ks 1876-2-2010 overhead power lines for kenya - safety (2)

7/31/2019 KS 1876-2-2010 Overhead Power Lines for Kenya - Safety (2)

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KENYA STANDARD KS 1876-2:2010ICS 29.260.20

KEBS 2010 First Edition 2010

Electrical power transmission and

distribution Overhead power lines forconditions prevailing in Kenya Part 2:Safety

BALLOT DRAFT, MAY 2010


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ii KEBS 2010 All rights reserved

TECHNICAL COMMITTEE REPRESENTATION

The following organizations were represented on the Technical Committee:

Nairobi City Council, City Engineers Department.Jomo Kenyatta University of Agriculture and TechnologyKenya Polytechnic

Kenya Power & Lighting CompanyFluid & Power Systems LtdMinistry of Public Works and HousingMinistry of EnergyKenafric Industries LtdPower Technics LtdRural Electrification AuthorityThe Energy Regulatory CommissionConsumer Information NetworkKenya Association of ManufacturersInstitute of Engineers of KenyaKenya Electricity Generating Company LtdABB LTD

Switchgear & Controls LtdPower Controls LtdCommunications Communication of KenyaInstrument LtdKenya Pipeline Company LtdTelkom Kenya LtdMeteorological DepartmentKenya Bureau of Standards Secretariat

REVISION OF KENYA STANDARDS

In order to keep abreast of progress in industry, Kenya standards shall be regularly reviewed. Suggestionsfor improvement to published standards, addressed to the Managing Director, Kenya Bureau of Standards,are welcome.

Kenya Bureau of Standards, 2010

Copyright. Users are reminded that by virtue of Section 25 of the Copyright Act, Cap. 12 of 2001 of the Laws of Kenya, copyrightsubsists in all Kenya Standards and except as provided under Section 26 of this Act, no Kenya Standard produced by Kenya Bureau ofStandards may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writingfrom the Managing Director.


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KENYA STANDARD KS 1876-2:20109ICS 29.260.20

KEBS 2010 All rights reserved iii

Electrical power transmission anddistribution Overhead power lines forconditions prevailing in Kenya Part 2:Safety

KENYA BUREAU OF STANDARDS (KEBS)

Head Office: P.O. Box 54974, Nairobi-00200, Tel.: (+254 020) 605490, 69028000, 602350, Mobile: 0722202137/8, 0734600471/2;Fax: (+254 020) 604031

E-Mail: [email protected], Web:http://www.kebs.org

KEBS Coast RegionP.O. Box 99376, Mombasa 80100Tel: (+254 041) 229563, 230939/40Fax: (+254 041) 229448E-mail: [email protected]

KEBS Lake RegionP.O. Box 2949, Kisumu 40100Tel: (+254 057) 23549,22396Fax: (+254 057) 21814E-mail: [email protected]

KEBS North Rift RegionP.O. Box 2138, Nakuru 20100Tel: (+254 051) 210553, 210555


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iv KEBS 2010 All rights reserved

F O R E W O R D

This Kenya standard was prepared by the Switchgear and Distribution Equipment in accordance with theprocedures of the Bureau and is in compliance with Annex 3 of the WTO/TB Agreement.

This part of this Kenya Standard has been prepared to enable competent persons to design safe and cost-effective overhead power lines by indicating the current technology and practices related to Kenyanconditions. This standard identifies the parameters to be considered in relation to safety and indicatesinternationally accepted references by which the values of these parameters can be determined.

In the development of this standard, SANS 10280-1:2008, Overhead power lines for conditions prevailing inSouth Africa Part 1: Safety, was extensively consulted. Assistance derived from this source is herebyacknowledged.

Normative and informative annexes

A 'normative' annex is an integral part of a standard, whereas an 'informative' annex is only for informationand guidance.

Summary of development

This Kenya Standard,having been preparedby the Switchgear andDistributionEquipment TechnicalCommittee was firstapproved by theNational StandardsCouncil in June 2010

Amendments issued since publication

Amd. No. Date Text affected


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KEBS 2010 All rights reserved v

Contents

1 Scope .................................................................................................................................................... 1

2 Normative references ........................................................................................................................... 1

3 Terms, definitions and abbreviations .................................................................................................... 1

3.1 Terms and definitions ........................................................................................................................... 1

3.2 Abbreviations ........................................................................................................................................ 2

4 Determination of mechanical loads ...................................................................................................... 2

4.1 General ................................................................................................................................................. 2

4.2 Simplified method ................................................................................................................................. 2

4.3 Detailed method .................................................................................................................................... 6

4.4 Design loads of temporary structures for emergencies ...................................................................... 13

5 Aviation considerations Application to the aviation authority (see foreword) ................................ 14

6 Waterway considerations Application to the relevant authority ..................................................... 14

7 Conductor current rating (ampacity) ................................................................................................... 15

8 Clearances .......................................................................................................................................... 15

8.1 Vertical clearance to ground and structures ....................................................................................... 15

8.2 Horizontal clearances ......................................................................................................................... 15

9 Crossings ............................................................................................................................................ 16

9.1 Crossings over roads, railways, tramways and telecommunication lines .......................................... 16

9.2 Crossings between power lines .......................................................................................................... 16

9.3 Crossings over water .......................................................................................................................... 16

9.4 Crossings of service connections ....................................................................................................... 17

10 Step and touch potentials around earthing of power line towers and poles ....................................... 17

11 Warning signs ..................................................................................................................................... 17

Annex A (informative) Ice load incidents on overhead lines recorded in Kenya ............................................ 18

Annex B (normative) Aircraft warning devices................................................................................................ 19

Annex C (normative) Clearances required for power lines that cross services.............................................. 21

Annex D (normative) Directives on power lines and telecommunication circuits ........................................... 22


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ardKENYA STANDARD KS 1876-2:2010

KEBS 2010 All rights reserved 1

Electrical power transmission and distribution Overhead power linesfor conditions prevailing in Kenya Part 2: Safety

1 Scope

This part of KS 1876 specifies the mechanical and electrical safety requirements of overhead power linesincluding requirements for supports, the conductor system, clearances and crossings.

2 Normative references

The following referenced documents are indispensable for the application of this standard. For datedreferences, only the edition cited applies. For undated references, the latest edition of the referenceddocument (including any amendments) applies.

2.1 Standards

IEC 60826:2003, Design criteria of overhead transmission lines

ITU-T K.53, Values of induced voltages on telecommunication installations to establish telecom and a.c.power and railway operators responsibilities

KS 516, Wood poles for power and telecommunications lines Specification

KS 1605, Specification for hardwood poles, droppers, laths, guardrail post and spacer blocks

IEC 61466-1, Composite string insulator units for overhead lines with a nominal voltage greater than 1000 V

Part 1: Standard strength classes and end fittings

2.2 Other publications

Cigr Working Group B2.12. Cigr Brochure 299. Guide for selection of weather parameters for bareoverhead conductor ratings. 2006. Available from .

