) shall be checked when one of the conductors or earth-wires (if any) acting on it are broken;
Each member specified must be inspected when any two conductors or earth-wires affecting it are broken, ensuring that these conductors or earth-wires do not simultaneously act on the same member.
Conductors or earth-wires that are deemed broken will be those that create the most adverse load conditions on each individual component of the support structure, within the specified limits.
Verification of tangent supports, or supports with angles not exceeding 5°, is not required for lines with a voltage of 45 kV or less, provided that the supports demonstrate a longitudinal mechanical resistance equal to or greater than their transverse resistance.
Safety loads
(ncpt) IT.1 Construction and maintenance loads: partial factor
Construction and maintenance loads shall be indicated in the project specifications: partial factors shall not be lower than 1,5
If E is the value of such loads, we obtain E d = 1,5 E.
Other special forces
The supports of overhead lines shall be verified with respect to seismic actions taking into account the seismic classification of the Italian territory
As per EN 50341-1, Annex C.2.4, the dynamic loads from conductors and earth-wires are considered negligible due to the higher frequency of supports Therefore, only the weights of supports, foundations, insulator chains, and accessories need to be taken into account.
Verifications must be conducted in calm conditions, and the permanent vertical loads on conductors and earth-wires should be assessed in regions prone to ice or snow accumulation, taking into account ice or snow sleeves with a return period of three years.
The following verifications shall be carried out:
- In areas where ice or snow sleeve formation is expected, it is assumed the following: a temperature of – 20°C without ice or snow, a temperature of – 2°C with ice or snow;
- In areas where ice or snow sleeve formation is not expected, a temperature of -7 °C shall be assumed
When verifying supports with separate footing foundations, it is essential to account for varying horizontal displacements of the footings The criteria for determining these displacement values should rely on precise physical models that are well-documented and supported by relevant tests In the absence of such models, reference should be made to the "Norme tecniche sulle costruzioni."
Load cases
(snc) IT.1 Standard load cases
The load cases in Table 4.12.2/IT.1 shall be considered
Table 4.12.2/IT.1 − The normal load cases
Load case Load as per subclause Conditions
Extreme wind load Wind load at minimum temperature 2a
Uniform ice/snow loads on all spans Uniform ice/snow loads, transversal bending Unbalanced ice/snow loads, longitudinal bending Unbalanced ice/snow loads, torsional bending
3 4.6 Combined wind and ice loads
Security loads, torsional loads Security loads, longitudinal loads
With reference to figures in subclause 4.2.10.2 of EN 50341-1 § 4.2.10.2 for the determination of load cases 2b, 2c, 2d, the following reduction factors due to ice load IT apply: α = 0,5 α 1 = 0,3 α 2 = 0,7 α 3 = 0,3 α 4 = 0,7
In the longitudinal bending scheme, the load case of α₁ = 0 and α₂ = 1, applicable in the absence of wind, may be considered if specified in the project requirements This scenario represents the "slope" condition and should only be applied to supports located at the peaks of hills or mountains, which separate line sections on opposing slopes.
(ncpt) IT.2 Loading conditions for lines with not self-supporting towers
In case of lines with not self-supporting towers, the following loading conditions shall apply: b) members connected to more than four conductors;
For lines with voltages exceeding 45 kV, it is essential to evaluate each support separately based on the number of conductors Specifically, supports connected to up to six conductors and those connected to more than six but fewer than eighteen conductors must be considered distinctly.
The conductors to be considered broken shall be selected, depending on the support member concerned, on the basis of the following criterion:
- Each of the member specified in a) shall be checked when one of the conductors or earth-wires (if any) acting on it are broken;
Each member listed in section b) must be inspected when any two conductors or earth-wires affecting it are severed However, it is important to note that these two conductors or earth-wires must not simultaneously act on the same member mentioned in section a).
Conductors or earth-wires that are deemed broken will be those that create the most adverse load conditions on each individual component of the support structure, within the specified limits.
Verification of tangent supports, or supports with angles not exceeding 5°, is not required for lines with a voltage of 45 kV or less, provided that the longitudinal mechanical resistance of the supports is at least equal to their transverse resistance.
Partial factors for actions are set to 1, while the partial safety factors for materials are assumed to be 90% of those specified in clauses 7 (supports), 8 (foundations), 9 (suspended conductors or earth-wires with or without telecommunication circuits), 10 (insulators), and 11 (line equipment – overhead line fittings).
