Types of Supporting Structures used in Overhead Transmission Lines

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CONTENTS
> Line Supports :
> Properties for LIne Supports :
> Types of Line Supports :
> Advantages and Disadvantages of Line Supports :




Line Supports

Line support palys a major role in power transmission. Line support (like Poles and Towers) are used for supporting the overhead lines or wires.

Desired properties for lIne Supports:
 
1) High mechanical strength to withstand the weight of conductors and wind load etc
2) Light in weight without the loss of mechanical strength.
3) Cheap in cost and economical to maintain.
4) longer life.
5) Easy accessibility of conductors for maintenance.

Line Supports Types:  

1) Wooden Poles
2) Steel Poles
3) R.C.C. Poles
4) Lattice steel towers
 
1) Wooden Poles :  These supports are cheap, easily available , provide insulating properties and widey used for distribution purpose in rural areas. 
# Span upto 50 meters.
# Made of seasoned wood (sal and chir)
 


Advantages 
1) Wooden poles have lower elecrical conductivity.
2) Economical for rural areas.
3) Less cost of transportation due to light weight.

Disadvantages
1) Tendency to rot below the ground level.
2)  Comparatively smaller life ( 20-25 years)
3) Cannot be used for voltages higher than 20kv
4) Less mechanical strength 
5) Require periodic inspection 

2) Steel poles : Steel poles have greater mechanical stength,  longer life , longer span and are generally used for distribution purposes in the cities. 
Steel poles are of three types- Rail poles, Tubular poles ,Rolled steel joints. This type of poles need to be galvanised or painted in order to prolong its life. 



Advantages 
1) Design flexiblity
2) High mecahnical strength 
3) Longer life 
4) less maintenance 
5) Permit longer span 

Disadvantages 
1) Requires coating to be corrosion resistive .
2) Reactive with chemicals and pollution.  


3) R.C.C Poles : In recent years Reinforced concrete poles have become very popular as line supports. They have greater mechanical strength ,longer life and permit longer spans then steel poles. 

Instead they have good outlook, require little maintenance and have good insulating  properties. 

Holes in the poles facilitate the climbing of poles and at the same time reduce the weight of line supports. 



Advantages 
1) Fire and weather resistive 
2) Maintenance cost is negligible
3) Can be molded in any required shape
4) Good structural apperance 

Disadvantages
1) Initial Cost is high.
2) High cost of transport due to their heavy weight so usually manufactured at site.
3) Skilled supervison is required


 
4) Steel towers :  
(a) Steel tower are used for long distance transmission at higher voltage. 

(b) Steel towers have greater mechanical strength , longer life, and can withstand most severe climatic conditions and permit the use of longer spans.

(c) The risk of interrupted service due to broken or punctured insulation is considerably reduced owing to longer spans.  

(d) Tower footing are usually grounded by driving rods into the earth to minimise the lightning troubles as each tower acts as a lightning conductor. 



Advantages 
1) Strength is much more.
2) Span is greater, so less number of units required.
3) Life of tower is more 
4) They can withstand bad weather/storms.
5) Less maintenance is required.
6) Suitable for transmission lines 33 kV to even 765 kV.

Disadvantage
1) One tower requires so many fittings.
2) The erection cost is much more.
3) The expert team is required.
4) Fault attending consumes more time.
5) Transport in hilly areas is difficult
 

    
 

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