International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) ISSN: 0976-1353 Volume 13 Issue 1 –MARCH 2015.
Analysis and Design of of Multi Circuit Circuit Transmission Line Tower Sakthivel. T#1 and Sanjeevi. R*2 #
* (Civil Engineering): dept. Easwari Eng. College, Ramapuram, Chennai – 600 089, India
[email protected]
Abstract— Due to rapid urbanization and space constraints narrow base towers provide an alternative solution to conventional broad based towers. A narrow base 200 KV multi circuit tower is analysed using using STADD.PRO. The choice of tower is made based on the available right of way. As per IS 5613 (Part 2/Sec 2) the required right of way for a 220 KV broad base tower is 35 m. But when adequate right of way is not available the base width of the tower is constrained. There is no standard of specification or limit up to which the tower acts as broad base or narrow base tower. The tower is considered as narrow base when its width is constrained. The tower is in Mumbai. It is a four circuit double peak tower and consists of 2 earth wires, 12 cross arms (6 box cross arms on one side and 6 triangular cross arms on the other side of the tower). It is a dead end tower with deviation of 0º - 15º. Since it is a dead end tower could also be an angle tower. The narrow base tower is also an angle tower with deviation of 30º-60º. The design wind pressure for the tower is 757 N/m². The maximum sag of the conductor is 9.626 m. The maximum sag of the conductor occurs at maximum temperature and nil wind. The transverse loads, vertical loads and the longitudinal loads on the towers are calculated for reliability condition, security security condition, and safety condition. The electrical electrical clearance diagram for the tower is drawn using AUTOCAD. The height of the tower is 56.335 m, and its width at plinth level at a body extension of 6 meter is 7.343 m. The entire tower is separated into 9 blocks. The tower is separated into panels consisting of A-Pattern, X-Pattern, bracings, and leg members. The body wind is calculated based on the boundary area and the projected area, and it acts at 10 wind points in the longitudinal face of the tower. The tower is designed based on IS 802 (Part 1/ Sec2).
broad based towers. The tower is designed as angle tower and also dead end tower.
Fig. 1 Dead End Tower
TABLE I PROPERTIES OF CONDUCTOR Material Standing (Aluminium/Steel) Diameter Cross Sectional Area Ultimate Tensile Strength Unit Weight Modulus of Elasticity Elasticit y Coefficient of Linear Expansion Wind Span W/A
Index Terms—Transmission Line Tower; Narrow Base Tower; Angle Tower; Sag and tension; Body Wind Calculation
I.
All Aluminum Alloy Conductor (AAAC)
INTRODUCTION
Electric power plays an important role in the life of the community and development of various sectors of economy. In India, high priority is given to power development programs. Transmission line (TL) structures support the phase conductors and shield wires of a transmission line. Due to rapid urbanization and space constraints, narrow base structures provide solution as an alternative approach to conventional
Units
61/3.31 29.79 5.25
mm cm²
14603 1.448 550800
kg kg/m kgf/cm²
2.30E-05 350 0.2758
/°C m kg/m/cm²
TABLE II PROPERTIES OF GROUND WIRE Material Standing (Aluminium/Steel) Diameter Cross Sectional Area Ultimate Tensile Strength
56
Units 7/3.15 9.45 0.5455
mm cm²
5710
kg
International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) ISSN: 0976-1353 Volume 13 Issue 1 –MARCH 2015. Unit Weight Modulus of Elasticity Coefficient of Linear Expansion Wind Span W/A
0.43 1933000
kg/m kgf/cm²
0.0000115 350 0.788267644
/°C m kg/m/cm²
TABLE IV SAG AND TENSION OF CONDUCTOR
TABLE III PROPERTIES OF INSULATOR Single Tension Insulator Details Number of Insulator (Single Tension Insulator) Length of Insulator Diameter of Insulator Weight of Insulator (Maximum) Weight of Insulator (Minimum) Number of Pilot Insulator Required Length of Pilot Insulator Diameter of Pilot Insulator Weight of Pilot Insulator (Maximum) Weight of Pilot Insulator (Minimum) Coefficient for Insulator Wind Pressure Factor for Unbalanced Tension
II.