Cigr Working Group SC 22.12. Probabilistic determination of conductor current ratings. EIectra No. 164,February 1996, pp. 103-119. Available from .

Cigr Working Group SC 22.12. The thermal behaviour of overhead conductors Section 1 and 2:Mathematical model for evaluation of conductor temperature in the steady state and the application thereof.ElectraNo. 144, October 1992, pp. 107-125. Available from .

3 Terms, definitions and abbreviations

For the purposes of this document, the following terms, definitions and abbreviations apply.

3.1 Terms and definitions

acceptableacceptable to the customer

conductor current ratingampacitycurrent which will meet the design, security and safety criteria of a particular line on which the conductor isused


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2 KEBS 2010 All rights reserved

high public exposure areaarea that the public frequent on a daily basis

proven methodmethod that has been in practice for at least ten years without any known failure, or a method that usesinternationally accepted calculation methods, or a method of testing that has been proven by acceptabletesting authorities

3.2 Abbreviations

ASL: at sea level

BIL: basic insulation level

RSL: residual static load

UTS: ultimate tensile strength

4 Determination of mechanical loads

4.1 General

Loads on the supports of lines of operating voltages 132 kV and lower may be determined by using eitherthe simplified method in 4.2 or the detailed method in 4.3. For lines of operating voltage exceeding 132 kV,the detailed method shall be used.

NOTE In the absence of detailed design data, the simplified method should be used. Users are cautioned not to use parts of thedetailed method or parts of the simplified method. Only a single method should be chosen and followed.

4.2 Simplified method

4.2.1 General

The simplified method incorporates experience of the successful history of the design, construction andoperation of the overhead lines that were based on the previous edition of this document, into the designcriteria based on the "limit state" concept (see 4.2.4).

The previous approach, where the loads were compared to the component strength reduced by the factor ofsafety, has been replaced by the design approach, which uses a load and resistance format, whichseparates the effects of component strengths and their variability from the effects of external/loads and theiruncertainty.

Design criteria based on simplified calculation of the wind loads were calibrated with the weather dataobtained from a statistical analysis for a 50 year return period.

4.2.2 Equation

The following general limit state equation is used in the simplified method:

XYGYWRxxxnn

++

where

is the appropriate strength factor, as given in Table 1, which takes into account variability of material,workmanship, etc.;

Rn is the nominal strength of the component, in newtons;

Wn is the wind load relevant to each load condition, in newtons;

Yx is the load factor that takes into account parameters such as variability of loads, importance ofstructure and safety implications;


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Gx is the vertical dead load, in newtons;

X is the applied load relevant to each load condition, in newtons (for example tension and additionalweight).

4.2.3 Strength factors for different material types

The strength factors shall be applied to various material types in accordance with Table 1.

4.2.4 Limit states

Load cases considered in the design of overhead lines are grouped into ultimate limit state and serviceabilitylimit state cases.

Ultimate limit state cases are those associated with load cases that lead to collapse, or with other similarforms of structural failure due to excessive deformation, loss of stability, overturning, rupture, buckling, etc.The load cases associated with these states are concerned with the safety of the public as well as thereliability of supports, foundations, conductors and hardware.

Serviceability limit state cases are associated with load cases that will be sustained in a satisfactory mannerby the structure and power line components without permanent deformation or damage. These load casesinclude vibration limits, support deflections and electrical clearances.

Table 1 Strength factors to be applied

1 2 3 4

Component Limit stateStrength factor

Strength verified by full-scaletesting

Strength not verified by full-scale testing

Steel lattice structures and cross-arms Strength 1.0 0.8

Fabricated tubular steel poles and members Strength 1.0 0.8Reinforced or pre-stressed concrete structuresand members

Strength 1.0 0.9

Wood structures, poles or members (that

comply with KS 516 and KS 1605)

Strength 0.7 or less (modulus of rupture)

Serviceability 0.3 (modulus of rupture) Line fittings, forged or fabricated Strength 0.8Line fittings, cast Strength 0.7

Porcelain or glass insulators Strength 0.8

Synthetic composite suspension or straininsulators

Strength0.5 (one minute mechanical

strength)

Synthetic composite line post insulators Strength0.9 (maximum design cantilever

load)

Foundations (for soil nominations in the field) Strength 0.7 0.7Conductors Strength 0.7

Stay (cable) members Strength 0.7

4.2.5 Loads

The calculated loads on a structure or on a component include conductor-imposed loads and the loadsdirectly imposed on the structure or component. Conductor-imposed loads include conductor tensions, self-weight, wind loads, ice loads and forces due to line deviations. The loads directly imposed on a structure or acomponent include wind loads, ice loads, self-weight, construction loads and maintenance loads.

The relevant loads that occur simultaneously are combined in accordance with the design situationconsidered and given in 4.2.6 as load cases.

4.2.6 Load cases Ultimate limit state

4.2.6.1 Wind loads

The structural components of an overhead line shall be designed for the joint effect of the following load

combination:

CCSnnTGGWR 5.11.11.1 +++


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where

is the appropriate strength factor, given in Table 1, which takes into account variability of material,workmanship, etc.;

Rn is the nominal strength of the components; in newtons;

Wn is the wind load, based on the wind pressure in Table 2, in pascals;

GS is the vertical dead load that results from the structure, in newtons;

GC is the vertical dead load that results from the conductors and insulators, in newtons;

TC is the conductor tension load produced by a healthy conductor subjected to a wind pressure of 880Pa at a temperature of 15 C, final condition, in n ewtons.

Table 2 Wind pressure

1 2

Structure or componentWind

pressurePa

Conductor and cylindrical objects (poles, insulators, etc.) 880

Supports of objects of rectangular cross-section 1900

Lattice towers of rectangular cross-section (projectedarea onwindward face(s) of the tower)

2850

The wind direction shall be taken as being horizontal and acting perpendicularly to the surface exposed tothe wind. In the case of asymmetrical structures, wind that acts from opposite directions shall be evaluatedand the case that results in the worst load shall be considered.

If the prevailing wind direction is not perpendicular to the surface being considered, the wind loads Wngivenin Table 2 shall be multiplied by cos

2 where is the angle between the wind direction and the bisector of

the line structure (see Figure 1).

Wind that acts at an angle of 45to the cross-arm axis (bisector) of the line structure shall be considered forall types of towers and poles.

