400KV TL History

SEPL/MEPL400kVD/CTransmissionlineDetailed Report

Herein this detailed report of the SEPL/MEPL 400kV D/C Transmission line, all particulars of thefoundations of the towers, erection of the towers and stringing of the conductor have been included.Also the process of execution of the line has been documented for the reference.

SEPL/MEPL 400kV D/C Transmission line

Prepared ByUmapathinaidu. R, Engineer (Projects) – Electrical

SIMHAPURI ENERGY PVT. LTD.

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400kV SEPL/MEPL D/C Quad moose Transmissionline is connecting to the 400kV PGCILSubstation, Nellore. This transmission line is26.377km length and has 82 no. of towers withrequired angle deviations and extensions withrespect to the areal clearances/ROWconsiderations.

As well as this line has an interconnectionpart of 0.630km to facilitate the uninterruptedpower supply requirements to the grid by theSEPL and MEPL thermal power plants together.This Interconnection makes the feasibility,towards accessing the second circuit in order toachieve the power requirement at load point evenin shutdown conditions by/of any one plant.

In full details, this 400kV Transmissionline is a Double Circuit (D/C) type to feed SEPLand MEPL circuits side by side. And the ACSR(Aluminum conductor steel reinforced) MOOSE isused as the conductor and it has been so chosenas in bunch of quad to carry the currentcapacity of both the circuits at a time. As wellas the string of disc insulators 160KN and 120KNwith 31mm creepage distance per 1KV are used astension and suspension insulators respectively.




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In this transmission line the galvanized,lattice structured steel towers are used to withstand the areal climatic conditions of a windzone-5. And there are 32no.of Angle Point (AP)towers (i.e.) Tension type towers and remainingare normal type (i.e.) suspension type towers.

Types of towers used: DA, DC and DD

Total no. of towers: 82

Total no. of DA type towers: 50

DA type towers with 0m extension DA+0: 31



Total no. of DC type towers: 12

DC type towers with 0m extension DC+0: 06








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Total no. of DD type towers: 20

DD type towers with 0m extension DD+0: 13





Where in the above particulars, the ‘+’indicates the extension length of the towerwhich has been chosen by depending on the ROWconsiderations at the particular areas to meetthe electrical clearance levels. And the ‘A’,‘C’ and ‘D’ represents the angle deviations ofthe towers with respect to the previous towers.The angle deviations of towers can be describedby depending on the following predefinedmeasurements.

DA type: 0-2°

DB type: 2-15°

DC type: 15-30°

DD type: 30-60°

Here the first letter ‘D’ represents thenumber of circuits of a tower and the followingletter represents the angle deviation from itsprevious tower.




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Technical particulars of Tower Foundations:

Foundations: By depending on the types of

the towers and their extensions,pit marking details and foundationpits sizes have been considered.Wherein these foundations, Fe-415graded steel used as reinforcementand M20 graded concrete has been sochosen for rafting the foundations.

The foundations depth hasbeen taken 3.5mtrs and it had beenvaried as per the soil conditions.For example in the loose soilconditions the depth was taken upto 2.5mtrs in minimum andautomatically the area of the pithas been increased to some extentto withstand the load of the toweraccording to their type andextensions.

And also nine number oftowers foundations are strengthenedwith pilings where the loose soilconditions are observed. There werefour numbers of pilings as per thedrawing for each pit out of fourfor one tower. These are locatednearby the revers crossing and fishponds throughout this line.




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Pit marking details of different type towers

along with their extensions are as following………

For DA type:

PIT MARKING DETAILS FOR TOWER TYPE ‘DA’TYPE A B C D E F0m

base7000 9900 14000 19799 4850 18850

+3mExtn

7487 10588 14973 21175 4850 19823

+6mExtn

7973 11276 15946 22551 4850 20796

+9mExtn

8460 11964 16919 23928 4850 21769




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Quantities per ‘DA’ tower:Concrete (M20): 37.640cum

Lean concrete (M10): 8.320cum

Reinforcement: 3443.38Kg

For DC Type:

