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Transmission lines


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ppt on transmission lines and it's types

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Transmission lines

  2. 2. INTRODUCTION • The electrical power generated in the generating station is transmitted with the help of transmission lines. • Transmission line is a conductor or conductors designed to carry electricity or an electrical signal over large distances with minimum losses and distortion. • The parameters associated with these transmission lines are inductance, capacitance, resistance and conductance. • These parameters are uniformly distributed along the length of transmission line .For good electric design of transmission line , a sound knowledge of all these parameters are essential.
  3. 3. FACTORS TO BE CONSIDERED WHILE DECIDING TRANSMISSION LINE • Type and size of the conductor • Efficiency of transmission • Corona loss • Power flow capability and stability • Economical aspects
  4. 4. CLASSIFICATION OF TRANSMISSION LINES 1- Overhead transmission lines • Short transmission lines • Medium transmission lines • Long transmission lines 2- Underground cables
  5. 5. Overhead Transmission Lines 1. Short transmission lines- • Line voltage is less than 20KV • Length of transmission line is upto about 50Km • Capacitance effect are small or negligible
  6. 6. 2- Medium transmission lines- Line voltage is moderately high. It is greater than 20KV but less than 100KV. Length of lines is about 50 Km to 150Km. Capacitance is significant.
  7. 7. 3- Long transmission lines- • Line voltage is very high (>100Km). • Length of an overhead line is more than 150Km. • Line constants are considered uniformly distributed over the whole length of the line.
  8. 8. Conductors used to design overhead transmission lines- • ASCR- Aluminium conductor with steel reinforcement • ACAR- Aluminium conductor with alloy reinforcement • Hard drawn copper conductor • Steel cored copper conductor(SCC) • Phosphor bronze conductor • Galvanized steel conductors • AAC- All Aluminium conductors
  9. 9. Overhead Line Insulators PORCELAIN- • It is a ceramic material. • It is free from cracks, holes etc. • It’s insulation resistance is very high. • Dielectric strength of porcelain is about 60kV/cm. GLASS- • Cheaper than the porcelain. • Less stronger than the porcelain. • Higher compressive strength than porcelain.
  10. 10. SYNTHETIC RESIN- • Tensile strength is high. • Weight is low • Comparatively cheaper.
  11. 11. Mechanical design of overhead transmission lines • Transmission lines are designed primarily on the basis of economy point of view. • But due to sag it requires more conductor material.
  12. 12. • For keeping the cost minimum, sag also must be kept minimum • But if sag is too low then wire gets subjected to an extra tension. • If sufficient sag is not kept then there is possibility of the mechanical failure of the transmission for favorable condition, the required amount of sag and tension are calculated considering all the sever conditions like ice coating and wind pressure.
  13. 13. Advantages of overhead transmission lines- • Cheaper to install and maintain than underground cables. • Quicker to fix whenever fault develops. • They have large transmission capacity. • Good cooling conditions.
  14. 14. Disadvantages of overhead transmission lines • Difficult to be erected in the area where the network is complex and concentrate. • Not very safe to be erected in densely populated area of the city. • Also is not beautiful. • Affected by environmental conditions such as temperature, wind, rain etc. • Influenced by thunder and lightening.
  15. 15. Underground cables • Undergrounding is the replacement of overhead cables providing electrical power or telecommunications, with underground cables. • In thickly populated areas, the use of overhead lines is not practicable and electrical energy is transmitted and distributes through underground cables. • An underground cable is a conductor provided with proper insulation. • As voltage increases, the cost of insulation increases and hence underground cables are restricted to low and medium voltage distribution.
  16. 16. Construction of an underground cable
  17. 17. By Voltage LT cables: Low-tension cables with a maximum capacity of 1000 V HT Cables: High-tension cables with a maximum of 11KV ST cables: Super-tension cables with a rating of between 22 KV and 33 KV EHT cables: Extra high-tension cables with a rating of between 33 KV and 66 KV Extra super voltage cables: with maximum voltage ratings beyond 132 KV By Construction Belted cables: Maximum voltage of 11KVA Screened cables: Maximum voltage of 66 KVA Pressure cables: Maximum voltage of more than 66KVA Classification of underground cables
  18. 18. Laying of underground cables 1-DIRECT LAYING-
  19. 19. • The trench is about 1.5m deep and 45cm wide in dug. The trench is covered with a layer of fine sand and the cable is laid over this bed. 2- DRAW IN SYSTEM- • Duct of cast iron or concrete are laid in the ground with manholes at suitable positions along the cable route. • Very less chances of fault occurrence. 3- SOLID SYSTEM- • The cable is laid in open pipes or trough dug out in earth along the cable route. • After the cable is laid, the toughing is filled with the bituminous compound and covered over. • It has poor heat dissipation facilities.
  20. 20. Advantages of underground cables • Low chances of developing faults. • Low maintenance cost. • Not influenced by environmental conditions. • More durable in comparison to overhead transmission lines. • Underground cables are more safer fore mankind. • Requires a narrow band of length to install.
  21. 21. Disadvantages of underground cables • Very expensive. It costs four times the overhead lines. • Repairing of underground cables is not easy and it takes more time to repair than overhead lines. • Maintenance cost is also very high.
  22. 22. THANK YOU