When calculating differential loads for conductors supported by suspension insulator sets, it is essential to account for the swing of the string Additionally, to determine the effects of a broken conductor (single or in a bundle) on a support, one can utilize the maximum tensile load of the section that includes the support.
(ncpt) IT.1 Construction and maintenance loads: partial factor
Construction and maintenance loads shall be indicated in the project specifications: partial factors shall not be lower than 1,5
If E is the value of such loads, we obtain E d = 1,5 E
The supports of overhead lines shall be verified with respect to seismic actions taking into account the seismic classification of the Italian territory
As per EN 50341-1, Annex C.2.4, the dynamic loads from conductors and earth-wires are considered negligible due to the higher frequency of supports Therefore, only the weights of supports, foundations, insulator chains, and accessories need to be taken into account.
Verifications must be conducted in calm conditions, and the permanent vertical loads on conductors and earth-wires should be assessed in regions prone to ice or snow accumulation, taking into account ice or snow sleeves with a return period of three years.
The following verifications shall be carried out:
- In areas where ice or snow sleeve formation is expected, it is assumed the following: a temperature of – 20°C without ice or snow, a temperature of – 2°C with ice or snow;
- In areas where ice or snow sleeve formation is not expected, a temperature of -7 °C shall be assumed
When verifying supports with separate footing foundations, it is essential to account for varying horizontal displacements of the footings The criteria for determining these displacement values should rely on precise physical models that are well-documented and supported by relevant tests In the absence of such models, reference should be made to the "Norme tecniche sulle costruzioni."
4.12 Load cases 4.12.2 Standard load cases
(snc) IT.1 Standard load cases
The load cases in Table 4.12.2/IT.1 shall be considered
Table 4.12.2/IT.1 − The normal load cases
Load case Load as per subclause Conditions
Extreme wind load Wind load at minimum temperature 2a
Uniform ice/snow loads on all spans Uniform ice/snow loads, transversal bending Unbalanced ice/snow loads, longitudinal bending Unbalanced ice/snow loads, torsional bending
3 4.6 Combined wind and ice loads
Security loads, torsional loads Security loads, longitudinal loads
With reference to figures in subclause 4.2.10.2 of EN 50341-1 § 4.2.10.2 for the determination of load cases 2b, 2c, 2d, the following reduction factors due to ice load IT apply: α = 0,5 α 1 = 0,3 α 2 = 0,7 α 3 = 0,3 α 4 = 0,7
In the longitudinal bending scheme, the load case of α₁ = 0 and α₂ = 1, applicable in the absence of wind, may be considered if specified in the project requirements This scenario represents the "slope" condition and should only be applied to supports located at the peaks of hills or mountains, which separate line sections on opposing slopes.
(ncpt) IT.2 Loading conditions for lines with not self-supporting towers
In case of lines with not self-supporting towers, the following loading conditions shall apply:
− with reference to wind load cases 1a and 3 of subclause 4.12.2, a wind blowing alternatively in the longitudinal and transversal direction with respect to the axis of the line shall be considered;
In sections of the line with non-self-supporting towers, any breaking of conductors, conductor bundles, or earth-wires will be treated as if they are completely absent In such cases, the two adjacent non-self-supporting towers will experience opposite longitudinal loads that correspond to the pull of the conductors or earth-wires, directed outward from the span Additionally, these towers will face transversal and vertical loads equal to those exerted by the broken conductors or earth-wires, as well as loads from any intact conductors or earth-wires present.
The load application points in sections a) and b) must align with the conductor attachment points, conductor bundles, or earth wires, where the breakage occurs.
In these conditions it is assumed that wind shall be considered blowing alternatively both in longitudinal and in transversal direction with respect to the axis of the line
The calculations under the specified conditions must consider the stabilizing reactions of conductors and any earth-wires associated with non-self-supporting towers, which are assumed to be intact.
Partial factors for actions
(A-dev) IT.1 Partial factor for wind action
The partial factor for wind action, simultaneously applied to all conductors and earth-wires, shall be set to 1 (one)
(A-dev) IT.2 Partial factor for ice or snow action
The partial factor for ice or snow action, simultaneously applied to all conductors and earth-wires, shall be set to 1 (one)
(A-dev) IT.3 Partial factor for all external loads in case of earthquakes
The partial factors for all external loads in case of earthquakes shall be set to 1 (one)
Load cases for clearances calculation
(A-dev) IT.1 Load cases for clearances calculation
Clearances shall be calculated with reference to the loading cases 1a and 2a of subclause 4.12.2 and under temperature conditions of Table 4.7/IT.1.
