Electric line support system

THE NATIONAL GRID SYSTEM

Line support  structures in electricity and over head conductors; are mechanism which are used to to give support and balance to electric over head conductors

The supporting structure for overhead line conductors are of various types of poles and towers; called line support. In general the line supports should have the following properties:

1. High mechanical strength 
2. Cheap in cost and economical maintenance 
3. Longer life span
4. Should be durable 
5. Light in weight without loss of mechanical strength 

Easy accessibility of conductors for maintenance Line support used for transmission and distribution of electric power are of various types including wooden

• Wooden poles
• Steel poles 
• Reinforce concrete poles (RCC)
• Lattice still tower

The choice of supporting structures for a particular case depend upon 

The line span

Cross_sectional area

Line voltage 

Cost and local conditions 

A. Wooden poles

This are made of season wood and are suitable for lines of moderate cross sectional area and of relatively shorter span say up to 50m. Such support are cheap, easily available, provide insulating properties therefore are widely used for distribution purposes I rural areas as an economic proposition. The wooden poles generally have the to root below the ground level causing foundation failure. In order to prevent this portion of the pole below the level is impregnated with preservatives compounds. Double pole structure of the 'A' or 'H' types are often used to obtain a higher transverse strength than could be economically provided by means of single poles

The structure to wooden poles are:

*Tendencies to root below the ground

*Comparatively smaller life span(20 - 25 years) 

*can't be used for voltage higher than 33kv

*Less mechanical strength 

*Requires periodic inspection 

B. STEEL POLES
The steel poles are often used as a substitute for wooden poles. They possess greater mechanical strength, longer life span and permit long spans to be used. Such poles are generally used for distribution purposes in the cities; this type of line support are to be galvanized or painted in order to prolong its life span. The steel poles are of three types

• Rail poles
• Tubular poles 
• Rolled steel joints 

(c) REINFORCE CONCRETE POLES (RCC) 

The Reinforce concrete poles have become very popular in recent years. They have greater mechanical strength, longer life span and permit longer spans than steel poles. Moreover they give good outlook, require little maintenance and have good insulating properties. The main difficulty with the use of these is the high cost of transport, owing to their heavy weight. Therefore such poles are often manufactured at site to avoid heavy cost of transportation.

(D)   STEEL TOWERS
    
In practice, wooden, steel and reinforce concrete poles are used for distribution  purposes at low voltages, up to 33kv. How ever for long distance transmission at higher voltages, steel towers are invariably used. Steel towers have greater mechanical strength, longer life span, can withstand most severe climate conditions and permit the use of longer spans. The risk of interrupted service due to broken of punctured insulation is considerably reduce owing to longer spans. The towers footings are usually grounded by driving rods into the earth. This minimizes the lightening troubles, as each tower act as a lightening arrestor or conductors. At moderate additional cost double circuit tower can be provided. The double circuit has the advantages that it ensures continuity of supply. In case there is a breakdown of circuit, the continuity of supy can be maintain by the other circuit.

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