BS/EN 50341-2-9-2017 pdf download.Overhead electrical lines exceeding AC 1 kV Part 2-9: National Normative Aspects (N NA) for Great Britain and Northern Ireland (based on EN 50341-1:2012).
5.6 Load cases for calculation of clearances
5.6.1 Load cases for calculation of clearances
(ncpt GB.1 Calculation of clearances to support
For extreme wind conditions the 50-year return period shall be used. For normal electrical clearances, the 3-year return values shall be used. These can be approximated by the application of a value of y of 0,75. applied to the 50-year return wind speed and ice thickness values. For wind with ice clearances the method of calculation shall be defined in the Proiect Specification. For clearances using design Approach 3, the method of calculation shall be defined in the Project Specification.
5.6.3 Wind load for determination of electric clearances
(ncpt) GB.1 Wind load for determination of electric clearances
For clearances using design Approach 3, the method of calculation shall be defined in the Project Specification.
5.6.4 Ice load for determination of electric clearances
(ncpt) GB.1 Ice load for determination of electric clearances
For clearances using design Approach 3, the method of calculation shall be defined in the Project Specification.
5.6.5 Combined wind and ice loads
(ncpt) GB.1 Combined wind and Ice loads
For clearances using design Approach 3, the method of calculation shall be defined in the Project Specification.
5.8 Internal clearances within the span and at the top of support
(ncpt) GB.1 Internal clearances within the span and at the top of the support
The value of Ki and the method of calculation shall be defined in the Project Specification
(ncpt) GB.2 Phase separation
For all structures designed according to Approach 1, phase separation shall be sufficient to prevent clashing of conductors under 3 year return climatic loadings. The maximum differences in wind loading, ice loading, and conductor temperature that should be assumed between adjacent conductors shall be specified in the Project Specification.
For wood pole lines designed using Approach 3 with conductors exceeding 35mm2 copper equivalent area, the conductor spacing shall comply with the requirements set out in EATR 111 based on the “weather zone” applicable to that area. A weather zone is a geographical area in which the likely mean wind pressure and absolute maximum ice accretion thickness may be described by a numeral and letter respectively. The wind co-ordinate is described in 190N/m2 increments, whilst the ice co-ordinate is measured in 10mm diametric thickness increments for each letter increment (A = 10mm, B = 20mm, etc.).
The gust and lull wind pressures shall be 1,832 and 0.546 times the mean wind pressure respectively. The minimum spacing to avoid conductor dash shall be the worst combination of wind and ice, expressed as a straight line between the wind and Ice axes, allowing for a withstand factor of 1,10.
Maps of weather zones, shown in lOOm increments of elevation above mean sea level, are reproduced as Figures NA.3 — NA.7 inclusive in this NNA.
For wood pole lines at Normal altitudes, the minimum recommended phase separation is defined by weather zone “2B”, whilst for lines at High altitude, the minimum recommended phase separation is defined by weather zone “3C”. Greater phase separations may be required due to the effect of funnelling or for altitudes greater than 500m. Details of such requirements will be given in the Project Specification.
For lines on wood poles having conductor sizes up to and including 35mm2 copper equivalent area, the phase spacing requirements will be detailed in the Project Specification.
For lines having supports other than wood poles, the requirements of BSEN 50341-1 shall apply.
7.5 Wood Poles
7.5.1 General
(ncpt) GB.1 BSEN 1995-1-1
The design of timber poles shall not consider the requirements BSEN 1995-1-1
7.5.5 Ultimate limit states
(ncpt) GB.1 Design of pole supports
If design Approach 1 is adopted, there shall be no limit on deflection unless specified otherwise in the Project Specification, subject to the following conditions:
1. The structures remain fit for their intended purpose In all respects.
2. Minimum electrical clearances shall be maintained under a 3-year return climatic loading, or a minimum of a 50-year return climatic loading if an infringement would result in significant risk to human life.
3. Design is based on second Order theory taking account of “p-delta” effects.
Under design Approach 1, any limit on deflection given in the Project Specification shall apply under a 3-year return climatic loading, unless an infringement would result in significant risk to human life, in which case a minimum of a 50-year return values shall be adopted.
The total deflection at the pole top under ultimate limit state shall, where required, be specified in the Project Specification in respect of designs to Approach 3.
For a design employing Approach 3, the partial factor of safety 7m to be applied shall be as specified in Table 4.13.21 GB,3 in this NNA in respect of timber poles.
(ncpt) GB.2 Internal forces
For a design to Approach 1. poles should be designed using second order theory, taking account of p-delta” effects, unless specified otherwise in the Project Specification.
For a design to Approach 3, the partial safety factor m to be applied for non-guyed timber poles shall be as specified in Table 4,13.2IGB.3 in this NNA. Unless otherwise defined in the Project Specification, non-guyed timber poles shall be designed using first order bending theory only.
(ncpt) GB.3 Pole straightness
The allowable out of straightness of a guyed pole is specified as follows: “a straight line drawn from the centre of the tip to the centre of the pole at a point I ,Sm from the butt shall lie inside the pole”.BS/EN 50341-2-9-2017 pdf download.