HIGH POWER TRANSMISSION SUSPENSION TOWERS
BACKGROUND
This invention relates to high voltage Transmission Suspension Towers and more specifically relates to a novel high voltage Transmission Suspension Towers which permits the Transmission of exceptionally high voltage of 1200 KV.
Transmission towers are tall structures, usually a steel lattice tower, used to support an overhead power line. They are high voltage AC and DC systems and come in several shapes and sizes. Typical height ranges from 15 to 55 metres, although heights in excess of 300 metres also exist. There are four major types of transmission towers i.e. Suspension Towers, Terminal Towers, Tension Towers and Transposition Towers. Some transmission towers combine these basic functions. Main role of a transmission line tower Is to keep the conductor sufficiently above the ground and away from conductive parts (metal etc.) and in the process pass the loads due to wind, weight and tension of conductor/ground wire to the foundation.
Insulator strings: these are connected to conductor on one side and to cross arms or boom in tower on other side. These can be in a suspended mode or in tension mode and thus have the name accordingly.
Cross arm: the structural part of tower body connected to conductor on one side and tower body on the other side. The function of a cross arm is to keep the conductor away form tower body in all the cases and pass the load coming on conductor (transverse, vertical and longitudinal) to the main tower body.
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Boom: this is a beam which is used in horizontal configuration tower. One phase of the three conductors is attached to it in the middle, the role of this part is to pass the conductor loads to window top and connect the right and left part of window top.
Window top and bottom: These are used in horizontal configuration towers, these parts are connected to boom on one side and to the tower body on the other side. The main role of these parts is to provide height for ground clearance and width for clearance from conductor.
Tower body and body extensions: These are parts which provide height for ground clearance and transfer loads to the ground.
Peal<: This part hold ground wires which shield the conductor from lightening.
Suspension type towers constitute major portion of a typical transmission line. These towers are used on the lines for straight run or for small angle of deviation upto 2 degree. Conductors on suspension towers are attached by means of suspension insulator strings. The transmission towers must be designed to carry multiple conductors and are usually made of steel, though wooden structures are also found in Canada, Germany and some Scandinavian areas. Steel towers include cross bars from which insulator strings are suspended, which in turn support metallic conductors, to insulate the conductors from the towers and the ground. The insulator strings are normally designed in view of the voltage of the conductors, being at least adequate to insulate these from the tower with the reasonable margin of safety. The insulators may be made of porcelain discs or composite insulators using silicone rubber or EPDM rubber material assembled in strings or long rods whose lengths are dependent upon the line voltage and environmental conditions.
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PRIOR ART:
Transmission lines in India are presently up to 765 KV voltage level. High voltage steel towers beyond 765 KV in India have not been constructed as yet.
An electric line right-of-way (ROW) is the width of the strip of land that an electric utility uses to construct, maintain, repair or replace an overhead or underground power line considering the safety and interference requirements.
Keeping in view long-term power transfer requirements and the constraint of Right of Way (RoW), a system of 1200 KV is designed. The MW transfer capacity per meter of RoW increases by 6 times in 1200 KV as compared to 400 KV system. The present practice of developing pit-head power plants requires transfer of bulk power, which in turn requires optimal utilization of Right of Way. This requires for the development of high voltage transmission systems. The specifications for the Ultra High Voltage system is not frozen yet internationally. For developing countries like India and China, where power generation projects are being developed in a phased manner with less power transfer requirements initially and also keeping in view the long term power transfer requirements, the system planners have to develop a road map accordingly.
INVENTION
To be future ready, a unique method is devised under this invention where a corridor for 1200 KV S/C line is identified and shall be initially used as 400 KV D/C line for the time upto which a complete confidence for 1200 KV system is developed. Further, to cater to this requirement, this invention presents a novel method where a 1200 KV Single circuit (S/C) tower may be used as a 400 KV Double circuit (D/C) Tower which can be later converted to 1200 KV Single circuit tower upon requirement without any alterations. This caters for
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present as well as future demands with a unique amalgamation of present and future solution.
SUMMARY OF THE INVENTION:
Embodiments of the present invention are directed to a power transmission tower capable of being used in ultra high voltage system of 1200 KV in such a manner that the same structure may be used for high voltage system of 400 KV efficiently, as and when required.
Also, embodiments of the present invention are directed to a power transmission suspension tower for 1200 KV S/C convertible into tower for 400 KV D/C line.
A tower of 1200 KV has been designed for the first time and has been successfully tested which is suitable for both 1200 KV S/C line as well as 400 KV D/C line in the same corridor.
The towers are highly indeterminate structures. Though the towers are normally analyzed as pinned structure, in actual, the joints carry some amount of fixity which adds to complexity in their design. Due to this shift of tower behavior, successful proto tower testing for validation of design is equally important for optimization.
Further to counter torsional loads due to long cross arms as per clearance requirements for 1200 KV system and provision for loading nodes for both 1200 KV S/C and 400 KV D/C makes this tower design structurally a challenging task. The present design has been tested and as a result, an optimal tower design was achieved.
ICNIRP {International Commission on Non-Ionizing Radiation Protection) is an institution concerned with radiation hazards from the electrical equipment / electrical transmission lines and after conducting relevant studies, necessary guidelines have been formulated for the safe human exposure limits of AC Electric and Magnetic Fields. ICNIRP guidelines
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limit the value of electric field and magnetic field for 50 Hz (power frequency in India) for safe operation as follows:
• Electric field - 10 kV/m within ROW and 5kV/m at the edge of ROW
• Magnetic Field - 500 |iT
The above limits are being maintained by POWERGRID for every voltage level in their transmission lines and has also been maintained for 1200 kV line. Besides the above, Interference norms for Radio Interference Voltage level (RIV) & Audible Noise (AN) are also followed by POWERGRID.
