Line Supports
The supporting structures for overhead line conductors are various sorts of poles and towers called line supports. generally, the road supports should have the subsequent properties:
1. High mechanical strength to face up to the load of conductors and wind loads etc.
2. Light in weight without
the loss of mechanical strength.
3. Cheap in cost and
economical to take care of.
4. Longer life.
5. Easy accessibility of
conductors for maintenance.
The line supports used for transmission and distribution of electrical power are of varied types including wooden poles, steel poles, R.C.C. poles and lattice steel towers. The selection of structure for a specific case depends upon the road span, X-sectional area, line voltage, cost and native conditions.
1. Wooden Poles: These are made from seasoned wood and are suitable for lines of moderate X-sectional area and of relatively shorter spans, say up to 50 meters. Such supports are cheap, easily available, provide insulating properties and, therefore, are widely used for distribution purposes in rural areas as a cheap proposition. The wooden poles have a tendency to rot below the bottom level, causing foundation failure. So as to stop this, the portion of the pole below the bottom level is impregnated with preservative compounds like creosote oil. Double pole structures of the ‘A’ or ‘H’ type are often wont to obtain a better transverse strength than might be economically provided by means of single pole.
The main objections to wooden supports are:
1. Tendency to rot below the
bottom level
2. Comparatively smaller life
(20-25 years)
3. Can't be used for voltage
above 20 KV
4. Less mechanical strength
and
5. Require periodical
inspection
2. 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 within the cities. This sort of supports got to be galvanized or painted so as to prolong its life. The steel poles are of three types viz., (i) rail poles (ii) tubular poles and (iii) rolled steel joints.
3. RCC Poles: The ferroconcrete poles became very fashionable as line supports in recent years. They need greater mechanical mechanical strength, longer life and permit longer spans than steel poles. Moreover, they provide good outlook, require little maintenance and have good insulating properties. RCC poles for single and double circuit. The holes within the poles facilitate the climbing of poles and at an equivalent time reduce the load of line supports. The main difficulty with the utilization of those poles is that the high cost of transport due to their heavy weight. Therefore, such poles are often manufactured at the location so as to avoid heavy cost of transportation.
4. Steel Towers: In practice, wooden, steel and ferroconcrete poles are used for distribution purposes at low voltages, say up to 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 most severe climate and permit the utilization of longer spans. The danger of interrupted service thanks to broken or punctured insulation is considerably reduced due to longer spans. Tower footing are usually grounded by driving rods into the world. This minimizes the lightning troubles as each tower acts as a lightning rod. A single circuit tower. However, at a moderate additional cost, double circuit tower are often provided. The double circuit has the advantage that it ensures continuity of supply. It case there's breakdown of 1 circuit, the continuity of supply are often maintained by the opposite circuit.
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