4.2.6.2 Ice loads

Ice and snow accumulation on conductors and structures is not often experienced in Kenya; these conditionsare associated with the high altitude areas of the country.

Designers shall be aware of these areas (see Figure 2) and investigate unbalanced loads produced by ice

that forms on conductors owing to local terrain topography (line sections with large adjacent span ratios inhilly terrains).


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Figure 1 Angle between wind direction and cross-arm axis (bisector) of the line structure

4.2.6.3 Construction and maintenance loads

The structural components of an overhead line shall be designed for the joint effect of the following loadcombination:

HCSn TQGGR 51515111 .... +++

where is the appropriate strength factor, given in Table 1, which takes into account variability of material,

workmanship, etc.;

Rn is the nominal strength of the component, in newtons;



Q is the construction and maintenance loads as described below, in newtons;

TH is the intact conductor horizontal tension for the specific condition, in newtons.

A factor of 1.5 applies to construction and maintenance loads that are static and reasonably well defined.This factor shall be increased to 2 if dynamic loads or loads that are variable or not so well defined are to becovered by the design.

In the simplified method the load Qshall be assumed to be a vertically acting force of at least 1.0 kN for thecross-arms of intermediate and angle suspension structures and at least 2.0 kN for all other types ofstructure. These forces shall act at the axis of the cross-arm at the attachment points of insulator assembliesor at the attachment points of conductors.

In the case of step bolts, ladders, and all members that can be climbed and that are inclined at an angle lessthan 30to the horizontal, a construction load of 1.0 kN shall be taken as acting vertically at a staticallyunfavourable position or in the centre of the member.

Any other aspects that can arise from construction and maintenance practices, which affect the load Q, shallbe identified by the designer and addressed using the detailed method.


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The maximum horizontal tension TH applied in the direction of the conductors shall be calculated for theconductors at 15 C in still air in initial conditi ons (before creep).

4.2.6.4 Exceptional loads (failure containment)

4.2.6.4.1 General

Dynamic loads on the structure owing to conductor breakage or failure of the adjacent structure areunpredictable, and the conductor's residual static load (RSL) shall be used to check structures forexceptional loads.

For sub-transmission and distribution lines that use post insulators and relatively flexible structures, it is notnecessary to specifically design intermediate (suspension) structures for the RSL load or broken conductorconditions. For more important lines, or where there is a concern that a cascading failure situation coulddevelop, the designer shall consider using the detailed method for intermediate structures.

In-line (section) strain, angle strain and terminal structures shall be checked for unbalanced load to providerigid points in an overhead line.

In the simplified method, the design loads shall be based on still air conditions with the joint effect of thefollowing load combination:

BHCSn .... TTGGR 51511111 +++

where

is the appropriate strength factor, given in table 1, which takes into account variability of material,

workmanship, etc.;

Rn is the nominal strength of the components, in newtons;



TH is the intact conductor horizontal tension for the specific condition, in newtons;

TB is the unbalanced conductor tension load that results from abnormal conditions, for example, abroken conductor, in newtons.

4.2.6.4.2 Loads due to broken conductors

At any terminal or angle strain structure, a broken conductor condition introduces a torsional load as a resultof the release of tension in one phase conductor while other healthy conductors are under the tensioncorresponding to the final condition with the conductor at a temperature of -5C without any wind load .

The above limit shall be tested with various phase conductors or with the earth wires, and the case that givesrise to the most unfavourable load conditions shall be considered.

4.2.6.4.3 Longitudinal unbalanced load at angle strain and in-line strain structures

Angle and in-line strain structures shall be dimensioned to resist a longitudinal unbalanced (cascading) loadcreated by applying tension corresponding to the final condition (at conductor temperature of -5C, wi thoutany wind load), to all attachment points at the head span, and applying 60 % of this tension to theattachment points at the back span.

4.3 Detailed method

4.3.1 General

Loads, which incorporate the following, shall be determined:


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a) wind loads;

b) ice loads;

c) construction loads; and

d) failure containment loads.

Loads shall be determined in accordance with IEC 60826. The requirements specified in 4.3 are intended toclarify and detail input requirements stipulated in IEC 60826, and therefore this part of KS 1876 shall be readin conjunction with that standard.

Certain deviations and additions to IEC 60826 are reflected in the requirements below, and shall takeprecedence over IEC 60826 in the event of a dispute.

4.3.2 Reliability requirements

In IEC 60826 the load on supports, modified by a load factor, is used to determine the minimum required

strength of components, which may be modified by a strength factor, as follows:

CT FRYQ <

where

Y is the load factor, based on a minimum reliability level, linked to a return period;

QT is the calculated load, in newtons;

F is the strength factor, based on failure sequencing and strength coordination between components;

RC is the characteristic strength of the component.

The reliability levels of lines, selected in accordance with 5.1.1.1 of IEC 60826:2003 are as stipulated inTable 3.

Table 3 Reliability levels

1 2 3 4

VoltageMinimum reliability

levelReturn period

yearsLoad factor for wind

YTW

Up to 132 kV 1 50 1.0>132 kV to


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given in Table 4 and Figure 3.

In each of these wind load cases, wind loads on insulator strings (see 6.2.6.3 of IEC 60826:2003) and windloads on supports (see 6.2.6.4 of IEC 60826:2003) shall be combined with wind loads on conductors (see6.2.6.1 of IEC 60826:2003).

4.3.3.3 Narrow wind loads on chainette and light guyed structures

Structures that are not subjected to significant bending through cross-arms (such as chainette towers andguyed monopoles), shall be subjected to a narrow wind load case, applied only to the tower at an angle of45to the line, while everyday tensions and weight s are considered on the conductors. The basic windspeed considered in these cases shall be in accordance with table 6. The consideration paid to the effect ofthis wind is to ensure that the structure has a minimum level of rigidity to resist tornado wind loads.

NOTE The narrow wind load case might not effectively yield a tornado-resistant tower, since failure during such climatic events isoften caused by impact loads from wind-borne objects.

For general conditions in South Africa, the wind load input parameters in table 5 shall be assumed.

Table 4 Wind load cases

1 2 3

Tower type Wind load case Description

Suspension tower

W1 Wind at 0to bisector



W4Narrow wind at 45to the structure (for chainette and guyedpole structures)

W5 Reverse wind at 180to bisector (for asymmetric al structures)

W6 Wind at 90to the left span

Strain tower

W7 Wind at 90to the right span

W8 Wind at 0to the left span

W9 Wind at 0to the right span

NOTE 1 See figure 3 for an illustration of the wind load cases.NOTE 2 The wind load cases for strain towers are applied in addition to those for suspension towers.

