1. Preliminary Survey 1. The alignment of the line route is carried out by survey using a theodolite. 2. The following positions are fixed during this survey. a) Fixing of angle tower positions. b) Finalizing of crossing points of major EHV lines (66 kV and above) & details of the lines. c) Finalizing of crossing points of Railway Tracks & details of such points. d) Finalizing of crossing points of major rivers & details of such points. 3. Measurements of the angles of deviation at all angle / section points are made. Resurvey of parts of the line route is done wherever it is possible to reduce the number of angle points and / or the magnitude of the angles of deviation. 4. A span is the part of the line between any two adjacent towers. A section is the portion of the line route with a single span or with a number of consecutive spans between two tension points with "B", "C", or "D" type towers, as applicable.

2. 5. The number of consecutive spans between two angle / section points shall not exceed 15 (fifteen) in plain terrain and 10 (ten) spans in hilly terrain. 6. The length of any section of the line, i.e., between two angle / section points, shall not exceed 5 km in plain terrain and 3 km in hilly terrain. In case longer sections are available, then cut points / section points shall be provided by using “B” type tower. 7. The basic spans, which are the design spans for towers, as adopted for the various voltage levels are as below: Voltage Level Basic Span 400 kV 400 metres 220 kV 350 metres 132 kV 335 metres

3. 2.0 CROSSING OF POWER LINES: The crossing of existing power lines shall be at an angle as close to 90 degrees as possible. 3.0 CROSSING OF THE TELECOMMUNICATION LINES: The crossing of such lines should preferably be at 90 degrees, but an angle less than 60 degrees is not permissible. 4.0 CROSSING OF RAILWAY TRACKS: The angle of crossing should preferably be 90 degrees, but an angle of upto 60 degrees may be permitted in special cases. The crossing span shall be restricted to 300 metres or to 80% of the basic span of the towers of the relevant voltage class, whichever is less. Angle towers are to be provided on both sides. The minimum distance of the towers of the crossing span from the center of the nearest railway track shall be equal to the height of the tower in metres above normal ground level plus 6 metres. The crossing span over already electrified railway track shall be located at the middle of overhead equipment span supported by two adjacent traction masts / structures. The distance between any of the crossing conductors of the line and the nearest traction mast or structure under the most adverse conditions shall not be less than 6 metres.

4. As far as possible, higher levels of land on both sides of the railway track are preferred at crossings so that there is minimum requirement for increase in the height of the towers. One tower of the crossing span is located nearer to the Railway track for taking advantage of the higher height of the conductor on the tower. 5.0 CROSSING OF ROADS: Transmission line crossings across National Highways and major roads shall preferably be at right angles or as near to 90 degrees as possible. For crossing of National Highways and major roads in case of lines upto 220 kV, it is advisable to provide at least one angle / section tower in the crossing span for the purpose of ease during stringing. For 400 kV lines, angle / section towers are to be provided on both sides in such cases.

5. RIGHT OF WAY: The width of the right of way should be kept as per the provisions of the applicable part / section of the Indian Standard Code of Practice for Design, Installation and Maintenance of Overhead Power Lines (IS: 5613). For lines upto 220 kV, IS 5613 (Part 2 / Sec 2) recommends the following right of way widths taking into consideration the theoretical requirement of right of way and transport requirements of maintenance: Transmission Voltage Recommended Width of Right of Way 132 kV 27 metres 220 kV 35 metres 400 kV 52 metres

6. Types of Towers  Type A Tower ( Tangent Tower with suspension string) o Used on straight runs and up to 2° line diversion  Type B Tower (Small Angle Tower with tension string) o Used for line deviation from 2° to 15°  Type C Tower (Medium Angle Tower with tension string ). o Used for line deviation from 15° to 30°.  Type D Tower (Large angle tower with tension string) o Used for line deviation from 30° to 60°  Type E Tower (Dead End Tower with tension string) o Used for line termination & starting  Special tower-  Suspension Tower (Span ≈ 1000 m) o Used for River crossing, Mountain crossing etc.  Transposition Tower o Used for transposition of tower

7. 7 Different Types of Towers

8. Selection of Tower Structure  Single circuit Tower/ double circuit Tower  Length of the insulator assembly (i.e.11kV Disc 225mm ; for say 220kv it would be 3.15m)  Minimum clearances to be maintained between ground conductors, and between conductors and tower  Location of ground wire/wires with respect to the outermost conductor  Mid-span clearance required from considerations of the dynamic behavior of conductors and lightning protection of the line  Minimum clearance of the lowest conductor above ground level