Internal clearances within the span and at the top of the tower
The clearances, in general, shall be calculated as follows
In the design of the towers, the following minimum air clearance shall be maintained:
Table 5.8/IT.1 − Minimum air clearances
Minimum distance between conductor within the span among points susceptible of approach: this spacing is reduced to D pp in case of points not susceptible of approaching each others m k⋅ ( f+I k )+D pp
Minimum distance between conductor and earth-wire within the span m k⋅ ( f +I k )+D el
Minimum clearance between live metal parts and earthed metal parts with wind speed V = 7,5 m/s m k 1 ⋅D el
Minimum clearance between live metal parts and earthed metal parts of suspension towers with max swing (wind speed with return period of 3 years) m D 50 Hz _ p _ e
Where: f is the sag, in metres, of the conductor at a temperature of +15°C in still air;
The length \( k \) in meters refers to the portion of any insulator that swings orthogonally to the line direction When there are varying swinging amplitudes on both supports of the span, the average value should be used The coefficient \( k \) is set at 0.6 for homogeneous aluminum or aluminum alloy conductors, while it is 0.5 for other types of conductors Additionally, the coefficient \( k_1 \) is assumed to be 0.75.
D pp is the minimum clearance voltage dependent (phase-phase), in metres, according to EN 50341-1;
D el is the minimum clearance voltage dependent (phase-earth), in metres, according to EN 50341-1
The minimum air clearances (phase-phase) in meters, denoted as D 50Hz_p_p, are voltage-dependent and essential to prevent disruptive discharges at power frequency voltages, as outlined in Table 5.5 of EN 50341-1 For overhead lines with voltages up to 45 kV, a clearance distance of 0.17 x Un/45 (m) should be considered.
D 50Hz_p_e represents the minimum phase-to-earth clearance in meters, which is voltage-dependent and necessary to endure power frequency voltage According to Table 5.5 of EN 50341-1, for overhead lines with a voltage of 45 kV or less, a clearance of 0.11 times the nominal voltage (Un) divided by 45 (in meters) should be considered.
These distances are not suitable for performing live works
For supports utilizing tension insulators, V-chains on the transversal plane, or post insulators, the current I_k is considered to be zero (I_k = 0) Additionally, for overhead lines with a voltage of 45 kV or less that are equipped with post insulators, the values obtained from the aforementioned formulas should be decreased accordingly.
The above mentioned minimum distance formulas shall not apply to spans of lines where f + I k > 40 m
− with reference to wind load cases 1a and 3 of subclause 4.12.2, a wind blowing alternatively in the longitudinal and transversal direction with respect to the axis of the line shall be considered;
In sections of the line with non-self-supporting towers, any breaking of conductors, conductor bundles, or earth-wires will be treated as if they are completely absent In such cases, the two adjacent non-self-supporting towers will experience opposite longitudinal loads that correspond to the pull of the conductors or earth-wires, directed outward from the span Additionally, these towers will endure transversal and vertical loads equivalent to those exerted by the broken conductors or earth-wires, as well as loads from any intact conductors or earth-wires present.
The load application points in sections a) and b) must align with the conductor attachment points, conductor bundles, or earth wires, if present, where the breakage occurs.
In these conditions it is assumed that wind shall be considered blowing alternatively both in longitudinal and in transversal direction with respect to the axis of the line
The calculations under the specified conditions must consider the stabilizing reactions of conductors and any earth-wires associated with non-self-supporting towers, which are assumed to be intact.
(A-dev) IT.1 Partial factor for wind action
The partial factor for wind action, simultaneously applied to all conductors and earth-wires, shall be set to 1 (one)
(A-dev) IT.2 Partial factor for ice or snow action
The partial factor for ice or snow action, simultaneously applied to all conductors and earth-wires, shall be set to 1 (one)
(A-dev) IT.3 Partial factor for all external loads in case of earthquakes
The partial factors for all external loads in case of earthquakes shall be set to 1 (one)
5.6 Load cases for clearances calculation
(A-dev) IT.1 Load cases for clearances calculation
Clearances shall be calculated with reference to the loading cases 1a and 2a of subclause 4.12.2 and under temperature conditions of Table 4.7/IT.1
5.8 Internal clearances within the span and at the top of the tower
The clearances, in general, shall be calculated as follows
In the design of the towers, the following minimum air clearance shall be maintained:
Table 5.8/IT.1 − Minimum air clearances
Minimum distance between conductor within the span among points susceptible of approach: this spacing is reduced to D pp in case of points not susceptible of approaching each others m k⋅ ( f +I k )+D pp
Minimum distance between conductor and earth-wire within the span m k⋅ ( f +I k )+D el
Minimum clearance between live metal parts and earthed metal parts with wind speed V = 7,5 m/s m k 1 ⋅D el
Minimum clearance between live metal parts and earthed metal parts of suspension towers with max swing (wind speed with return period of 3 years) m D 50 Hz _ p _ e
Where: f is the sag, in metres, of the conductor at a temperature of +15°C in still air;
The length \( k \) (in meters) refers to the portion of an insulator that swings orthogonally to the line direction When there are varying swinging amplitudes on both supports of the span, the average value should be used The coefficient \( k \) is set at 0.6 for homogeneous aluminum or aluminum alloy conductors, while it is 0.5 for other types of conductors Additionally, the coefficient \( k_1 \) is assumed to be 0.75.
