Aerial bunched Cable (ABC) is a very novel concept for Over Head Power distribution. When compared to the conventional bare conductor overhead distribution system, ABC provides higher safety and reliability, lower power losses and ultimate system economy by reducing installation, maintenance and operative cost. This system is ideal for rural distribution and specially attractive for installation in difficult terrains such as hilly areas, forest areas, coastal areas etc.
ABC is also considered to be the best choice for power distribution in congested urban areas with narrow lanes and by-lanes. In developing urban complex, ABC is the better choice because of flexibility for rerouting as demanded by changes in urban development plan.
CONSTRUCTION OF AB CABLE
XLPE insulated power conductors of Aluminium (Neutral conductor and street lighting conductors if and when necessary) are laid together (twisted) around a high tensile stranded and galvanized steel (Aluminium Alloy may be used) insulated messenger wire to form the Aerial Bunched Cable. This assembly is directly strung on to distribution pole/towers by means of standard hardwires available in the market but care shall be taken to render the messenger wire completely insulated from earthling at any point of distribution in case of HT ABC.
The XLFE (Cross-linked Polyethylene) insulation is black in colour and is stabilized against deterioration caused by exposure to direct sunlight and ultraviolet radiation. XLPE is cross linkable low density polyethylene which is made thermos set by special formulation from base polymer of thermoplastic low density polyethylene. XLPE combines the best electrical properties of LDPE and superior thermos mechanical properties.
MATERIALS
(i) Aluminium conductors conform to IS:8130 (Class-II)
(ii) Aluminium Alloy messenger wire conforms to IS:398 (Part-IV)
(iii) XLPE insulation of Power conductors conform to IS :14255/1995.
Since, the tension from the current carrying conductor is totally removed by introduction of messenger wire the operation temperature of the conductor is 90 °C as against 75 °C of the bare conductor under tension thereby allowing ABC to Carry current equivalent to that of bare conductor of the same size.
STRINGING
No difficulty is envisaged during stringing of ABC in the conventional method but care shall be taken that insulated conductors do not get damaged during installation. Dragging the ABC on the ground is to be avoided. Tension to be applied during stringing shall be 25 % of the breaking load of the messenger wires. This will allow line to have sag within specified limit of 1 .5% of the span at the lowest ambient temperature.
JOINTING
While mid-span jointing permissible for LT ABC system by conventional technique, our recommendation will be to draw the line in such a way as to bring the joints at the supports. Mid-span jointing is not at all recommended in the case of HT lines, our recommendation is for outdoor type HV terminations only. Under unavoidable circumstances, line tapping at the support points may be allowed through suitably designed clamp connectors / PG clamps. The semi conducting screen continuity shall be maintained at all joints as far as possible to avoid fluctuations during system disturbances. The 3-phase screens may be shorted and earthed through suitable no surge arrestor. Attempting to make a tap-off from power conductors in the region where catenary is under tension is not recommended.
