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TYPES OF TRANSMISSION TOWER, ANATOMY, CONDUCTOR, INSULATOR, FOUNDATION, STEEL LATTICE TRUSS,

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transmission tower

TRANSMISSION TOWER

R.Saravanan, PGET, L&T, UAE

R.SARAVANAN, PGET, L&T UAE

power in uae
Power in UAE..?
  • Production capacity – 18.74 GW. (lack in peak seasonal times)
  • Lack of natural gas
  • Gulf Cooperation Council – UAE, Kuwait, Qatar, Bahrain, Saudi Arabia & Oman
  • GCC began region-wide power grid – demand
  • UAE has no spare power capacity
  • Phase 3 of GCC grid to southern system of UAE
  • In Dec’2009 $20 billion contract to Korean Electric Power – 4 nuclear reactors
  • 1st reactor may 2017 – each reactor 1400 MW

R.SARAVANAN, PGET, L&T UAE

slide5

Electric power transmission..?

  • The bulk transfer of electrical energy, from generating power plants to substations
  • Power is usually transmitted through overhead power lines
  • Underground power transmission has a significantly higher cost and greater operational limitations - urban & sensitive areas

Overhead Power lines..?

  • An electric power transmission line suspended by towers
  • It is the lowest-cost method of transmission for large quantities of electric energy (most of insulation by air)
  • The bare wire conductors on the line are generally made of aluminum

R.SARAVANAN, PGET, L&T UAE

slide6

Transmission tower..?

  • Tall structure usually a Steel lattice tower, used to support an overhead power line
  • Electricity pylon – UK & parts of Europe
  • Ironman – Australia
  • Hydro tower in parts of Canada

R.SARAVANAN, PGET, L&T UAE

tower geomentry
TOWER GEOMENTRY

R.SARAVANAN, PGET, L&T UAE

tower anatomy
Tower Anatomy
  • Peak - supports G.W
  • Cage - b/w peak & tower body
  • Cross Arm - Support Conductor/G.W
  • Boom – supports power conductors (horizontal)
  • Tower body – main portion, connects cage/boom to foundation/(leg/body )extensions

R.SARAVANAN, PGET, L&T UAE

bracings
Bracings
  • Provided for interconnecting the legs
  • To afford desired slenderness ratio for economical tower design
  • Framing angle b/w bracings & main leg members shall not be < 15 degree
  • Patterns are
  • Single web system
  • Double web or warren system
  • Pratt system
  • Portal system
  • Diamond Bracing system
  • Multiple Bracing System

R.SARAVANAN, PGET, L&T UAE

tower extension
Tower Extension
  • Body Extension
  • Leg Extension

Body Extension

  • Used to Increase the height of tower to obtain the reqd min Ground clearance & over road crossings, river crossings, ground obstacles
  • Body extensions upto7.5m height in steps 2.5m can be used & thus form a part of standard tower
  • Extensions having greater heights (25m) the suitability is checked by reducing span length and angle of deviation. Practice in tower industry is also to specify negative body extension (portion of tower body is truncated)

R.SARAVANAN, PGET, L&T UAE

slide15

Leg Extension

  • Tower Leg extensions are required when the tower was spotted in the undulated surface / Hilly terrain.
  • While spotting the tower locations in hilly areas requires more benching or revetment or both are involved , but suitable hill side (leg extensions) can be used to minimize benching or revetment or both.
  • Two types of Leg extension :
  • i) Universal leg extension
  • ii) Individual leg extension

R.SARAVANAN, PGET, L&T UAE

types of tower
Types of Tower
  • Type of Insulator
    • Suspension
    • Tension/Dead end
    • Transposition
  • Type of Support
    • Self Supporting
    • Guyed
  • Shapeat the base
    • Square
    • Rectangle
  • kVRating.
    • Ranges from 33 to 1200 kV
    • HVDC
  • No. of Circuits
      • Single Circuit
      • Double Circuit
      • Multi-Circuit
  • Deviation Angle.
      • Ranges from 0 to 90 deg.

R.SARAVANAN, PGET, L&T UAE

slide17

Vertical Configuration

Horizontal Configuration

R.SARAVANAN, PGET, L&T UAE

tension tower
Tension Tower

Suspension Tower

R.SARAVANAN, PGET, L&T UAE

guy towers
Guy Towers

R.SARAVANAN, PGET, L&T UAE

conductor configuration
Conductor Configuration

R.SARAVANAN, PGET, L&T UAE

slide21

66 kv

132 kv

220 kv

400 kv

R.SARAVANAN, PGET, L&T UAE

slide22

66 kv

132 kv

400 kv

220 kv

R.SARAVANAN, PGET, L&T UAE

tower nomenclature
Tower Nomenclature

R.SARAVANAN, PGET, L&T UAE

height of tower structure
Height of Tower Structure

Height of tower is determine by-

h1=Minimum permissible ground clearance

h2=Maximum sag

h3=Vertical spacing between conductors

h4=Vertical clearance between earth wire and top conductor

R.SARAVANAN, PGET, L&T UAE

electrical clearances
ELECTRICAL CLEARANCES

R.SARAVANAN, PGET, L&T UAE

slide26

Right of Way :

