Over the years, significant technological strides have been made on the transmission infrastructure front. Power transmission utilities are adopting newer technologies to address the issue of right-of-way (RoW) constraints, ensure cost-effective network expansion and reduce network losses. In the cables and conductors space, the use of higher ampacity conductors such as high temperature low sag (HTLS) conductors is gaining traction. These conductors have higher power transmission capacity than conventional conductors of the same size. Apart from this, the deployment of digital substations that allows the sharing of substation status and performance parameters in real time through digital signals is gaining traction. Digital substations are likely to be useful in maintaining grid stability with the large-scale integration of renewable energy.
Apart from this, IT and OT solutions can help utilities in optimising the performance of transmission systems and creating new models for efficiency. Technologies such as asset management, data analytics, IoT, smart sensors and process bus architecture aid in streamlining grid operations. Power Grid Corporation of India Limited (Powergrid) is the pioneer in implementing technology solutions in the transmission space. As of March 31, 2019, Powergrid owned and operated 1,235 lines and 245 extra high voltage substations, including 15 high voltage direct current substations up to ± 800 kV level, 726 transformers, 11 STATCOMs, 5 static var compensators (SVCs) as well as series reactors and thyristor controlled series compensators/fixed series compensators at various places.
Cables and conductors
With the objective of minimising the RoW requirement for transmission network expansion, utilities are focusing on optimising power transfer per unit of RoW with the use of higher ampacity conductors. To this end, the use of HTLS conductors is gaining ground. These conductors can withstand temperatures of up to 250°C and are characterised by high temperature resistance and greater ampacity than conventional conductors such as aluminium conductor steel reinforced (ACSR) and all-aluminium alloy (AAAC) conductors that are designed to operate continuously at temperatures of 85°C and 95°C respectively. The first HTLS transmission line project was implemented by Powergrid for the line-in-line-out (LILO) of one circuit of the 400 kV double-circuit (D/C) (quad) Dadri-Ballabgarh transmission line at Maharani Bagh, New Delhi, wherein it deployed INVAR type HTLS conductors. Another major application of HTLS conductors has been in reconductoring the existing lines to increase power transfer capacity. Reconductoring refers to the upgrade of conductors, while the towers and other infrastructure remain mostly unaltered. It enables utilities to augment the quantum of power supplied as well as improve the quality of power transmitted through the existing corridors. This has been done by a number of utilities including those in Kerala and West Bengal, thus enabling them to meet higher load demand without laying new lines and achieve greater reliability. Another emerging technology solution in the cable and conductor space is the use of high surge impedance loading (HSIL) lines. The transmission capacity of overhead lines is limited owing to reactance. When such a limitation occurs, HSIL lines help limit the voltage drop and thus increase the power transfer capability. The HSIL lines concept can be applied to new lines as well as to existing lines. Countries with very long lines (more than 250 km), such Brazil, Russia and China, have HSIL lines in successful operation. Powergrid has also deployed the technology in the 400 kV (Quad Moose) Kaithal-Meerut line (about 16 km).
Switchgear and substations
In order to manage space constraints and the high cost of land, utilities are adopting newer substation and switchgear technologies such as gas insulated switchgear (GIS) and hybrid switchgear. These are rapidly replacing the conventionally used air-insulated switchgear (AIS). GIS are indoor-type substations in which the equipment is placed inside the modules filled with SF6 gas. They require significantly less space (around 35 per cent less than AIS), entail lower maintenance costs and have a lower outage rate as compared to AIS. Although the initial cost of a GIS substation is around 50 per cent more than that of AIS, when the cost of land is considered in the capital cost, the overall capital cost of the two is comparable. Besides this, the use of hybrid switchgear that deploys a mix of AIS and GIS technologies is also gaining traction. It combines the benefits of both and can be installed indoors as well as outdoors. GETCO is one of the pioneers in the installation of hybrid switchgear. Some examples of GETCO’s switchgear are the 220 kV Sartanpur and 220 kV Suva substations.