Units 2 3.416 0.305 150 150 1 2.500 0.280
m m Kg
150 Kg 150 0.50 0.0
SAG AND TENSION
The sag is calculated for various temperature and wind pressure conditions. It could be calculated by catenary method or by parabolic method. The parabolic method of sag and tension calculation is followed in IS: 5613 (Part 2/Sec 1). The sag and tension are determined for the following temperature and wind pressure combinations,
• • • •
Tension (Kg)
Factor of Safety (Required)
0 32 32 85 0
0 0 175.22 0 63.08
4030.11 3138.37 7564.48 2303.50 5198.40
1.4285 4.5454 1.4285 1.4285 1.4285
Factor of Safety (Actual) 3.62 4.65 1.93 6.34 2.81
Vertical Sag (m)
Tension %
5.50 7.06 2.93 9.626 4.27
27.60 21.49 51.80 15.77 35.60
LOAD CONDITIONS
The tower is designed as dead end and angle tower. The loads acting on the tower are considered for the following loading conditions, for angle tower (30º-60º) and for dead end tower (0º-15º). • 30º deviation reliability condition • 30º deviation security condition – Loads for intact spans • 30º deviation security condition – Loads for broken spans • 30º deviation safety normal condition • 30º deviation safety broken condition – Loads for intact spans • 30º deviation safety broken condition – Loads for broken spans • 30º deviation anticascading condition • 60º deviation reliability condition • 60º deviation security condition – Loads for intact spans • 60º deviation security condition – Loads for broken spans • 60º deviation safety normal condition • 60º deviation safety broken condition – Loads for intact spans • 60º deviation safety broken condition – Loads for broken spans • 60º deviation anticascading condition • 0º deviation reliability condition • 0º deviation security condition – Loads for intact spans • 0º deviation safety normal condition • 15º deviation reliability condition • 15º deviation security condition – Loads for intact spans • 15º deviation safety normal condition
The wind intensity is lower at the ground level and the air flow is turbulent because of friction with the rough surfaces of the ground. The basic wind speed map of India is applicable at 10 m height above mean ground level for the six wind zones of the country. The basic wind speed Vb is 44 m/s. the meteorological wind speed VR is 32 m/s. Vd = VR x K1 x K2. Pd = 0.6 Vd². Pd = design wind pressure in N/m2. The design wind pressure is Pd = 757 N/m².
•
Wind Pressure (kg/m2)
IV.
m m Kg Kg
DETERMINATION OF WIND PRESURE
III.
Tem pºC
Everyday temperature and nil wind Everyday temperature and full wind Maximum temperature and nil wind Minimum temperature and 36 % of full wind Minimum temperature and nil wind
V.
The maximum temperature of all aluminum alloy conductor is 85º (Clause 10.2.4, IS: 802 (Part 1/Sec 1). The maximum temperature of the ground wire is 53º (Clause 10.2.4, IS: 802 (Part 1/Sec 1).
ELECTRICAL CLEARANCES
The design of transmission line towers are classified into structural design and electrical design. The electrical clearance forms the electrical design of transmission line tower. As per clause 13.1 of IS 5613 (Part 2/Sec 1) a minimum ground clearance of 7 meter is provided. As per clause 7.3.2 the vertical spacing between conductors is a minimum of 4.9
The maximum sag of the conductor occurs at maximum temperature and nil wind
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International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) ISSN: 0976-1353 Volume 13 Issue 1 –MARCH 2015. meter. As per clause 13.2 the mid span clearance between earth wire and power conductor is 8.5 m.
Fig. 3(a) Panel of Tower
Fig. 3(b) Tower Model
Fig. 2 Electrical Clearance Diagram
VI.
STAAD.PRO MODELLING OF NARROW BASE TOWER
Fig. 4 Sample Loading Tree
The tower is modelled using Staad.Pro. During the modelling phase the tower is separated into various blocks for the ease of analysis and design. The blocks comprise of bracings of APattern, X-Pattern and V-Pattern. A sample panel with APattern is shown in the following figure.
VII.
GENERATION OF LOADING TREE
The lengths of the members are identified from the tower model. The broken wire conditions are identified. Either earth wire or one conductor could be broken in a phase or two
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International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) ISSN: 0976-1353 Volume 13 Issue 1 –MARCH 2015. conductors and an earth wire can be broken as per clause 16 of IS 802 (Part 1/Sec 1). The sample loading tree is shown in the following figure.
As per clause 6.3 of IS 802 (Part 1/Sec 2) the limiting slenderness ratio is 120 for leg members, ground wire peak member, and lower members of cross arms in compression; and for other members except redundant members the limiting slenderness ratio is 200, and for redundant members the limiting slenderness ratio is 250. The total weight of the tower without redundant member is 51667.84 Kg. Star angle and quadruple plate angle sections are used for leg members. Double angle sections are used for bracings subjected to more forces. Single angle sections are used for belt members. The factor of safety provided for leg members is 1.01-1.1. The factor of safety provided for bracings and belt members vary from 1.2-1.3. The factor of safety for the cross arm bottom members is 1.3-1.4. The sections used for leg members are 150x150x20 QL, 150x150x16 QL, 200x200x25 star angle, 200x200x20 star angle, 200x200x16 star angle, 150x150x20 star angle, and 150x150x12 star angle. The various members used for bracings are 150x150x10 DL, 130x130x10 DL, 120x120x10 L, 100x100x10 L, and 100x100x8 L. The various members used for belt and plan-x-bracing are 100x100x10 L, 100x100x8 L, 80x80x6 L, 70x70x6 L. High tensile steel of fy=350 N/mm² is used for leg members, top cross arm and bottom cross arm members. Mild steel of fy=250 N/mm² is used for belt, bracings. The leg members are split into maximum of 3 rvv. The belt members are split into maximum of 3 rvv. Very few bracings are split to 4 rvv in order to maintain the slenderness ratio and produce effective members.
VIII. BODY WIND CALCULATION OF TOWER Trial sections are assigned to the generated model. The projected area and the boundary area of the tower are calculated. Then the body wind is determined on 10 wind points in the tower. Then the wind load is obtained. The body wind is applied in the longitudinal face of the tower. TABLE V BODY WIND ON TOWER Wind Point (kg/m2) 10 9 8 7 6 5 4 3 2 1
IX.
