Tower Design Sasha Dimov

SUMMARY

SUMMARY ......................................................................................................... I PREFACE......................................................................................................... III 1. 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11

2. 2.1 2.2 2.3

3. 3.1 3.2

4. 4.1 4.2

5. 5.1 5.2 5.3 5.4 5.5

6. 6.1 6.2 6.3 6.4 6.5

7. 7.1 7.2

TERMINOLOGY....................................................................................... 1 GENERAL TERMS........................................................................................................................................ 1 MECHANICAL DESIGN ................................................................................................................................ 2 SPANS ......................................................................................................................................................... 4 PROFILES .................................................................................................................................................... 6 CONDUCTOR ARRANGEMENTS ................................................................................................................... 7 SUPPORT STRUCTURE................................................................................................................................. 9 POLES - BRACKETS................................................................................................................................... 10 TOWERS ................................................................................................................................................... 10 BARE CONDUCTORS ................................................................................................................................. 13 CONDUCTOR FITTINGS ............................................................................................................................. 15 INSULATOR SETS - ACCESSORIES ............................................................................................................. 17

PARAMETERS IN OVERHEAD LINE TOWER DESIGN ............... 21 GEOMETRICAL PARAMETERS ................................................................................................................... 21 LOADING PARAMETERS ............................................................................................................................ 28 MATERIALS .............................................................................................................................................. 30

STATIC CALCULATION ...................................................................... 32 TOWER MODEL ........................................................................................................................................ 32 COMPUTER PROGRAM .............................................................................................................................. 32

TOWER DIMENSIONING..................................................................... 34 BAR DIMENSIONING ................................................................................................................................. 34 BOLT DETERMINATION ............................................................................................................................ 38

DETAILING AND FABRICATION ...................................................... 40 DRAWINGS ............................................................................................................................................... 40 CONNECTIONS .......................................................................................................................................... 40 MATERIAL ................................................................................................................................................ 40 SHOP OPERATIONS .................................................................................................................................... 40 MARKING ................................................................................................................................................. 40

TOWER PROTOTYPE ........................................................................... 42 PROTOTYPE DOCUMENTS ......................................................................................................................... 42 CHECKING OF MAIN DIMENSIONS ............................................................................................................. 42 CHECKING OF BARS .................................................................................................................................. 42 PLATES CHECKING ................................................................................................................................... 42 BOLTS CHECKING ..................................................................................................................................... 42

TOWER TESTING .................................................................................. 44 CHOICE OF LOADING CASES .................................................................................................................... 44 ELABORATION OF TOWER TESTING PROGRAM ........................................................................................ 44

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7.3 7.4

PROTOTYPE ERECTION CHECKING ........................................................................................................... 45 TESTING PROCEDURE ............................................................................................................................... 45

8.

BIBLIOGRAPHY .................................................................................... 46

9.

ANNEXES ................................................................................................. 47

ANNEX 1: TOWER COMPUTER PROGRAM MANUAL ........................................................................................... 47 ANNEX 2: AMERICAN STANDARD FOR DESIGN OF OVERHEAD LINE TOWERS ....................................................... 47 ANNEX 3: EUROPEAN STANDARD FOR THE STEELS USED IN DESIGN OF OVERHEAD LINE TOWERS ...................... 47 ANNEX 4: EUROPEAN RECOMMENDATION FOR DESIGN OF OVERHEAD LINE TOWERS .......................................... 47 ANNEX 5: AMERICAN RECOMMENDATION FOR DESIGN OF OVERHEAD LINE TOWERS .......................................... 47 ANNEX 6: INTERNATIONAL STANDARD FOR OVERHEAD LINE TOWER TESTING .................................................... 47 ANNEX 7: BARE OVERHEAD LINE CONDUCTOR CATALOGUE.............................................................................. 48 ANNEX 8: OVERHEAD LINE INSULATORS CATALOGUE ........................................................................................ 48 ANNEX 9: STRING HARDWARE CATALOGUE ......................................................................................................... 48

10. INDEX ....................................................................................................... 49

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PREFACE DOMAIN OF UTILISATION This Guide, prepared by Mr. Sasha DIMOV, B.Sc. Civil Engineering, is presenting overhead line lattice towers design. This Guide does not represent any standard or norm; it just gives the technical details to be considered in overhead line design and in any case cannot be applied to any other civil work design other then overhead line. OBJECT This Guide object is to establish tower design rules in order to satisfy safe overhead line exploitation, people security, and minimal costs in construction as well in maintenance of overhead line. All rules are to be in accordance with national and international standards concerning the overhead lines. DIFFUSION This Guide is distributed to the GPC design engineers, who are mentioned in Contract between SNIG and GPC. All examples are numerated and nominal. Any other copies have to be ordered from SNIG, mentioning the names of dedicated persons. PROPRIETY This Guide is exclusive propriety of SNIG. All reproduction, complete or partial, is forbidden without the authorisation in written form of SNIG representatives.

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Terminology

1 1. Terminology 1.1 1.1.1

General Terms (Electric) Line A generic term for a set of conductors with insulation and accessories used for the transmission or distribution of electrical energy.

1.1.2

Overhead Line A line in which the conductors are supported above ground, generally by means of insulators and appropriate supports.

1.1.3

AC Line A line connected to an alternating current source of supply, or connecting two alternating current networks.

1.1.4

Phase (of an AC Line) Any conductor, or bundles of conductors, or terminals of a polyphase laser case system, which is at a voltage in normal use.

1.1.5

Direct Current Line A positive (negative) line conductor or terminal of a direct current system.

1.1.6

Positive (Negative) Pole A positive (negative) line conductor or terminal of a direct current system.

1.1.7

Circuit A conductor or system of conductors through which an electric current is intended to flow e.g. a set of three conductors of a laser case transmission line connected to a three-phase source of supply, or a set of two conductors connected to a single phase source of supply, or to two phases of a three-phase source of supply, etc…

1.1.8

Monopolar Line A direct current line in which only one pole connects the load to the supply, the return path being through earth.

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Terminology

1 1.1.9

Bipolar Line A direct current line in which, the two poles connect the load to the supply.

1.1.10 Transmission Line A line used for electric power transmission. Normally restricted to overhead construction and operated at high voltage.

1.1.11 Distribution Line A line that delivers electric energy from transformation points on the transmission, or bulk power, to the consumers.

1.1.12 (Overhead) Conductor A wire or combination of wires not insulated from one another, suitable for carrying an electric current. It may be bare or lightly insulated.

1.1.13 Conductor Vibration Periodic motion of a conductor relative to a static position.

1.1.14 Aeolian Vibration Periodic motion of a conductor predominantly in a vertical plane, or relatively high frequency and small amplitude of the order of the conductor diameter induced by laminar wind flow.

1.1.15 Sub-span Oscillation Periodic motion of one (or more) sub-conductor(s) predominantly in a horizontal plane, of intermediate frequency and amplitude of the order of the bundle spacing.

1.1.16 Conductor Galloping Periodic motion of a conductor (or bundle) predominantly in a vertical plane of low frequency and high amplitude (with a maximum value of twice the original sag.

1.2

Mechanical Design (Note: In this section, the expression “load”, “loading” refer to mechanical forces applied to a component of a line)

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Terminology

1 1.2.1

Loading Assumptions Set of loading conditions, resulting from national or particular statutory regulations (as well as from a study of meteorological data) to be accepted for designing each element of an overhead line.

1.2.2

Loading Case Combination, or set, of loads applied to an element of an overhead line for a particular loading assumption.

1.2.3

Working Load The load derived from the specified loading assumption excluding factors of safety or overload factors.

1.2.4

Normal Load Loads resulting from the action of the wind or of gravity on wires, insulators and/or supports (structures) under ice or no ice condition.

