For transmitting electricity to consumers, utilities use overhead and underground cables. Conventionally, bare overhead conductors are used since they are the cheapest and easiest to build. They utilise air as natural insulation and there is no need for additional insulation, and have specially designed isolators present only on line supports. When installed using efficient fitting techniques, these conductors help in achieving a relatively low cost of construction of the overhead electricity network. However, they are difficult to erect in complex network areas and are not safe, especially in densely populated areas. On the other hand, underground cables offer a safer alternative. Their other advantages include lower maintenance costs and lower risks from harsh weather conditions as compared to overhead cables. However, underground cables are costlier to build than overhead systems as the ground needs to be excavated. This can be difficult when passing through geographic obstructions such as hills, marshes and rivers. Special trenches need to be constructed when passing through loose soil. Besides, heat dissipation in underground cables is an issue. Therefore, the conductors need to be thicker and require expensive insulation. Aerial Bunched Cable (also aerial bundled conductors or simply ABC) is an innovative concept for Over Head (OH) power distribution. Aerial bundled cables are overhead power lines using several insulated phase conductors bundled tightly together, usually with a bare or Insulated neutral conductor. This contrasts with the traditional practice of using uninsulated conductors separated by air gaps. When compared to conventional bare conductor OH distribution systems, ABC provides higher safety and reliability, lower power losses, stability in voltage regulation and ultimate system economy by reducing installation, maintenance and operation costs. This system is ideal for rural distribution as well as in congested urban areas . In Rural area, it is very attractive for installation in difficult terrain such as hilly areas, dense forests, coastal regions, etc. These lines can also be laid without cutting or trimming any trees. In Urban area ABC is considered to be the best choice for Power Distribution in congested areas with narrow lanes and by-lanes. Due to its insulation, it is convenient to lay even in densely populated areas with narrow gaps between buildings, where it is usually not possible to run bare conductors. Additionally, accidental electrocutions are avoided by the insulation of the cable. Since the cables are clearly visible, the faults can be detected and rectified quickly and with ease. Damage due to water logging is also avoided as compared to underground cables. ABCs are highly reliable and the insulation has been developed to withstand heat, cold and intense sunlight. The insulation reduces the number of short circuits, over-voltages and transformer burnouts caused by thunderstorms. Fewer hardware accessories are needed as each one can be used with many different sizes of cable. Since the cable can also be supplied with conductors for street lighting, it is more cost-effective. Classification of ABC:- As per the constructional features of Voltages to which it is to be used ,ABCs are classified LT ABC and HT ABC. The Standard applied for the use of ABC:- IS 14255-Aerial Bunched Cables for working Voltages up to and including 1100 Volts. REC Specification-Aerial Bunched Cables for LT Lines. REC Specification-Aerial Bunched Cables for 11kV Lines. Hardware Accessories for Drawing ABCs:- The following common and specially designed accessories are required for drawing LT and HT ABCs on Electric poles. 1. Suspension Clamp assembly. 2. Dead End (Anchor) Clamp assembly. 3. Stainless Steel Strap. 4. Stainless steel Buckle. 5. UV Plastic Ties. The standards to be adopted for the selection, testing and installation of these items are NF C 33 040 -1998, NF C 33-041 -1998.The Technical Specification of these accessories will vary depending upon the Voltage and size of cables used. For LT ABCs, the following accessories additional- exclusive are required
confirm to flexibility class 2 of IS 8130 : 1984. The Size os street light Conductor shall be 16 Sq.mm. The Messenger/Neutral Conductor shall be made of heat treated Aluminium-magnesium ( 0.5%)-silicon( 0.5%) alloy wires. The messenger (Neutral conductor) or otherwise shall be either stranded circular or compacted circular type and shall have minimum 7 strands. The surface of the conductor shall be smooth. A protective barrier may be applied between the conductor and insulation, if required. Such barrier, when used, shall be compatible with insulating material and suitable for the operating temperature of the cable. The size of Messenger conductor and its breaking load shall be as per the table below: Single Core Armoured Cable
Core Identification:- The phase conductors shall be provided with one, two or three ‘ridges’ for quick identification. The street lighting Conductor and messenger conductor (if insulated) shall not have any identification mark. ASSEMBLY (LAYING UP): Three insulated phase couductors, and a street lighting conductor (if required) shall be twisted around the insulated messenger conductor without fillers with a lay not exceeding 3.5 times the diameter of the insulated phase conductor. Different sizes of LT ABCs:- As per the requirement based on the load, the different sizes of LT ABCs are available as below:-
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