Bsi bs en 50341 2 23 2016

General

(ncpt) SK.1 New overhead line

As a new overhead line is considered a brand new electric overhead line with nominal voltage exceeding 1 kV AC, between the points A and B

The new branch line of the existing overhead line will be treated as a separate overhead line, with the exception of a junction support, for which specific requirements will be outlined in the Project Specification.

The application of this standard for the reconstruction, relaying, and extension of existing overhead lines will be defined in the Project Specification Additionally, the Project Specification will specify which previous national standards are applicable and to what extent they will be utilized for the project.

Field of application

(ncpt) SK.1 Field of application

The requirements of this standard shall be adopted, where applicable (e.g requirements on loads, external clearances, etc.), for telecommunication cables as well

In case of overhead line under the design stage, parties concerned shall agree the extent of the application of this standard

The construction of overhead lines must adhere to the standards applicable at the design stage All involved parties should reach an agreement on the potential application of specific clauses from these standards.

(ncpt) SK.2 Installation of telecommunication equipment on supports

This standard applies to telecommunication equipment, such as aerials and dish antennas, installed on individual supports of overhead power lines, focusing on wind and ice load considerations The design and installation must adhere to the utility's requirements, ensuring safe access and maintenance for both the power line and telecommunication equipment Additionally, it is essential to implement technical solutions that protect personnel from electric shock and safeguard the telecommunication equipment from potential hazards like short-circuits, switching, and lightning overvoltages.

Normative references

National laws, Government regulations and other binding regulations are included in following 2.1/SK.2 International and national standards quoted in EN 50341-2-23 and not included in 2.1 EN 50341-1 are included in 2.1/SK.3

The Eurocodes, as outlined in 2.1 EN 50341-1, are applicable in Slovakia, along with the associated Slovak National Application documents for relevant standards, unless specified otherwise by EN 50341-1 or the Slovak National Normative Aspects (EN 50341-2-23).

NOTE Some EN, IEC, ISO and CISPR publications implemented as Slovak National Standards (STN) include informative notes and informative annexes useful in Slovakia

(A-dev) SK.2 National laws, government decrees and other binding rules of law

22/2001 Z.z Vyhláška, ktorou sa ustanovujú podrobnosti o zaradení vodných ciest a ich jednotlivých úsekov do príslušných tried podľa klasifikácie európskych vodných ciest

Regulation, which establishes the details on classification of waterways and their individual sections into relevant classes according to European waterway classification

534/2007 Z.z Vyhláška o podrobnostiach o požiadavkách na zdroje elektromagnetického žiarenia a na limity expozície obyvateľov elektromagnetickému žiareniu v životnom prostredí

Regulation on the details on requirements on electromagnetic radiation sources and on limits of population exposure to electromagnetic radiation in the environment

251/2012 Z.z Zákon o energetike a o zmene a doplnení niektorých zákonov

Act on energetics and on amendment to certain laws (Energy Act)

FMPE 994/11:1981 FMD 621/1981-SM Dohoda o postupu při interferenčním ovlivnění zabezpečovacího zařízení celostátních drah zařízeními elektrizační soustavy

The agreement on the common practice on interference influence of state railway security equipment by electricity system devices

STN EN 1991-1-4 Eurokód 1 Zaťaženia konštrukcií Časť 1-4: Všeobecné zaťaženia Zaťaženie vetrom (Národná príloha NA pre SR, Mapa vetrových oblastí

Eurocode 1: Action on structures Part 1-4: General actions – Wind Actions (National Annex NA for Slovakia, Wind zone map)

STN 33 2040 Elektrotechnické predpisy Ochrana pred účinkami elektromagnetického poľa 50 Hz v pásme vplyvu zariadenia elektrizačnej sústavy

Electric engineering regulations Protection against effects of the electromagnetic fields 50 Hz in the zone of influence of electric power system device

STN 33 2160 Elektrotechnické predpisy Predpisy na ochranu oznamovacích vedení a zariadení pred nebezpečnými vplyvmi trojfázových vedení VN, VVN a ZVN

Electric engineering regulations Rules for the protection of telecommunication lines and equipment against dangerous influences of three-phase high voltage, very high voltage and ultra high voltage lines

EN 50443 Účinky elektromagnetickej interferencie spôsobenej vysokonapọťovými elektrickými trakčnými sieťami striedavộho prỳdu a/alebo vysokonapọťovými napỏjacớmi sieťami striedavộho prúdu na potrubia

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

STN 73 6133 Stavba ciest Teleso pozemných komunikácií

Road Building – Road embankments and subgrades

EN 13501-1+A1 Klasifikácia požiarnych charakteristík stavebných výrobkov a prvkov stavieb Časť 1: Klasifikácia využívajúca údaje zo skúšok reakcie na oheň

Fire classification of construction products and building elements – Part 1:Classification using data from reaction to fire tests.

EN 13501-5+A1 Klasifikácia požiarnych charakteristík stavebných výrobkov a prvkov stavieb Časť 5: Klasifikácia využívajúca údaje zo skúšok striech namáhaných vonkajším ohňom

Fire classification of construction products and building elements - Part 5: Classification using data from external fire exposure to roofs tests

EN 50522 Uzemňovanie silnoprỳdových inštalỏciớ na striedavộ napọtia prevyšujúce 1 kV

Earthing of power installations exceeding 1 kV AC

EN 62305-3 Ochrana pred bleskom Časť 3: Hmotné škody na stavbách a ohrozenie života

Protection against lightning – Part 3: Physical damage to structures and life hazard

EN ISO 14688-1 Geotechnický prieskum a skúšky Pomenovanie a klasifikácia zemín Časť 1: Pomenovanie a opis

Geotechnical investigation and testing - Identification and classification of soil - Part 1: Identification and description

EN ISO 14688-2 Geotechnický prieskum a skúšky Pomenovanie a klasifikácia zemín Časť 2: Princípy klasifikácie

Geotechnical investigation and testing - Identification and classification of soil – Part 2: Principles for a classification

EN ISO 14689-1 Geotechnický prieskum a skúšky Pomenovanie a klasifikácia skalných hornín Časť 1: Pomenovanie a opis

Geotechnical investigation and testing - Identification and classification of rock – Part 1: Identification and description

EN 206 Betón Špecifikácia, vlastnosti, výroba a zhoda

Concrete Specification, performance, production and conformity

STN 73 3050 Zemné práce Všeobecné ustanovenia

STN 73 1001: 1988 (withdrawn on 1.4.2010) Zakladanie stavieb Základová pôda pod plošnými základmi

Foundation of structures Subsoil under shallow foundations

CIGRE TB 207:2002 CIGRÉ technical brochure No 207 “Thermal behaviour of overhead conductors”

CIGRE TB 273:2005 CIGRÉ technical brochure No 273 “Overhead conductor safe design tension with respect to Aeolian vibrations”

CISPR TR 18-2 Radio interference characteristics of overhead power lines and high-voltage equipment Part 2 : Methods of measurement and procedure for determining limits

Definitions

(ncpt) SK.1 span part of a line between attachment points of a conductor on two consecutive supports (IEV 466-03-01)

NOTE This definition is included for the reason that the English word “span” corresponds with the Slovak conversion used in STN IEC 50 (466) which means “a span length”

(ncpt) SK.2 overhead telecommunication line and equipment wire or cable line and telecommunication equipment leading above ground and outside buildings and transmitting information via electromagnetic waves

The SK.3 aluminium-based conductor is a bare conductor composed of round or shaped wires that are stranded in concentric layers with alternating stranding directions It may be produced with or without grease and is made from various materials according to specified alternatives.

Aluminium wires and aluminium alloy wires are essential components in various applications, often used in combination with each other or with other materials The integration of aluminium wires with steel zinc coated wires enhances durability, while the pairing of aluminium wires with aluminium clad steel wires offers improved conductivity Similarly, aluminium alloy wires can be effectively combined with steel zinc coated wires or aluminium clad steel wires to achieve optimal performance The SK.4 steel-based conductor, a bare conductor made from round or shaped wires, features a concentric lay stranded design with alternating stranding directions, and can be produced using various materials, including the aforementioned combinations.