Figure 3 Incidence of wind loads


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Table 5 Wind load input parameters

1 2 3Parameter Input value IEC 60826 subclause

Terrain category B (Open country with few obstacles) 6.2.2Reference (10 min) wind speed 28 m/s 6.2.3Combination of wind speed and

temperature

Only consider high wind speed and

reference temperature of 15 C

6.2.4

Altitude 0 m ASL 6.2.5

Table 6 Narrow wind loads applied to towers with no direct bending

1 2

Tower typeBasic 10 min wind speed

m/sSuspension chainette 30Guyed strain towers, guyed monopoles 40

4.3.3.4 Terrain-specific modification of wind span

4.3.3.4.1 Wind span reductions

Allowable wind spans of structures, which were designed in accordance with the wind load cases given4.3.3, require adjustment for certain terrain conditions. Calculate the allowable wind span Waas follows:

tgda =WW

where

Wa is the allowable wind span;

Wd is the design wind span;

g is the wind span reduction factor due to the geographical location (see Table 7);

t is the wind span reduction factor due to the erection of structures in category A terrain (a largestretch of water or upwind or flat coastal areas), or spans that traverse significant ridges, valleys orescarpments (see Table 8).

4.3.3.4.2 Reductions due to geographical location

The ten minute reference wind speeds for specific areas can be adjusted in accordance with Figure 4 andTable 7.

Where overhead lines traverse areas with ten minute wind speeds that exceed a 28 m/s wind as indicated in

figure 4, allowable wind spans shall be reduced by the factors given in table 7.

Table 7 Reduction of allowable wind span for geographical location

1 2

Ten minute reference wind speed Reduction factor (g)

m/s28 132 0.7535 0.65

4.3.3.4.3 Reductions due to topographical and terrain influences

Since failures of overhead lines are also attributed to local terrain influences, the following location-specificwind span reduction factors are required where lines traverse the following areas:


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a) in the case of wind spans that traverse category A terrain (a large stretch of water, upwind or flatcoastal areas):

t= 0.86

b) in the case of wind spans that traverse ridges or escarpments of height exceeding that of the structure

or valley crossings longer than 800 m, t is given in Table 8.

Table 8 Reduction of allowable wind span for topographical influences

1 2 3 4 5Topography wind span reduction factor

t

Upwind slopee Z/Lu EscarpmentTwo-dimensional

hillAxi-symmetric hill

0.05 0.05 0.87 0.71 0.780.10 0.89 0.76 0.810.20 0.91 0.81 0.870.30 0.92 0.86 0.91

0.1 0.05 0.77 0.56 0.63

0.10 0.80 0.59 0.680.20 0.83 0.67 0.770.30 0.86 0.74 0.83

0.2 0.05 0.61 0.35 0.430.10 0.64 0.40 0.490.20 0.71 0.48 0.600.30 0.76 0.57 0.71

> 0.3 0.05 0.55 0.29 0.370.10 0.58 0.33 0.420.20 0.65 0.42 0.540.30 0.71 0.50 0.65

NOTE Upwind slope e can be calculated by using the equation

ue

L

H

2=

Where

e is the upwind slope;H is the height of the hill;Lu is the horizontal distance from the crest to the mid-slope;Z is the height of the conductor above ground level at the crest.

Figure 5 Characteristic dimensions of topographical features


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4.3.4 Ice loads

Since the frequency of overhead line failures due to ice loads does not warrant detailed investigation, thecalculation of ice loads shall be done in accordance with 6.3 of IEC 60826:2003 only, in which ice withoutwind is considered. See Annex A.

Where overhead lines traverse the ice load risk areas indicated in Figure 2, a nominal additional load of 10mm of radial ice shall be applied without wind, see 6.3.2 of IEC 60826:2003. This load shall be added to thedead load of the un-factored conductor self-weight, which might or might not result in a reduction ofallowable weight spans over the area traversed.

NOTE The nominal ice load will, in some instances, be less than construction safety loads in which the dead weight of theconductor is usually multiplied by 2.

Where overhead lines traverse terrain where there has been an instance of ice load failure, the radial icethickness may be applied in accordance with observed known instances of line failures. When the radial icethickness to be applied in such cases is being considered, consider the information given in Table A.1.

Thus, towers can specifically be designed for ice loads. In an ice load case (only applicable to risk areas),consider the information given in Table A.1.

It might also be deemed practicable to design structures for no ice load, and determine the net reduction inallowable weight span, which is applied during the tower spotting process.

4.3.5 Construction and maintenance loads

The construction and maintenance load cases are relevant to the construction phase, when safety is themain consideration. Unless specifically catered for in the design, all strain structures (except terminalstructures) from which stringing on one side is initiated, are back-stayed during stringing.

Conductor tensions for construction load cases are based on stringing tensions, and the initial E-values(Young's modulus) of conductors.

Maximum stringing tensions are calculated by using the following values with respect to the everyday

conductor tension (the relevant conductor tension at 15 C):

temperature: 0 C (-15 C from the reference tempe rature);

conductor E-values: initial E-values as specified by the conductor manufacturer.

A conductor tension factor of 2,0 for conductors being moved and 1.5 for all conductors in place shall beapplied (see 6.5.3.1 of IEC 60826:2003).

In conjunction with the stringing tensions, a vertical load factor of 2 shall be applied to the dead weight of allconductors (including spacers, conductor hardware and insulation), in accordance with 6.5.3.2 of IEC60826:2003.

No wind pressure shall be considered during stringing (see 6.5.3.3 of IEC 60826:2003).

As a minimum, construction load cases under the following scenarios shall be determined:

load case 1 - stringing of first phase from longest cross-arm (no other conductors attached);

load case 2 - installation failure during regulation of last phase (tension factor of 2.0) and all otherconductors in place (tension factor of 1.5); and

load case 3 - maintenance loads on temporary lifting points on the structure (such as lifting points formaintenance).

4.3.6 Exceptional loads (failure containment)

4.3.6.1 Broken conductor loads

The object of designing for failure containment is to prevent cascading failures over a series of sequentialstructures. The assumption is that the full impact load of all phases can only partially be absorbed, implyingthat more than one structure might collapse before the cascading failure is contained.


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Suspension structures that support conductors of 132 kV and lower need not be designed for failurecontainment. For such lines, a strain structure capable of containing failure shall be placed at intervals notexceeding 5 km. Crossing over roads with strain structures for lower voltages shall be considered, to ensurethat cascaded towers do not occur on roads.

Static loads shall be applied at each attachment point (including all conductors and earthwires) on onelongitudinal face of the structure, in accordance with 6.6.3.2 of IEC 60826:2003. The conductor tension shallbe calculated assuming only the conductor self-weight (including all spacers, weights and in spanattachments) under everyday, post-creep conditions, with no coincident wind.