PIT MARKING DETAILS FOR TOWER TYPE ‘DC’TYPE A B C D E F

0mbase

9022 12759 18044 25518 8300 26344

+3mExtn

9769 13816 19539 27632 8300 27839

+6mExtn

10517 14873 21033 29746 8300 29333

+9mExtn

11264 15930 22528 31860 8300 30828

+12mExtn

11806 16696 23612 33392 6300 29912

Quantities per ‘DC’ tower:Concrete (M20): 117.627cum






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For DD Type:

PIT MARKING DETAILS FOR TOWER TYPE ‘DD’TYPE A B C D E F

0m base 9739 13774 19479 27547 9050 28529+3m Extn 10482 14824 20964 29647 9050 30014+6m Extn 11224 15873 22448 31747 9050 31498

+9m Extn 11967 16923 23933 33847 9050 32983

+0mExtn(2.75depth)

6866 9710 13733 19421 5950 19683

+3mExtn(2.75depth)

7353 10398 14706 20797 5950 20656

+6mExtn(2.75depth)

7839 11087 15679 22173 5950 21629

+9mExtn(2.75depth)

8326 11775 16652 23549 5950 22602

+18mExtn(forwet soil)

13928 19697 27856 39394 9950 37806

+30mExtn(forwet soil)

16898 23897 33795 47794 9950 43745

+18mExtn(forblackcottonsoil)

14052 19872 28103 39744 12050 40153

+30mExtn(forblackcottonsoil)

17021 24072 34043 48144 12050 46093

+18mExtn(forfully

submergedsoil)

14052 19872 28103 39744 10150 38253

+30mExtn(forfully

submergedsoil)

17021 24072 34043 48144 10150 44193




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Quantities per ‘DD’ normal tower:

Concrete (M20): 146.720cum



Quantities per ‘DD’ normal tower (for 2.75m depth):

Concrete (M20): 890267cum



Quantities per ‘DD’ tower with 18m & 30m extn.For Wet soil conditions:




Quantities per ‘DD’ tower with 18m & 30m extn.

For Black cotton soil conditions:







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Quantities per ‘DD’ tower with 18m & 30m extn.For fully submerged soil conditions:




Technical particulars of Towers:

Type of Tower: Four legged, self-supported,

47.350m height and galvanizedlattice steel structured towersare used in this project. Theyare double circuited type andfeeding the two no. of circuitsside by side. With six number ofcross arms and two number of peakarms, the towers have beendesigned. Two peak arms arefeeding the earth wire andOptical fiber ground wiresthrough them for the betterprotection communication purposesrespectively. The main legs ofthe tower are supported by thebracing members like horizontals,Diagonals and redundant membersetc. connected by gusset/spliceplates with nuts, bolts &washers.




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Grades of the steel:

Only two grades of the steel permitted areMild steel–IS: 2062 (Grade A) and High tensilesteel of grade BS 4360 Grade – 50A.

Maximum thickness of materials:

Leg members, Cross and peak arm members: 5mmOther members: 4mm

Wind Velocity withstands ability:

The towers are well designed to with standthe wind velocity in wind zone–5. In 5th windzone the velocity of wind is 50m/s i.e.200km/hr). So to withstand that much load, thetowers are designed to allow up to 925.41N/sq.mwind pressure.

Earthing of the towers:

By depending on the Tower Footage

Resistance (not exceed 10Ω) of the tower, typeof earthing was so chosen. Counter poiseearthing has been done for few towers which arelocated at the 220KV and 400kV crossingsthroughout the line. In this earthing, 7/3.66mmstranded steel wire is connecting the four legs.And four lengths (25mm each) of the wire fromfour legs have been earthed individually in 1mdepth and 25m away from the tower legs. As wellas the rest of the towers are earthed wellthrough the aluminum pipe inserted into the pitmade with the combination of coke and salt.




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Verticality of the Tower:

The verticality of the tower shall be

within ±50mm. i.e. the line of the center of thetop of the tower should be within ±50mm from thecenter of the base of the tower. This tower’sverticality can be checked at the site by usingtheodolite or plumb.