– steel zinc coated wires – aluminium clad steel wires

Symbols

Symbols which are contained in EN 50341-2-23 and are not contained in EN 50341-1, or which are contained in EN 50341-2-23 also with a different meaning than in 2.3 EN 50341-1, are included below

Symbol Signification References b emp Minimum clearance between conductors within the span according to empirical formula 5.8/SK.3 c

D el1 Minimum clearance required to prevent a disruptive discharge between phase conductor and external object at earth potential during fast front and slow front overvoltages (external clearance)

D el2 Minimum clearance required to prevent a disruptive discharge between phase conductor and support structure during fast front and slow front overvoltages (internal clearance)

D el3 Minimum clearance required to prevent a disruptive discharge between phase conductor in window of a support and support structure during fast front and slow front overvoltages (internal clearance)

D el4 Minimum clearance required to prevent a disruptive discharge between phase conductor and earth wire during fast front and slow front overvoltages (internal clearance)

D tr Horizontal distance of a tree trunk from the most endangered conductor 5.9.2/SK.2 f Conductor sag under specified conditions 5.8/SK.3 g c Self-weight of a conductor per unit length 5.8/SK.3

The height of a tree is denoted as \( H_{tr} \) with a measurement of 5.9.2/SK.2, while the pole height above ground is represented as \( h_s \) at 7.6.5/SK.2 Additionally, the height of the most endangered conductor above the horizontal plane of the tree base is referred to as \( h_{c\_tr} \) with a value of 5.9.2/SK.2 Lastly, the mean height of phase conductors for a specific circuit on a support is indicated as \( h_{pc} \) at 4.4.1.1/SK.2.

I R50 Extreme reference ice load per conductor unit length at 10 m height above ground with return period T = 50 years 4.5.1/SK.3

K aH Altitude factor for altitudes H > 1 000 m 5.3/SK.2

K a1000 Altitude factor for altitude H = 1 000 m 5.3/SK.2

K h Height factor for the ice load 4.5.1/SK.3

K Ic Local condition factor for the ice load 4.5.1/SK.3 k emp , k emp_r

Factor depending on weight and diameter of a conductor and on mutual position of both conductors 5.8/SK.3

The vertical length (\$L\$) of the insulator set can swing perpendicularly to the line, measuring 5.8/SK.1 m The mass of the insulator set is indicated as 5.8/SK.5 Additionally, the horizontal distance (\$r\$) is defined as the space between the attachment point of a shorter insulator set and the location in a span where the distance between conductors is verified.

5.8/SK.1 t I Ice thickness on a conductor with a diameter of 30 mm according to the actual load combination 4.6.2/SK.2

U rwH Required withstand voltage for altitude H > 1 000 m 5.3/SK.2

U rw1 000 Required withstand voltage for altitude H = 1 000 m 5.3/SK.2

U rwLI Required withstand voltage for lightning impulse 5.3/SK.1

U rwSI Required withstand voltage for switching impulse 5.3/SK.1

U rw50Hz Required withstand voltage for power frequency overvoltage 5.3/SK.1

The V 2 wind velocity, with a return period of 2 years, is specified as 4.6.6.1/SK.1, while the probability factor is denoted as H.4.4/SK.1 The depth of the geotechnical soil investigation below the foundation base is outlined in section 8.3/SK.1 The TSL reduction factor for ice load concerning torsional security loads is indicated as α, with a reference to 4.8.2/SK.1, and the LSL reduction factor for longitudinal security loads is represented as α, according to 4.8.3/SK.2 The angle describing the mutual position of both conductors is defined as δ in section 5.8/SK.3, while the insulator set swing angle is noted as φ in 5.8/SK.5 Lastly, the partial factor for resistance, as per EN 1997-1, Design approach 2, is represented by γ in section 8.2.2.

Requirements of overhead lines

Reliability requirements

(ncpt) SK.1 Reliability level of permanent lines

Reliability level 1 (Return period of climatic action 50 years) is considered, unless a higher reliability level is specified in the Project Specification

(ncpt) SK.2 Reliability level of temporary lines

The return period of climatic actions for temporary lines, which have a lifespan of less than one year, may be shortened due to their limited exposure to climatic effects Additional details on the return periods of climatic loads can be found in Table 3/SK.1.

Table 3/SK.1 – Return periods for temporary lines

Life duration Return period (years)

When installing temporary lines for a nominal duration of 3 days, it is advisable to consider the meteorological forecast for the specific location For lines expected to last longer than 3 days, it is not recommended to use a basic mean wind speed lower than 20 m/s Additionally, ice loads can be disregarded if the installation occurs during the ice-free season, which runs from April 1st to November 1st.

Strength coordination

This standard specifies strength coordination solely for the above-ground portion of the steel structure of lattice tower stubs (refer to 7.3.6.1/SK.3) Additional requirements may be outlined in the Project Specification.

Additional considerations

Specific requirements such as the installation of aircraft warning spheres, night aircraft warning markers, fittings to prevent biological pollution of insulators, and bird protection fittings must be detailed in the Project Specification.

Wind loads

Field of application and basic wind velocity

(snc) SK.1 Basic wind velocity, wind zone map

Basic wind velocities in Slovakia are given in Table 4/SK.1 Data given in this table are taken from National Annex of STN EN 1991-1-4

Slovakia's territory is categorized into two primary wind zones, which are further segmented based on altitude This classification results in four main wind zones, each associated with distinct basic wind speeds, denoted as \$V_{b,0}\$ These wind zones are illustrated on the Map of Fundamental Wind Speed \$V_{b,0}\$ values, included in the National Annex of STN EN 1991-1.

4 More accurate data on the borders of wind zones may be provided by Slovak Hydrometeorological Institute

Table 4/SK.1 – Basic wind velocities V b,0

Wind zone I II III IV

NOTE 1: Zones I and II are given by a geographical location Zone III corresponds to locations with altitudes between 700 and 1300 m above mean sea level and Zone IV corresponds to locations with altitudes exceeding 1300 m above mean sea level

NOTE 2: Based on long-term experience and monitoring in a given location, the wind zone may be specified otherwise than given in the Wind zone map in STN EN 1991-1-4.

Mean wind velocity

(snc) SK.1 Wind directional factor

Mean wind velocity in Slovakia is independent of wind direction The value of wind directional factor c dir = 1,0 shall be used

The value of orography factor c o = 1,0 shall be used, unless otherwise specified in the Project Specification

(ncpt) SK.3 Mean wind velocity for lines with nominal voltage up to 45 kV

For elements associated with supports with nominal voltage up to 45 kV and with a maximum height of 24 m, the value of mean wind velocity V h(h), calculated at 10 m height above ground is considered.

Mean wind pressure

The air density ρ in formula for calculation of mean wind pressure at a reference height h according to 4.3.3 is taken as 1,25 kg/m 3 independently of air temperature and altitude H.

Wind forces on overhead line components

Wind forces on conductors

(ncpt) SK.1 Wind force on conductor, transferred to a support

When calculating the wind force on a conductor, an alternative method can be employed in addition to the one outlined in section 4.4.1.1 This approach determines the total wind force on the conductor, which is transferred to a support, as the sum of halved wind forces acting on the conductor in both adjacent spans The peak pressure, denoted as \$q_p(h)\$, and the structural factor for the conductor, \$G_c\$, are calculated separately for each adjacent span The reference height of the conductor above ground, \$h\$, for the corresponding span is determined as the arithmetic average of the reference heights on the supports that define the span, as specified in section 4.4.1.1/SK.2.

(ncpt) SK.2 Reference height of conductor above ground

When calculating the transversal wind forces on conductors and the tensions in conductors, reference heights above ground must be specified according to method 4 or an alternative method Unless stated otherwise in the Project Specification, a more conservative approach may be used, considering the heights of insulator attachment points instead of conductor attachment points For lines with a nominal voltage up to 45 kV and supports up to 24 m high, a uniform reference height of 10 m can be applied for all conductors.

The reference height of conductors above ground, denoted as \$h\$, is determined by the mean height of the phase conductors on a support, calculated using the formula \$h_{pc} = \frac{(h_1 + h_2 + h_3)}{3}\$, where \$h_1\$, \$h_2\$, and \$h_3\$ represent the heights of individual conductor attachment points In the absence of specific instructions in the Project Specification, the heights of the insulator set attachment points at the support may be used in place of the conductor attachment heights.

For the earth wires and for the different circuits, placed one above the other, reference heights h above ground are calculated separately

When insulator sets on suspension supports equalize conductor tensions in adjacent spans, it is feasible to use a uniform reference height \( h \) for all conductors in a line section This reference height can either apply to all conductors of a circuit or to an individual conductor across all spans However, the reference height for phase conductors must not be lower than the average mean heights of the phase conductors on all supports, while the reference height for an individual conductor should not fall below the average height of that conductor on all supports For lines with a nominal voltage of up to 45 kV and supports not exceeding 24 m in height, a common reference height of 10 m can be utilized for all conductors.

(ncpt) SK.1 Structural factor for conductors (span factor)

Insulator sets on suspension supports help equalize conductor tensions in adjacent spans When calculating conductor tensions in a line section under wind load, the structural factor \( G_c \) is specified according to section 4.4.1.2 In the formula for the background factor \( B_2 \), \( L_m \) represents the length of the line section, which should not exceed 3 km, while \( h \) denotes the reference height of the conductor(s) in the line section as outlined in 4.4.1.1/SK.2.

(ncpt) SK.1 Drag factor for conductors

The value of drag factor C c = 1 (Method 1 according to 4.4.1.3) shall be used for commonly used bare stranded conductors, when calculating the wind forces on conductors

The value of drag factor C c = 1 shall also be used for covered conductors and overhead insulated cable systems.