9. Tower Design Tower height Base width Top damper width Cross arms length Fig. Typical 765 KV Tower Structure

10. Height of Tower Structure Height of tower is determine by- h 1 =Minimum permissible ground clearance h 2 =Maximum sag h 3 =Vertical spacing between conductors h 4 =Vertical clearance between earthwire and top conductor

11. Spacing and Clearances Ground Clearances Where- S.No.Voltage levelGround clearance(m) 1.≤33 KV5.20 2.66 KV5.49 3.132KV6.10 4.220 KV7.01 5.400 KV8.84 Minimum permissible ground clearance as per IE Rules, 1956,Rule 77(4)

15. 15 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

17. 1Code of Conductor ACSR panther 2Size 30/3 mm Al./ steel 7/3.00mm dia 3Overall Diametermm21 4Areamm2261.5 5Unit wt of Conductorkg/m0.974 6Ultimate tensile strenghthkg9144 7Coeff of Linear Expansionper deg C0.0000178 8Young's moduluskg/mm27870 9Crossing Spanm245 10Max. Temp.Deg C75 11Min. Temp.Deg C-2.5 12Max Sag at 75 deg c at normal spanm7.592 13Crossing Spanm245 14Min. sag at -2.5degC at normal spanm4.75 15FOS 2 16FOS at 32.2 degC 4 17Wind Presssurekg/m245 18Wind Load per metre (Wh)kg/m0.630

18. 1Code of Conductor ACSR Zebra 2Size 54/3.18 mm Al./ steel 7/3.18mm dia 3Overall Diamm28.62 4Areamm2484.5 5Unit wt of Conductorkg/m1.621 6Ultimate tensile strenghthkg13290 7Coeff of Linear Expansionper deg C0.0000193 8Young's moduluskg/mm26860 9Crossing Spanm175 10Max. Temp.degC32 11Min. Temp.degC0 12Max Sag at 75 deg c at normal spanm9.22 13Normal Spanm350 14Min. sag at -2.5degC at normal spanm6.01 15FOS 2 16FOS at 32.2 degC 4 17Wind Presssurekg/m245 18Wind Load per metre (Wh)kg/m0.859

19. Economic Voltage of Transmission of Power – E = Transmission voltage (KV) (L-L). L = Distance of transmission line in KM KVA=Power to be transferred

20. Spacing Between Conductor(Phases) 1)Mecomb's formula 2) VDE formula Where- V= Voltage of system in KV D= Diameter of Conductor in cm S= Sag in cm W= weight of conductor in Kg/m Where- V= Voltage of system in KV S= Sag in cm

21. 3) Still's formula Where- l = Average span length(m) 4) NESC formula Where- V= Voltage of system in KV S= Sag in cm L= Length of insulator string in cm

22. 5) Swedish formula Where- E= Line Voltage in KV S= Sag in cm 6) French formula Where- E= Line Voltage in KV S= Sag in cm L= length of insulating string(cm)

23. SAG Sag is defined as the vertical distance between the point where the line is joined to the tower and the lowest point on the line. The sag is as a result of the tensioning of the line and must not be too low otherwise the safety clearances may not be met. Also, the sag had to be such that it caters for ice loading in the winter of temperate climates. If the sag is large, and the line becomes heavily loaded, then the sag will further increase and breach the safety clearances. Similarly, if the sag is low, then when the line contracts in the winter, a low sag will indicate a high tension, and as a result of this contraction, the line may snap. Sag is inversely proportional to the tension of the line, and is given by the formula below.

24. Diagram showing the definition of sag

25. Sag and Tension Calculation Parabolic formula: Catenary formula: Span >300 m Sag & Tension Span ≤300 m

26. When an object is heated or cooled, its length changes by an amount proportional to the original length and the change in temperature. Linear thermal expansion of an object can be expressed as dl = L 0 α (t 1 - t 0 ) (1) where dl = change in length (m, inches) L 0 = initial length (m, inches) α = linear expansion coefficient (m/m o C, in/in o F) t 0 = initial temperature ( o C, o F) t 1 = final temperature ( o C, o F) Linear Temperature Coefficients - α - of some common metals aluminum : 0.000023 (m/m o C) steel: 0.000012 (m/m o C) copper: 0.000017 (m/m o C) Linear temperature expansion