1.2.5

Exceptional Loads The loads produced by the reasonable activities of construction and maintenance personnel, and those resulting from the failure of some component of a line.

1.2.6

Legislative Load The loads arbitrarily dictated by local or national regulating bodies.

1.2.7

Test Load The load applied to an element or elements of an overhead line for testing purposes.

1.2.8

Rupture Load That loading which causes failure to occur in any element.

1.2.9

Ultimate Design Load The loading resulting from multiplying the working load by the factor of safety or overload factor and which all elements should just sustain without failure, during the specified duration.

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Terminology

1 1.2.10 Vertical, Transverse, Longitudinal Loads

The three components, in a three-dimensional system of co-ordinates, of any load applied at a given point of the support. The longitudinal load (parallel to the line axis) and the transverse load (perpendicular to the line axis) are supposed to be in the horizontal plane.

1.2.11 Wind Load Horizontal load resulting from the wind pressure applied to any element of the overhead line, with or without ice loading.

1.2.12 Ice Loading Additional mass resulting from ice accretion on any element of the overhead line.

1.2.13 Uniform Ice Loading Ice load uniformly distributed over the length of each conductor (and earth-wire) and over all the spans of a section of line.

1.2.14 Unequal Ice Loading Ice load not uniformly distributed over the length of each conductor (and earth-wire) and over all the spans of a section of line. This may be due to ice shedding or from non-uniform accumulation, or from non-uniform detachment.

1.3 1.3.1

Spans Span The part of an overhead line between two adjacent point of support of a conductor.

1.3.2

Span Length (Horizontal Span Length) The horizontal distance between two adjacent point of support of a conductor.

1.3.3

Level Span A span in which the conductor support points are in the same horizontal plane.

1.3.4

Inclined Span A span in which the conductor support points are not in the same horizontal plane.

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Terminology

1 1.3.5

Difference in Levels Vertical distance between the two horizontal plans, each containing the support points of a span.

1.3.6

Wind Span The distance between the points at mid-span on each side of a support.

1.3.7

Weight Span The horizontal distance between the low points of a conductor (or bundle) on either side of a support. In steeply sloping terrain, both low points may be on the same side of the support.

1.3.8

Span Depth The vertical distance between two horizontal planes, one through the highest point of support of the conductor in a span, and the other tangential to the lowest point of the conductor curve. This lowest point may be imaginary.

1.3.9

Sag The maximum vertical distance in a span of an overhead line between a conductor and the straight line joining its points of support.

1.3.10 Section (Of an Overhead Line) A part of an overhead line between two tension supports.

1.3.11 Equivalent Span – Ruling Span (US) A fictitious single span in which tension variations, due to load or temperature changes are nearly the same as in the actual spans of a section. Note: The approximate value of the equivalent (ruling) span is calculated from:

∑a ∑a

3

a

c

=

i i

1.3.12 Catenary Equation of the curve assumed by a perfectly flexible, in-extensible cord suspended at its ends.

⎛ ⎞ x Y = ρ ⋅ ⎜⎜ cosh − 1⎟⎟ ρ ⎠ ⎝ In practice, the simple parabola formula is often used,

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Terminology

1 Y=

1

2

⋅ ρ ⋅ x2

which represents the first two terms of the series expansion of the catenary. NOTE: The catenary curve represents a cable with constant unit weight per unit of length of curve, while the parabola represents a wire with a constant unit weight per horizontal unit of length. Use of the parabola will indicate less sag as the wire becomes more steeply inclined and may introduce significant errors in steeply inclined sections of cable.

1.3.13 Catenary Constant The constant in the catenary and parabola equations geometrically represented by the radius of curvature at the lowest point of the span. It is given as the ratio between the horizontal tension in the conductor To and its unit weight ω , which can take into account the ice or wind overloads.

ρ=

1.4 1.4.1

To

ω

Profiles Longitudinal Profile A representation of the ground contours in the vertical plane through the axis of the overhead line.

1.4.2

Side Slope at “X” meters A representation of the ground contour in the vertical planes located X meters from, and parallel to the axis of the overhead line.

1.4.3

Transverse Profile (Section Profile) Profile in a vertical plane perpendicular to the axis of the line.

1.4.4

Diagonal Leg Profiles Representation of the ground contour in vertical planes containing diagonally opposite legs of a tower.

1.4.5

Line Angle The angular change in the direction of an overhead line at a support.

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Terminology

1 1.5 1.5.1

Conductor arrangements Conductor Configuration The geometrical arrangement of the conductors in relation to the support.

1.5.2

Horizontal Configuration A configuration in which all conductors on a support are in the same horizontal plane.

1.5.3

Semi-Horizontal Configuration A variation of the horizontal configuration in which the centre phase is a slightly higher or lower level than the lateral phases.

1.5.4

Triangular Configuration A configuration in which the conductors of a circuit are located at the apexes of the triangle whose base is not necessary horizontal.

1.5.5

Delta Configuration A configuration in which the conductors of a circuit are located at the apexes of an isosceles triangle whose base is not necessary horizontal.

1.5.6

Vertical Configuration A configuration in which the conductors of a circuit are virtually located in the same vertical plane.

1.5.7

Semi - Vertical Configuration A variation of the vertical configuration in which the centre phase is horizontally offset.

1.5.8

Double Circuit Vertical Configuration A configuration in which each of the two circuits, in vertical formation, is located on either side of the support.

1.5.9

Double Circuit Semi - Vertical Configuration A variation of the double circuit vertical configuration in which the centres phase is horizontally offset.

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Terminology

1 1.5.10 Transposition

A change of the relative positions of the phase conductors of an overhead line, carried out in order to establish adequate electrical symmetry of the conductors one to another or with respect to earth or with respect to neighbouring systems.

1.5.11 Transposition Interval Length of the section of a line between two successive transpositions.

1.5.12 Ground Clearance (Clearance to Ground) The minimum distance to be maintained at all times between a live conductor, or metal fitting, and the ground.

1.5.13 Live Metal to Earth Clearance (Clearance – Live Metal to Grounded Parts) The minimum distance to be maintained at all times between live conductors or live components and any steelwork deemed to be at earth potential.

1.5.14 Clearance to Obstacles – Working Clearance (US) The minimum distance to be maintained at all times between a live conductor, or live metal fitting, and any obstacle at ground potential, under or passing under or close to the line.

1.5.15 Phase Spacing The distance between the axes of two adjacent line conductors, or between the centres of two adjacent bundles of line conductors.

1.5.16 Angle of Protection – Angle of Shade – Shielding Angle The angle between the vertical planes through the earth-wire and the plane through the earth wire and the conductor to be protected against lightning.

1.5.17 Minimum Angle of Shade – Minimum Shielding Angle The angle within the line conductors must lie in order to obtain a desired magnitude of protection against direct lightning strokes.

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Terminology

1 1.6 1.6.1

Support Structure Support (UK) – Structure A generic term for any device designed to carry, through insulators, a set of conductors of an overhead line.

1.6.2

Straight Line Support – Intermediate Support – Tangent Support Straight Line Structure – Intermediate Structure – Tangent Structure A support located on a straight-line portion of an overhead line route, where the conductors are attached by suspension; pin or line post insulators.

1.6.3

Flying Angle Support – Running Angle Support Flying Angle Structure – Running Angle Structure A support used on small or medium angles of deviation of the route, the conductors being attached by suspension type insulator sets.

1.6.4

Angle Support – Angle Structure Section Support – Section Structure Anchor Support – Anchor Structure Dead-end Support – Dead-end Structure A support to which the conductors (or bundles) are attached through tension insulator sets. The loads due to the adjacent spans are applied independently to the attachment points.