Body Wind (Kg) 560 2961 1994 1996 2086 2270 2543 3076 2716 969
LOAD CASES AND COMBINATIONS
The load combinations and combination load cases are assigned and the tower is analysed. Then the forces are obtained and grouping of forces is done.
XI.
DESIGN OF TOWER
In order to validate the design, the tower is analyzed and designed using STADD.PRO. The total weight of the tower obtained using STADD.PRO is 48784.76 Kg. Since the result shows that the tower weight could be reduced further. Hence, the body wind is calculated. Then the body wind is applied on the tower and the maximum compression and tension forces acting on the tower are obtained. The weight of the tower obtained by optimizing the angle section is 48608 Kg. XII.
INTERPRETATION OF RESULT
The maximum displacement is experienced by the dead end tower for 0º condition. Since the dead end tower will be located in the substation it may not be a narrow base tower, however if the due to space constraints if the dead end tower is supposed to be a narrow base tower then the dead end tower’s safety should be given more importance than the economy. Fig. 5 Load Case Details
X.
PRIMARY DESIGN OF TOWER
The tower is designed based on IS 802(Part 1/Sec 2). Trial sections are assigned.
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International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) ISSN: 0976-1353 Volume 13 Issue 1 –MARCH 2015.
XV.
The weight of the tower is optimized by using sections of various sizes. The reduced weight is obtained by using single angle sections for belt members. Since the scope of the project is not obtaining the least weight of the tower with adequate safety, the width of the tower is not increased further, to validate the economy of the tower. Further the redundant members are not designed. Considerable change in the total weight of the tower would be obtained after the redundant members are designed. The reduction in weight is achieved by using angle sections of thickness varying from 5-6 mm, but not less than 5 mm.
Fig. 6 Displacement of the Tower for Critical Load Combination
XIII. GRAPHICAL REPRESENTATION OF MOMENT, FORCE AND DISPLACEMENT The graph of moment, force, and displacement is shown in the following figure.
ACKNOWLEDGMENT We would like to thank the management and staff of Easwari Engineering College for their guidance and support.
Mz(kNm) 1.22
1.40 0.70 1 0.70
COCLUSION
1.40 0.70
2.51
0
5
2
4
6.03 6 0.70
-0.688
1.40
1.40
References [1] Alam M. J. and Santhakumar, A. R, “Reliability analysis and full scale testing of Transmission Tower”, Journal of Structural Engineering © ASCE., Vol. 122, No. 3, pp. 338-344, (1996). [2] Albermani F., Chan R. W. K., and Kitipornchai S, ‘Failure analysis of transmission towers’, ‘Engineering Failure Analysis’, © ELSEVIER., Vol. 16, pp. 1922-1928, (2008). [2] CBIP – Central Board of Irrigation and Power manual [3] IS: 802 (Part1/Sec1):1995 – Use of structural steel in overhead transmission line towers – Code of practice. Part 1 – Materials, Loads and Permissible Stresses. Section 1 – Materials and Loads. [4] IS: 802 (Part1/Sec2):1992 – Use of structural steel in overhead transmission line towers – Code of practice. Part 1 – Materials, Loads and Permissible Stresses. Section 2 – Permissible Stresses. [4] IS: 5613 (Part 2/Sec 1): 1985 – Code of Practice for Design, Installation and Maintenance of Overhead Power Lines. Part 2 – Lines above 11 KV and up to and including 220 KV. Section 1 – Design. [5] IS: 5613 (Part 2/Sec 2): 1985 – Code of Practice for Design, Installation and Maintenance of Overhead Power Lines. Part 2 – Lines above 11 KV and up to and including 220 KV. Section 2 – Installation and Maintenance. [6] Knight G. M. S and Santhakumar A. R, “Joint effects on behaviour of Transmission Towers,” Journal of Structural Engineering © ASCE., Vol. 119, No. 3, pp. 698-712, (1993).
Fig. 7 Moment of Beam 1 (Leg Member)
Fy(kg) 150 100 50
150 100 50
62.6
1 50 100
2
4
5 6.03 6 50 100
-104
150
150
Fig. 8 Vertical Force along Y axis for Beam 1 (Leg Member) Fx(kg) 20000
15187
13575
10000
10000
1 10000 20000
20000
5 2
4
6.03 6 10000 20000
Fig. 9 Horizontal Force along X axis for Beam 1 (Leg Member)
XIV. ADVANTAGES OF NARROW BASE TOWER Even though the narrow base tower might not be completely economical as a conventional tower, it is the only best solution for urban cities. And with adaption of emerging trends and technologies in engineering, narrow base towers could be an alternative to conventional broad base towers, when adequate right of way is not available.
Sakthivel. T, Post Graduate student, Structural Engineering Department, Easwari Engineering College
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International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) ISSN: 0976-1353 Volume 13 Issue 1 –MARCH 2015.
. Sanjeevi. R, Assistant Professor, Structural Engineering Department, Easwari Engineering College
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