Wind forces on insulator sets

According to (ncpt) SK.1, wind forces on insulator sets may be disregarded unless specified otherwise in the Project Specification This is applicable when the reference heights of conductors are established using method 7 as outlined in 4.4.1.1, or through the alternative method provided in 4.4.1.1/SK.2, which takes into account the heights of the attachment points of insulator sets at the support.

For lines with nominal voltage up to 45 kV, wind force on insulator sets is not considered.

Wind forces on lattice towers

(ncpt) SK.1 Calculation method for wind forces on lattice towers itself

Wind force on lattice towers shall be specified by Method 1 according to 4.4.3.2

(ncpt) SK.1 Structural factor, reference height and drag factor for lattice towers

The value of structural factor G t = 0,9 shall be used when calculating wind forces on lattice towers (tower body as well as crossarms)

For towers with a nominal voltage greater than 45 kV, the reference height above ground, denoted as \( h \), is defined as the height of the geometrical center of the relevant tower section However, if this height is below 10 m, a standard height of 10 m is used instead.

For towers with nominal voltages up to 45 kV, the reference height for all sections is standardized at 60% of the total tower height In cases where the total height does not exceed 24 m, a reference height of 10 m is applied uniformly across the entire tower.

The drag factor for a lattice tower with a rectangular cross-section is defined in section 4.4.3.2 For towers supporting lines with a nominal voltage of up to 45 kV, the value of \( C_{t1} = C_{t2} \times 2.6 \) should be applied.

Wind forces on poles

(ncpt) SK.1 Structural factor, reference height and drag factor for poles

The value of structural factor G t = 0,9 and the value of drag factor according to 4.4.4 shall be used when calculating wind forces on poles

For lines with nominal voltage exceeding 45 kV, the reference height above ground shall be determined by Method 1 according to 4.4.4, when calculating wind force on poles

For poles with nominal voltages up to 45 kV, the reference height is established using Method 2 as outlined in section 4.4.4 For poles that reach a total height of 24 m, a reference height of 10 m is applied to the entire pole.

Ice loads

General

Slovakia's territory is categorized into specific icing zones, as illustrated in the Icing Zone Map included in the informative annex S/SK of the standard These zones are defined by the ice mass per meter length of a conductor, measured in kg/m, for a conductor with a 30 mm diameter positioned 10 meters above ground.

The classification of a line route and its components into specific icing zones for design purposes will be outlined in the Project Specification This classification will consider the Icing zone map, the long-term experience of the transmission or distribution system operator in the area, and potentially the recommendations from a specialized organization.

For the lines where ice removal during its accretion is expected (e.g wiping, heating, etc.), it is possible to adequately decrease the ice load

Unless otherwise specified in the Project Specification, the ice load on supports and insulator sets is not considered

For the accessories of larger dimensions, located on conductors, the ice load with a thickness corresponding to the design thickness of ice on the conductor with a diameter of

30 mm in the relevant icing zone is considered

(ncpt) SK.3 Extreme reference and extreme ice load on conductors

The extreme reference ice load on conductors I R50, with a diameter \(d\) at a height of 10 m above ground, is detailed in Table 4/SK.2 The method for applying this load to overhead insulated cable systems will be specified in the project documentation.

Table 4/SK.2 – Extreme reference ice load on conductors

Extreme reference ice load I R50 (N/m) per unit length of a conductor with diameter d (mm) d ≤ 30 mm d >30 mm

I-K Shall be evaluated separately case by case NOTE 1 For lines with nominal voltage exceeding 45 kV, the ice load in zone I-0 is considered the same as in zone I-1

Extreme ice load per unit length of a conductor I 50 (N/m) at height h above ground is determined by the following formula:

I R50 extreme reference ice load per unit length of a conductor with diameter d at height 10 m above ground with return period T = 50 years according to the table 4/SK.2;

K lc local condition factor for ice load;

K h(h) height factor for ice load

For a defined area, it is possible to specify the value of local condition factor for ice load

In the Project Specification, the coefficient \( K_{lc} \) indicates the deviation from the extreme reference ice load in a specific area, based on the long-term experience of the transmission or distribution system operator By default, \( K_{lc} \) is set to 1.0 unless stated otherwise Additionally, the height factor for ice load, \( K_h(h) \), can be defined for a specific area, reflecting the relationship between extreme ice load and height above ground, also derived from the operator's long-term experience Unless specified differently in the Project Specification, \( K_h(h) \) is assumed to be 1.0.

Combined wind and ice loads

Combined probabilities

(ncpt) SK.1 Combined loads for lines with nominal voltage up to 45 kV

For lines with a nominal voltage of up to 45 kV, the Project Specification stipulates that only the combination of extreme ice load \(I_T\) and high probability wind velocity \(V_{IH}\) as outlined in sections 4.6.6.1 and 4.6.6.1/SK.1 will be taken into account, unless otherwise specified.

Drag factors and ice densities

When determining ice loads on line components according to this standard, only in-cloud ice in the form of rime with a density of ρ I = 500 kg/m 3 is considered

The value of drag factor for ice covered conductors C Ic = 1,1, independently of conductor diameter and the size of ice

When assessing wind forces on iced conductor accessories, it is important to consider the increased projected area due to ice thickness For a conductor with a diameter of 30 mm, the ice thickness \( t_I \) must be factored in under identical wind and ice load conditions Additionally, the appropriate drag factor \( C_{Ix} \) for the iced accessory should be applied.

Wind forces on support for ice covered conductors

(ncpt) SK.1 Wind force on ice covered conductors

When calculating the wind force on an ice-covered conductor, an alternative method can be employed alongside the one outlined in section 4.6.5 This method determines the total wind force transferred to a support as the sum of halved wind forces acting on the iced conductor in the adjacent spans The peak pressure \( q_{Ip}(h) \) and the structural factor for the conductor \( G_c \) are calculated separately for each adjacent span, while the reference height of the conductor above ground \( h \) is taken as the arithmetic average of the reference heights on the supports that define the span, as specified in section 4.4.1.1/SK.2.

Combination of wind velocities and ice loads

(ncpt) SK.1 Combination factor for wind loads Ψ W and reduction factor of wind velocity associated with icing B I

The value of combination factor for wind loads Ψ W = 0,25

The factor Ψ W includes the effect of reduction factor of wind velocity associated with icing B I

= 0,656 and the ratio of nominal wind pressure with the return period T = 3 years to extreme wind pressure with the return period T = 50 years (V 3/V 50) 2 = 0,58

Higher values of reduction factor of wind velocity associated with icing B I and combination factor for wind loads Ψ W may be specified in the Project Specification

For temporary lines the values of combination factor for wind loads are given in Table 4/SK.5

4.6.6.2 Nominal ice load I 3 combined with a low probability wind velocity V IL

(ncpt) SK.1 Combination factor for ice loads Ψ I

The value of combination factor for ice loads, corresponding to nominal ice load with return period T = 3 years, Ψ I = 0,35

The low probability wind velocity \( V_{IL} \), when combined with the nominal ice load \( I_3 \), is equivalent to the extreme wind velocity \( V_T \) with a specified return period \( T \) at a chosen reliability level, adjusted by the wind velocity reduction factor due to icing \( B_I \).

Temperature effects

(ncpt) SK.1 Design situations and associated conductor temperatures

The minimum temperature requirements for reliability levels are -30 °C for level 1, -35 °C for level 2, and -40 °C for level 3, unless specified otherwise in the Project Specification based on local conditions.

(b) A temperature of -5 °C is assumed under extreme wind speed

Nominal wind speed and minimum temperature are not included unless explicitly stated in the Project Specification If this design condition is necessary, the Project Specification must also define the corresponding minimum temperature.

(d) A temperature of -5 °C is assumed under ice load

(e) A temperature of -5 °C is assumed under combined wind and ice loads

(f) Average temperature in the coldest month of the year is taken as -5 °C

Relevant temperatures to check clearances are specified in Clause 5 of this part of the Standard.

Security loads

General

(ncpt) SK.1 Security loads for supports of lines with nominal voltage up to 45 kV

For lines with a nominal voltage of up to 45 kV, security loads for supports are generally not included unless explicitly stated in the Project Specification If such security loads are necessary, the Project Specification must also outline the conditions for their calculation.

Torsional loads

(ncpt) SK.1 Torsional loads for supports of lines with nominal voltage exceeding 45 kV

The residual static load at any earth wire or phase conductor attachment point arises from the tension release of a phase conductor, sub-conductor, or adjacent earth wire It is essential to account for the tension release in these conductors and the two adjacent spans to determine the maximum loading effect on any individual member of the structure or foundation.

In circuits utilizing bundle conductors, tension release is evaluated differently based on the type of support: for suspension and non-section tension supports, only one sub-conductor's tension release is considered, while for section and terminal (dead-end) supports, the tension release of all sub-conductors within the bundle is taken into account.