4.3.6.2 Conventional suspension structures

Suspended insulator arrangements will, in the event of complete conductor or adjacent structure failure,experience swung out conditions that will diminish away from the failure point. The net effect of suchrelaxation in conductor tension may be derived by adding half of the insulator length to the span length ateveryday tension as illustrated in figure 6.

The tension reduction on more complex suspension assemblies that carry all phases on a single suspendedarrangement (such as suspended delta or chainette configurations), may be derived by adding half of the

length from the axis of rotation to the centroid of conductors, to the span length at everyday tension asillustrated in Figure 6.

KeyL is the catenary length

Figure 6 Determination of increase in catenary length for swung out conditions

4.3.6.3 Suspension structures with collapsible cross-arms

Suspension structures may be specifically designed to allow for the local failure of cross-arms, or postinsulators at the tower body attachment, in order to relieve static tension. The net reduction in static tensionmay be derived by adding half of the post insulator or cross-arm length (in addition to half of the length ofsuspension assemblies as stipulated above) to the span at everyday tension. The loads shall be applied tothe body of the superstructure, which shall be designed to contain the longitudinal load.

4.3.6.4 Strain structures

In accordance with 6.6.3.3 of IEC 60826:2003, strain or terminal structures shall withstand greater resilienceto impact loads. A factor of 1.5 shall be applied to the static everyday tension. However, it shall not be

assumed that strain structures designed in accordance with this requirement will fully absorb impact loads,since experiments have revealed that impact loads can be as high as 2.5 times the everyday tension.

The failure containment load case can thus be summarized as follows:


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F1 Full static load after swung out conditions;

1 for suspension towers; and

1.5 for strain or terminal towers.

4.3.7 Failure sequencing

In the case of overhead lines of operating voltage exceeding 132 kV, and in the event of conditions that leadto structural failure, the failure shall be controlled in the way shown in Table 9, in order to minimize safetyrisks and reconstruction implications.

The upper strength limit for each component designed in accordance with Table 9 should be within 10 % ofthe applicable minimum strength requirement. The use of local plastic failure in cross-arms and post insulatorconnections should be considered in order to absorb and limit the effects of extreme event failures.

4.4 Design loads of temporary structures for emergencies

Where conductors are supported over road or rail crossings, or where public safety is at risk, an emergencystructure shall be designed to reliability level 1 (see Table 3).

In the case of other conditions where structures are intended to remain in service for not longer than sixmonths, the loading of emergency structures may be as given in Table 10.

Table 9 Failure sequencing requirements

1 2Component Strength factor application

Superstructures

Suspension structures 1.0 x strength of steelStrain or terminal tower 0.9 x strength of steelHardware

Hardware and insulation - Strain structures 0.95 x UTS of conductor bundle

Hardware and insulation - Suspension structures 0.8 UTS of assemblies> Maximum load that results in the collapse ofa superstructure.

Guy wires and guy fittings0.83 UTS of guy wires and fittings> Maximum guy tension of all loadcases.

Foundations

Foundations in compression only 0.9 UTS of foundation> Maximum compressive load of all load cases.Foundations for self-supporting structures (incompression and tension)

0.83 UTS of foundation> Maximum compressive or tensile load of allload cases.

Guyed foundations for guyed monopoles and guyedvee structures

0.75 UTS of foundation> Maximum guy tension of all load cases.

Conventional augered piles in guyed structuresc

0.7 UTS of foundation> Maximum guy tension of all load cases.Permanently loaded guyed foundations supportingoutside angle on running angle towers

0.65 UTS of foundation> Maximum guy tension of all load cases.

aThe strength selection of hardware and insulation shall be in accordance with the strength classes for insulators in IEC 61466-1.

b

The load that causes the collapse of a superstructure in this case is defined as the maximum tension in the insulator string for all loadcases divided by the maximum member utilization percentage for that load case.

cNot applicable to specialist piles such as continuous flight augered, precast driven, and piles with shaped under reams or bulbs.

Table 10 Simplified load cases for emergency structures

1 2Load case Requirement

Transverse load800 Pa applied at 900 to the direction of the line with the conductors ateveryday tension

Vertical loadTwice the self-weight of all suspended conductors (including hardwareand insulation)

Longitudinal load No requirements

NOTE It is considered preferable to leave conductors in conductive running blocks to prevent any transmission oflongitudinal loads to the structure.

In the case of all temporary bypasses and structures, appropriate signage should warn the public not to


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approach the area of reconstruction.

5 Aviation considerations Application to the aviation authority (see foreword)

5.1 The supplier or user of an overhead line shall, in the early planning phase of such a power line route,identify potentially hazardous conditions for aircraft.

5.2 In a case where a potentially hazardous condition has been identified, the supplier or user shallconsult with the aviation authority (see foreword).

5.3 The following documented information shall be submitted on request from the aviation authority (seeforeword):

a) the name of the power line;

b) a map that indicates the power line route;

c) a list of co-ordinates of all bend points (latitude and longitude, in degrees, minutes, seconds and tenthsof seconds); and

d) the maximum height of the structures above ground level.

5.4 The aviation authority (see foreword) shall evaluate the route and require the supplier or user tomark or re-route those sections of the line (if any), that are considered a danger to aviation. The aviationauthority may require that the supporting structures be marked by a specific marking pattern, or lighted by acombination of low- to high-intensity obstacle lights (or both).

5.5 Where overhead power lines cross a river which is wide enough to be navigable or a valley of suchdepth that it is considered to be navigable, the supplier or user shall provide the co-ordinates (latitude andlongitude, in degrees, minutes, seconds and tenths of seconds) and the height of the line above the valleyfloor or water level, to the aviation authority (see foreword) for publication in the appropriate media.

5.6 Where required by the aviation authority (see foreword), the requirements in Annex B shall apply.

Any deviation from these requirements shall be approved by the aviation authority.

6 Waterway considerations Application to the relevant authority

NOTE Harbours and marinas are considered waterways.

6.1 Where practically possible, the supplier or user of an overhead line shall not make use of overheadlines over waterways and marinas. In the absence of alternative routes, the supplier or user shall identify, inthe early planning phase of such a power line route, the potential hazardous conditions for marine craft.

6.2 Where hazards are identified, the supplier or user shall submit an official submission to the relevantauthority (see foreword) on the identified hazards. The following documented information shall be included inthe submission:

a) the name of the power line;

b) a map that indicates the power line route and possible hazards;

c) a list of co-ordinates of all bend points (latitude and longitude, in degrees, minutes, seconds and tenthsof seconds); and

d) the minimum clearance below the line from the highest expected water level (tide and five year floodline).