D pp is the minimum clearance voltage dependent (phase-phase), in metres, according to EN 50341-1;
D el is the minimum clearance voltage dependent (phase-earth), in metres, according to EN 50341-1
D 50Hz_p_p represents the minimum air clearances (phase-phase) in meters, which are voltage-dependent and necessary to avoid disruptive discharges at power frequency voltages According to Table 5.5 of EN 50341-1, for overhead lines with voltages up to 45 kV, a clearance distance of 0.17 x Un/45 (m) should be considered.
D 50Hz_p_e represents the minimum phase-to-earth clearance in meters, which is voltage-dependent and necessary to endure power frequency voltage According to Table 5.5 of EN 50341-1, for overhead lines with a voltage of 45 kV or less, a clearance distance of 0.11 times the nominal voltage (Un) divided by 45 (in meters) should be considered.
These distances are not suitable for performing live works
For supports utilizing tension insulators, V-chains on the transversal plane, or post insulators, the current \( I_k \) is considered to be zero (\( I_k = 0 \)) Additionally, for overhead lines with a voltage of 45 kV or less that are equipped with post insulators, the calculated values from the aforementioned formulas should be decreased accordingly.
The above mentioned minimum distance formulas shall not apply to spans of lines where f + I k > 40 m
In such cases it is merely necessary that the spacing, in metres, between the conductors are not less than:
(3,8 + D pp ) m for aluminium or aluminium alloy conductors;
The previous requirements are not applicable to conductor in bundles or to single sub-conductors of the same bundle
For loading case 1a of subclause 4.2.10.2, with a conductor temperature of 15°C, the spacing \(d\) must not be less than \(D_{50Hz_{p_e}}\) For overhead lines with voltages of 45 kV or less, a distance of \(0.11 \times \frac{U_n}{45}\) meters is recommended.
At conductor temperature of 15°C, with a wind speed of 7,5 m/s, the spacing d, in metres, shall not be less than k 1 x D el with k 1 = 0,75
The above requirements shall not apply to any insulation spark gaps for co- ordination.
External clearances
(A-dev) IT.1 Height of conductors above ground and non navigable waters
To mitigate the risks associated with exposure to electrical and magnetic fields, conductors of the lines, under the specified temperature conditions and loading case, must maintain a vertical clearance from the ground and non-navigable bodies of water, ensuring safety and compliance with regulations.
(5 + D el ) m and, in any case, not less than 6 metres, where D el is the voltage dependent minimum clearance (phase-earth) in metres
The specified clearances for intact conductors across all spans must be measured without considering any layers of ice or snow, vegetation, or ground unevenness caused by cultivation.
Clearances do not need to be checked in case of conductors breakage or of unevenly loaded conductors
The above requirements may not be complied with in case of lines passing over enclosed land with access reserved for authorised electrical personnel
Conductors must be vertically spaced from the ground to comply with the regulations set forth in the "Decree of the President of the Minister's Council dated July 8, 2003."
A structure is considered crossed when the vertical projection of at least one electrical power line conductor intersects it, as specified in sections 4.7 f) and g), under load case 2a of subclause 4.12.2, with the catenary plane forming a 30° angle with the vertical.