1.6.5

Terminal Support – Terminal Structure A support situated at the end of a line and designed to terminate the line tension of conductors on one side.

1.6.6

Transposition Support A support specifically designed to permit the change of the relative position of the phases along the route of a line.

1.6.7

Self-supporting Structure A support having intrinsic stability.

1.6.8

Guyed Structure (US) – Stayed Support (UK) A support whose stability is ensured by guys (stays).

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Terminology

1 1.6.9

Stay – Guy A separate member, usually in tension, used for ensuring the stability of stayed (guyed) support.

1.7 1.7.1

Poles - Brackets Pole A vertical single member support in wood, concrete, steel etc …, with one end buried in the ground, either directly or by means of a separate base.

1.7.2

Portal Structure – “H” Pole – “H” Frame (US, CA) A “H” shaped support comprising two spaced vertical main legs with a horizontal cross-arm at the top.

1.7.3

Cross-arm – Beam The horizontal transverse member of a portal or H structure supporting the insulators and the conductors.

1.7.4

Bracket A small fitting attached to the outside of a building, or any support.

1.7.5

“A” Pole – “A” Frame (US –CA) A double member support in which the tops of each member are shaped, keyed and bolted together at the apex of the letter “A” and are joined by a common cross-block

1.8 1.8.1

Towers Tower A support which may be made of any material, comprising a body which is normally four sided, with cross-arms.

1.8.2

Lattice Tower A compound structure resulting from an assembly of small structural members.

1.8.3

Bracing System (UK) – Lacing System (US – CA) Arrangement of the members in a lattice support.

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Terminology

1 1.8.4

Single Warren – Single Lacing (US – CA) See Figure 1.1.1

1.8.5

Double Warren – Double Lacing (US – CA) See Figure 1.1.2

1.8.6

Triple Warren – Triple Lacing (US – CA) See Figure 1.1.3

1.8.7

“K” Bracing (“K” Panel) See Figure 1.1.4

1.8.8

Double Warren Redundant Support Double Lacing Redundant Support (US – CA) See Figure 1.1.5

1.8.9

Top Hamper – Super Structure See Figure 1.2.1

1.8.10 Earth Wire Peak See Figure 1.2.11

1.8.11 Beam Gantry – Bridge – Girder See Figure 1.2.12

1.8.12 Cross-arm See Figure 1.2.13

1.8.13 Fork – “K” Frame See Figure 1.2.14

1.8.14 Waist See Figure 1.2.115

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Terminology

1 1.8.15 Tower Body The vertical structure of a tower. See Figure 1.2.2

1.8.16 Plan Bracing - Diaphragm See Figure 1.2.21

1.8.17 Main Bracing See Figure 1.2.22

1.8.18 Redundant (Secondary) Bracing See Figure 1.2.23

1.8.19 Main Leg See Figure 1.2.24

1.8.20 Leg Slope See Figure 1.2.25

1.8.21 Node – Panel Point See Figure 1.2.26

1.8.22 Anti-Climbing Guard – Device A device installed on, or attached to, a support, structure, tower, guy, etc… to make climbing difficult by unauthorised persons. See Figure 1.2.30

1.8.23 Foot (Footing) See Figure 1.2.30

1.8.24 Hill Side Extension – Leg Extension Portion at base of tower constructed with equal or different standard lengths used for variations in tower heights or on hillsides.

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Terminology

1 1.9 1.9.1

Bare conductors Conductor (of a Line) That portion of an electric line, which has the specific function of conveying current.

1.9.2

Solid Conductor A conductor consisting of a single wire.

1.9.3

Wire, Strand One of the individual wires used in manufacture of a stranded conductor.

1.9.4

Stranded Conductor A conductor consisting of a number of individual un-insulated wires laid up together in the alternating left and right helical formation.

1.9.5

Layer In a stranded conductor, that group of wires, arranged to form a cylinder of constant radius, with the same axis as the conductor and having the same direction and length of lay.

1.9.6

Length Of Lay The axial length of one complete turn of the helix of a wire in a stranded conductor.

1.9.7

Lay Ratio The ratio of the length of lay to the mean diameter of the helix.

1.9.8

Direction Of Lay Direction of rotation of the helix formed by a wire of a stranded conductor. With right-hand lay the wires conform to the direction of the central part of the letter Z when the conductor is held vertically. With left-hand lay, the wires conform to the direction of the central part of the letter S when the conductor is held vertically.

1.9.9

Smooth Body Conductor; Segmented or Locked Coil Conductor A conductor with a relatively smooth surface obtained by using, for the outer layer, wires whose shape is that of a radial section of an annulus (segmental), of whose shape prevents them from having any radial movement (locked coil).

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Terminology

1 1.9.10 Hollow Conductor

A tubular conductor made up of wires or segments stranded sometimes around a helical arrangement of reinforcing wires.

1.9.11 Expanded Conductor A conductor where some of the internal wires have been omitted, or replaced by nonmetallic, lighter wires to obtain an artificial increase in diameter.

1.9.12 All Aluminium Conductor AAC All Aluminum Conductor (US) AAC All Aluminium Alloy Conductor AAAC All Aluminum Alloy Conductor (US) AAAC A conductor where, all wires are made of aluminium, or aluminium alloy.

1.9.13 Aluminium Conductor Steel reinforced (A.C.S.R.) Aluminum Conductor Steel reinforced (US) (A.C.S.R.) Aluminium Alloy Conductor (A.A.C.S.R.) Aluminum Alloy Conductor (US) (A.A.C.S.R.) Bimetallic conductor in whom the aluminium or aluminium alloy wires are stranded around an inner core of steel wires, with successive layers of opposite lay.

1.9.14 Aluminium Conductor Steel Reinforced With Alumoweld Core (ACSR/AW) Aluminum Conductor Steel Reinforced With Alumoweld Core (US) (ACSR/AW) An ACSR conductor as in 1.9.13 with the steel core wires replaced with bimetallic aluminium sheathed steel wire (Alumoweld).

1.9.15 Aluminium Conductor Alloy Reinforced (ACAR) or Alumoweld/Aluminium Conductor Aluminum Conductor Alloy Reinforced (ACAR) or Alumoweld/Aluminum Conductor (US) An aluminium conductor with a portion of the aluminium strands replaced by aluminium alloy or alumoweld strands in a configuration within the conventional stranding arrangement.

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Terminology

1 1.9.16 Core (Of A Bimetallic Conductor)

The inner steel, or aluminium alloy or Alumoweld wires of a bimetallic conductor. The proportion of strength contributed by the core may be greater or smaller than contributed by the conducting outer aluminium alloy layers.

1.9.17 Single Conductor Each phase or pole consists of a single conductor.

1.9.18 Bundle Conductor/Sub-Conductor Each phase consists of two or more single conductors connected in parallel, spaced one from the other, and supported by common suspensor insulator sets. The individual conductors in the bundle constitute sub-conductors.

1.9.19 Twin, Triple, Quad Bundle etc… - (Two, Three, Four etc… Conductor Bundle (US) A phase conductor consisting of two, three, four or more sub-conductors installed in parallel.

1.9.20 Earth-wire, Earth Conductor, Shield Wire, Overhead Groundwire A conductor connected to earth at intervals, which is suspended usually above but not necessarily over the line conductor to provide a degree of protection against lightning discharges.

1.9.21 Jumper A short length of conductor, not under mechanical tension, making an electrical connection between two separate sections of line.

1.9.22 Counterpoise A conductor, or system of conductors, arranged beneath the line, located on, above or most frequently below the surface of the earth, and connected to the footings of the towers of poles supporting the line.