The Project Specification may define more severe requirements, i.e tension release in several sub-conductors of a bundle, or simultaneous release of tension in several conductors

Loads on supports and conductor tensions are determined at a conductor temperature of -5 °C, without wind load, and considering reduced ice loads that correspond to a 50-year return period for permanent lines, as specified in 4.5.1/SK.3 The reduction factor, α TSL, is set at 0.4 for lines with nominal voltages up to and including 110 kV, and at 0.5 for lines rated at 220 and 400 kV It is important to note that the weight of ice deposits on insulator sets is not taken into account, and the same conditions apply to other unreleased conductors.

When determining torsional security loads for temporary line supports, the extreme ice load with a return period of T years is calculated as \$I_T = \gamma_I I_{50}\$, where the partial factor for ice action \$\gamma_I\$ varies based on the temporary line's lifespan as outlined in 4.13/SK.2 This value is then adjusted by a reduction factor \$\alpha_{TSL}\$, which may be increased or supplemented with additional conditions as specified in the Project Specification.

Longitudinal loads

(ncpt) SK.1 Longitudinal security loads for non-section supports of lines with nominal voltage exceeding 45 kV

Longitudinal loads resulting from unbalanced conductor tensions in all attachment points at a temperature of -5 °C and a fictitious one-sided overload according to 4.8.3 shall be applied

Fictitious overload may be modified by a factor in the Project Specification

(ncpt) SK.2 Longitudinal security loads for section supports of lines with nominal voltage exceeding 45 kV

Longitudinal loads for section supports are based on one-sided release of tension in all conductors in that of the adjacent spans, leading to higher loads

Conductor tensions and loads on supports are determined at a temperature of -5 °C, without accounting for wind load, and considering reduced ice loads For permanent lines, this corresponds to the extreme ice load with a 50-year return period, as specified in 4.5.1/SK.3, and is adjusted by a reduction factor of α LSL = 0.5 The weight of ice accumulation on insulator sets is excluded from this calculation, although higher ice loads may be specified in the Project Specification.

When determining the longitudinal security loads for temporary line section supports, the extreme ice load with a return period of T years is calculated as \$I_T = \gamma_I I_{50}\$, where the partial factor for ice action \$\gamma_I\$ varies based on the temporary line's lifespan as per 4.13/SK.2 This value is then multiplied by a reduction factor of \$\alpha_{LSL} = 0.5\$.

Vertical loads on the support exclude the weight of insulator sets, conductors, and ice accumulation on the conductors from the span, taking into account the release of conductor tensions.

Safety loads

Construction and maintenance loads

(ncpt) SK.1 Construction and maintenance loads

Requirements for construction and maintenance loads shall be specified in the Project Specification.

Loads related to the weight of linesmen

(ncpt) SK.1 Loads related to the weight of linesmen

Characteristic construction and maintenance loads, acting on crossarms for single conductors and earth wires shall not be less than 1,0 kN, on crossarms for bundled conductors less than 2,0 kN

Concurrent permanent load is considered at temperatures of -20 °C and +40 °C

More severe conditions may be specified in the Project Specification.

Forces due to short-circuit currents

(ncpt) SK.1 Forces due to short-circuit currents

Unless otherwise specified in the Project Specification, forces due to short-circuit currents are not considered.

Other special forces

Avalanches, creeping snow

(ncpt) SK.1 Avalanches, creeping snow

Unless otherwise specified in the Project Specification, forces acting on lines, due to avalanches or creeping snow, are not considered.

Earthquakes

Additional loads resulting from an earthquake or seismic tremors, may occur only in seismically very active or undermined areas They are considered only if required in the Project Specification.

Load cases

General

Standard load cases are listed in 4.12.2/SK.1

When an external load, such as ice accumulation on a middle conductor in a horizontally arranged gantry, reduces stress in a specific member or cross-section, it is essential to define special load cases with a diminished load component in the Project Specification.

(ncpt) SK.2 Failure of one string of a multiple insulator set

When a double or multiple insulator set is installed on a support structure for lines with a nominal voltage exceeding 45 kV at multiple attachment points, it is essential to assess the impact of load release from one attachment point In this scenario, the remaining attachment points are subjected to forces from both the phase conductor and the insulator set, based on maximum load conditions outlined in load cases 1, 3a, and 4 from Table 4/SK.3 It is important to note that neither the reduction of static tension in the conductor nor dynamic effects from string failure are taken into account, as forces from the same load cases also affect the attachment points of other insulator sets.

Conditions for the verification of strength of insulators and insulator sets fittings for the failure of one string of a multiple set are specified in 10.7/SK.3 and 11.6/SK.2

(ncpt) SK.3 Load cases for serviceability limit states verification

The verification of serviceability limit states is guided by Clause 7 of the standard or the Project Specification, utilizing load cases outlined in section 4.12.2/SK.1 For this verification, climatic loads and temperatures corresponding to reliability level 1 are applied Additionally, Clause 7 and the Project Specification will specify which load cases are to be used for the verification process.

Standard load cases

(ncpt) SK.1 Standard load cases

Standard load cases are given in table 4/SK.3, which replaces table 4.6 in 4.12.2 All specified load cases shall be used for supports, unless otherwise specified in notes in Table 4/SK.3

In section 4.12.2, the characteristic ice load is substituted with the extreme ice load in items (b), (c), and (d) Additionally, unbalanced wind load as outlined in item (a) and the combined unbalanced wind and ice load in item (e) are excluded unless explicitly stated in the Project Specification.

Load cases for junction supports are determined according to the standard load cases outlined in Table 4/SK.3 Further details regarding load arrangement and specific requirements will be provided in the Project Specification.

If special supports are required, requirements shall be specified in the Project Specification

Table 4/SK.3 – Standard load cases

2b Uniform ice load, transversal bending α = 0,5 (0,5 I T / I T) 1)

2c Unbalanced ice load, longitudinal bending α 1 = 0,30, α 2 = 0,70 (0,30 I T / 0,70 I T)

2d Unbalanced ice load, torsional bending α 3 = 0,30, α 4 = 0,70 (0,30 I T / 0,70 I T) 2)

3a Combined wind and ice load

− Wind load with high probability wind velocity V IH

3b Combined wind and ice load

− Wind load with low probability wind velocity V IL

4 Minimum temperature without other climatic loads

− Tension release in conductor or bundle sub-conductor under reduced ice load (α TSL I 50) according to 4.8.2/SK.1

− Unbalanced tensions of all conductors resulting from fictitious overload equal to the self-weight of conductors in all spans in one direction from the support according to 4.8.3/SK.1

− Tension release in all conductors in one direction from the support under reduced ice load (α LSL I 50) according to 4.8.3/SK.2

6a Safety loads, construction and maintenance loads

6b Safety loads, loads due to the weight of linesmen Temperature of -5 °C is considered for all load cases, except for load case 4

1) Considered only when required in the Project Specification

2) Considered for lines with bundle conductors, for lines with single conductors only considered when required in the Project Specification

3) For lines with nominal voltage up to 45 kV only considered when required in the Project Specification

4) Considered for non-section supports

For lines with nominal voltage up to 45 kV only considered when required in the Project Specification

5) Considered only for section supports

For lines with nominal voltage up to 45 kV only considered when required in the Project Specification

In load cases with unbalanced ice load (2c, 2d), the relevant reduced ice loads α 1 I T and α 3 I T are always considered in all spans in one direction from the support.

Partial factors for actions

(ncpt) SK.1 Partial factors for actions, combination factors for actions and reduction factors for permanent lines

Table 4/SK.4 provides the values of partial factors for actions (\( \gamma_F \)), combination factors for wind actions (\( \Psi_W \)) and ice actions (\( \Psi_I \)), the squared reduction factor for wind velocity related to icing (\( B_I^2 \)), and the reduction factors (\( \alpha \)) for ice loads used in verifying permanent lines under ultimate limit states, replacing the previous Table 4.7.

(ncpt) SK.2 Partial factors for actions, combination factors for actions and reduction factors for temporary lines

Table 4/SK.5 provides the values of partial factors for actions (\( \gamma_F \)), combination factors for wind actions (\( \Psi_W \)) and ice actions (\( \Psi_I \)), the squared reduction factor for wind velocity related to icing (\( B_I^2 \)), and the reduction factors (\( \alpha \)) for ice loads used in the verification of temporary lines in ultimate limit states, replacing the previous Table 4.7.