List of Quantities:

TYPEOF

TOWER

MILDSTEEL inKg/1tower

HT STEELin

Kg/1tower

HARD WARE inKg/1tower

TOTALSTEEL inMT/1towerHexa Bolt Anti-

Theft

DA+0 8887.1 9901.36 584.78 185.06 19.558

DA+3 11132.5 10432.8 644.96 219.5 22.429

DA+6 12010.78 10949.92 660.23 242.3 23.863

DA+9 13312.36 11405.04 717.88 259.33 25.694

DC+0 7288 26230 1505 35.023

DC+3 7669 31734 1727 41.130

DC+6 8272 34348 1789 44.409

DC+9 9067 36029 1921 47.017

DC+12 11850 35385 1529 315 49.079

DD+0 10689 34393.65 1751.78 159.97 46.994

DD+3 13491.32 39117.07 1977.76 183.56 54.769

DD+6 15161.32 40870.15 2027.07 205.45 58.263

DD+9 16405.2 43182.43 2167.5 215.58 61.97

DD+18 23732 53655 2546 273 80.205

DD+30 33481 70002 2839 348 106.69




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Tower Accessories:

Danger plate, number plate, phase plate(set of three R, Y & B), circuit plate (one percircuit), anti-climbing device & bird guards(set of six per one tower) come under thiscategory.

Quantities of tower accessories:

Danger plates: 82no.Number plates: 82no.Phase plates: 164sets (Set of 3 i.e. R, Y & B)Circuit plates: 164no. (One per circuit)Anti-climbing device: 82no.Bird guards: 110sets (set of six)

Particulars of Stringing:

The stringing of 400kV transmission lineis a very tough technic to execute at the site.According to the design criteria, Quad MooseACSR type conductors are used as the mainconductor for the stringing purpose. ‘ACSR QuadMoose’ stands for the bundle of four numbers ofACSR MOOSE conductors. These conductors arealuminum with steel reinforced type, so thatnamed as ACSR (Aluminum Conductor SteelReinforced). The basic advantage of this type iswell in conductance by made with the aluminumand rigid due to steel reinforcement. These foursub-conductors are equal-spaced by using thespacer clamps. And the 7/3.66mm galvanizedstranded steel wire is used as the earth wire.




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Technical specifications of ACSR:

Type: ACSR MOOSE (54aluminum/7steel/3.66mm)Overall Diameter: 31.77mmCross section: 597.5sq.mm.Unit weight: 2.004kg/mUltimate tensile strength: 16434kgCo-Eff. of Thermal expansion: 0.0000193/Deg.C

Modulus of Elasticity: 703000kg/sq.cm.

Technical specifications of Ground wire:

Type: Galvanized steel wire (7/3.66mm)Overall Diameter: 10.98mmCross section: 73.65sq.mm.Unit weight: 0.583kg/mUltimate tensile strength: 6975kgCo-Eff. of Thermal expansion: 0.0000115/Deg.C

Modulus of Elasticity: 1936800kg/sq.cm.

Insulators:

The towers are being insulated by usingthe insulator sets which are chosen by dependingon their insulation capacity levels. There isporcelain and polymer insulators together havegiven place in this prestigious project oftransmission line. The porcelain is used, wherethere was the high mechanical strength requiredand on the other hand the polymer is used, wherethe easy accessing of mobilization of thematerial has been required. And also the polymerinsulators served the purpose where the towersare existed with more angle deviations.




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Due to the lighter weight of polymerinsulators those can be easily installed. Byhaving Hydrophobicity characteristics, thepolymer insulators are having the self-cleaningquality. Depend on these characteristics; thoseare so chosen to serve the insulation purposefor few towers, which are located in pollutedareas and existed with high angle deviationstoo. As well as the porcelain insulators areused in large extent due to their high weight,which are so useful in the windzone-5 to stiffthe conductor from the undesirable vibrations.

