Cables and conductors are the most essential components of a power transmission network. They are crucial not just in the development of a new network but also in the strengthening of the existing grid in areas with increasing power demand but less, or no space available to lay down new lines. With increased urbanisation, space is often constrained in most parts of the country, necessitating the need to install more compact transmission lines. Aimed at increasing the quantum of power that can be transmitted through conductors and minimizing the right-of-way (RoW) requirements, the transmission conductor industry has witnessed a number of technological advancements. Advanced conductor technologies are also centred on efficiency, safety, reliability, ease of design and environmental friendliness.
New conductors are being deployed for carrying higher currents, while allowing higher temperature ratings. These include aluminium conductor alloy reinforced (ACAR), aluminium conductor steel reinforced (ACSR) and aluminium conductor carbon fibre reinforced (ACFR) cables. High temperature low sag (HTLS), gas-reinforced, and high performance superconductors are some of the more advanced variants of conductors.
With a growing emphasis on the development of a robust power grid in the country to meet the rising demand for reliable power, a number of government initiatives and programmes have been undertaken that have helped create a positive market for cables and conductors. The government is determined to provide access to electricity to all consumers, which has further boosted the demand for cables and conductors. As per various industry estimates, it is expected that the industry will grow at a compound annual growth rate (CAGR) of about 20 per cent in the coming years.
A look at the market for cables and conductors and advanced conductor technologies…
The market for cables and conductors in India has grown significantly in the past few years on the back of investments in the power and infrastructure sectors. As per the Indian Electrical & Electronics Manufacturers’ Association (IEEMA), the overall size of the cables industry in India was estimated to be around Rs 412.5 billion in 2016-17, recording a growth of around 5.1 per cent over 2015-16. In 2017-18 (till January), the industry registered a remarkable growth of around 21 per cent. However, the power transmission cables segment registered a growth of 5.2 per cent in 2016-17 and 8.5 per cent in 2017-18 (till January). While the cable segment is on a positive path for growth, the conductor segment has been experiencing a rather sluggish demand. The conductors market saw a decline of 10.76 per cent in 2016-17, from Rs 81.25 billion in 2015-16 to Rs 72.5 billion in 2016-17. This is largely owing to the delays in order finalisations by major buyers that resulted in negative growth in 2017-18 as well. In 2017-18 (till January), the growth was – 7.6 per cent.
The power transmission segment is shifting increasingly towards high voltage transmission lines. This trend is essentially driven by the need to deliver power through long distances and to integrate the increasing share of renewable energy into the grid. Further, while the transmission line network in India is dominated by overhead lines, underground cabling is gaining increased acceptance amongst state and central transmission utilities as it provides greater safety (against electrocution) as compared to overhead cables, requires lower RoW and is aesthetically better than overhead transmission lines. Cost, however, remains a key consideration. According to industry estimates, underground cabling costs up to 4 to 10 times the cost of overhead cables of the same voltage. However, the high initial cost is offset by benefits such as low chances of developing faults and low maintenance costs.
Further, due to the risks associated with bare overhead cables, covered cables such as cross-linked polyethylene (XLPE), high-density polyethylene and aerial-bunched cables have been gaining importance in the market. These are also cheaper than underground cable installations.
On the technology front, a number of technologies have been introduced that enable utilities to augment their capacities, while minimising the RoW requirements and increasing reliability. These include ACAR, ACSR, ACFR, high-temperature low sag (HTLS) conductors, gas-insulated lines (GILs) and high temperature super-conductors (HTSs).
ACAR consists of one or more layers of aluminium strands helically wrapped over one or more aluminium alloy wires and provides a transmission conductor with an excellent balance of electrical and mechanical properties. ACSR, on the other hand, consists of a solid or stranded steel core surrounded by one or more layers of strands of aluminium. Conventionally, more steel (26 to 40 per cent) was used to obtain greater strength. More recently, as conductors have become larger, the trend has shifted to less steel content (11 to 18 per cent). ACFR, which is more efficient than ACSR, uses carbon fibre at its core. It is lighter in weight (one-fifth the weight of steel), highly flexible, has low linear expansion, low sag and high tensile fatigue.