• Radio Interference Voltage level (RIV) at the edge of ROW as less than 40dB/1 pV/m
• L5 Audible Noise (AN) levels at the edge of ROW not exceeding 58dBA & L50 AN levels at the edge of ROW not exceeding 55dBA.
The ROW for a 400 kV, 765 kV and 1200 kV line is 46m, 64m and 90m (approx.), respectively. 1200kV Transmission line is designed to transmit 6000- 8000 MW of electricity. To transfer the same power 10 to 12 circuits of 400 kV or 2 to 3 circuits of 765 kV line are required. This can be stated in terms of Power corridor density, i.e., Power which can be transferred for every metre of the ROW which is approximately 15 MW/m for 400 kV, 45 MW/m for 765 kV and 87 MW/m 1200 kV. Power density (MW/m) is about 2 times in 1200kV as compared to 765kV and is about 6 times to that of 400kV system. Hence using same width of land 1200 kV system can transfer 193% more power as compared to 765 kV system & 580% more power as compared to 400 kV system. This resolves the ROW issues to an extent and significantly reduces environmental impact.
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BRIEF DESCRIPTION OF THE DRAWINGS:
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FIG-1 shows a power transmission tower in accordance with an embodiment of the present invention. Referring to Fig.1, a power transmission tower in accordance with an embodiment of the present invention includes an Extension 1 which is a set of variable heights of panels which can be adjusted depending on ground clearance. Further provision of suitable extensions attachable to Extension 1 has also been kept for the same purpose.
Extension 1 is attached to body 2 which is also attached to window bottom 3 at the upper end. Window bottom 3 is attached to window top 4. Geometry of window bottom 3 and window top 4 has been decided keeping provision for 1200 KV S/C as well as 400 D/C conductor attachment points providing sufficient live metal clearance to the middle conductor(s).
Boom 5 is connected to the window top 4 which transfers conductor loads to main tower body. Peaks 6 and 7 are connected at the far ends of the boom 5 for earth wire attachment.
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Cross arms 8 & 9 are also connected at the far ends of the boom 5 for conductor attachment.
Control dimensions a, b, c, d, e, f, g & h have been suitably decided to achieve desired electrical clearances as well as optimal use of steel sections in tower members.
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Fig.2 shows tower structure of Fig.1 being used as 400 KV D/C tower. The conductor attachment from points 10,11,12,13,14 & 15 has been provided through l-insulator strings.
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Fig.3 shows tower structure of Fig.1 being used as 1200 KV S/C tower. The conductor attachment from points 16,17,18,19, 20 & 21 has been provided through V-insulator strings.
DESCRIPTION OF SPECIFIC EMBODIMENTS:
The advantages, features and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth herein under:
FIG-1 shows a power transmission tower in accordance with an embodiment of the present invention. Referring to Fig.1, a power transmission tower in accordance with an embodiment of the present invention includes an Extension 1 which is a set of variable heights of panels which can be adjusted depending on ground clearance. Further provision of suitable extensions attachable to Extension 1 has also been kept for the same purpose.
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Extension 1 is attached to body 2 which is also attached to window bottom 3 at the upper end. Window bottom 3 is attached to window top 4. Geometry of window bottom 3 and window top 4 has been decided keeping provision for 1200 KV S/C as well as 400 D/C conductor attachment points providing sufficient live metal clearance to the middle conductor(s).
Boom 5 is connected to the window top 4 which transfers conductor loads to main tower body. Peaks 6 and 7 are connected at the far ends of the boom 5 for earth wire attachment. Cross arms 8 & 9 are also connected at the far ends of the boom 5 for conductor attachment.
Control dimensions a, b, c, d, e, f, g & h have been suitably decided to achieve desired electrical clearances as well as optimal use of steel sections in tower members.
Fig.2 shows tower structure of Fig.1 being used as 400 KV D/C tower. The conductor attachment from points 10,11,12,13,14 &15 has been provided through l-insulator strings.
Fig.3 shows tower structure of Fig.1 being used as 1200 KV S/C tower. The conductor attachment from points 16,17,18,19, 20 & 21 has been provided through V-insulator strings.
"Although the present invention has been described in connection with a preferred embodiment thereof, many variations and modifications will now become apparent to those skilled in the art".
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What is claimed is;
1. A power transmission suspension tower of 1200 KV S/C with an angle of deviation upto 2° (degree) comprising of variable length Extension, Tower Body, Window Bottom, Window Top, Boom, Two Peaks and Two Cross Arms.
2. A power transmission S/C suspension tower of 1200 KV of claim 1 wherein a provision of 400 KV D/C suspension tower with an angle of deviation of upto 2° (degree) is provided via suitable structural mechanisms.
3. A power transmission S/C suspension tower of 1200 KV of claim 1 with control dimensions a=15.75m, b=9m, c=21.64m, d=49.67m, e=53.1, f=69.92m, g=47.2m and h=7.8m with optional provision of fixed length attachment to increase/decrease tower height.
4. A power transmission S/C suspension tower of 1200 KV of Claim 3 wherein a provision of 400 KV D/C suspension tower with an angle of deviation of upto 2° (degree) is provided via suitable structural mechanisms.