R.SARAVANAN, PGET, L&T UAE

design parameters
DESIGN PARAMETERS
  • Transmission Voltage
  • Number Of Circuits
  • Climatic Conditions
  • Environmental and Ecological Consideration
  • Conductor
  • Earth Wire
  • Insulators
  • Span

R.SARAVANAN, PGET, L&T UAE

slide28

Economic Voltage of Transmission of Power

E = Transmission voltage (KV) (L-L).

L = Distance of transmission line in KM

KVA=Power to be transferred

  • Standard Voltage - 66,110,132, 220, 400 KV

R.SARAVANAN, PGET, L&T UAE

conductor

Aluminum is used

  • it has about half the weight of copper for the same resistance, as well as being cheaper
  • Types:
  • AAC : All Aluminium conductors.AAAC : All Aluminium Alloy conductorsACSR : Aluminium conductors, Steel-ReinforcedACAR : Aluminium conductor, Alloy-Reinforced
  • Bundle conductor
  • Bundle conductors are used to reduce corona loses & audible noise
  • It consists of several conductors cables connected by non-conducting spacers
  • It is used to increase the amount of current that may be carried in line
  • As a disadvantage, the bundle conductors have higher wind loading
  • Spacers must resist the forces due to wind, and magnetic forces during a short-circuit
Conductor

spacers

R.SARAVANAN, PGET, L&T UAE

earth wire
Earth Wire
  • Earth wire provided above the phase conductor across the line and grounded at every tower.
  • It shield the line conductor from direct strokes
  • Reduces voltage stress across the insulating strings during lightning strokes
  • Galvanized steel earth wires are used
  • Aerial marker balls (>600mm dia) (Red, Orange, White)
  • Shield angle
    • 25°-30° up to 220 KV
    • 20° for 400 KV and above

R.SARAVANAN, PGET, L&T UAE

insulators
Insulators
  • Insulator are required to support the line conductor and provide clearance from ground and structure.
  • Insulator material-
      • High grade Electrical Porcelain
      • Toughened Glass
      • Fiber Glass

Type of Insulator-

    • Disc Type
    • Strut Type
    • Long Rod Insulator

R.SARAVANAN, PGET, L&T UAE

insulator strings

single string

Insulator Strings
  • Disc insulator are joint by their ball pins and socket in their caps to form string.
  • No of insulator disc is decided by system voltage, switching and lighting over voltage amplitude and pollution level.
  • Insulator string can be used either suspension or tension.
  • Two suspension string in parallel used at railways, road and river crossing as statutory requirement.
  • Swing of suspension string due to wind has to be taken into consider.

Double string

R.SARAVANAN, PGET, L&T UAE

design span lengths
Design Span lengths
  • 1.Basic Span
  • Most economic span
  • Line is designed over level ground
  • The requisite ground clearance is obtained at maximum specified temperature

R.SARAVANAN, PGET, L&T UAE

slide36

2.Ruling Span

  • Assumed design span that will produce, between dead ends
  • It is used to calculate the horizontal component of tension (which is applied to all spans b/w anchor pts)
  • Tower spotting on the profile is done by means of sag template, (which is based on ruling span)

3.Average Span

  • Mean span length between dead ends
  • It is assumed that the conductor is freely suspended such that each individual span reacts to change in tension as a single average span

Average span = (L1+ L2+...+L6) /6

Ruling span = √ ( L1^3 + L2^3 +….+L6^3 / L1 + L2 + … + L6)

R.SARAVANAN, PGET, L&T UAE

slide37

4.Wind Span

5.Weight Span

  • Half the sum of the two spans, adjacent to support
  • It is assumed that the conductor is freely suspended such that each individual span reacts to change in tension as a single average span
  • Horizontal distance between the lowest point of conductor, on the two spans adjacent to the tower
  • The lowest point is defined as point at which the tangent to sag curve
  • It is used in design of cross-arms

Wind span = 0.5(L1 + L2)

Weight span = a1 + a2

R.SARAVANAN, PGET, L&T UAE

slide38

Determination of Base Width

  • The base width(at the concrete level) is the distance between the centre of gravity at one corner leg and the centre of gravity of the adjacent corner leg.
  • A particular base width which gives the minimum total cost of the tower and
  • foundations.
  • The ratio of base width to total tower height for most towers is generally about one-fifth to one-tenth.

