Underground cabling plays a crucial role in providing 24×7 reliable power supply. It offers a host of benefits such as resilience in severe weather conditions, ease of network expansion in densely populated areas and protection against theft. Underground cabling by distribution utilities is primarily being done under the government’s Integrated Power Development Scheme (IPDS). Meanwhile, underground cabling is important for network expansion in the transmission segment since these cables entail minimum right of way (RoW) and require fewer clearances. While underground power cabling is undoubtedly an expensive choice, demand continues to be driven by the need for reliable supply, safety and aesthetic considerations and availability of clearances.
At the distribution and sub-transmission levels, the majority of underground cable projects are being implemented under the IPDS. The scheme has earmarked Rs 20 billion for executing these projects. It envisages the implementation of underground cables aggregating 18,008 km across various states. Maharashtra has the highest target with 5,762 km, followed by Uttar Pradesh with 2,864 km and Rajasthan with 2,179 km. As of December 2019, works on underground/aerial bunched cables has been completed across 62,668 ckt. km. This represents 73 per cent of the total work envisaged in this area.
Underground cabling projects have also been proposed under the Smart Cities Mission to ensure reliable power supply and enhance aesthetics. Underground distribution cabling projects are also being implemented under other state and central government schemes for network improvements such as the Andhra Pradesh Disaster Recovery Project, the National Cyclone Risk Mitigation Programme, and the North Eastern Region Power System Improvement Project.
Underground cables are less prone to damage from severe weather conditions such as lightning, hurricanes, cyclones, typhoons, tornados and freezing temperatures as they are not directly exposed to the environment. Besides, underground cables are protected against power theft, thereby reducing aggregate technical and commercial losses. In an underground cabling system, it is almost impossible to tap the conductor, thereby checking illegal connections. Apart from this, underground cables are useful in network expansion. Underground cables require minimum RoW and other clearances such as wildlife and forest clearances, which often delay transmission projects. In the distribution segment, underground cables help in network expansion in densely populated areas. Since these cables are laid under the ground, they do not require physical ground space. They also add to the aesthetics of the area, as they do not obstruct the view.
As per the Central Electricity Authority, the cost of an underground cabling system is three to four times that of an equivalent overhead system. The estimated cost of an 11 kV overhead single-circuit line with dog conductor is Rs 0.5 million-Rs 0.6 million per km, while the estimated cost of a 3×300 sq. mm 11 kV underground cabling system is around Rs 2 million per km. The cost of the underground cabling system also depends on the cost of the road restoration work required.
Issues and challenges
One of the key concerns for underground cabling is the damage caused to cables from other underground activities. The uncoordinated underground development activities undertaken by multiple agencies and private contractors result in frequent cable cuts, leading to depreciated cable life and an increase in operating costs. Besides, the cable insulation deteriorates over time, owing to various loading cycles. Over a period of time, the cable insulation weakens, which increases the potential for line faults. Besides, since these cables are below the ground, they require specialised techniques for fault detection and restoration, and repair time is much longer. Also, it is difficult to modify underground lines once the cables have been laid.
Net, net, underground cabling is a boon for the transmission and distribution segment, as it helps in network expansion in densely populated areas, minimises power theft and requires minimum clearances. Undertaking underground cabling projects based on the specific needs and requirements of an area is essential for meeting the government’s goal of providing 24×7 reliable power supply.