The Indian power transmission segment is taking large strides in adopting new technologies to enhance power evacuation and maintain a robust power grid, with the increasing renewable energy integration. Transmission utilities have been deploying advanced technologies in response to spatial constraints, limitations on existing line capacity and environmental concerns posing significant challenges to grid expansion and modernisation.
New technologies for substations
- Hybrid substations: This techno-economic solution is for optimum land utilisation and for the augmentation of existing substations. Modern switchgear for hybrid substations utilises sealed enclosures filled with pressurised sulphur hexafluoride gas. This technology offers a space-saving advantage compared to traditional air-insulated substations, while maintaining a similar footprint to gas-insulated substations. Hybrid substations have already been implemented in India at Hapur and Ghaziabad substations by Uttar Pradesh Power Transmission Corporation Limited.
- Digital substations: This technology digitalises protection, control and monitoring data of primary processes after measurement. It departs from conventional substations by incorporating a dedicated communication protocol known as IEC 61850. This protocol facilitates seamless exchange of digital information amongst all substation equipment via a dedicated communication network, often referred to as a process bus or station bus. It has non-conventional instrument transformers with digitalised sensor technology. Digital substations leverage merging units and process bus communication to achieve digitalisation and offer cost savings, safety improvements and reduced space requirements.
- Mobile substations: Vehicle-mounted mobile substations enable immediate power restoration during disasters. They comprise a trailer, incoming and outgoing high-voltage and low-voltage hybrid switchgears, a power transformer and associated connectors.
- VSC-based HVDC: Voltage source converter (VSC)-based high-voltage direct current (HVDC) can enhance and increase power transfer per meter of right of way (RoW). Forced switching converters, a new HVDC technology, use VSCs with controllable valves. Unlike traditional HVDC, these converters offer independent control of active and reactive power, voltage and frequency through pulse width modulation. This allows operation with weak alternate current (AC) systems and even black start capability.
- FACTS devices: Flexible AC transmission systems (FACTS), categorised as shunt or series compensation, addresses the challenge of power flow management and optimal infrastructure use rising due to the growing presence of renewable energy and expanding grids. Shunt devices such as static var compensator and static synchronous compensator (STATCOM) manage voltage fluctuations by dynamically adjusting reactive power at connection points. STATCOMs, using VSCs, offer even greater control over both active and reactive power, allowing them to function in weak AC systems. Series compensation devices, fixed or thyristor-controlled, are also employed within the Indian power system.
- Phase shifting transformer (PST): To maximise transmission line efficiency, managing power flows is essential, achievable through PSTs. PSTs control power flow across different lines by adjusting phase displacement.
- Static synchronous series compensators (SCCC): SCCC enhances system utilisation by managing power flow on meshed network. SSSC solutions, deployed in series with transmission lines, either divert power away from the line or inject power into it, thus alleviating overloads. SSSCs inject a voltage in quadrature with the line current, effectively mimicking adjustments to line impedance or phase angle, particularly useful in scenarios such as unequal power flow or varying voltages in parallel circuits.
- Grid forming inverters: Grid-forming inverters offer the ability to initiate a black start, for restoring power post-grid failures. By autonomously re-establishing grid operation, these inverters minimise downtime, prevent economic losses and bolster grid resilience. They also provide stability to grids transitioning away from conventional generation and help maintain grid frequency and voltage, ensuring consistent electricity supply despite intermittent renewable sources.
New technologies for transmission lines
- Insulated cross arm (ICA): ICA can address the concern of growing electricity demand by modifying towers for higher voltages. It offers significant advantages in reducing insulator swing, raising conductor height without requiring additional tower height, and resolving ground clearance issues on existing transmission lines. Adoption of high temperature low sag conductors with ICA further enhances power transfer capability by increasing conductor height above ground. While not widely utilised in the Indian transmission system, utilities in Telangana and Kerala have implemented ICAs to upgrade lines, reduce RoW, increase clearance to buildings and enhance ground clearance, offering potential benefits for voltage upgradation and compact tower design.
- EHV XLPE cable: To circumvent RoW challenges, utilities turn to EHV cross-linked polyethylene (EHV XLPE) cables, although their use is limited by technical constraints and vulnerability to failure at joints and terminations, resulting in system outages. Gas-insulated lines (GIL) have emerge as a promising alternative in areas with short lengths and high current/power flow demands. While manufacturing facilities for XLPE cables up to 400 kV exist in the country, GIL is considered advantageous for specific applications.