1.10

Conductor fittings

1.10.1 Spacer; Spacer Damper A device which keeps apart the sub-conductors of a bundle at a pre-determinate distance

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Terminology

1 1.10.2 Mid-Span tension joint

A joint inserted between two lengths of a conductor, designed to carry the full current and to withstand 90% of the breaking load of the conductor

1.10.3 Dead-end Tension Joint A joint inserted at the end of a conductor for attachment to an insulator tension set, designed to carry the full current and to withstand 90% of the breaking load of the conductor.

1.10.4 Jumper Lug, Jumper Terminal The component of a joint which permits an electrical continuity with another joint or conductor.

1.10.5 Repair Sleeve A special fitting which can be installed over a damaged conductor in order to restore its electrical and mechanical properties.

1.10.6 Clamp A term used to define any fitting which can be fixed on (to) a conductor.

1.10.7 Suspension Clamp A fitting, which attaches a conductor to a suspension insulator set.

1.10.8 Tension Clamp; Dead-end Clamp A clamp which attaches a conductor to a tension insulator set or to a support, and designed to withstand the full tension of the conductor.

1.10.9 Pivot Type Suspension Clamp A suspension clamp designed so that it can oscillate around a horizontal axis normal to the conductor and normally on its centre line.

1.10.10 Body (Of a Suspension Clamp) That part of the suspension clamp which supports the conductor.

1.10.11 Suspension Straps (Of a Suspension Clamp) That part of a suspension clamp which supports the body of the fitting.

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Terminology

1 1.10.12 Trunnion (Of a Pivot Type Suspension Clamp)

The circular projection from the body of the clamp, which acts as an axis of rotation within the straps, permitting some oscillation of the clamp.

1.10.13 Hold Down Weights – Counterweight (US) A mass attached to a suspension clamp (assembly) utilised to reduce or eliminate uplift, to provide positive loading to insulator sets to prevent turning-over, or to reduce the angle of swing of suspension insulator sets during high transverse winds.

1.10.14 Vibration Damper In an overhead line, a device attached to a conductor in order to suppress or minimise vibrations due to wind.

1.10.15 Night Warning Light (For Conductor) Device, which becomes luminous generally by capacitive induction from a live conductor to which is attached. Used as a night warning device.

1.10.16 Aircraft Warning Marker (For Cables) A warning device visible during the day, used on conductors or earth wires.

1.10.17 Armour Rods – Armor Rods (US) A set of protective metal rods wound helically around a conductor at the suspension point and placed prior to the installation of the suspension clamp.

1.10.18 Patch Rods A set of metal rods, similar to armour rods, wound helically around a conductor over damaged areas to restore the electrical properties of the conductor.

1.11

Insulator Sets - Accessories

1.11.1 Insulator Set (UK) – Insulator Assembly (US) An assembly of one or more string insulator units, suitably connected together, complete with metal fittings, for flexible mechanical attachment of an overhead conductor to a support while insulating it electrically.

1.11.2

Insulator String A chain of several insulator units in series flexibly connected together.

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Terminology

1 1.11.3 Suspension Set (UK) – Suspension Assembly (US)

An insulator set complete with all fittings and accessories to support one or more conductors at his lower end.

1.11.4 Tension Set (UK) – Tension Assembly (US) An insulator set complete with all fittings and accessories to withstand the tensile load of one or more conductors.

1.11.5 “U” Bolt A fitting in the form of a “U” attached to a support.

1.11.6 Dropper (UK) – Swinging Bracket (US) A fitting that lowers the upper attachment point of a suspension insulator set.

1.11.7 Tower Swivel Clevis A fitting free to rotate rounds an axis and attached to the steelwork of a support.

1.11.8 Yoke Plate A special fitting for the attachment of several insulator strings or other parallel elements, to a single point.

1.11.9 Insulator Protective Fittings Metal accessories, installed at one or both extremities of an insulator set to drive the flashover arc away from the insulator set and provide a better voltage distribution along the insulator string.

1.11.10 Arcing Horn A protective fitting in the shape of a horn.

1.11.11 Arcing Ring A protective fitting in the shape of a ring.

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Terminology

1

1

2

3

4

5

Figure 1.1. 1-5 - BRACING SYSTEM

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Terminology

1 Figure 1.2. 1-35 - LATTICE TOWERS

11 12 13

1

14

15

22

21

23 24

2

25 26

27

30

31

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Parameters in Overhead Line Tower Design

2 2

2. Parameters in Overhead Line Tower Design In the design of new overhead line towers, we are obliged to follow the technical specification for the specific overhead line. In our approach, we will base our design on the GECOL TECNICAL SPECIFICATION and ANSI/ASCE 10-90 standard. Of course, in the case that some solutions, specified in other international standards are more appropriate we will incorporate them in our design approach. 2.1

Geometrical parameters The rules of overhead line design satisfying the geometrical conditions, are imposed by three things: ■ Security of the people and the goods ■ Electrical conditions of the object insulating ■ Possibility of intervention on the objects in the exploitation conditions All those conditions are elaborated by the client, in our case GECOL. Anyhow, it is our duty to react in the case when we doubt in the technical specifications, and ask the clarification of the suspected point.

2.1.1

Tower types The determination of tower types to be designed is generally linked to the needs of a client, which, in our case is GECOL. For one overhead line with one type of conductor, four or five tower types are necessary. Those towers having the similar outline are making a family. In common use is to give the names as A, B, C, D etc or ADT, BDT, CDT, DDT etc. In GECOL’s case, the tower names are fixed per internal codification. For example, the tower types of one 220kV overhead double circuit line are: 1. TYPE 2BB02 -

This is the suspension tower designed for line deviation of 0° to 2°

2. TYPE 2BB30 -

This is medium angled tower designed for line deviation of 2° to 30°

3. TYPE 2BB60 -

This is the large angled tower designed for line deviation of 30° to 60°

4. TYPE 2BB90 -

This is the dead-end (terminal) tower and maximum angle tower designed for line deviation of 60° to 90°

In this case, the first digit represents the number of sub-conductors per phase, the letters in second and third position represent the nominal voltage and the last two digits represent the maximum line angle for the tower. If the choice of the tower type used in design were different than initially specified by GECOL, then this choice has to be approved by GECOL or the other client (in the case of a design for export).

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Parameters in Overhead Line Tower Design

2 2

Some of tower types are presented in the following table and the family names will be the object of discussion with GECOL.

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Parameters in Overhead Line Tower Design

2 2

Geometrical Characteristics

EDF Designation

Triangular configuration

Triangle

GECOL Designation

Schema

To ask GECOL

T

Drapeau Flag configuration

V

Double circuit flag configuration

Sapin

To ask GECOL

S&B

Double circuit semivertical configuration

Tonneau

Nine cross-arms

Neuf consoles

No English equivalent

To ask GECOL

To ask GECOL

H&B

To ask GECOL

Danube

To ask GECOL

D

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Parameters in Overhead Line Tower Design

2 2

Geometrical Characteristics

Delta configuration

EDF Designation

GECOL Designation

Schema

Anjou To ask GECOL

B

Double circuit vertical configuration

Quadruple drapeau

Special configuration

Spécial

Semi_horizontal configuration

Chat

Q

To ask GECOL

To ask GECOL

To ask GECOL

C&B

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Parameters in Overhead Line Tower Design

2 2

Geometrical Characteristics

EDF Designation

Horizontal configuration

Nappe

Portal

GECOL Designation

Schema

To ask GECOL

N&M

Nappe – Trianon

To ask GECOL

N&M

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Parameters in Overhead Line Tower Design

2 2

2.1.2

Clearance to Obstacles The clearance to obstacles is important in the spotting of towers. It is imposed by GECOL and for the maximum conductor sag at 75°C without wind, the minimum clearances are:

Crossing-Over

30kV

66kV

220kV

Normal ground

7.0m

8.0m

9.0m

Power and T.T. lines

3.0m

3.0m

7.0m

Main roads

10.0m

12.0m

12.0m

Secondary roads

9.0m

10.0m

10.0m

Trees

2.5m

4.5m

4.5m

Shrubs

2.5m

4.0m

4.0m

Figure 2.1.2-1

The values for the column “66kV” are marked to be subject of discussion with GECOL. In the tower design, only the values for the Normal ground crossing-over are to be considered. In the tower spotting, we have to respect all of them.

