Types of Electric poles

Line supports: The supporting structure for overhead line conductors are various types of poles, towers called Line supports.

Properties of Line supports:

• High mechanical strength.
• Light in weight without loss of mechanical strength.
• Low cost.
• Easy maintenance.
• Longer life.

Wooden Poles:

These are made of seasoned wood and are suitable for lines of the moderate X-sectional area and of relatively shorter spans, say upto 50 metres. Such supports are cheap, easily available, provide insulating properties and, therefore, are widely used for distribution purposes in rural areas as an economic proposition. The wooden poles generally tend to rot below the ground level, causing foundation failure. In order to prevent this, the portion of the pole below the ground level is impregnated with preservative compounds like creosote oil. Double pole structures of the ‘A’ or ‘H’ type are often used to obtain a higher transverse strength that could be economically provided by means of single poles.

• comparatively smaller life (20-25 years)
• cannot be used for voltages higher than 20 kV
• less mechanical strength
• require periodical inspection.

RCC Poles:

The reinforced concrete poles have become very popular as line supports in recent years. They have greater mechanical strength, longer life and permit longer spans than steel poles. Moreover, they give a good outlook, require little maintenance and have good insulating properties. The figure shows RCC poles for the single and double circuit. The holes in the poles facilitate the climbing of poles and at the same time reduce the weight of line supports.

• Span : 80-150 m
• Withstanding voltage: up to 33kV
• comparatively smaller life (50-55 years)

Steel poles

The steel poles are often used as a substitute for wooden poles. They possess greater mechanical strength, longer life and permit longer spans to be used. Such poles are generally used for distribution purposes in the cities. This type of support needs to be galvanized or painted in order to prolong its life. The steel poles are of three types (i) rail poles (ii) tubular poles and (iii) rolled steel joints.

• Span : above150m
• Withstanding voltage: up to 33kV
• High mechanical strength  & Longer life
• Costly due Galvanization and painted structure.