6.3 The relevant authority (see foreword) shall evaluate the route and require the supplier or user tomark or re-route those sections of the line (if any), that are considered a danger to marine craft. The relevant

authority may require that the supporting structures be marked by the application of a specific markingpattern, or lighted by a combination of low- to high-intensity obstacle lights (or both).

6.4 The relevant authority (see foreword) may also require the supplier or user of the overhead power


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line to limit approaching marine craft from making contact with the power line by applying overhead barriers.

6.5 Minimum vertical clearance of overhead power lines to rivers and dams that do not form part ofwaterways shall be in accordance with 9.3.

6.6 The supplier or user of the power line together with the owner of the waterway shall take jointresponsibility for ensuring that any marking or barriers are installed and maintained.

7 Conductor current rating (ampacity)

7.1 Conductor current ratings (ampacity) can be determined by either assuming the worst case coolingconditions (deterministic method) or by assessing the risk of an unsafe condition that arises (probabilisticmethod).

7.2 In the case of deterministic ratings, the weather assumptions shall be with regard to bare overheadconductor ratings.

The weather parameters are:

wind speed perpendicular to line 0.6 m/s;

absorptivity and emissivity 0.8;

solar radiation 1 000 w/m2;

ambient temperature 40 C.

7.3 The deterministic ampacity calculations shall be performed based on the equations found in thearticle titled The thermal behaviour of overhead conductors Section 1 and 2: Mathematical model forevaluation of conductor temperature in the steady state and the application thereof. (Article in the Cigrpublication, Electra, No. 144).

7.4 In the case of the deterministic method, the templating or design temperature of the line is thetemperature that shall be used in the calculation of the current.

7.5 If the probabilistic method is used, it shall be performed in accordance with the article titledProbabilistic Determinationof Conductor Current Ratings. (Article in the Cigr publication Electra. No. 164).

7.6 The current ratings in different geographical areas with different weather conditions and differentload profiles shall not result in the probability of an unsafe condition arising that is higher than the highestprobability that already exists in areas in which lines are in operation. Based on current analysis, the

probability of an unsafe condition arising shall be not higher than 6 10-6

for normal operating conditions.

7.7 Designers shall ensure that the temperatures, which the conductors are likely to reach, shall nothave a detrimental effect on the safety of the public who relate to the operation of the line.

8 Clearances

8.1 Vertical clearance to ground and structures

The minimum vertical clearance above ground or to a structure is in accordance with the values in columns 5to 9 in Table C.1. The conditions at which the clearance shall be determined shall be

a) at maximum conductor blow-out (at a wind pressure of 880 Pa and an air temperature of 15 C);

b) at a maximum operating temperature of at least 50 C with a wind pressure of 550 Pa.

8.2 Horizontal clearances

8.2.1 Except in the case of low-voltage lines of insulated wire of a type approved by the machineryauthority (see foreword), the horizontal clearances between any live conductor and buildings, poles,

structures and vegetation which are not part of power lines, shall be in accordance witha) column 10 of Table C.1 in the case of maximum conductor blow-out at extreme wind at 15 C but not

less than 880 Pa; and


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b) column 9 of Table C.1 in the case of maximum operating temperature but not less than 50 C and windof 500 Pa.

NOTE 1 Extreme wind refers to a return period of at least 50 years.

8.2.2 In the case where the overhead power line conductor can be approached from buildings, poles,structures and vegetation which are not part of power lines, the clearance shall be in accordance withcolumn 9 of Table C.1 for maximum conductor blow-out at 15 C and at extreme wind not less than 880 Pa .

8.2.3 The horizontal distance of objects, including vegetation, likely to fall onto an overhead line conductor,shall be limited by the height of such object.

9 Crossings

9.1 Crossings over roads, railways, tramways and telecommunication lines

9.1.1 The line design shall ensure that the crossing span is not adversely jeopardized by joints in the spanwhether they be tee, terminal or in-line joints.

9.1.2 The line shall be designed to ensure that the likelihood of the conductor or subconductor burningdown in a crossing is minimized. This can be achieved by the use of arcing horns, or armour rods, or proven

methods (see 3.1).

9.1.3 The line shall be so designed as to ensure that damage to the line conductors adjacent to thecrossing cannot jeopardize the integrity of the crossing span.

9.1.4 If the crossing span is strained off at each end, the crossing will not be affected by damage to theconductors beyond the crossing. It is, therefore, unnecessary to fit arcing horns or armour rods to the liveend of insulators on strain or intermediate structures beyond the crossing span. In the crossing span itself,however, arcing horns are required where the conductor could be burnt off in the event of a flashover.

9.1.5 Conventional armour rods shall not be used where the conductor is secured to a rigid insulator bymeans of a preformed tie, because in the event of a breakage, the conductor can slide through the ungrittedarmour rods and the crossing span clearance would consequently be reduced to below the minimum of 4.5

m. To overcome this problem, a full-wrap preformed twin tie shall be used, which, in addition to fixing theconductor securely to the rigid insulator, also protects the conductor against damage in the event offlashover.

9.1.6 In the absence of a mutually acceptable agreement between the power utility and the tele-communications network service licensee on line crossing angles, Table D.2 shall be used.

9.2 Crossings between power lines

The clearance between power lines shall be determined using the worst physical case (largest separation) ofthe two lines crossing, considering the maximum operating temperature of the top line and the cold conditionof the bottom line.

The clearance values to be maintained shall correspond to the values in Table C.1 for the higher voltage linegiven in

a) column 4 of Table C.1 in the case of conductor crossing over conductor; and

b) column 8 of Table C.1 in the case of a conductor that crosses over or in close proximity of thestructure.

9.3 Crossings over water

In general, normal ground clearances shall be provided. However, where crossings are made over rivers,dams or lakes, which are, or could be, used as recognized sailing waters, a clearance of 2.5 m plus therelevant minimum outdoor clearance (see Annex C) shall be provided over the tallest boat mast likely to beencountered on such water under conditions of normal high-water level and maximum conductor sag.

The tallest boat mast to be encountered on inland waters is not likely to exceed 15.5 m. Checks should,however, be carried out for the particular stretches of water that are to be crossed.


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9.4 Crossings of service connections

9.4.1 Power service connection cables that cross bare telecommunication lines shall maintain a separationdistance of at least 0.9 m at attachment points and 0.5 m at mid-span, and shall not cross below baretelecommunication services.