Another emerging technology trend in the transmission infrastructure space is the use of smart and automated switchgear. This switchgear is a part of digital substations, which enable the collection of real-time data on primary equipment and the conversion of this data into actionable intelligence in order to help utilities monitor, control and maintain assets, as well as achieve cost efficiencies. Digital substations are expected to play a vital role in maintaining grid stability with the large-scale integration of intermittent renewable energy into the grid.
In the power transformer segment, the key emerging technologies include HVDC converter transformers, phase shifting transformers (PSTs), coupling transformers, mobile transformers and smart transformers. HVDC technology has gained traction in recent years due to its ability to transmit large amounts of electricity over long distances with lower losses. An HVDC system can reduce transmission losses by around 50 per cent compared to a high voltage alternating current system. HVDC converter transformers form the core of HVDC projects as they transfer power between an AC system and the DC transmission network.
Meanwhile, phase-shifting transformers are special purpose transformers, which are used to control the active power flow in the network by regulating the phase of line voltage. These transformers are used in networks where intensive power wheeling takes place due to deregulation. They help ensure optimum utilisation of transmission lines, thereby enhancing their efficiency. Bharat Heavy Electricals Limited commissioned its first indigenously developed phase-shifting transformer at the Kothagudem thermal power station in Telangana in 2014. The transformer is used to control and improve the power flow between 400 kV and 220 kV networks in either direction by shifting the phase as the system requires. Apart from this, coupling transformers find application in flexible AC transmission systems (FACTS) to enhance the control and stability of the transmission system and increase its power transfer capabilities. These transformers connect the grid with a static synchronous compensator (STATCOM), which is a FACTS device that ensures the supply of a dynamic, precise and adjustable amount of reactive power to the AC power system that the transformers are connected to.
Another key trend in the power transformer segment is the use of smart or digital transformers, which are an integral part of digital substations. They independently regulate voltage and maintain contact with the smart grid in order to allow remote administration and real-time feedback on power supply parameters. These transformers are equipped with intelligent electronic devices, and intelligent monitoring and diagnostics features. The benefits of digital substations are plenty, including better productivity and functionality, greater reliability of assets and safety of substation operators, and lower cost and space requirements.
Towers and structures
On the tower design front, in order to minimize RoW requirements, reduce the visual impact, save costs and ensure ease of construction and installation, new tower designs such as pole structures, narrow-base towers and multicircuit towers are being adopted by utilities. Monopoles offer faster installation and greater flexibility in design. They can withstand extreme weather conditions and require much less space than lattice towers, thus significantly reducing the RoW requirement. Powergrid has been installing monopoles since 2008-09 to save space and avoid tree felling. It is also using symmetrical monopoles at its 320 kV HVDC Pugalur-Thrissur line. Delhi Transco Limited has installed monopoles in some areas. Utilities are also using narrow-base lattice towers for space optimisation. APTRANSCO has deployed narrow-base towers with a base roughly equal to that of a monopole in narrow corridors and on traffic dividers in cities. Another emerging transmission tower design is multicircuit towers, which are designed to carry three, four or even six circuits to transmit bulk power at an economical rate. They are used at high voltage levels, particularly in forest areas and at substation entries.
Pre-construction surveys are an essential step in the development of transmission projects. They help identify the exact and shortest possible route of the transmission line and the number of towers required along the route. Owing to the time-consuming nature and inaccuracy of conventional surveying techniques such as walkover surveys, utilities are now deploying LiDAR technology and drones for surveys. LiDAR is used in aerial surveys for topographic mapping. Powergrid is deploying helicopters equipped with LiDAR and thermovision cameras for aerial patrolling, and operations and maintenance of transmission lines and towers. Sterlite Power has also deployed LiDAR technology for its Bhopal Dhule transmission project. Besides, utilities are using drones to assess potential site locations, design site layouts, generate 3D visualisations and make RoW estimations.
To conclude, technological advancements in the transmission infrastructure segment are expected to play a vital role in efficient network upgrade and expansion. This is expected to help in meeting the government’s objective of 24×7 power for all, maintaining a congestion-free transmission network and ensuring grid stability. However, since these technologies entail high costs, identifying the best-suited technology through a detailed cost-benefit analysis is essential to obtain the desired results and meet utilities’ needs and requirements.