2.1.3

Tower height under cross-arm In our personal engineering practice, we had sometimes problems with the client due to a misunderstanding of the terms explained in this article. This is important for both, the client and designer. In the tower height determination, first at all, we have to make sag and tension calculation for the overhead line conductor. In this calculation, using the equivalent span and respecting the maximum allowable conductor tension, we obtain the maximum sag of the conductor Sc. If an allowable soil clearance is Sd, and the isolator string length id Sl, the tower height under cross-arm is for the suspension tower Hs=Sd+Sc+Sl and for the tension tower Hs=Sd+Sc. This height is generally called the zero height. Please pay attention; the zero height of tower is composed of the tower head, basic body and the zero leg extensions. During the tower spotting, we require the tower to be higher or less then the zero height. In this case we use the terms–6m, -3m etc or +3m, +6m, +9m etc. For the minus height, in general, we have to modify the basic body to be adapted to desired height. To obtain the plus

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Parameters in Overhead Line Tower Design

2 2

heights we use the basic body adding the body extensions. Therefore, for the +6 height we have the basic body with a +6 body extension. For the hilly areas, the terrain slope has a great impact on the design because we need unequal leg extensions. In tower design, we have to consider this because of efforts in the main member. Generally, the effort in the main member for the configuration of four zero leg extensions, can be increased even a 10%. To avoid this, there are two possibilities. First is, to calculate the worst combination of unequal legs. For a long time, this was the only method. The second way is, to calculate the tower with a configuration of four zero leg extensions, and then to verify, tower per tower, the mechanical characteristics for each. With the new computers and the new programs, this is now possible. The specification of the different tower heights is generally made by GECOL. If this is not the case, all mentioned criteria have to be satisfied.

2.1.4

Live metal distances The live metal distances between any metallic element of support and the pieces under voltage (conductors, isolator string extremities, counterweights etc…) to be respected in our tower design are specified in GECOL Technical specification. For the different swing of suspension string, the values are:

Live metal distances

Hypothesis

30 kV

66 kV

220 kV

0° swing of suspension string

?????

?????

?????

reduced swing of suspension string

?????

760mm (10°)

1980m (20°)

maximum swing of suspension string

450mm (60°)

650mm (30°) 1500mm (60°)

Figure 2.1.4-1

The values in this table have to be subject of serious discussion with GECOL, especially for the unspecified distances.

2.1.5

Earth-wire shield angle According to the GECOL Technical specification the earth-wire shield angles (see definition 1.5.16 Angle of Protection – Angle of Shade – Shielding Angle) are: 30kV double circuit overhead line 66kV double circuit overhead line 220kV double circuit overhead line

=>35° =>35° =>30°.

We assumed that for the double circuit towers, only one earth-wire is demanded.

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Parameters in Overhead Line Tower Design

2 2

For the horizontal conductor configurations, we need a clarification from GECOL, concerning the shield angle, and the shield angle covering an internal conductor.

2.1.6

Horizontal and vertical conductor distances Both, horizontal and vertical distances, are fixed by TECNICAL SPECIFICATION and their values are:

Description

30 kV

66kV

220kV

Minimum horizontal distance between phase conductors

5000mm

5000mm

5000mm

Minimum vertical distance between phase conductors

2000mm

2700mm

2700mm

Figure 2.1.6.1

Of course, in case of horizontal arrangement of conductors, the vertical distance between them doesn’t exist. The conductor spacing between phases or phases and earth wire in the mid span shall be regulated by following formula:

C [m] = 0.8 ⋅ s

( Sag + L) +

E 150

where Sag represent the conductor sag at +75ºC expressed in meters, L is length of string also in meters, but for “V” and tension-string is equal to zero, E is nominal line voltage expressed in kV.

2.1.7

Special conditions Any special condition, for the particular tower family, or specific overhead line, will be discussed with GECOL whenever is the case.

2.2

Loading parameters The tower resistance is represented by the ratio of ultimate efforts and working loads, and is called a safety factor. The ultimate effort represents the effort causing the tower irreversible deformation. The working loads are the loads that the tower is submitted during his life.

2.2.1

Normal conditions The normal (every day) loading cases are:

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Parameters in Overhead Line Tower Design

2 2

Permanent loads Wind and temperature loads (ice is not mentioned in GECOL technical specification and will be not considered) According to the load vector orientation, we can distinguish a vertical, transversal and longitudinal effort. Vertical efforts: Weight of tower Weight of insulator string Weight span of conductor (earth wire) multiplied by specific weight of the conductor (earth wire) Transversal efforts: Wind pressure on each conductor and earth wire Wind pressure on each insulator string Wind pressure on the flat surface of structural member Transversal component of wire tension Longitudinal efforts: For the angle towers, unbalance conductor and earth wire tensions, due to unequal spans For the dead end towers, conductor and earth wire tension on one side only. This is because the other side of tower is not loaded at all. The values for the wind pressure, coefficient for the structural member exposed area to the wind, are specific for the different geographical area and the nominal line voltage. Safety factor for the normal loading cases is 2.5

2.2.2

Exceptional conditions Under exceptional conditions, we assume the broken wire cases. The towers shell be designed for the following broken wire conditions:

2.2.2.1 SUSPENSION TOWER BROKEN WIRE CONDITION Any one bundled phase conductor broken or earth wire broken whichever is more stringent for a particular member of the tower. The tension due to broken conductor shall be considered as 30% of maximum tension of all the phase conductors whereas the tension due to broken earth wire shall be considered as 70% of the maximum tension.

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Parameters in Overhead Line Tower Design

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2.2.2.2 TENSION TOWER BROKEN WIRE CONDITION Any of the phase conductors broken on the same side and on the same span or any one of the phase conductor and earth wire broken on the same span whichever is more stringent. The tension due to broken conductors or earth wire shall be full maximum tensions.

2.2.2.3 TERMINAL TOWER BROKEN WIRE CONDITION Three phase conductors broken on the same side and on the same span (? To discuss with GECOL “same span” expression because we have a terminal tower case) or any two of the phase conductors and earth wire broken on the same span. In addition, they shall be designed for six phase conductors on the same side unconnected. The tension due to broken conductors shall be considered as the maximum tension The vertical and transversal loads shall be computed on same pattern while considering 60% of weight and wind spans as mentioned above in Normal conditions. Safety factor for the broken wire loading cases is 1.5

2.2.3

Line erection and maintenance conditions The line erection and maintenance conditions are not precisely determinated by GECOL and will be discussed with them. Safety factor for the line erection and maintenance conditions loading cases is 1.5

2.3

Materials Materials used in design of towers are in accordance to the GECOL specifications. They are two of kind: steels and bolts.

2.3.1

Steels The steel used in our design shall be mild or high tensile according to the international DIN or ASTM standards. The ultimate tensile strength for the mild steel is between 37 and 45 kp/mm2 and yield stress is not less than 24 kp/mm2. The ultimate tensile strength for the high tensile steel is between 52 and 62 kp/mm2 and yield stress is not less than 36 kp/mm2. This steel designation has to be discussed with GECOL in order to respect the new European Standard. All details are in annex 3 of this Guide. The minimum thickness for the angles is: Leg and other corner members

- 5 mm

Bracings and other members

- 4 mm

An unequal leg angle is permitted in the design. The minimum size of flange without holes is 3mm. Anyhow; the unequal leg angle type is to avoid, for the different raisons, like symmetry, fabrication problems, possibility of mistake in the erection etc.

