transmission tower 1216390_634537377958061250
DESCRIPTION
Transmission TowerTRANSCRIPT
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TRANSMISSION TOWER
R.Saravanan, PGET, L&T, UAE
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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
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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
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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
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TOWERGEOMENTRY
TOWERTYPES
ELECTRICALCLEARANCES
DESIGN PARAMETER
LOAD CALCULATION
ANALYSIS & DESIGN FOUNDATION STUB SETTING
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TOWER GEOMENTRY
ANATOMY
BRACINGS
EXTENSIONS
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Tower Anatomy
Peak - supports G.WCage - b/w peak & tower bodyCross Arm - Support
Conductor/G.WBoom – supports power
conductors (horizontal)Tower body – main portion,
connects cage/boom to foundation/(leg/body )extensions
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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 area) Single web systemb) Double web or warren systemc) Pratt systemd) Portal systeme) Diamond Bracing systemf) Multiple Bracing System
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1.Struts are designed in compression & Diagonals in tension2.NARROW BASE 3.66Kv single circuit
1.Tension diagonal give eff.support to compression one @ pt of connections2.Used in both large and small towers
1.Shear carried by diagonal member(t)2.Large deflection under heavy loads3.Unequal shears at top of four stubs for design
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1.1half of Horizontal member in T & another C2.Advantageous to use it in BOTTOM panel3.Extensions & Heavy river crossing
1. Similar to waran system2.Horizontal member carry no primary loads designed as redundant supports
1.Increse in strenght reducing member sizes2.Increase in No.of bolts, fabrication & erection cost,3.Overal reduction in Wt & cost of steel
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Tower ExtensionBody ExtensionLeg 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 upto 7.5m 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)
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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
Types of Tower
5) No. of Circuits• Single Circuit• Double Circuit• Multi-Circuit
6) Deviation Angle.• Ranges from 0 to 90 deg.
1) Type of Insulator• Suspension• Tension/Dead end• Transposition
2) Type of Support• Self Supporting• Guyed
3) Shape at the base• Square• Rectangle
4) kV Rating.• Ranges from 33 to 1200 kV• HVDC
R.SARAVANAN, PGET, L&T UAEEDRC-TL Design
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Vertical Configuration Horizontal Configuration
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Tension TowerSuspension Tower
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Guy Towers
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Conductor Configuration
R.SARAVANAN, PGET, L&T UAE 2166 kv 132 kv 220 kv 400 kv
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66 kv 132 kv 220 kv 400 kv
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Tower Nomenclature
Sr. No. Nomenclature Deviation Remark
1 A/DA/S/SLC/T0/TDL/QA/SA/V 0-20 Suspension Tower
2 B/DB/AT/DLB/TD2/QB/X 0-300 •Used Small angle tower.• Used as a Section Tower
3 C/DC/BAT/DLC/TD3/QC/CZ 30-60• Used as Medium Angle Tower•Used as a Transposition
4 D/DD/BAT/DE/TD6/TDT/QD/DE 60-900/Dead End
•Used as a large angle Tower•Used as a Dead End Tower
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Height of Tower Structure
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4321 hhhhH
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
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ELECTRICAL CLEARANCES
Sr. No
Type of Clearance 132 kV 220 kV 400 kV 765 kV
1 Ground Clearance 6.1 m 7.0 m 8.84 m 15.5 m
2 Live Metal Clearance in mm Swing
132 / 220 400 / 765
•Suspension insulator 15 15 1530 1980 3050 4400 (25°)
30 30 1370 1830 1860 1300 (55°)
45 - 1220 1675 -
60 1070 - -
•Tension Insulator 0 0 1530 2130 3050
•Jumper 10 20 1530 2130 3050 4400
20 40 1070 1675 1860 1300
30 - 1070 - - -
3 Mid Span Clearance (m) 6.1 8.5 9.0 12.4
4 Shielding Angle (Deg) 30 30 20 20
5 Phase to Phase Clearance Vertical 3.9 m 4.9 m
Horizontal 6.8 m 8.4 m
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Right of Way :
Sr. No Type of Clearance 132 kV 220 kV 400 kV 765 kV
1 ROW width 27 m 35 m 52 m 85 m
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DESIGN PARAMETERS
Transmission Voltage
Number Of Circuits
Climatic Conditions
Environmental and Ecological
Consideration
Conductor
Earth Wire
Insulators
Span
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Economic Voltage of Transmission of Power
E = Transmission voltage (KV) (L-L). L = Distance of transmission line in KM KVA=Power to be transferred1506.15.5
KVALE
Standard Voltage - 66,110,132, 220, 400 KV
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ConductorAluminum is used it has about half the weight of copper for the same resistance, as well as being cheaperTypes:AAC : All Aluminium conductors.AAAC : All Aluminium Alloy conductorsACSR : Aluminium conductors, Steel-ReinforcedACAR : Aluminium conductor, Alloy-Reinforced
Bundle conductorBundle conductors are used to reduce corona loses & audible noiseIt consists of several conductors cables connected by non-conducting spacersIt is used to increase the amount of current that may be carried in lineAs a disadvantage, the bundle conductors have higher wind loadingSpacers must resist the forces due to wind, and magnetic forces during a short-circuit
spacers
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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
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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
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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.
single string
Double string
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Design Span lengths
1.Basic SpanMost economic spanLine is designed over level groundThe requisite ground clearance is obtained at maximum specified temperature
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2.Ruling SpanAssumed design span that will produce, between dead endsIt 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)
Ruling span = √ ( L1^3 + L2^3 +….+L6^3 / L1 + L2 + … + L6)
3.Average Span
Mean span length between dead endsIt 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
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4.Wind Span 5.Weight Span
Horizontal distance between the lowest point of conductor, on the two spans adjacent to the towerThe lowest point is defined as point at which the tangent to sag curveIt is used in design of cross-arms
Half the sum of the two spans, adjacent to supportIt is assumed that the conductor is freely suspended such that each individual span reacts to change in tension as a single average span
Wind span = 0.5(L1 + L2)
Weight span = a1 + a2
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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.
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Ryle Formula
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Determination of Weight of tower
Rough approximationFrom knowledge of the positions of conductors & ground wire above ground level & overturning momentsRyle gives empirical formula in term of its height & maximum overturning moment at base
132 kv – 1.7 metric tones220 kv – 2.5 metric tones400 kv – 7.7 metric tones765 kv – 14 metric tones
Approximate values
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LOADINGSLoads 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.
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Loads on TowerNormal Condition
Broken Wire Condition
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•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
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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.
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FOUNDATIONIt costs 10-30 % of overall cost of towerIt is the last step in designing process but precedes the constructionOverload factors assumed in designs are 2.2 under Normal condition & 1.65 under broken-wire conditions
Data's for foundation design
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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
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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
Hybrid design Large uplift force are
to be resisted SBC is low
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
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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
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 dia into the rock
Special circumstances River crossing towers
& towers on embankments
The raft at bottom makes the foundation substantially rigid to minimize differential settlement
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Raft foundationPyramid chimney type foundation
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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
Stub-setting
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