Table 4/SK.4 – Partial factors for actions, combination factors for actions and reduction factors for verification of permanent lines in ultimate limit states

Reliability level 1 Reliability level 2 Reliability level 3 Weight Wind Ice γ W γ I γ W γ I γ W γ I γ G ψ W ψ I ψ W ψ I ψ W ψ I

2b Uniform ice load, transversal bending 1, α (1) 1,00 1,25 1,50 1,00

2c Unbalanced ice load, longitudinal bending α 1 , α 2 (1) 1,00 1,25 1,50 1,00 2d Unbalanced ice load, torsional bending α 3 , α 4 (1) 1,00 1,25 1,50 1,00

3a Extreme ice load combined with a high probability wind speed V IH

3b Nominal ice load combined with a low probability wind speed V IL

5a Security loads, torsional bending α TSL (2) γ A1 = 1,00 1,00

5c Security loads, longitudinal bending α LSL (3) γ A2 = 1,00 1,00

6 Safety loads, construction and maintenance loads γ P ≥ 1,50 (4) 1,00 NOTES

(1) Values of reduction factors α for load cases 2b, 2c and 2d are given in table 4/SK.3 in 4.12.2/SK.1

The reduction factors αTSL for ice loads, essential for assessing torsional bending security loads, are specified in section 4.8.2/SK.1 and are applicable to lines with nominal voltages up to 45 kV as outlined in the Project Specification.

The reduction factor \$\alpha_{LSL}\$ for ice loads, essential for calculating the longitudinal security load for section supports, is specified in section 4.8.3/SK.2 and is applicable to lines with a nominal voltage of up to 45 kV as outlined in the Project Specification.

(4) Load factor γP = 1,5 shall be used, unless a higher value is specified in the Project Specification

Table 4/SK.5 – Partial factors for actions, combination factors for actions and reduction factors for verification of temporary lines in ultimate limit states

Life duration ≤ 1 year (but > 3 months) Weight Return period T =

2b Uniform ice load, transversal bending 1, α (1) 0,26 0,50 0,65

2c Unbalanced ice load, longitudinal bending α 1 , α 2 (1) 0,26 0,50 0,65

2d Unbalanced ice load, torsional bending α 3 , α 4 (1) 0,26 0,50 0,65

3a Extreme ice load combined with a high probability wind speed V IH

3b Nominal ice load combined with a low probability wind speed V IL

5a Security loads, torsional bending α TSL (2) γ A1 = 1,00 1,00

5c Security loads, longitudinal bending α LSL (3) γ A2 = 1,00 1,00

6 Safety loads, construction and maintenance loads γ P ≥ 1,50 (6) 1,00 NOTES

(1) Values of reduction factors α for load cases 2b, 2c and 2d are given in table 4/SK.3 in 4.12.2/SK.1

The reduction factors αTSL for ice loads, essential for assessing torsional bending security loads, are specified in section 4.8.2/SK.1 and are applicable to lines with nominal voltages up to 45 kV as outlined in the Project Specification.

The reduction factor values, denoted as αLSL, for ice loads used to determine the longitudinal security load for section supports are specified in section 4.8.3/SK.2, as well as in the Project Specification for lines with a nominal voltage of up to 45 kV.

(4) For lines, installed for nominal duration of 3 days, it is possible to take into account the meteorological forecast for the given site

(5) For lines, installed for nominal duration more than 3 days but less than 3 months in Wind zone I (basic wind speed Vb,0 = 24 m/s ), value of γW = 0,70 shall be used

(6) Load factor γP = 1,5 shall be used, unless a higher value is specified in the Project Specification.

Insulation coordination

(ncpt) SK.1 Required withstand voltages

Required withstand voltages are given in Table 5/SK.1

Table 5/SK.1 – Required withstand voltages

1) The reduced insulation level, which requires the application of surge arresters in the line for reduction of atmospheric and switching overvoltages

(ncpt) SK.2 Required withstand voltages of insulator sets for lines with nominal voltage exceeding 45 kV

For insulator strings designed for heavy pollution, which are longer than those chosen based on insulation coordination, the coordination spark gaps must be utilized to maintain withstand voltages within specified limits as outlined in Table 5/SK.2 Additionally, external clearances from persons or objects must exceed 1.1 times the specified distance (refer to 5.9.1/SK.4).

Table 5/SK.2 – Required withstand voltages of insulator sets

(kV) minimum maximum minimum maximum

1) The reduced insulation level, which requires the application of surge arresters in the line for the reduction of atmospheric and switching overvoltages

Values of withstand voltages in Table 5/SK.1 and Table 5/SK.2 apply to altitudes up to 1000 m For altitudes exceeding 1000 m the withstand voltages shall be determined according to formula: aH

U rwH required withstand voltage for altitude H > 1 000 m;

U rw 1 000 required withstand voltage for altitude H = 1 000 m;

K aH altitude factor according to annex E.2 for altitudes H > 1 000 m;

K a 1 000 altitude factor according to annex E.2 for altitudes H = 1 000 m.

Classification of voltages and overvoltages

Application of the theoretical method in Annex E

(ncpt) SK.1 Method to determine minimum air clearances

The determination of minimum clearances relies on a method that integrates long-term operational experience, calculation analyses as outlined in Annex E, and experimental results These clearances are regarded as empirical in nature.

Empirical method based on European experience

(ncpt) SK.1 Minimum clearances D el and D pp

Minimum clearances D el and D pp are given in Table 5/SK.4, which replaces Table 5.6

Table 5/SK.4 – Minimum clearances D el and D pp

(m) internal conductor - structure (in window)

(m) internal and external conductor - conductor

1) Clearances between phase conductors of the same circuit and to conductors of another circuit or line of electrical system For electric circuits of different utilities, greater clearances might be determined

2) Marked clearances D el2 and D el3 may be shorter, if proven by tests that these clearances ensure required withstand voltages levels, given in Table 5/SK.1 and Table 5/SK.2, or if appropriate measures are adopted to lower maximum overvoltage values to the values of withstand voltages corresponding to shortened clearances D el2 and D el3

For lines with a nominal voltage of up to 45 kV, a clearance distance of D el = 0.6 m should be maintained for ground and object clearances, while a distance of D pp = 0.7 m is required for crossings with other lines of the same voltage level.

(ncpt) SK.2 Minimum clearances D 50Hz_p_e and D 50Hz_p_p

Minimum air clearances to withstand power frequency voltages at extreme wind load are specified in Table 5/SK.5, which replaces Table 5.5

Table 5/SK.5 Minimum clearances D 50Hz_p_e and D 50Hz_p_p

Load cases for calculation of clearances

Maximum conductor temperature

(ncpt) SK.1 Maximum design temperature of phase conductors

The Project Specification will outline the maximum design temperature for phase conductors, which is essential for verifying minimum internal and external clearances The criteria for determining this maximum design temperature can be found in section 9.2.2/SK.1.

When assessing internal and external clearances at the maximum conductor temperature, it is assumed that the temperature of conductors from other circuits or lines, including earth wires, is +40 °C, unless the Project Specification indicates a lower temperature.

NOTE External and internal clearances are not checked in case of a specified power system fault (e.g short-circuit), unless otherwise specified in the Project Specification

(ncpt) SK.2 Minimum conductor temperature

Conditions for the verification of clearances under minimum conductor temperature:

This load case is used to check internal clearances on a support and to check external clearances in case of undercrossing.

Wind loads for determination of electric clearances

Conditions for the verification of clearances under still air:

− conductor temperatures -5 °C and maximum design temperature

5.6.3.2 Nominal wind loads for determination of internal and external clearances

(ncpt) SK.1 Nominal wind load

Conditions for the verification of clearances under nominal wind load according to 5.6.3.2:

Minimum external clearances under wind actions from still air to nominal wind load shall comply with the values of minimum external clearances specified in the following subclauses

(ncpt) SK.2 Unequal wind load

Conditions for the verification of clearances under unequal wind load:

The wind force exerted on a conductor is influenced by wind blowing perpendicularly to it, with wind pressure ranging from 0 to the average wind pressure associated with a three-year return period, denoted as \(q_h C_T^2\).

The wind force acting on the second conductor, which is influenced by the same wind direction as the first, experiences a mean wind pressure that is consistently 36% lower than that acting on the first conductor.

This load case is used to check internal clearances between conductors and external clearances in case of crossing and parallel lines

When assessing clearances between non-parallel conductors, it is crucial to consider the angle of incidence between the wind direction and the conductor's normal This angle affects the calculation of wind load on the conductor, as the wind direction is not perpendicular to it.

5.6.3.3 Extreme wind loads for determination of internal clearances

(ncpt) SK.1 Extreme wind load

Conditions for the verification of clearances under extreme wind load according to 5.6.3.3:

− no ice, This load case is used to check internal clearances within the span and at the top of support according to 5.8.

Ice loads for determination of electric clearances

(ncpt) SK.1 Extreme ice load

Conditions for the verification of clearances under uniform ice load:

− extreme ice load with 50-year return period

(ncpt) SK.2 Non-uniform ice load for lines with nominal voltage exceeding 45 kV

Conditions for the verification of clearances under non-uniform ice load:

− 50 % of extreme ice load on conductors only in certain spans (see cases A and B) Case A

When assessing external clearances for crossed objects, traffic routes, and overhead lines, it is important to consider 50% of the extreme ice load on conductors solely within the crossing span, while assuming no ice on conductors in other spans Additionally, for overhead line crossings, ice accumulation is not taken into account on the bottom line.