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Parameters in Overhead Line Tower Design

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2.3.2

Bolts and nuts Bolts and nuts in our design are conforming to DIN 7990 and 555. Grade of bolts is minimum 4.6 (to discuss with GECOL a value of minimum). The size we will use in our design shall be M16 and M20. It is preference to have only one diameter for the whole tower. We shell discuss with GECOL a possibility to use a M12 in our tower design.

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Static calculation

3 2

3. Static calculation All previous steps have to be accomplished before starting a static calculation. A dynamic calculation is possible, but generally, we are replacing the concentrated mass elements that are multiplied by the acceleration and statically applied on the structure. The hypothesis to be respected in tower analysis is that a tower is an ideal three-dimensional truss, and in that case, only axial forces in the members are possible. This hypothesis is very important and any other assumption is very dangerous for a non-experienced designer. I am saying this because of recent collapse of one angle tower design (year 2000) made by one Spanish college who considered some elements (leg members) as beam elements, without the control of moments occurred in the nodes of structure. 3.1

Tower Model We know too well that the tower is composed from a lot of elements, bars, plates, bolts, etc. For the calculation purposes, we have to assume that the tower is presented by the lines connected to the nodes. The tower has a high degree of symmetry which is facilitating the tower modelling, and almost all specialised computer programs has this facility in the nodes and bars generating. The rules describing how to respect these static lines in the tower detailing is described in the chapter “Detailing and fabrication”. All members have to be triangulated in order to have a static system and not mechanism. The members who are inside a triangle have an axial forces equal to zero. Therefore, the members with forces as result of a loading case we call a primary bars, and the bars without any force secondary members. The secondary bars are used to reduce un-braced lengths of the primary members, and for this reason we call them also redundant members. Having secondary bars is not useful in tower modelling and our advice is to avoid them.

3.2

Computer Program Our choice of computer program was “TOWER”, software made by Power Line Systems, Inc. All descriptions of his use are presented in the program manual that is in annex 1 of this Guide. However, we have to pay attention on few things. A computer program is always a tool, and for now being, cannot replace an engineer experience. We have one expression for this case called GIGO; it means “Garbage in garbage out”. For the good utilisation of this program, you have to make a certain number of towers, designed under the control of somebody with experience in this field. Even then, continue to read and study the literature in this domain. This will allow you to

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Static calculation

3 2

be in the contact with the newest experience and solutions to the problems in the tower design.

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Tower Dimensioning

4 2

4. Tower Dimensioning 4.1

Bar dimensioning The methods described in this chapter are to be applied for the dimensioning of hot-rolled and cold-formed bars. Once the static calculation finished, the most important task to do is bar dimensioning. Every designer has to take in the consideration all necessary elements to make the profile choice. On this point, we have to finalized the tower outline; make the choice of secondary (redundant) bars necessary to add in order to reduce the slenderness ratio, etc… Please, don’t forget to recalculate the wind on tower efforts, due to the final bar sections.

4.1.1

Slenderness ratios According to the GECOL technical specifications, the limiting values of the slenderness ratio for the bars with calculated compressive stress shall be as follows:

Leg members and main corner members of earth-wire peak and cross arms

120

Other members

200

For the bars without calculated stress or with the nominal stress, we have to respect the following limit:

Redundant members and those carrying nominal stress 250 Also:

Members carrying axial tension only

4.1.2

375

Tension members In the bar determination due to the tension effort, we have to pay attention on only one thing: the net section of bar. To determinate the net section, we need to have two parameters, the cross section of the bar and the characteristics of bolted connection (diameter of holes and the number of holes).

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Tower Dimensioning

4 2

In the GECOL technical specification, for the bolts M16 and M20, the diameter of the holes is equal to the bolt diameter + 1.5mm

4.1.2.1 Angles connected by one leg Allowable tension effort for the angles connected by one leg is equal to design stress Ft multiplied by net cross section.

Tc = Ft ⋅ An In this case, the net section of unbolted leg is equal to the 0.5 of leg section, and net section of the bolted leg is equal to the leg section minus the holes. On the end the formula of the net section is:

An = 0.75 ⋅ A − D ⋅ t Where “A” is the angle section, “D” is hole diameter and “ t” is the thickness of leg.

4.1.2.2 Angles connected on both legs Allowable tension effort for the angles connected on both legs is equal to design stress Ft multiplied by net cross section.

Tc = Ft ⋅ An In this case, the net section of angle is equal to angle section minus the holes. On the end the formula of the net section is:

An = A − n ⋅ D ⋅ t Where “A” is the angle section, “D” is hole diameter, “ t” is the thickness of leg and n is the number of bolts, generally with value of two. In case of diagonal or zigzag chain of holes, we have to check the angle section formed by the shortest line connecting the bolts on both legs. If this section is less then the previously calculated then we have to replace net section by the new one.

4.1.3

Compression members The compression calculation is explained in details in the annex 2. Anyhow, some details are to be repeated twice. The allowable compression stress Fa is given by formulas: 2 ⎡ KL ⎞ ⎤ ⎛ 1 r ⎟ ⎥⋅F Fa = ⎢1 − ⎜ ⎢ 2 ⎜ Cc ⎟ ⎥ y ⎝ ⎠ ⎥⎦ ⎢⎣

Fa =

π 2E

(KL r )

Cc = π

2

KL ≤ Cc r

KL ≥ C c r

2E Fy

(4.1.3-1)

(4.1.3-2)

(4.1.3-3)

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Tower Dimensioning

4 2

Fy

- Minimum guaranteed yield stress

E

- Modulus of elasticity

L

- Un-braced length

r

- radius of gyration

K

- Effective length coefficient

4.1.3.1 Maximum

w/t Ratio

The maximum w / t ratio is 25, where w is the flat angle width and t is angle leg thickness.

80Ψ ⎛ w⎞ ⎟ = Fy ⎝ t ⎠ lim

If the w/ t exceeds ⎜

(4.1.3.1-1)

Then the value of allowable stress Fa shall be replaced with Fcr , as given by:

⎡ w/t ⎤ Fcr = ⎢1.667 − 0.677 ⎥ ⋅ Fy ( w / t ) lim ⎦ ⎣

w 144Ψ ⎛ w⎞ ⎟ ≤ ≤ Fy ⎝ t ⎠ lim t

for the value of ⎜

(4.1.3.1-2)

or

Fcr =

0.0332π 2 E (w / t )2

for the value of

w 144Ψ ≥ t Fy

(4.1.3.1-3)

The value of Ψ , mentioned in (4.1.3.1-1) trough (4.1.3.1-3), is equal to 1 if the Fy is expressed in ksi, and equal 2.62 if the Fy is expressed in MPa.

4.1.3.2 Effective lengths The only value not explained is previous formulas K

is - Effective length coefficient.

For the members with L / r ≤ 120 the value for effective slenderness ratio in (4.1.3-1) and (4.1.3-2) is :

KL / r = L / r

For no eccentricity at both ends, as for example the main member (Curve 1)

4.1.3.2-1

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Tower Dimensioning

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KL / r = 30 + 0.75 L / r

For eccentricity at one end only, as for example the bottom cross-arm member (Curve 2)

4.1.3.2-2

KL / r = 60 + 0.5 L / r

For eccentricity at both ends, as for example the diagonals (Curve 3)

4.1.3.2-3

For the members with L / r > 120 the value for effective slenderness ratio in (4.1.3-1) and (4.1.3-2) is :

KL / r = L / r

For the member unrestrained at both ends (Curve 4)

4.1.3.2-4

KL / r = 28.6 + 0.762 L / r

For the member with partial restraint at one end only (Curve 5)

4.1.3.2-2

KL / r = 46.2 + 0.615 L / r

For the member with partial restraint at both ends (Curve 6)

4.1.3.2-3

Regarding the complexity of realisation, the Curve 5 and 6 are not recommended for use.

