Reahblitation of AC Transmission Linepptx

this document is helpful in learning how to rehabilitation of a broken transmission Line

1. NTDC 1 REHABLITATION OF TRANSMISSION LINE Engr . Syed Ghulam Mustafa Deputy Manager TSG (South) NATIONAL TRANSMISSION & DESPATCH COMPANY

2. 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 2 NTDC Engr. Syed Ghulam Mustafa

3. 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 Engr. Syed Ghulam Mustafa

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5. TOWER GEOMENTRY EXTENSIONS BRACINGS ANATOMY Engr. Syed Ghulam Mustafa

6. 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 Engr. Syed Ghulam Mustafa

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8. 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 Engr. Syed Ghulam Mustafa

9. 1.Struts are designed in compression & Diagonals in tension NARROW BASE 66Kv single circuit 1.Tension diagonal give eff.support to @ compression one pt of connections 2.Used in both large and small towers 1.Shear carried by diagonal member(t) Large deflection under heavy loads Unequal shears at top of four stubs for design Engr. Syed Ghulam Mustafa

10. 1.1half of Horizontal member in T & another C 2.Advantageous to use it in BOTTOM panel 3.Extensions & Heavy river crossing 1. Similar to waran system 2.Horizontal member carry no primary loads designed as redundant supports 1.Increse in strenght member reducing sizes 2.Increase in No.of bolts, fabrication & erection cost, 3.Overal reduction in Wt & cost of steel Engr. Syed Ghulam Mustafa

11. 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 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) Engr. Syed Ghulam Mustafa

12. 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 : Universal leg extension Individual leg extension 12 NTDC HVDC Engr. Syed Ghulam Mustafa

13. Types of Tower EDRC- TL Design Type of Insulator Suspension Tension/Dead end Transposition Type of Support Self Supporting Guyed No. of Circuits Single Circuit Double Circuit Multi- Circuit Deviation Angle. Ranges from to 90 deg. Shape at the base Square Rectangle kV Rating. Ranges from 33 to 1200 kV HVDC NTDC Engr. Junaid Azam Kazi (SDO NTDC) HVDC Engr. Syed Ghulam Mustafa

14. Vertical Configuration Horizontal Configuration Engr. Syed Ghulam Mustafa

15. Tension Tower Suspension Tower Engr. Syed Ghulam Mustafa

16. Guy Towers Engr. Syed Ghulam Mustafa

17. Height of Tower Structure H  h 1  h 2  h 3  h 4 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 earth wire and top conductor Engr. Syed Ghulam Mustafa

18. DESIGN PARAMETERS Transmission Voltage Number Of Circuits Climatic Conditions Environmental and Ecological Consideration Conductor Earth Wire Insulators Span Engr. Syed Ghulam Mustafa

19. 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 conductors ACSR : Aluminium conductors, Steel- Reinforced ACAR : Aluminium conductor, Alloy-Reinforced 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 spacers Engr. Syed Ghulam Mustafa

20. 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 Engr. Syed Ghulam Mustafa

21. 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 Engr. Syed Ghulam Mustafa

22. 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 Engr. Syed Ghulam Mustafa

23. Design Span lengths Basic Span Most economic span Line is designed over level ground The requisite ground clearance is obtained at maximum specified temperature Engr. Syed Ghulam Mustafa

24. 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) Ruling span = √ ( L1^3 + L2^3 +….+L6^3 / L1 + L2 + … + L6) 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 Engr. Syed Ghulam Mustafa

25. 4.Wind Span 5.Weight 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 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 Wind span = 0.5(L1 + L2) Weight span = a1 + a2 Engr. Syed Ghulam Mustafa

26. 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. Engr. Syed Ghulam Mustafa

27. Loads on Tower Normal Condition Broken Wire Condition Engr. Syed Ghulam Mustafa

28. 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 Engr. Syed Ghulam Mustafa

29. 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 Data's for foundation design Engr. Syed Ghulam Mustafa

30. 0.5 to 2m dia Shaft depth 3 to 15m Skin friction between ground & shaft resists uplift Used in USA. Uplift loads are resisted by undistrube material Develop uplift load of 2 to 3times that of an identical footing without undercut Non- cohesive soil For non- cohesive soils such as uncemented sand or gravel Provide pad footing without undercut Usually followed in Pakistan at present Engr. Syed Ghulam Mustafa

31. 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 Engr. Syed Ghulam Mustafa

32. In usa ,canada Steel corroded, periodic excavation & maintanence Medium dry sand, clay or sandy clay soils (no special precautions necessary) The steel is treated with one coat of 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 dia E n g i r n . J t u o n a t i d h A e z a r m o K c a k z i (SDO NTDC) 32 NTDC H V b i D t u m C i n o u s paint & Engr. Syed Ghulam Mustafa

33. HVDC TRANSMISSION LINE FOUNDATION 1. CONVENTIONAL FOUNDATION (PAD & CHIMNEY) EXCAVATION

34. HVDC TRANSMISSION LINE FOUNDATION 1. CONVENTIONAL FOUNDATION (PAD & CHIMNEY) Stub Setting & Steel Fixing Engr. Syed Ghulam Mustafa

35. HVDC TRANSMISSION LINE FOUNDATION 1. CONVENTIONAL FOUNDATION (PAD & CHIMNEY) Stub Setting & Steel Fixing Engr. Syed Ghulam Mustafa

36. HVDC TRANSMISSION LINE FOUNDATION 1. CONVENTIONAL FOUNDATION (PAD & CHIMNEY) Steel Fixing Engr. Syed Ghulam Mustafa

37. HVDC TRANSMISSION LINE FOUNDATION 1. CONVENTIONAL FOUNDATION (PAD & CHIMNEY) Concrete Pouring Engr. Syed Ghulam Mustafa

38. HVDC TRANSMISSION LINE FOUNDATION 1. CONVENTIONAL FOUNDATION (PAD & CHIMNEY) Backfilling/Compaction Engr. Syed Ghulam Mustafa

39. HVDC TRANSMISSION LINE FOUNDATION 2. PILE FOUNDATION

40. HVDC TRANSMISSION LINE FOUNDATION 2. PILE FOUNDATION Pile Cap & Bitumen Coating Engr. Syed Ghulam Mustafa

41. HVDC TRANSMISSION LINE FOUNDATION 2. PILE FOUNDATION Double Pile Cap Engr. Syed Ghulam Mustafa

42. HVDC TRANSMISSION LINE FOUNDATION 2. PILE FOUNDATION Double Pile Cap Engr. Syed Ghulam Mustafa

43. HVDC TRANSMISSION LINE FOUNDATION 2. PILE FOUNDATION Double Pile Cap & Stub Setting Engr. Syed Ghulam Mustafa

44. HVDC TRANSMISSION LINE FOUNDATION DOUBLE PILE FOUNDATION Engr. Syed Ghulam Mustafa

45. 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 Engr. Syed Ghulam Mustafa

46. Questions? Engr. Syed Ghulam Mustafa