Different Types of Line Supports

September 24, 2022

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What are Line Supports and Its function?

The main function of line support is to support the line live conductor and provide a suitable distance from the ground level.
The various types of poles and towers are used as line supports depending upon the working voltage and region where these poles or towers are used.
The Line supports are capable to carry the load of the conductor, insulators, wind load on the conductors, and also wind load on the line supports themselves.

The main requirements of line supports are

The line supports should have the high mechanical strength to withstand the load of the conductors, insulators, and wind load on the conductors and supports themselves.
The line supports should have lightweight without losing mechanical strength.
The line supports should be cheaper in cost.
The line supports should have a low maintenance cost.
The line supports should have a longer life,
The line supports should be good-looking.
The light supports should be easily accessible for painting and the erection of the conductors on it.

The various types of line supports are

1. Steel poles

2. Wooden poles

3. RCC poles

4. Steel towers

1. Steel poles

The steel poles are used for the voltage up to 33Kv.
The steel poles are used in low and high-voltage distribution systems.
The steel poles used for the span from 50 meters to 80 meters.
The steel poles have a longer life. light in weight and greater tensile strength than wooden poles.
The steel poles are galvanized to protect them from corrosion.
Steel poles have a life of 30 years, but steel poles are more costly than wooden poles.

The steel poles are three types

1. Tubular poles -

These poles have a round cross-section.
These poles have 9 to 11 meters in length and are used for distribution purposes in city areas to give good look.

2. Rail poles -

These poles have shapes like a railway track.
These poles have heights of 11 to 13 meters and are used for the transmission of electrical power from 11kv to 33kv.

3. Rolled steel joist -

2. Wooden poles

The wooden poles are made from seasoned wood like sal or chir.
The wooden poles are suitable for distribution lines having moderate cross-sectional area and shorter line span lengths.
The wooden poles are used for the voltage up to 20KV.
The wooden poles are used for the span length of up to 50 meters.
The wooden poles have a shorter life of 20 to 25 years.
The Height of the wooden poles is approximately 10 to 12 meters, with 38 cm circumference at the top and 66cm circumference at the bottom.
There are two types of wooden pole structures are used. one is A type pole and the second is an H-type pole.
The H pole type structure is used for overhead transmission lines operating at voltage up to 130kv with a span length of 150 meters.
The wooden poles are easily available, provide good insulation properties to live conductors and the public, cheap in cost than steel and RCC poles.
The wooden poles are used for distribution purposes in rural areas for economic purposes.
The major disadvantage of wooden poles is foundation failure or the tendency to rot below ground level.
The portion below the ground of wooden poles is impregnated with a preservative compound like creosote oil.
The wooden poles have smaller mechanical strength and a periodical inspection of the foundation is required.
The wooden poles are divided into 1. A type Pole 2. H type pole and 3. Single Poles.

3. RCC or Concrete poles

The RCC poles are made from cement concrete.
RCC means reinforced concrete poles become very popular as line supports.
The RCC poles are used for the low and high voltage distribution line up to the 33kv.
The RCC poles are used for longer spans from 80-200 meters.
The RCC poles have good mechanical strength and longer span length, longer span length than the wooden and steel poles.
The RCC poles have good insulating properties, give good look and the maintenance of the RCC poles is very easy.
The RCC poles are heavy in weight, so the transportation cost of the RCC poles is very high compared to other poles. To reduce the high cost of transportation, RCC poles are constructed at the site where it is commissioned.
The prestressed concrete poles called PCC poles are light in weight than RCC poles.
The PCC poles are mostly used for 11kv lines.

4. Steel towers

The Steel towers are used for the transmission of power above 66kv.
The steel rails or narrow base and lattice steel towers are used for the transmission of electrical power from 11kv to 33kv.
The broad base lattice steel towers are used for transmission of voltage at 66kv or above.
The construction of the steel tower is robust.
The steel towers are used for the span length of 300 meters or above.
The steel towers are mostly used for valleys, crossing fields, railway lines, and rivers.
The steel towers have a longer life and higher mechanical strength than the steel poles.
The lighting problems are resolved in steel towers due to the top lightning conductor or earth wire.
The steel towers are fabricated from well-galvanized or painted angle sections.
The steel towers can withstand severe climate conditions like forest fires, earthquakes, and cyclones.
The steel towers are designed for the double circuit line which gives insurance against discontinuity of power supply.

The steel towers are divided into two types

1. Tangent towers -

The tangent towers are used for a straight run of the line and up to 2 degrees of deviation from the straight run of the line.

2. Deviation tower -

For deviation exceeding 2 degrees, special steel towers are used are called deviation towers.
These towers are used where the transmission line changes its direction.
The single-circuit towers have a length of 25.3 meters.
The double-circuit towers have a length of 28 meters.