Page 328 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

available, provide insulating properties and, therefore are widely used for distribution purposes in rural areas as
an economical proposition.

Fig 1

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 supports need to be galvanized or painted in order to prolong its life. The steel poles
are of three types viz (i) rail poles (ii) tubular poles and (iii) rolled steel joints.
RCC Poles: The reinforced cement concrete (RCC) 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 good outlook, require little maintenance and have good insulating properties. Fig 2 shows R.C.C poles
for 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.

Steel towers
In practice, wooden, steel and reinforced concrete poles are used for distribution purpose at low voltages, say
upto 11 KV. However for long distance transmission at higher voltage, steel towers are invariably employed. Steel
towers have greater mechanical strength, longer life, can withstand more severe climatic conditions and permit the
use of longer spans. The risk of interrupted service due to broken or punctured insulation is considerably reduced
owing to longer spans. Tower footings are usually grounded by driving rods into the earth. This minimizes the
lightning troubles as each tower acts as a lightning conductor.

Fig 3(a) shows a single circuit tower. However, at a moderate additional cost, double circuit tower can be provided
as shown in Fig 3(b). The double circuit has the advantage that it ensures continuity of supply. In case there is
breakdown of one circuit, the continuity of supply can be maintained by the other circuit.

315

CITS : Power - Electrician & Wireman - Lesson 106-116 CITS : Power - Electrician & Wireman - Lesson 106-116