Ryle

Formula

R.SARAVANAN, PGET, L&T UAE

38

slide39

Determination of Weight of tower

  • Rough approximation
  • From knowledge of the positions of conductors & ground wire above ground level & overturning moments
  • Ryle gives empirical formula in term of its height & maximum overturning moment at base

Approximate values

132 kv – 1.7 metric tones

220 kv – 2.5 metric tones

400 kv – 7.7 metric tones

765 kv – 14 metric tones

R.SARAVANAN, PGET, L&T UAE

loadings
LOADINGS

Loads are applied in all three directions namely Transverse ( FX ),

Vertical ( FY) and Longitudinal (FZ) direction.

  • Transverse loads consists of –
    • Wind on Conductor
    • Wind on Insulator
    • Component of Wire Tension in Transverse Direction (Deviation Load)
    • Wind on Tower Body
  • Vertical Load consists of –
    • Weight of Wire
    • Weight of Insulator
    • Weight of Line man & Tools
    • Self Weight of Tower
  • Longitudinal Load Consist of –
    • Component of Unbalanced pull of the wire in the longitudinal direction.

R.SARAVANAN, PGET, L&T UAE

loads on tower
Loads on Tower

Normal Condition

Broken Wire Condition

R.SARAVANAN, PGET, L&T UAE

slide42

Loads are calculated as per the guide lines furnished in specification/standard.

  • Standards for Calculation of Loads
    • IS – 802 – 1977
    • IS – 802 – 1995
    • DIN – VDE 0210
    • ASCE Manual
    • IEC – 826
  • The loads are calculated for following Conditions.
    • Reliability / Working condition
    • Security / Broken wire condition
    • Safety / Erection & maintenance Condition

R.SARAVANAN, PGET, L&T UAE

analysis design
ANALYSIS & DESIGN
  • Analysis is carried out by finite element software

STAAD

  • Required FOS is provided in input file to find out ultimate force
  • The critical compression and tension in each member group is found out
  • Members and Connections are designed for these forces.
  • Iterations are carried out for the optimum usage of tower.

R.SARAVANAN, PGET, L&T UAE

foundation

Data's for foundation design

FOUNDATION
  • It costs 10-30 % of overall cost of tower
  • It is the last step in designing process but precedes the construction
  • Overload factors assumed in designs are 2.2 under Normal condition & 1.65 under broken-wire conditions

R.SARAVANAN, PGET, L&T UAE

slide48

0.5 to 2m dia

  • Shaft depth 3 to 15m
  • Skin friction between ground & shaft resists uplift
  • Used in usa, acceptance for wide use in India
  • Uplift loads are resisted by undistrube material
  • Develop uplift load of 2 to 3times that of an iidentical footing without undercut
  • Non-cohesive soil
  • For non-cohesive soils such as uncemented sand or gravel
  • Provide pad footing without undercut
  • Usually followed in INDIA at present

R.SARAVANAN, PGET, L&T UAE

slide49

Adopted in firm cohesive soils

  • Undercut on the pads
  • Experience shows that this type of footing develop resistance to uplift 2 to 3 times that given footing without undercut
  • Augered footing with more than one bulb is used to increase the uplift capacity
  • 35m long under reamed to 2.5 times dia of shaft
  • Clayey black cotton soils & medium dense sandy soils
  • Hybrid design
  • Large uplift force are to be resisted
  • SBC is low

R.SARAVANAN, PGET, L&T UAE

slide50

In usa ,canada

  • Steel corroded, periodic excavation & maintanence
  • Medium dry sand, clay or sandy caly soils (no special precautions necessary)
  • The steel is treated with one coat of bituminous paint & top coat of asphalt
  • Special circumstances
  • River crossing towers & towers on embankments
  • The raft at bottom makes the foundation substantially rigid to minimize differential settlement
  • Suitable in areas with rock out crop
  • Based on uplift, the anchor be single bar or group of bars welded to tower leg
  • Vertical bars below stub angle form cage for footing
  • Grouted to a depth of about 50 times diainto the rock

R.SARAVANAN, PGET, L&T UAE

slide51

Pyramid chimney type foundation

Raft foundation

R.SARAVANAN, PGET, L&T UAE

stub setting
Stub-setting
  • Important steps in tower erection
  • The stubs are set with the help of stub setting templates
  • Excavated pits are lean concreted to correct level
  • Stubs are placed on lean concrete pad
  • Alignment is carried by four plumb bobs hung from centre of the horizontal bracing
  • If any pit over excavated by mistake, the extra depth should be filled by concreting
  • After the stub is set, the heel distance of four faces of the tower and two diagonals should be checked

R.SARAVANAN, PGET, L&T UAE