9.4.2 Provided that the power service connection cable is concentric or armoured and crosses non-bare

telecommunication lines, the following shall apply.a) The power and telecommunication service connection cables may be secured at common attachment

points on structures that support only service connection cables and at the service termination.Precautions shall be taken to prevent mechanical damage to either service connection cable.

b) The power service connection cable may cross a telecommunication service connection cable (eitherabove or below it) and may be attached to the telecommunication authority's (see foreword) structure,provided that the separation distance at the crossing point is at least 0.2 m.

9.4.3 Other power service connection cables (e.g. non-concentric or unarmoured) shall maintain aseparation distance of at least 0.9 m at attachment points and 0.2 m at mid-span.

10 Step and touch potentials around earthing of power line towers and poles

10.1 The tower and the down conductors on structures made of insulating or semi-insulating material (e.g.wood poles, concrete poles, fibre-glass poles) present a potentially hazardous condition under faultconditions. In the case of LV systems certain faults can go undetected for very long periods.

10.2 Where such structures are situated in high public exposure areas, safe step and touch potentialdesign norms shall be applied.

NOTE 1 Due to the costs involved in achieving the safe step and touch potential criteria around a tower, the requirement in 10.2 is notapplicable to structures in areas of low public exposure. Compliance with safe transferred potentials is practically not possible. Generallyno remote fences should be brought close to structures.

NOTE 2 General measures that can be applied in areas of low public exposure, to ensure that fences do not come near a structureand deep driven electrodes, are ring trench electrodes and insulation of exposed metal work on semi-insulating poles.

11 Warning signs

11.1 The utility shall ensure that the public understands the dangers of overhead lines. This informationcan be disseminated in one of the following ways:

a) warning signs shall be installed in a conspicuous place on all structures; or

b) an educational programme shall be put in place that covers a wide section of the public especiallylearners who attend schools.

11.2 Notwithstanding the requirements in this clause, in a high public exposure area (see 3.1), warningsigns shall be installed in a conspicuous place on all structures irrespective of whether an educationalprogramme is in place.

Examples of such places are:a) in the vicinity of areas where children or youths are known to, or are suspected of, playing or

congregating or are likely to frequent (e.g. adjacent to schools, housing estates, play areas, pedestrianways, isolated or derelict buildings or structures). Play areas might or might not be close to houses andcan be indicated by worn or trampled ground such as where football is played or where rope swingsare attached to nearby trees or structures,

b) in the vicinity of a recreational area or site (e.g. parks, beaches, fishing areas, sailing clubs, caravanparks and camping sites, etc.).

11.3 The warning signs shall clearly indicate that there is imminent danger in that vicinity. Due to variouslanguages being in use, the signs shall be pictorial in nature, for example a lightning flash.


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Annex A(informative)

Ice load incidents on overhead lines recorded in Kenya


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Annex B(normative)

Aircraft warning devices

B.1 Marking of overhead power lines with aircraft warning devices

The supplier or user shall mark overhead power lines with aircraft warning devices (AWD) on the sections ofline where conditions are considered hazardous to normal aircraft that do not perform inspection ormaintenance activities. The following conditions are considered potentially hazardous to aircraft and shall beverified by the design engineer:

a) overhead lines located close to an airport or airfield (registered aerodromes). Overhead lines routedclose to a registered aerodrome shall comply with the requirements of the Civil Aviation Regulations;

b) overhead lines where the distance between the lowest conductor and the ground level of the valleyfloor or riverbed exceeds 60 m, and the width of the valley is such that the valley can be considerednavigable by aircraft in the event of it being forced down into such a valley by poor weather conditions(and not by the pilot performing acrobatics);

c) overhead lines that are routed along a valley or on a plateau and that cross a ravine of considerabledepth, if the width of the ravine is such that the ravine is considered navigable;

d) all support structures that are located close to aerodromes and that are of height equal to or exceeding45 m;

e) any other condition indicated by the aviation authority; and

f) any other conditions considered by the designer engineer to be potentially hazardous to aircraft.

B.2 Design requirements for aircraft warning devices

8.2.1 The supplier or user of aircraft warning devices shall ensure that the specification for the aircraftwarning device is such that:

a) aircraft warning devices are visible from at least 1 000 m from an airborne perspective and 300 m fromthe ground;

b) the colour of aircraft warning devices is specified to be clearly visible against the typical backgroundthat it will be viewed against. In order to render the conductor catenary visible, an appropriate colourshall be selected for viewing against a light background and a dark background;

c) a fully assembled aircraft-warning device is of one colour only. Where the aircraft-warning device ismanufactured in various parts, the design of the parts shall be such that the components of different

colours cannot be mixed when the aircraft-warning device is being assembled;

d) the aircraft-warning device is designed to suit the life span of the line on which it is intended to beinstalled in order to limit the maintenance and re-installation of such devices on the line;

e) the aircraft-warning device is spherical in concept when viewed from any direction;

f) the attachment device will not damage the conductor during or after installation or when beingremoved from the conductor; and

g) the attachment device will prevent the aircraft-warning device from sliding along the conductor afterinstallation.

8.2.2 The design engineer shall check the limitations on the design span length and electrical clearancesbased on the type of structure used and relevant load conditions.


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B.3 Installation requirements for aircraft-warning devices

The supplier or user of overhead power lines shall ensure that

a) aircraft-warning devices are installed not lower than the level of the highest conductor (phase or shieldwire) of an overhead line;

b) different coloured aircraft warning devices are used to identify the catenary of an overhead line. Thedifferent coloured aircraft-warning devices shall be alternated along the span;

c) aircraft-warning devices are spaced evenly over the span for a pilot to identify the shape of theconductor catenary. The maximum distance between adjacent aircraft-warning devices shall be inaccordance with Table B.1 when viewed in the horizontal plane;

d) in a case where no shield wires are used on the structures, the aircraft-warning devices shall beinstalled on all three phase conductors (alternating the colours) and spaced equally so that theyappear to be spaced apart when viewed in the horizontal plane; and

e) if the clearance between phase conductors for horizontal configurations does not allow the aircraft-warning devices to be installed on each phase, then only the two outer phase conductors shall be

used. Phase spacing shall be checked at all times when the electrical design span for the structure isbeing evaluated.

Table B.1 Maximum spacing of aircraft warning devices on overhead lines

1 2 3

Overhead line typeMaximum separation distance

mMaximum distance from structure

mHV transmission lines 30 15MV distribution lines 16 8

B.4 Marking of overhead line crossings

8.4.1 When the requirements for the use of line-crossing labels are being specified, the design engineershall ensure that

a) line-crossing labels are visible in deteriorated daylight conditions;

b) overhead line support structures are so designed as to accommodate line-crossing labels at the top ofthe structure;

c) line-crossing labels are installed on the first three structures, on either side, from the crossing or anglestrain structure of a line deviation; and

d) line-crossing labels face the direction of approach to the crossing or line deviation.