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4.2

Bolt Determination The last things to determinate are bolts. First, we have to make the choice of bolt diameters to use in our design. We suggest you to avoid more then two diameters for one tower type. Sometimes, when is possible, we rather use a single bolt diameter. This is very important decision. The consequences are not only for the fabrication facility but for the erection work also. In GECOL specification, we found that M12 is forbidden for use. We suggest to GECOL to reconsider this decision and allow us his use. Once diameter(s) accepted, we can start with calculation of bolt quantities. Two element of this calculation are necessary to do, described later in articles “4.2.1 Shearing” and “4.2.2 Bearing”, of this chapter. For the bolt determination, we prefer the method described in “Recommendation for Angles in Lattice Transmission Towers” rather then ASCE method.

4.2.1

Shearing The shear strength of bolt is related to the bolt quality only. First, we have to determinate the values of 0.69σt and 0.95σy and to accept the smallest σs as allowable shear stress. Then the shear strength of bolt is given by the following formula: Ft = σs⋅A where A is cross sectional area of bolt. The number of bolt (n), for a particular bar connection, is calculated in order to satisfy a condition that maximum bar ultimate tension or compression effort is less than shear strength of bolts. This is described by following formula: Fu(t,c) ≤ n⋅σs⋅A In case of double shear, the value of Fu(t,c) is double also. The case of triple shear is rarely or impossible to find in common tower design. In addition, we have to pay attention that the number of bolts has to be in accordance with the bar curve.

4.2.2

Bearing The bearing capacity is linked to the allowable deformation of holes. In France, EDF is accepting three times yield stress, but the theory of allowable edge distances is too much complicated. In our design we shall use two times yield stress and the edge distances x=1.5⋅D; y=1.25⋅D and z=2.5⋅D; where D is bolt diameter. In this is the case, the ultimate compression or tension effort for one bolt is:

Fu(t,c)=σb⋅Ds⋅t where σb is allowable bearing stress and equal to twice yield stress of bar.

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Tower Dimensioning

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In some special cases, when we need to use the edge distances less then specified, we have to check the bearing capacity by using the formulas:

x

z t

y

Fu(t,c) = σb⋅(x-Ds⋅t)

Î for the longitudinal edge distances

Fu(t,c) = 1.33⋅σb⋅(y- ½⋅Ds)⋅t Fu(t,c) = ½⋅σb⋅(z- ½⋅Ds)⋅t

Î for the transversal edge distances

Î for the hole centre distances.

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Detailing and fabrication

5 2

5. Detailing and fabrication Detailing problem consists in transforming statical lines in angles and plates connected bye bolts. Our choice of drafting aid program was AutoCAD®. The rules to follow are described in ANSI/ASCE 10-90 and have to be respected. 5.1

Drawings Tower detail drawings are composed of workshop drawings and bills of material. In some cases, to facilitate the tower erection procedure, we are producing the erection drawing – simplified workshop drawings, showing the complete assembly and indicating the position of each element. Bill of material will be made in excel sheet. Approval of workshop drawings is a task of GECOL, who will control correctness of dimensional detail calculations and give his opinion once test of tower finished.

5.2

Connections The best way to connect members is making directly on each other with minimum eccentricity. Minimum bolt spacing, end and edge distances shell respect those mentioned already in “4.2.2 Bearing” and those specified in GECOL technical specification.

5.3

Material Workshop drawings have to clearly specify member and connection materials. As told before, we are using maximum two kind of steel: mild steel and high tensile steel. High tensile steel has to be marked with letter A on the workshop drawings.

5.4

Shop operations Shop operations consist essentially of cutting, punching, drilling, blocking or clipping, and either cold or hot bending. Every operation has to be indicated on the workshop drawing. For more details, see Annex 2, Article 7.2.2

5.5

Marking For the marking of pieces, you have to keep on mind the necessary elements: ⇒ Mark of fabricator

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Detailing and fabrication

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⇒ Tower designation ⇒ Item number ⇒ Steel quality The mark of fabricator in our case is special logo of GPC. This is needed in case of problems on erected towers. In case that erected tower pieces don’t have GPC mark, no any responsibility of GPC is engaged. Tower designation is normally limited on three characters, because of limit of CNC machines (8 characters in total). Item number has to unique to the specific tower, and generally is limited on three characters (numbers). Steel quality is the last mark on tower elements. It is in GECOL case, a letter A for the high tensile steel, and blank for the mild steel. For the other details, see Annex 2, article 7.2.4.

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Tower Prototype

6 2

6. Tower Prototype It is highly recommended to make a tower prototype before to start any serial production. This is valuable for the new design as well as for the old one. The prototype is assembled on the ground in horizontal position. This chapter is describing the procedure in the prototype approval. 6.1

Prototype documents The documents to be checked are: ◊

Workshop drawings

◊

Material lists

◊

Steel certificates

◊

Bolt and nuts certificates

All documents revisions have to correspond to the assembled prototype. This is very important point in later serial production of towers.

6.2

Checking of main dimensions The main dimensions have to be checked to avoid a possible capital error that the workshop drawing is not corresponding to statical outline. Sometimes it arrives that during detailing we made some error on one element provoking a general main dimension error.

6.3

Checking of bars Bars have to be with all dimensions and steel quality as indicated on workshop drawings. After this check, we have to check that all bars were assembled without any forcing and any deformation. Any interferences between bars or bars any other tower element have to be reported, corrected, and workshop drawings have to be changed with a new revision note.

6.4

Plates checking Plates have to satisfy the same criteria as bars.

6.5

Bolts checking During our checking of prototype, we have to check the following bolts parameters: ‰

Bolt diameter

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Tower Prototype

6 2

‰

Length of bolts

‰

Bolt hole (holes)

All bolt diameters have to correspond to those in workshop drawings. The length of bolts has to be same as indicated on workshop drawings. The length of remaining part of bolts has to be between two and three treads. Any bolt has to be mounted without any forcing, the holes he is passing through have to be perfectly aligned. All mistakes can be dangerous for the test of tower, provoking premature tower failure.

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Tower testing

7 2

7. Tower testing Before to start this chapter, we would like to say one thing. The overhead line tower is the only structure tested up to the failure, and that is the reason to have so precise design method. In the design, we are always trying to have an optimum dimensioned tower. We are newer making a reserve more than 10%, because the weight supplement for one tower, multiplied by total number of towers, is giving a very expensive transmission line. Don’t forget that extra weight of towers has also the repercussions on the tower transport and erection costs. Every designer assisting on the tower test has two fears, first is the resistance of tower on 100% of loading, and the second is that the failure of tower arrives before the 125% of loading for the ultimate test case. This is increased knowing that the good tower test result is not depending on the good tower design. A lot of factors are involved in this process, like material tolerances (+ or -), fabrication mistakes, testing equipment problems, external (non calculated) wind during the test, etc… In the case that the tower collapse arrives before 100% of loading, don’t panic. You are not the first, either last designer confronted with this problem. In addition, please, do not continue the test without knowing the failure reason. This is important for the good finishing of tower test and it will be a good experience for the future tests. 7.1

Choice of Loading Cases The choice of loading cases is generally made by client him self or his consulting engineer. Sometimes, it is up to the designer to propose the loading cases. Anyhow, you have to know that too much loading cases applied on the tower can provoke his collapse even that the tower can resist to the each of them separately. This is the reason to have a maximum of five loading cases. The last case is a destructive test, except when the client asks to not have one. This is generally decision for the towers of a small serial production, and where we want to recuperate the prototype for the later use. Please, pay attention that it is forbidden to recuperate, and use in normal exploitation, the tower submitted to the destructive test.