HTLS conductors are made up of new materials such as invar steel (Fe-Ni alloy), aluminium-zirconium (Al-Zr) alloys, annealed aluminium, high strength steel, and metal and polymer matrix composites. These materials impart a high temperature resistance to conductors while increasing ampacity and preventing thermal stress. HTLS conductors are stranded with a combination of aluminium and alloy wires for conductivity, and reinforced by core wires. HTLS conductors not only enhance operational efficiency but can also be used for the purpose of reconductoring the existing lines that enable utilities to transmit a higher quantum of power through existing corridors, and can significantly scale down losses as well as instances of power outages. However, in the case of very long lines, the performance of HTLS is constrained by surge impedance loading and losses are also higher. Further, the average cost of HTLS conductors is 2-3 times that of ACSR and AAAC (all aluminium alloy conductors).
GILs have gas (nitrogen and sulphur hexafluoride) as the insulating medium, as against physical layers of separation in conventional transmission lines. A GIL comprises aluminium conductors supported by sealed tubes pressurised with gas (nitrogen and sulphur hexafluoride in a 80:20 ratio) as the main insulation. GILs can be installed under the ground as well as in tunnels and trenches. Due to resistive losses of GILs being lower than those of overhead lines and other types of underground cables, they offer greater reliability with no risk of fire. This technology can serve as a viable alternative to overhead lines, where RoW is not available for the transmission of electricity. However, it is still awaiting widespread adoption in the domestic market.
HTSs consist of the cable comprising several strands of superconducting wire wrapped around a copper core, and a cryogenic cooling system to maintain proper operating conditions. HTS-based devices including cables can limit overcurrents and protect the grid from damage. HTS can carry five to ten times the current carried by conventional conductors, they are compact in size, reduce RoW requirements, offer less transmission loss (one fourth times as compared to conventional conductors, can operate at a wide voltage range from 5 kV to 765 kV and have lower impedance than conventional technology. HTS can be installed in dense urban areas with a high load requirement, and to connect two existing substations to create redundancy when transformer addition is not feasible. So far, HTS have mostly been deployed by global utilities, and not on a large scale.
XLPE cables consist of cross-linked polyethylene as the main insulating material. Cross-linking inhibits the movement of molecules under the stimulation of heat, and this gives these cables greater stability at elevated temperatures compared with thermoplastic materials. XLPE cables can operate at higher temperatures, both for normal loading and under short-circuit conditions. XLPE-insulated cables are quite useful in direct current (DC) power transmission. Traditional DC power cables include oil-filled or mass-impregnated non-drain (MIND) cables and have limitations for long distance power transmission, since they require frequent oil refilling. XLPE cables, however, cannot operate efficiently in low operating temperatures.
The cables and conductors industry has significant opportunities that lay ahead, on account of investments planned in the power sector by the government. Various ongoing government schemes supporting investment in network strengthening and upgradation include Integrated Power Development Scheme and Deendayal Upadhyaya Gram Jyoti Yojana, the large-scale grid integration of intermittent renewable energy, the government’s focus on achieving Power for All and the Indian Railways plans for 100 per cent rail electrification, which are some of the growth indicators for the industry. Meanwhile, the challenges facing the industry include volatility in raw material (steel, aluminium, zinc, etc.) prices and high dependence on imports from China, the UAE, Russia and Japan. Further, a delay in the execution of projects due to the requirement of multiple clearances and approvals poses a major impediment to the growth of the industry. These issues that deter the growth of the industry need to be addressed.
Overall, increasing industrialisation, growing population, the need for reliable and efficient power supply and increasing renewable energy capacities have kept the demand high for cables and conductors. Going forward, this demand trend is expected to continue for the industry.