When assessing internal clearances between conductors as specified in the project requirements, and evaluating external clearances for parallel lines, it is essential to maintain the required clearance at less than 50% of the maximum ice load on the upper conductor in any single instance.

When assessing external clearances, this load case applies only to spans where the conductor is connected to a suspension insulator set at one end, allowing it to swing in the direction of the line.

In Case B, the load case is essential for verifying external clearances during crossings and parallel lines, as well as for assessing internal clearances between conductors within the same or different circuits, as specified in the project requirements It is important to note that when evaluating external clearances, the load case applies only to spans where the bottom conductor is connected to a suspension insulator set at one end, allowing for movement in the line direction.

When crossing, 50% of the extreme ice load on the upper line's conductors is applied to all spans, while 50% of the extreme ice load on the bottom line's conductors is considered for all spans except the crossing span, where ice load is not taken into account.

When assessing internal clearances between conductors as specified in the project requirements, and evaluating external clearances for parallel lines, it is essential to maintain clearances below 50% of the maximum ice load on the upper conductor across all spans Additionally, the same clearance standard applies to the lower conductor in all spans, with the exception of one span in the line section where ice load is not taken into account.

(ncpt) SK.3 Non-uniform ice load in crossings spans of lines with nominal voltage up to 45 kV

In accordance with the Project Specification, this load case applies to lines equipped with suspension insulators If verification is necessary, the Project Specification must outline the conditions and requirements for minimum external clearances.

Combined wind and ice loads

(ncpt) SK.1 Combined wind and ice loads

Conditions for the verification of clearances under combined wind and ice load:

− extreme ice load on conductors with return period 50 years,

− wind load on ice covered conductors with wind velocity from 0 up to the high probability mean wind velocity combined with ice (V h C T B l), while structural factor for conductors G c = 1

This load case verifies external clearances when the sag of conductors under ice exceeds the sag at a conductor temperature of +40 °C The minimum clearances from the surface of iced conductors are the same as those required under nominal wind load for this scenario.

(ncpt) SK.2 Combined ice and unequal wind loads

Conditions for the verification of clearances under combined ice and unequal wind load:

− extreme ice load with return period 50 years on conductors of upper line, conductors of bottom line without ice,

The wind force exerted on a conductor is influenced by wind blowing perpendicularly to it, with speeds ranging from 0 to the high probability mean wind velocity combined with ice (V h C T B l) For this analysis, the structural factor for conductors is set at G c = 1.

The wind force acting on the second conductor is influenced by the wind blowing in the same direction as the first conductor This force corresponds to a mean wind speed that is consistently 20% lower than that experienced by the first conductor.

This load case verifies the external clearances between conductors of different lines when they cross or run parallel to each other The minimum clearances required from the surface of iced conductors are the same as those under nominal wind load for this scenario.

Coordination of conductor positions and electrical stresses

(ncpt) SK.1 Coordination of conductor positions and electrical stresses

Subclause 5.7 does not apply to lines with nominal voltage up to 45 kV, where internal clearances are derived from values D pp and D el even under extreme wind load.

Internal clearances within the span and at the top of support

(ncpt) SK.1 Reduction factor for minimum internal clearances

In Tables 5.8 and 5.9, the reduction factor \( k_1 \) is set at 0.7, unless a higher value is indicated in the Project Specification for the clearances between phase conductors of different circuits within the same utility.

Internal clearances D el and D pp in Tables 5.8 and 5.9 are represented by relevant clearances

D el2, D el3, D el4 and D pp given in 5.5.3/SK.1 in Table 5/SK.4

NOTE Clearances to a line of a different utility on the common supports are considered to be external clearances

(ncpt) SK.2 Additional conditions for internal clearances verification

For lines with nominal voltage exceeding 45 kV, clearances for still air without ice shall be applied even under wind with mean speed up to 10 m/s

Unless otherwise specified in the Project Specification, minimum internal clearances D el, specified in Table 5.8, are reduced by reduction factor k 1= 0,7 under minimum conductor temperature according to 5.6.2/SK.2

For the load case of Unequal wind load as per section 5.6.3.2/SK.2, the reduced clearances \( k_{1D_{el}} \) and \( k_{1D_{pp}} \) are set at \( k_1 = 0.7 \), similar to the Nominal wind load case, unless the Project Specification outlines stricter clearance requirements between phase conductors of different circuits, specifically where \( 0.7 < k_1 \leq 1 \).

When assessing internal clearances between phase conductors and earth wires, as well as between phase conductors of the same or different circuits under non-uniform ice load, the minimum internal clearances D pp and D el4 can be reduced by specified reduction factors k 1, as outlined in section 5.6.4/SK.2 of the Project Specification.

(ncpt) SK.3 Empirical method for the determination of internal clearances within the span

This subclause replaces subclause F.1 of annex F

To ensure that the clearances between conductors remain safe under wind action, the minimum clearance between two conductors with equal cross-sections, composition, and sags in still air is calculated using a specific method.

To ensure safety and compliance, a minimum distance, denoted as \$b_{emp}\$, must be maintained between bare phase conductors, between bare phase conductors and earth wires, and between bare phase conductors of different circuits This distance is determined by the equation: \$$b_{emp} = k_{emp} \times f_L + ins + c_{emp} \times D_{pp}\$$ This formula accounts for the spacing required between phase conductors and conductors of separate circuits.

The equation describes the relationship between the minimum clearance between two conductors or bundles in the middle of the span, denoted as \$b_{emp}\$ (in meters), and the conductor sag, \$f\$ (in meters), at a temperature of +40 °C Additionally, it highlights the importance of maintaining a safe distance, represented by \$D_{el4}\$, between a phase conductor and an earth wire.

The vertical length of the suspension insulator set, denoted as \$L_{ins}\$, can swing perpendicularly to the line and is measured in meters When the lengths of insulator sets on both supports differ, their arithmetic mean is used in calculations For insulator sets that cannot swing perpendicularly, such as tension insulator sets, insulator crossarms, and line post insulators, \$L_{ins}\$ is considered to be zero.

If values of L ins are different for the two conductors, higher value of L ins shall be used,

When verifying clearances between phase conductors of distinct circuits with varying nominal voltages, the distance D pp, as specified in Table 5/SK.4, must correspond to the higher voltage.

According to Table 5/SK.4, the constant \( c_{emp} \) is set at 0.6 for verifying internal clearances A higher value may be specified in the Project Specification, particularly for clearances between conductors of different circuits The factor \( k_{emp} \) is determined by the weight of the conductor and the mutual positioning of both conductors, as defined by a specific formula.

The diameter of the conductor or sub-conductor in a bundle is denoted as \(d\) (in mm), while \(g_c\) represents the weight of the conductor or one sub-conductor per meter of length (in N⋅m\(^{-1}\)) The angle \(\delta\) is formed between the horizontal plane and the straight line defined by the intersection of the axes of both conductors (or bundles) with a plane perpendicular to the line direction at the midpoint of the span, measured in degrees (°) and ranging from 0° to 90°.

Figure 5/SK.1 Angle between conductors

Minimum clearances between conductors within the span, determined by the specified empirical relations, must not be less than the minimum clearance values D pp or D el4 as outlined in Table 5/SK.4.

Minimum clearances between covered conductors within the span are specified as 1/3 of the distance b emp, calculated for a line with bare conductors

NOTE The method does not substitute the verification of internal clearances under ice action

(ncpt) SK.4 Approximate method for the determination of clearances between conductors with different cross-sections, materials, sags or mutual positions on supports

When dealing with conductors that have varying cross-sections, materials, or sags, the clearances between the conductors can be calculated according to the guidelines outlined in 5.8/SK.3 The clearance values, denoted as b emp, are determined individually for each conductor, taking into account the specific values of k emp and (f + L ins).

Higher of the two values b emp calculated for both conductors is selected

When the horizontal and vertical distances between conductors on both supports of a span differ, it is essential to ensure that the clearances between the conductors at every point within the span meet or exceed the values calculated according to 5.8/SK.3 In such cases, the sag factor \( f_r \) must be incorporated at the checked point of the span, along with the factor \( k_{emp_r} \) determined for the angle \( \delta_r \) at that point Additionally, if the lengths of the suspension insulator sets on both supports vary, the equivalent length \( L_{ins_r} \) should be calculated using the appropriate equation.

L ins_r = L ins1 + (L ins2 – L ins1) r / L where L ins1 is the length of a shorter insulator set (m),

L ins2 is the length of a longer insulator set (m),

The span length, denoted as \( L \) (in meters), represents the distance between two points, while \( r \) indicates the horizontal distance from the attachment point of the shorter insulator set to the specific point in the span where the distance between conductors is measured (in meters).