8.4.2 In addition to 8.4.1, the supplier or user shall mark overhead power lines with line-crossing labels onthe structures of such a line where conditions are considered hazardous to aircraft that perform inspection ormaintenance activities. The following conditions are considered potentially hazardous to aircraft:

a) where two overhead power lines of system voltage 66 kV and above cross each other, line-crossinglabels shall be installed on both overhead power lines. Subject to 8.4.2 (d), where an overhead line ofsystem voltage 66 kV and above crosses an overhead line of system voltage below 66 kV, it is notrequired to indicate the crossing with a label;

b) where the servitude of two overhead lines of system voltage 66 kV and above converge into acombined servitude or joint to run next to one another;

c) all T-offs, loop-in and loop-out and line deviation angles exceeding 60; and

d) any condition considered by the designer engineer to create potential hazards to aircraft.


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Annex C(normative)

Clearances required for power lines that cross services

C.1 Table C.1 shows the minimum clearances required in accordance with legislation (see foreword).

C.2 The values in Table C.1 are based on the assumption that clearances shall be determined for aminimum conductor temperature of 50C and for a swi ng angle that corresponds to a wind pressure of 500Pa; provided that where, under normal conditions, power line conductors operate at a temperature above 50C, the clearance at the higher temperature at whic h the conductors operate is in accordance with theclearance indicated in the table.

C.3 The safety clearances in column 3 of Table C.1 shall not be interpreted as specifying line equipmentclearances. The line equipment clearances are based on the equipment insulation level for the appropriatevoltage level of the power line, the latter being chosen to ensure a flashover across the insulation of the linerather than from the line to other objects within the basic clearance in the case of an overvoltage.

Table C.1 Minimum clearances for power lines that cross services

1 2 3 4 5 6 7 8 9 10

Highestsystemr.m.s.

voltage

Systemnominal

r.m.s.voltage

Safetyclearancephase-to-

earth

Safetyclearancephase-to-

phase

Outsidetownship

s

Minimum vertical clearancesm

Minimumvertical andhorizontalclearances

m

Tower-topclearances at

maximuminsulator swingand minimumclearances atextreme wind

conductorblowout

Intown-ships

Roads intownships,

andproclaimed

roads,railways,

tramways

Totelecommunicat

ion lines,between power

lines andcradles and

between power

lines

To buildings,poles,

structures notpart of power

lines andvegetation

kV kV m m m m


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Annex D(normative)

Directives on power lines and telecommunication circuits

D.1 Notification and approval of the electronic communication network service licensee

The notification and approval of the building of a power line shall be done in accordance with electroniccommunication legislation.

D.2 Telecommunication system induced safety voltage limits

The ITU-T Recommendation K.53 permissible safety levels shall be adopted.

Induced voltages under steady state and fault conditions shall not exceed the values given in Table D.1.

Table D.1 Induced safety voltage limits for telecommunication systems

1 2

Induced duration t Induced voltage Vrms

s V

t < 0.2 1030

0.2 < t < 0.35 780

0.35 < t < 0.5 650

0.5 < t < 1.0 430

t> 1 60

D.3 Combined and parallel routes

D.3.1 Common structures

Common structures shall comply with the relevant requirements.

D.3.2 Independent structures

If an overhead telecommunication line and a power line or if two power lines are erected parallel to eachother along the same route, the separation between lines shall be such that, with both lines healthy, theclearance between any conductor of the higher-voltage line and any conductor or earth- wire of the lower-voltage line is never less than the minimum phase-to-phase clearance applicable to the higher-voltage line.See table C.1.

This clearance shall be maintained for all conditions up to maximum sag and maximum sideswing of theconductors of either line. It is assumed that the other line remains in the templated position for still air, andthat the maximum sideswing occurs at design wind pressure at a conductor temperature of 50 C below th edesign temperature but not less than 40 C.

D.4 Minimum separating distances

D.4.1 Minimum distances

The minimum horizontal separating distances between power lines and telecommunication lines shall bedetermined from the curves given in figures D.1, D.2, D.3 and D.4. These curves have been based onconsiderations of the inductive and electrostatic interference with communication circuits.

D.4.2 Several exposures in series

In practice, it is generally found that topographical features at power line crossings over communication linesdo not permit the exact minimum separating distances being maintained throughout the exposure. Where a


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particular power line and a particular telecommunication line are involved in this way, the curves may beapplied to each of the resulting exposures separately. The separating distances given by the curves should,wherever practicable, be increased by a factor of 1.5, or as near to this as possible, to cater for the additionaleffect of several exposures in series.

D.5 Ultimate terminal of power line route

If, in submitting a power line proposal to the telecommunications authority for approval, the supply authorityis aware that the power line might be extended beyond the immediate proposal at some future date, theprobable ultimate terminal of the power line route should be indicated by the supply authority.

D.6 Power line and telecommunication line crossings

The power line route should cross the telecommunication lineroute, as nearly as possible, at right angles.Where this is impracticable, the deviations from a right-angle crossing in Table D.2 are permitted, providedthat the provisions in D.4.2 are observed.

Table D.2 Maximum deviation angles on telecommunication line crossings

1 2

Operating voltage of line Permissible deviation from right angle

Below 48 kV 45

48 kV and above 30

D.7 Power line faults

Where power line faults are likely to cause acoustic shock of serious proportions, the supply authorityconcerned and the telecommunications authority should co-operate in providing preventive measures.

D.8 Exposures exceeding 48 km in length

Where the power line proposal involves exposures exceeding 48 km in length, the supply authority shouldrefer the project to the telecommunications authority after a preliminary survey, but before a detailed survey.It will then be possible to indicate the minimum separation with greater accuracy in each particular case.

D.9 Radio receiving stations

If power lines exceeding 44 kV have to be erected in the vicinity of radio receiving stations, the separationrequired between the power line and the radio receiving aerials is of the order of 1.5 km. This separationdepends on several factors, and the appropriate authority (usually the telecommunications authority (seeforeword)) will indicate, in the case of every proposal, what the separation should be.


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Figure D.1 Power line separation distance versus exposure to parallel telecommunication lines (upto 33 kV)


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Figure D.2 Power line separation distance versus exposure to parallel telecommunication lines(from 44 kV to 132 kV)


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Figure D.3 Power line separation distance versus exposure to parallel telecommunication lines(from 275 kV to 400 kV)


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Figure D.4 Power line separation distance versus exposure to parallel telecommunication lines(for 765 kV)

ks 1876-2-2010 overhead power lines for kenya - safety (2)

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