Types of Towers

Types of Towers

The structures which are used to support the transmission lines are called towers or line supports. The performance of transmission line depends also on the design of the towers. The towers must be designed so that they can carry the load of the conductors with extreme loading conditions alongwith the insulators.

The basic requirements of a tower are,

i) Must be mechanically strong, capable of carrying load of conductors and insulators with extreme loading conditions.

ii) Maintenance cost must be low.

iii) Must be long lasting having longer life.

iv) Must be light in weight.

v) Must have minimum number of members.

vi) Easily accessible for erection of conductors.

vii) Must be economical.

viii) Should not affect appearance of the locality.

The various types of towers are,

1. Wooden poles : The towers use wooden structure hence simplest and cheapest. These structures are used for low voltages and for distribution purposes only. The Fig. 4.11.1 shows a wooden pole structure. The main limitation of such a tower is that it is elastic and tend to decay hence its life is short.

A metallic cap is used at the top to protect it from decay. The underground portion of the tower must be properly treated with a preservative. 

2. Reinforced concrete poles : In recent times, the use of reinforced concrete poles for the towers is popular. These towers are mechanically very strong and their maintenance cost is low. Their life is very long. These towers are attractive in appearance. But these towers are very heavy and hence cost of transportation is very high. These are used for systems upto 33 kV voltage level.

3. Steel tubular poles : These towers are designed for high and extra high voltage transmission lines. Due to steel poles, these towers can be used for longer spans. These towers have low base area hence preferred in localities where base area is an important consideration. For longer life, such towers must be galvanized or painted regularly. The Fig. 4.11.2 shows the structure of a tower using steel tubular poles. These poles can have different diameters throughout its length. These are used for the systems upto 33 kV voltage level.

4. Latticed steel towers : The steel towers are very commonly used as these are suitable for the systems with voltages higher than 33 kV and useful for long spans. Generally self supporting broad base lattice galvanized steel towers are used. These are mechanically very strong and have longer life. The lattice structures are light in weight and economical. The structures can be easily transported and can be erected in very inaccessible locations. These are useful for crossing valleys, railway lines, rivers etc. These are fabricated from galvanized angle iron sections and then transported seperately to the site where towers are assembled and erected. The towers are finally painted to provide protection from adverse weather conditions. The steel towers are further classified as,

i) Self supporting ii) Guyed towers and iii) Chainnet type towers.

The main disadvantage of such towers is more right of way (ROW) which is the area of land required along the lengh of the line keeping the towers in the middle. For higher voltage lines, more right of way is required. The Fig. 4.11.3 shows the various types of steel towers. 

Review Question

1. Write a detailed note on types of towers.