7.2

Elaboration of Tower Testing Program Elaboration of testing program is to be discussed with GECOL

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Tower testing

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7.3

Prototype Erection Checking The prototype erection is made by testing station team, and they are responsible for this. Anyhow, the designer have to check the prototype erection him self and to pay attention on following:

7.4

-

All bars mounted and all bolts tied well

-

Level of artificial foundations has to be in tolerances zero

-

Tower have to be vertical position

Testing Procedure The testing procedure have to be in accordance to the International standard for overhead line tower testing “LOADING TESTS ON OVERHEAD LINE TOWERS” made by International Electro technical Commission. Many countries listed on page 3 of this publication, voted explicitly in favour of publication. There is not need to give more explanations for the testing procedure; everything is already described in this publication.

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Bibliography

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8. Bibliography

ANSI/ASCE 10-90 (1991) “Design of Latticed Steel Transmission Structures” American Society of Civil Engineers

ASCE MANUALS AND REPORTS ON ENGINEERING PRACTICE NO. 52 (1984) “Guide for Design of Steel Transmission Towers” ECCS – TECHNICAL COMMITTEE 8 – STRUCTURAL STABILITY TECHNICAL WORKING GROUP 8.1 (1985) “Recommendations For Angles in Lattice Transmission Towers” EDF/CERT (1996) “Directives Lignes Aériennes” GENERAL ELECTRIC COMPANY OF LIBYA-PLANNING & PROJECTS DEPARTMENT (1999) “Technical Specification for 30 kV Double Circuit Overhead Transmission Lines” GENERAL ELECTRIC COMPANY OF LIBYA-PLANNING & PROJECTS DEPARTMENT (1996) “ 66 kV Double Circuit Overhead Transmission Lines - Technical Specification ” GENERAL ELECTRIC COMPANY OF LIBYA-PLANNING & PROJECTS DEPARTMENT (1999) “Technical Specification of 220 kV Overhead Double Circuit Transmission Lines” GRAÐEVINSKI FAKULTET SARAJEVO (1980) “Otpornost materijala” GTMH (1999) “Directives Lignes Aériennes” Michel Bougue

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Annexes

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9. Annexes Annex 1: TOWER Computer Program Manual Power Line Systems “TOWER – Analysis and Design of Steel Latticed Towers used in Transmission and Communication Facilities ”

Annex 2: American standard for design of overhead line towers ANSI/ASCE 10-90 (1991) “Design of Latticed Steel Transmission Structures” American Society of Civil Engineers

Annex 3: European Standard for the Steels used in design of overhead line towers BS EN 10025 (1993) “Hot rolled products of non-alloy structural steels – Technical delivery conditions”

Annex 4: European recommendation for design of overhead line towers ECCS – Technical Committee 8 – Structural Stability Technical Working Group 8.1 (1985) “Recommendations for Angles in Lattice Transmission Towers”

Annex 5: American recommendation for design of overhead line towers ASCE Manuals and Reports on Engineering practice No. 52 (1984) “Guide for Design of Steel Transmission Towers”

Annex 6: International standard for overhead line tower testing INTERNATIONAL ELECTROTECHNICAL COMMISION “LOADING TESTS ON OVERHEAD LINE TOWERS”

- 47 Rev. A

Annexes

9 2

Annex 7: Bare Overhead Line Conductor Catalogue ALCATEL CABLE – France

Annex 8: Overhead Line Insulators Catalogue SEDIVER – France

Annex 9: String hardware catalogue Derveaux groupe SICAME – France

- 48 Rev. A

Index

10 2

10. Index

A AC Line ...................................................................................................................................... 1 Aeolian Vibration ....................................................................................................................... 2

B Bearing ..................................................................................................................................... 38 Bipolar Line................................................................................................................................ 2 bolt diameter ............................................................................................................................. 38 Bracing System ........................................................................................................................ 10

C Catenary ................................................................................................................................. 5, 6 Circuit ............................................................................................................................... 1, 7, 46 Clearance to Obstacles ......................................................................................................... 8, 26 compression .............................................................................................................................. 38 conductor ...................................................................... 1, 2, 4, 5, 6, 8, 13, 14, 15, 16, 21, 26, 28 Conductor ............................................................................................................. 2, 7, 13, 14, 15 Conductor fittings ..................................................................................................................... 15 Conductor Galloping .................................................................................................................. 2 Conductor Vibration ................................................................................................................... 2 Cross-arm ........................................................................................................................... 10, 11

D Delta Configuration .................................................................................................................... 7 Diagonal Leg Profiles................................................................................................................. 6 Difference in Levels ................................................................................................................... 5 Direct Current Line .................................................................................................................... 1 Distribution Line ........................................................................................................................ 2

E Earth Conductor ....................................................................................................................... 15 Earth-wire ........................................................................................................................... 15, 27 Exceptional Loads ...................................................................................................................... 3

G Ground Clearance ....................................................................................................................... 8 Guy ........................................................................................................................................... 10

H Horizontal Configuration ........................................................................................................... 7

- 49 Rev. A

Index

10 2

I ice ....................................................................................................................................... 3, 4, 6 Ice Loading ................................................................................................................................. 4

J Jumper ...................................................................................................................................... 15

L Legislative Load ......................................................................................................................... 3 Line........................................................................................................... 1, 2, 5, 6, 9, 13, 21, 30 Loading Assumptions ................................................................................................................. 3 Loading Case .............................................................................................................................. 3 Longitudinal Profile ................................................................................................................... 6

M Mechanical Design ..................................................................................................................... 2 Monopolar Line .......................................................................................................................... 1

N Normal Load .............................................................................................................................. 3

O Overhead Ground-wire ............................................................................................................. 15 Overhead Line ............................................................................................................................ 1

P Phase....................................................................................................................................... 1, 8 Pole ........................................................................................................................................... 10 Positive (Negative) Pole ............................................................................................................. 1

R Rupture Load .............................................................................................................................. 3

S Sag ........................................................................................................................................ 5, 28 shear ......................................................................................................................................... 38 Shearing .................................................................................................................................... 38 shield angle ............................................................................................................................... 27 Shield Wire ............................................................................................................................... 15 Span .................................................................................................................................. 4, 5, 16 structural members ................................................................................................................... 10 Support ................................................................................................................................. 9, 11

- 50 Rev. A

Index

10 2

T tension .................................................................................................. 5, 6, 9, 10, 15, 16, 26, 38 Test Load .................................................................................................................................... 3 Tower ....................................................................................... 10, 12, 18, 21, 26, 32, 34, 42, 44 Transmission Line ...................................................................................................................... 2 Transposition .......................................................................................................................... 8, 9 Transverse Profile ...................................................................................................................... 6 Triangular Configuration............................................................................................................ 7

U Ultimate Design Load ................................................................................................................ 3

V Vertical Configuration................................................................................................................ 7 Vertical, Transverse, Longitudinal Loads .................................................................................. 4

W wind .......................................................................................................................... 2, 3, 4, 6, 26 Wind Load .................................................................................................................................. 4 Working Clearance ..................................................................................................................... 8 working load ............................................................................................................................... 3 Working Load ............................................................................................................................ 3

Y yield .......................................................................................................................................... 38

- 51 Rev. A