When insulator sets that cannot swing perpendicular to the line, such as tension insulator sets, insulator crossarms, or line post insulators, are installed on one or both supports of the examined span, the value of L ins1 (or L ins2) is equal to 0.

External clearances

General

(ncpt) SK.1 Other load cases for minimum clearances to buildings, roads, other lines and recreational areas

In addition to the load cases outlined in the relevant tables, this article addresses Non-uniform ice load as per sections 5.6.4/SK.2 and 5.6.4/SK.3, as well as Combined wind and ice load according to 5.6.5/SK.1 The minimum clearances for Non-uniform ice load are consistent with those for Extreme ice load, unless specified otherwise in subsequent subclauses Similarly, the minimum clearances for Combined ice and wind load align with those for Nominal wind load.

(ncpt) SK.2 Application of double and multiple insulator sets

For overhead lines with a nominal voltage greater than 45 kV, it is essential to utilize double or multiple insulator sets on both supports of spans This requirement applies particularly in areas where the line crosses buildings frequented by people and spans that intersect railways and roads, excluding national roads classified as 3rd category and local or country roads of the same classification.

4 th category and tertiary, special-purpose roads), recognized navigable waterways, recrea- tional and sports areas, low voltage overhead power lines and overhead telecommunication lines

The Project Specification may require the application of double or multiple insulator sets also in other cases

The application of double insulator sets for lines with nominal voltage up to and including

45 kV shall be specified in the Project Specification

(ncpt) SK.3 Conductor joints within the span

In areas where high-voltage lines exceeding 45 kV intersect with buildings frequented by people, as well as national and local roads of the 1st or 2nd category, navigable waterways, or recreational and sports zones, it is permitted to have only one in-span tension joint per conductor or bundle sub-conductor.

In spans, where the line crosses railways, motorways or speedways, splicing of conductors is not permitted

The Project Specification may limit in-span splicing of conductors also in other cases, or for the whole line respectively

When constructing a new line with a nominal voltage greater than 45 kV, it is essential that no span, where conductor splicing is permitted, contains more than one joint per individual conductor or bundle sub-conductor.

The use of in-span joints for lines with nominal voltage up to 45 kV shall be specified in the Project Specification

(ncpt) SK.4 Verification of a som

When the withstand voltage of insulator sets exceeds the values specified in Table 5/SK.2 due to air pollution or other factors, and if there are permanent objects in proximity where humans may be present, it is essential to ensure that the external clearances to these objects or individuals are greater than 110% of the arcing distance, denoted as \$a_{som}\$ Here, \$a_{som}\$ represents the minimum arcing distance of the insulator set or the minimum distance between live parts and other earthed components of the support.

In this case a som is investigated on both supports of the crossing span Such verification is performed for load cases according to 5.6.2/SK.1 and 5.6.4/SK.1.

External clearances to ground in areas remote from buildings, roads, etc

(ncpt) SK.1 Non-uniform ice load

The load case Non-uniform ice load according to 5.6.4/SK.2 and 5.6.4/SK.3 does not apply for this subclause

(ncpt) SK.2 Restriction for heights of trees

The Project Specification may necessitate cutting trees at a certain distance from the power lines or trimming them to ensure they do not make contact with the conductors if they fall, particularly in areas where enhanced operational reliability is essential.

The distance is then determined according to the following formula:

D tr = H tr 2 –h c_tr 2 where D tr is the horizontal distance of a tree trunk from the most endangered conductor (m),

The height of a tree, denoted as \$H_{tr}\$, accounts for its future growth in meters, while \$h_{c\_tr}\$ represents the height of the most endangered conductor above the horizontal plane at the tree's base, considering maximum sag conditions The conductor's height is measured in a vertical plane that is perpendicular to the conductor and intersects the tree base.

External clearances to residential and other buildings

(ncpt) SK.1 External clearances to residential and other buildings

Table 5.11 is replaced by Table 5/SK.6

Table 5/SK.6 Minimum clearances to residential and other buildings and structures

Clearance cases: Residential and other buildings (m)

To fire resistant parts of the buildings where the slope is greater than 15° to the horizontal

To fire resistant parts of the buildings where the slope is less than or equal to 15° to the horizontal

To non-fire resistant parts of the buildings and fire sensitive installations

2,0 + D el but at least 3,0 3,0 2,0 4,0 + D el but at least 5,0 4,0 3,0 10,0 + D el but at least 10,6 10,6 10,6 Extreme ice load 2,0 + D el but at least 3,0 3,0 2,0 4,0 + D el but at least 5,0 4,0 3,0 10,0 + D el but at least 10,6 10,6 10,6

2,0 + D el but at least 3,0 3,0 2,0 4,0 + D el but at least 5,0 4,0 3,0 10,0 + D el but at least 10,6 10,6 10,6

It is considered that it is reasonable for a person to stand on the roof for maintenance and to use a hand tool

It is considered that it is reasonable for a person to stand on the roof for maintenance and to use a small ladder

The clearance shall be sufficient to remove the possibility that induced voltages could cause fire

Antenna, flag poles, advertising signs and similar structures

Load case Antennas and lightning protection facilities

Street lamps, flag poles, advertising signs and similar structures which cannot be stood on

2,0 + D el but at least 3,0 2,0 1,5 2,0 + D el but at least 2,6 2,0 1,5 2,0 + D el but at least

Extreme ice load 2,0 + D el but at least 3,0 2,0 1,5 2,0 + D el but at least 2,6 2,0 1,5 2,0 + D el but at least

2,0 + D el but at least 3,0 2,0 1,5 2,0 + D el but at least 2,6 2,0 1,5 2,0 + D el but at least

If this horizontal distance cannot be met the vertical clearances in the case of a line above buildings shall be met

In the fall of the structure towards conductors, clearance between conductor and structure shall not be less than

0,5 + D 50Hz_p_e This condition is checked only for load cases Maximum conductor temperature and Extreme ice load

The coding for column headings includes B for Bare conductors, C for Covered conductors, and I for Insulated cable systems It is important to note that the clearances for C- and I-conductors apply only to voltage levels exceeding 1 kV.

(ncpt) SK.2 Non-uniform ice load for lines with nominal voltage exceeding 45 kV

Minimum clearances to antennas, lightning protection systems, street lamps, advertising signs, and similar structures that cannot be stood on are decreased by 1 meter for this load case, as outlined in (A-dev) SK.3 regarding restrictions in the line protection zone.

Act No 251/2012 Coll on energy outlines the regulations for protection zones around power system facilities, as specified in § 43 It establishes the purpose and extent of these zones, prohibiting the construction of any structures or similar facilities without the approval of the line owner Additionally, the act forbids the placement of gas stations and the storage of flammable or explosive substances within these protection zones.

When a line owner grants approval for the placement of structures within the line protection zone, the clearances outlined in Table 5/SK.6 must be adhered to, unless the line owner imposes stricter conditions.

(ncpt) SK.4 Fire resistance of parts of buildings for overhead line crossings

The parts of buildings resistant to fire are considered:

− parts of buildings, whose surface finish complies with the classification of construction products as reaction to fire class A1 and A2 according to EN 13501-1;

− roofing, classified as BROOF class according to EN 13501-5 (meet the requirements for behaviour functional characteristics during external fire);

When building and roofing surfaces are constructed from specified materials, these components are classified as non-fire-spreading from the exterior, thereby enhancing their fire resistance.

Objects, which do not meet the above specified criteria, shall be assessed as buildings or roofing, which are not resistant to fire spreading and thus non-fire resistant.

External clearances to crossing traffic routes

(ncpt) SK.1 Minimum clearances to local and tertiary roads

The minimum clearances for local roads of the 4th category and special-purpose roads, including field and forest roads, cycling routes, and pavements, as outlined in Table 5.12, are decreased by 1 meter Additionally, the load case for non-uniform ice load specified in sections 5.6.4/SK.2 and 5.6.4/SK.3 is not applicable in this scenario.

