Aerial Bunched Cable (ABC) is a very novel concept for overhead Power distribution. ABC provides higher safety and reliability compared to bare conductor overhead distribution system. The other advanctages are lower power losses and system economy by reducing installation, maintenance and operation cost. This system is ideal for rural distribution and specially suitable in difficult terrains like hilly areas, forest and coastal areas etc.
ABC is also considered as a better choice for power distribution in densely populated areas where laying of underground cable is either difficult or extremely expensive. This is attributed by narrow lanes and by-lanes of congested urban areas. Needless to mention that ABC is a better choice due to the flexibility of re-routing demand, should there be any changes in urban development plan.
Bare overhead Transmission lines are more prone to system failures causing immense loss and inconvenience to the consumers.
Aerial Bunched Cables systems for both HT & LT have been introduced across the globe to arrest such problem. It is basically a compromise between Insulated Power Cable system and bare overhead conductor.
There are 3 or 4 Power carrying conductors suitably insulated and laid around a bare or insulated Neutral/Earth conductor. This earth/neutral conductor carries the entire weight of the cable when hanged on Transmission poles/towers suitably.
The chances of faults are reduced to a great extent because the conductors are insulated. However, it lacks the Safety and mechanical strength of Underground cables. The fact that ABC runs overhead and hence it is never subjected to the mechanical abuses that an underground cable undergoes.
ABC ensures good protection against ground and line faults ensuring system reliability, increased system efficiency compared to bare overhead lines. The problem of free clearance is also minimized. ABC system hinders tampering with power-line like hooking resulting in efficient Power utilization.
- Easier Installation particularly in congested, forest or Hilly areas.
- Saving in cost of Poles, Insulators, cross-arms etc.
- Human Safety in case of accidental contacts.
- Water proof system, no corrosion.
- Syatem reliability hence customer satisfaction.
- Reduced clearance.
Insulated Neutral :
In low voltage networks, in case of unbalanced load on the 3 phases, a current can flow in the neutral. This flow of current causes a voltage to be present in the neutral. This voltage can reach dangerous levels even in ‘Earthed’ conditions.
It is observed that the permissible voltage shift between neutral and earth can go up 100 volts! This surely establishes the need for an insulated neutral. Moreover, parallels can be drawn with the underground cables. A single insulation damage on the conductor will not necessarily trip the system, unless an adjacent conductor also suffers an insulation damage at the same point. Unlike in underground cables system there are lot of relative movements between the conductors leading to abrasion which more likely to damage the adjoining insulation if the netural is not insulated
Laser Cable produces LT Power Cable with PVC or XLPE Insulation of Voltage grade upto 3.3 Kv conforming to Indian and various International Standards.
Cross Linked Polyethylene (XLPE) :
XLPE means crosslinked Polyethylene. The compound is based on high molecular weight polymer. High degree of crosslinking is attained in the processed form and thus attains excellent electrical and mechanical properties.
Advantages of XLPE Cables :
- Higher current rating allows to select lower size of XLPE cable compared to PVC cable
- Higher short circuit rating 250°C compared to 160°C that for PVC cables
- Resistant to heat deformation while PVC is prone to heat deformation
- Respective short circuit/overload condition is reliable
- Lower dielectric loss
- Jointing & Termination is easy
- Lighter in weight considering lower overall diameter
Comparative properties of PVC and XLPE Insulation :
|Permitivity(50 Hz, 200)||–||4-6||2.3|
|Dielectric loss factor (50 Hz, 200)||–||0.05-0.07||0.0004|
|Volume Resistivity (270C)||Ohms cm (min)||10^13||10^14|
|Max. conductor temperature||Deg. C||70||90|
|Max. short circuit temperature||Deg. C||12.5||12.5|
|Tensile Strength||N/mm2 (min)||12.5||12.5|
|Elongation at break||–||Excellent||Medium|
|Flexibility at – 100C||–||Poor||Good|
|Resistance to abrasion||–||Medium||Good|
Applicable Standards :
- PVC Power & Control Cable : IS 1554/Part 1/1988
- XLPE Power & Control Cable : IS 7098/Part 1/1988