Under specified conditions, overhead power lines must maintain minimum clearance distances to ensure safety These distances include: a) at least \(9 + D_{el}\) meters from motorways, railways, and navigable rivers, reduced to \(7 + D_{el}\) meters for lines with voltage ≤ 45 kV; b) \(6.5 + D_{el}\) meters from private cable railways; c) \(4.4 + D_{el}\) meters (minimum 4 m) from cableways and ski-lifts; d) \(2 + D_{pp}\) meters from other electrical or telephone lines, reduced to \(1.75 + D_{pp}\) meters for fixed conductors; e) \(3.5 + D_{el}\) meters from supports of other lines, which can be reduced to \(1 + D_{el}\) by mutual agreement; f) \(3.5 + D_{el}\) meters from any standable position of surrounding structures; and g) \(1.5 + D_{el}\) meters from unstandable positions and tree branches These regulations also apply to clearances from radio and television antennas.
A position is deemed accessible if an average person can stand there comfortably, even if it requires traversing areas that are not easily navigable.
Clearances must be verified with intact conductors across all spans, ensuring measurements account for any ice or snow, vegetation, and ground unevenness caused by cultivation.
Clearances do not need to be checked in case of conductors breakage or of unevenly loaded conductors
The above requirements may not be complied with in case of lines passing over enclosed land with access reserved for authorized electrical personnel
(A-dev) IT.4 Clearances to buildings
In view of the risk of discharge and of the possible effects caused by exposition to electrical and magnetic fields, the conductors of the lines, under the
In such cases it is merely necessary that the spacing, in metres, between the conductors are not less than:
(3,8 + D pp ) m for aluminium or aluminium alloy conductors;
The previous requirements are not applicable to conductor in bundles or to single sub-conductors of the same bundle
For loading case 1a of subclause 4.2.10.2, with a conductor temperature of 15°C, the spacing \(d\) must be no less than \(D_{50Hz_{p_e}}\) For overhead lines with voltages of 45 kV or less, a distance of \(0.11 \times \frac{U_n}{45}\) (in meters) is recommended.
At conductor temperature of 15°C, with a wind speed of 7,5 m/s, the spacing d, in metres, shall not be less than k 1 x D el with k 1 = 0,75
The above requirements shall not apply to any insulation spark gaps for co- ordination
(A-dev) IT.1 Height of conductors above ground and non navigable waters
To mitigate the risks associated with exposure to electrical and magnetic fields, conductors of the lines, under the specified temperature conditions and loading case, must maintain a vertical clearance from the ground and non-navigable bodies of water, ensuring safety and compliance with regulations.
(5 + D el ) m and, in any case, not less than 6 metres, where D el is the voltage dependent minimum clearance (phase-earth) in metres
The specified clearances for intact conductors across all spans must be measured without considering any layers of ice or snow, vegetation, or ground unevenness caused by cultivation.
Clearances do not need to be checked in case of conductors breakage or of unevenly loaded conductors
The above requirements may not be complied with in case of lines passing over enclosed land with access reserved for authorised electrical personnel
Conductors must be vertically spaced from the ground to comply with the limits set by the Decree of the President of the Minister's Council dated July 8, 2003.
A structure is considered crossed when the vertical projection of at least one electrical power line conductor intersects it, as specified in sections 4.7 f) (with vertical catenary) and g).
(with swung catenary) and in load case 2a of subclause 4.12.2, assuming the plane of the catenary forming an angle of 30° with the vertical
Under specified conditions, overhead power lines must maintain minimum clearance distances to ensure safety These distances include: a) at least \(9 + D_{el}\) meters from motorways, railways, and navigable rivers, reduced to \(7 + D_{el}\) meters for lines with voltage ≤ 45 kV; b) \(6.5 + D_{el}\) meters from private cable railways; c) \(4.4 + D_{el}\) meters (minimum 4 meters) from cableways and ski-lifts; d) \(2 + D_{pp}\) meters from other electrical or telephone lines, reduced to \(1.75 + D_{pp}\) meters for fixed conductors; e) \(3.5 + D_{el}\) meters from supports of other lines, which can be reduced to \(1 + D_{el}\) by mutual agreement; f) \(3.5 + D_{el}\) meters from any standable position on surrounding structures; and g) \(1.5 + D_{el}\) meters from unstandable positions These regulations also apply to clearances from radio and television antennas.
A position is deemed accessible if an average person can stand there comfortably, even if it requires traversing areas that are not easily standable.
Clearances must be verified with intact conductors across all spans, ensuring measurements account for any ice or snow, vegetation, and ground unevenness caused by cultivation.
Clearances do not need to be checked in case of conductors breakage or of unevenly loaded conductors
The above requirements may not be complied with in case of lines passing over enclosed land with access reserved for authorized electrical personnel
(A-dev) IT.4 Clearances to buildings