(ncpt) SK.2 Minimum clearances to railways

For the crossings of electric overhead lines with railways, the clearances given in 5.9.4 in Table 5.12 are replaced by clearances, given in the following Table 5/SK.7

Table 5/SK.7 – Minimum clearances to crossing railways

Minimum clearances to crossing railways (m)

To rail level (if no electric traction is used)

To live parts of traction system To earthed parts of traction system

To rail level (if overhead traction system is planned) column (a) (b) (c) (d)

Nominal line voltage > 1 kV ≤ 45 kV > 45 kV ≤ 45 kV > 45 kV ≤ 45 kV > 45 kV

6,0 + D el, but at least 6,6 2,5 2,0 + D el 2,0 1,0 + D el, but at least 2,5 12,0 12,0 + D el

Extreme ice load 6,0 + D el, but at least 6,6 2,5 2,0 + D el 2,0 1,0 + D el, but at least 2,5 12,0 12,0 + D el

Nominal wind load 6,0 + D el, but at least 6,6 2,5 2,0 + D el 2,0 1,0 + D el, but at least 2,5 12,0 12,0 + D el

Non-uniform ice load 6,0 + D el, but at least 6,6 2,5 2,0 + D el 2,0 1,0 + D el, but at least 2,5 12,0 12,0 + D el

(ncpt) SK.3 Additional requirements for crossing with railway

The minimum distance from any part of a support to a vertical plane aligned with the nearest rail track must be at least 4 meters for non-electrified railways, as specified in column (a) of Table 5/SK.7 For electrified railways or those with planned overhead traction systems, this distance increases to at least 9 meters, following the guidelines in column (d) of the same table Additionally, the foundations of supports must always be positioned behind the trench or any railway drainage systems.

In a line section intersecting with national or regional railways, a maximum of three intermediate supports is permitted between two section supports or between a section (or terminal) support and a substation structure Additionally, the angle of the line at these supports must not exceed 10°.

Conditions for building of overhead line crossing and locating the line supports shall be negotiated with the railway owner

It is prohibited to construct an overhead electric line crossing at a railway level crossing, ensuring that the nearest conductor is more than 5 meters away from the railway crossing indicator in still air Additionally, the placement of line supports must not obstruct the visibility of the railway crossing indicator from the intersecting road Furthermore, using rail or any railway equipment for earthing is not allowed.

(A-dev) SK.4 Clearances to waterways significant in terms of shipping transport

The minimum heights of conductors above the highest navigable water level of significant waterways, as outlined in the Regulation of the Ministry of Transport, Posts and Telecommunications No 22/2001 Coll., are determined based on the line nominal voltage These heights, specified in Table 5/SK.8 under the column "Above waterways significant in terms of shipping transport," supersede the clearances listed in the column "To recognized waterways" in Table 5.12.

The load case Non-uniform ice load according to 5.6.4/SK.2 and 5.6.4/SK.3 does not apply to clearances to significant waterways

Classification of waterways is specified in the Regulation of the Ministry of Transport, Posts and Telecommunications No 22/2001 Coll

Overhead power lines shall not be routed over a lock (lock chamber with docks and weir) and in its vicinity

Table 5/SK.8 – Minimum clearances to crossing navigable waterways and other water areas and waterways

Above waterways significant in terms of shipping transport (classification according to Regulation No 22/2001

Above special-purpose waterways and other watercourses and water areas

Waterways classified IV and Va

VIII Above water level at normal water stage

Above water level at highest water stage

Nominal voltage (kV) ≤110 >110 ≤110 >110 Maximum conductor temperature 12 12 110 n 100

Combined wind and ice load 12 12 110 n 100

The highest sailing level will be specified by Inland waterway transport division of Transport Authority of Slovakia

A normal water stage refers to the water level associated with a flow rate that has a 180-day return period in natural water streams, or it corresponds to the design flow rate in artificial water streams.

The highest water stage is defined as the water level associated with a flow rate that has a 50-year return period in a water stream Hydrological data is supplied by the regional branches of the Slovak Hydrometeorological Institute.

(ncpt) SK.5 Minimum conductor height above other waterways

The minimum heights of conductors above the water level for special-purpose waterways and other water areas, as defined under the highest and normal water stages, are detailed in Table 5/SK.8 These specified heights supersede the clearances for crossing recognized waterways listed in Table 5.12.

The load case Non-uniform ice load according to 5.6.4/SK.2 and 5.6.4/SK.3 is not considered in this case

(ncpt) SK.6 Additional conditions for permanent ski lifts

For crossings of power lines over permanent ski lifts, the same requirements as for crossings over ropeways apply.

External clearances to adjacent traffic routes

(ncpt) SK.1 External clearances to adjacent traffic routes

Clearances to adjacent railways are given in the following Table 5/SK.9 These clearances replace clearances to railway components, given in Table 5.13

For minimum clearances between supports and the nearest tracks of a railway requirements given in 5.9.4/SK.3 apply

Table 5/SK.9 – Minimum external clearances to adjacent railways

Clearance cases: Line adjacent to railways (m)

Load case Horizontal clearance to components of traction system of a railway

Horizontal clearance between nearest part of the overhead line and the outer edge of the nearest track of a railway

Without electrical traction In case of planned electrical traction

0,5 + D el, but at least 1,5 1,5 1,5 4,0 + D el, but at least 4,6 4,0 4,0 12,0 + D el, but at least 12,6

0,5 + D el, but at least 1,5 1,5 1,5 4,0 + D el, but at least 4,6 4,0 4,0 12,0 + D el, but at least 12,6

0,5 + D el, but at least 1,5 1,5 1,5 4,0 + D el, but at least 4,6 4,0 4,0 12,0 + D el, but at least 12,6

Remark If this horizontal clearance cannot be met, clearances for crossing of railway installations, as given in Table 5/SK.7 shall be met

The coding for column headings is defined as follows: B represents Bare conductors, C denotes Covered conductors, and I stands for Insulated cable systems It is important to note that the clearances for C- and I-conductors are applicable only for voltage levels greater than 1 kV and up to 45 kV.

External clearances to other power lines or overhead telecommunication lines

(ncpt) SK.1 Minimum clearances of lines with nominal voltage exceeding 45 kV to other power lines and telecommunication overhead lines

Table 5.14 is in terms of clearances of lines with nominal voltage exceeding 45 kV to other power lines and telecommunication overhead lines replaced by the following Table 5/SK.10

For lines with nominal voltage up to 45 kV, clearances according to Table 5.14 apply

Table 5/SK.10 – Minimum clearances of lines with nominal voltage exceeding 45 kV to other overhead power lines and telecommunication overhead lines

Crossing of power lines exceeding

1 kV, parallel power lines exceeding

1 kV of different utilities on common supports and parallel or converging power lines exceeding 1 kV on separate supports (m)

Crossing of telecommunication lines and power lines up to 1 kV, parallel telecommunication lines or power lines up to 1 kV (m)

Minimum clearance between conductors of both lines

Minimum clearance between conductor of one line and a support of the other line

Minimum clearance between conductor of power line exceeding 45 kV and conductor of power line up to 1 kV or conductor of telecommunication line

Minimum clearance between conductor of power line exceeding

45 kV and a support of the power line up to 1 kV or telecommunication line

D pp is the higher of the values of

D pp for the two lines a) Horizontal distance If this distance cannot be met, minimum spatial clearance given in brackets shall be met

If requirements on maximum withstand voltages of insulator sets according to 5.3.1/SK.2 are not met, minimum clearances higher than 1,1 a som, in compliance with 5.9.1/SK.4, shall be met

1) upper line: maximum design temperature of phase conductors (5.6.2/SK.1); if upper line is existing, its maximum design temperature shall be specified in the Project Specification, lower line: conductor temperature 40 °C, no wind action,

2) both lines: minimum conductor temperature (5.6.2/SK.2),

3) upper line: extreme uniform ice load (5.6.4/SK.1), lower line: conductor temperature -5 °C, conductors without ice,

4) non-uniform ice load (see 5.6.4/SK.2) For clearances between conductors of lines with nominal voltage exceeding 1 kV, cases A and B, for other clearances only case A,

5) in case of crossings and parallel lines with nominal voltage exceeding 1 kV, clearances between conductors of one line swung due to wind velocity from 0 to nominal wind speed according to 5.6.3.2/SK.1 and supports of the other line are to be checked; in case of crossings and parallel lines with nominal voltage up to 1 kV and telecommunication lines, clearances between conductors of power line with nominal voltage exceeding 45 kV, swung due to wind velocity from 0 to nominal wind speed according to 5.6.3.2/SK.1 and supports, conductors or other components of the line with nominal voltage up to 1 kV, respectively telecommunication line, are to be checked,

6) both lines unequal wind load (5.6.3.2/SK.3)

7) combined wind and ice load according to 5.6.5/SK.1 Check is to be made when the sag of conductor of line with nominal voltage exceeding 45 kV under ice load is higher than its sag under temperature of +40 °C,

8) combined ice and unequal wind load according to 5.6.5/SK.2.

Corona effect

Electric and magnetic fields

Introduction

Ratings with regard to corrosion and mechanical strength

Dimensioning with regard to human safety

Lattice steel towers

Steel poles

Wood poles

Concrete poles

Guyed structures

Corrosion protection and finishes

Maintenance facilities

Basis of geotechnical design (EN 1997-1:2004 – Section 2)

Aluminium based conductors

Steel based conductors

Conductors and ground wires containing optical fibre telecommunication circuits

General requirements

Type test requirements

Basis for the verification

Installation of earth electrodes and earthing conductors

Measurements for and on earthing systems

Typical values of the geotechnical parameters of soils and rocks

Sample semi-empirical models for resistance estimation