- High performance conductors (HPCs): Unlike aluminium conductor steel reinforced (ACSR) and all aluminium alloy conductors, HPCs operate at higher temperatures, enabling increased ampacity without exceeding existing size and weight constraints. They can carry 1.5 to 2 times more current than ACSR conductors, while maintaining similar tensile strength. This facilitates enhanced power transmission capacity within existing corridors and new lines, reducing construction time and costs.
- Photonic coating on conductor: Thermal limitations on overhead transmission lines can restrict capacity at 66 kV, 132 kV and 220 kV levels. Applying photonic coatings to conductors can lower operating temperatures, potentially increasing line capacity.
- Dynamic line rating (DLR): DLR technology allows for real-time monitoring of ambient conditions that can impact conductor capacity for safety compliance, which optimises grid performance for over a decade. European experiences demonstrate substantial capacity growth, sometimes up to 30-40 per cent, with proper DLR implementation, offering a cost-effective solution for congestion issues.
Tower and structures
The landscape of power transmission infrastructure is witnessing a growing trend towards the utilisation of monopole structures in strategically selected areas. This shift is primarily driven by the significant reduction in footprint. Compared to traditional lattice towers, monopoles require a smaller base installation space, even when exceeding heights of 40-50 metres. This translates to a minimised environmental impact due to a reduced land footprint. Second, it gives faster erection times due to the simpler structure of monopoles, leading to quicker project completion. Finally, it enables shorter delivery times associated with the streamlined design of monopoles that further expedites project timelines. These compelling benefits have resulted in the successful implementation of monopoles at various locations across India, demonstrating their potential as a viable and advantageous alternative to traditional lattice towers in specific applications. While installing transmission line construction in highly constrained areas such as congested urban environments, challenging terrain, or hilly regions, a long-term perspective is crucial to optimise both RoW (land use) and cost. This can be achieved by incorporating multi-circuit towers, which are designed to accommodate multiple circuits on the same structure. This significantly reduces the required RoW compared to building separate towers for each circuit. The initial construction might involve operating the lines at a voltage level below their ultimate capacity. However, the infrastructure itself is built with the future in mind, allowing for additional circuits to be strung on the same towers when needed. This forward-thinking approach with multi-circuit technology offers a space-saving and cost-effective solution for transmitting power in areas with limited space or challenging geographical features.
Communication equipment
Technologies such as phasor measurement units and wide area measurement systems offer real-time dynamic monitoring, enabling the development of control features such as remedial action schemes and system-integrated protection schemes. Utilities are also adopting advanced monitoring with asset management technologies, necessitating highly reliable communication systems with high bandwidth and low latency. Fibre optic-based communication systems such as optical ground wire are increasingly favoured for their ability to meet the high bandwidth requirements of differential protection and other communication services in 110 kV transmission lines and above.
The widespread adoption of fibre optic communication has spurred the use of associated terminal equipment such as synchronous digital hierarchy (SDH) and plesiochronous digital hierarchy, offering higher data rates and lower power requirements compared to traditional power line carrier communication gear. These terminals facilitate multi-directional linking and have evolved from circuit switching to packet switching technology such as multi-protocol label switching (MPLS), enabling dynamic routing and scalability. While SDH has been a staple, power utilities are eyeing MPLS for its operational advantages.
Surveying technologies
Pre-construction surveys are vital for planning transmission lines and substations, determining optimal routes and tower placements. Utilities are considering advanced technologies such as light detection and ranging (LiDAR) and drones for surveys, topographic mapping, site assessment, layout design and three-dimensional visualisation, improving accuracy and efficiency. Helicopters and drones equipped with LiDAR, thermal cameras and corona cameras are also utilised for aerial inspections and maintenance of transmission infrastructure.
Conclusion
The integration of these cutting-edge technologies signifies a significant step forward for India’s transmission sector. By embracing these advancements, utilities can expect enhanced capacity, minimise transmission losses and maximise power delivery, minimise the environmental footprint, real-time monitoring and control, enhance grid resilience and minimise downtime. However, the path forward requires establishing clear standards and regulations for the implementation and operation of these new systems. Looking ahead, continued advancements in areas such as automation, artificial intelligence and energy storage hold the potential to further revolutionise India’s transmission sector.