1.Conductors and their supporting structures and insulators (poles) arc the main items of overhead distribution system. Conductors are carried over on poles situated at suitable spans.
2.Insulation between the two is provided by means of pin, shackle or desi insulator which are mounted on horizontal cross arm fixed on a pole Overhead line poles are can hed at approximately 300 metres interval
Overhead conductors:
3.Hand drawn copper and aluminium, cadmium, copper and galvanized or aluminized steel wire are being used as overhead conductors.
4.Rule no 74 of Indian Electricity Rules 1956 presents minimum breaking strength of conductors a 350 kg which can be related to 150 kg if used in consumer’s premises in LV circuit for span less than 15 meters.
(i)Hard drawn copper conductor :
1.Electrical, copper is by far superior conductor as compared to other three. It has highest conductivity, very good tensile strength, least resistance and best weather resisting properties.
2.Due to non-availability of enough copper indigenously and high cost. copper wire is no more being used in distribution circuits except in exceptional cases.
3.Single bare copper conductors of approximately 8 to 80 sq.mm size are recommended for use in electrical circuits as per IS:282 and in multistrands these are available in sizes of 16 to 150 sq.mm.
(ii)Cadmium copper :
1. Tensile strength of copper can be doubled, if 1% cadmium copper alloy is used, although conductivity shall be reduced by 15%. ACSR conductor has now completely replaced this.
2.This is much more useful for larger spans.
(iii)All aluminium conductor (AAC):
1.This is also called as aluminium stranded conductor. Aluminium as a conductor is being extensively used in medium voltage and low voltage circuits whether overhead or underground.
2.For the same voltage drop, the area of conductor in case of aluminium conductor shall be 1.61 times that of copper conductor but due to low density, the weight ratio is only 0.48 times.
3.For equal diameter current carrying capacity of aluminium conductor is only 0.78 times less than that of copper. Due to less weight ratio for equal resistance, aluminium is being preferred.
(iv)ACSR conductor :
The ultimate tensile strength of AAC is poor, it is to be used in span exceeding 35 m. To save it from breaking in Strands is made of steel wire due to which the tensile strength is doubled. This steel conductor reinforces the remaining conductor of aluminium This combined conductor is known as ACSR conductor
(v)Aluminium alloy conductors :
They have recently been approved by ISI. Aluminium alloy conductor has got little less breaking Strength than the equivalent size of ACSR conductor but far less weight
(v)Steel conductor : Galvanized steel wires are not supposed to carry currents normally but are used as earth wire in which current will Now only in case of leakage or short circuits It is extensively used as earth wire, guard wire, telecommunication circuits and as reinforcement in ACSR conductor.