As per the designing aspects, 24 numbersof 11kV disc insulators have been assembled perone insulator string. This is to maintain theinsulation creepage distance which should be31mm/1kV and also to with stand the maximumvoltage. The set of four number of insulatorstrings is used as Tension insulator string pereach phase. And the set of two number ofinsulator strings is used as suspensioninsulator per each phase of normal suspensiontowers. As well as the polymer insulators alsoused as same as the porcelain insulators wheretheir service has been required. And for thepilot strings, one insulator string of 24discshas been used per each phase to stiff thejumpers to avoid the clearance problems. Forsuspension & tension, set of 120KN & 160KN discinsulators strings are preferred respectively.




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Technical specifications of Insulators:

Type: Porcelain & PolymerMechanical strength: 160KN for Tension

120KN for Suspension

Minimum creepage distance: 31mm/kV

Max. Withstand voltage of disc: 11kV

Bill of Required Quantity of Insulators:

Porcelain – 160KN: 18144(including gantries)

Porcelain – 120KN: 7152

Polymer – 160KN: 720

Polymer – 120KN: 360

NOTE: The above quantities indicated here are as per therequirement per total number of towers only. The total order isdifferent and more in quantity too.

Stringing Hardware:

Spacers/Dampers, Corona rings, Arcing horns,Polymer CC rings, Copper bonds and Vibratingdampers are taken place in this category.

Here in the spacer clamps are having thevibrations damping properties also. Due to thisfacility there is no need of vibrating dampersseparately. But the vibrating dampers are usedto serve the purpose for earth wires.




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ACSR Conductor Hardware Bill of Quantities:

Spacer dampers: 2734Rigid spacers for Jumpers: 685Repair sleeves: 42

Earth wire Hardware Bill of Quantities:

Flexible copper bonds (9.81mm dia.): 220Vibration Dampers: 440Earth wire suspension clamps: 110Earth wire tension clamps: 130

Tests/Checks to be done:

1. Soil resistivity test2. Tower footage resistance test3. Final Acceptance Test (FAT) for towers4. Line Acceptance Test (LAT) for line

In the way of executing the transmissionline, the above tests are to be done in theprocess to for further clarifications which areto be cleared before the process of string to bestarted.

The resistance test for the soil to be donethroughout the spans of transmission line, inorder to get the knowledge of the soilresistivity to fore plan the earthing process.




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The tower footing resistance test to becompleted in right time to access the selectionof earthing type to maintain the minimumresistance value at the footing of the tower.

As well as the Final acceptance test forthe towers to be carried out for the clearanceof starting the stringing process. Theverticality test for the towers, random checkingof the tightness and checking the shortages ofhardware of the towers are the sub-tests ofFinal Acceptance Test (FAT). So the stringingworks are being influenced by the Finalacceptance of the towers. If any modificationsare required, they should be immediately donebefore stringing the line. The stringing processwe used is a tension stringing technic. So theload on the towers is very high. In this casethe FAT must to be carried out well in order toclear the all punch points of the towers beforestringing to be started.

And the Line Acceptance Test (LAT) shouldbe checked out before charging the line to getawareness about the shortages and modificationsof the stringing hardware. Because, theaccessing of modifications is so difficult oncethe line charged. Hence the line should bechecked properly before charging the line. Andalso the ROW & electrical clearances of the lineshould be measured to avoid the tripping.




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Various Clearances of the line:

1. Clearance for Right of Way (RoW): 48m.2. Min. clearance for top conductor and earth

wire at mid span: 9000mm3. Minimum ground clearance: 8800m.4. Min. clearance when 400kV line is crossing

the telecommunication line: 4480mm5. Clearance between power line crossing each

other has been given in below table:

6. Min. clearance between power line(400kV)crossing railway track:a) Above Track: 17900mmb) Over Crane: 6000mm

Highlights of the transmission line project:

In this transmission line projectexecution, the ‘Hot Line Stringing Technic’ hasbeen preferred to string the line at three no.of 220kV and one no. of 400kV crossings. This isthe first time in south India to utilize thistechnic ever to string the 400kV line to crossanother power lines.

Nominal System Voltage 132kV 220kV 400kV±500kVHVDC 765kV

400kV 5490mm 5490mm 5490mm 6790mm 7940mm

400KV TL History

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