The transmission segment in India has witnessed phenomenal growth over the years in terms of network length/ capacity as well as technology. The formation of a national grid, increase in interregional capacity from near zero to over 110,000 MW and the green energy corridors have been important developments in the segment over the past two decades. The voltage level has also increased from 220 kV to 765 kV, ±800 kV HVDC and 1,200 kV and advanced technology such as voltage source converters (VSC) and flexible alternating current transmission system (FACTS) are being deployed in the transmission system.
Going forward, the grid is expected to evolve further with changes in the power sector. The changes in the energy mix with a growing share of renewables and declining share of fossil fuels, growth of distributed generation and battery storage, electrification of sectors such as transport, and expansion of regional interconnections will make the power grid increasingly complex. The management and control of a highly complex transmission system will require the implementation of advanced smart grid and digital technologies. There will be a need for greater automation to enable real-time control for load management and power despatch. Moreover, the transmission grid needs to become resilient to deal with the variability of renewables and the resultant frequency fluctuation with the decline in inertia. Digitalisation will be essential in the coming years, with sensors capturing information about the equipment and grid parameters.
A look at the key smart grid initiatives and digital technologies being implemented in the transmission segment…
Digital substations are equipped with IEDs (intelligent electronic devices) with integrated information and communications technology, non-conventional instrument transformers (NCITs), merging units and phasor measurement units (PMUs) that are interfaced with the process bus and station bus architecture. These substations offer several benefits. Digital substations completely eliminate the need for switchyard panel rooms, thus significantly reducing project commissioning time. They also permit remote administration, help in independently regulating voltage through smart transformers and provide real-time feedback on power supply parameters. Other intangible benefits of digital substations include improved productivity and functionality, greater asset reliability, substation operator safety, and lower cost and space requirements. It has also been observed that the installation of modern equipment to digitalise substations increases system availability while optimising manpower requirements.
In December 2020, Power Grid Corporation of India Limited (Powergrid), in collaboration with Bharat Heavy Electricals Limited, successfully commissioned India’s first indigenously developed 400 kV optical current transformer and digital substation components at the 400/220 kV Bhiwadi substation. It comprised a switchgear controller, an NCIT (optical CT), GPS, ethernet switches, a distance-protecting relay and a capacitor voltage transformer merging unit. This collaborative research and development project was a major step towards the complete digitalisation of the substation as well as towards indigenisation. Powergrid has also commissioned a digital substation based on IEC 61850 process bus technology at Malerkotla, Punjab. The technology provides flexibility in engineering, paves the way for faster commissioning, reduced downtime, enhanced diagnostics and ease in troubleshooting during asset management.
In recent times, the wide area monitoring system (WAMS) has emerged as an efficient solution for addressing reliability and operational concerns in power supply and generation. It enhances real-time power transfer capabilities, enables automatic corrective actions such as adaptive islanding, allows better visualisation through state measurements, provides decision support tools, etc. The basic infrastructure of WAMS technology comprises PMUs, wideband communication network and phasor data concentrator (PDC) units. As part of WAMS implementation, PMUs are dispersed throughout the electricity grid and placed at strategic locations in order to cover the diverse footprint of the grid. The PDC unit is installed at the central location. It collects information from PMUs and sends out alerts and alarms in emergency situations. It facilitates the development of different types of analytics for smooth grid operation. The PMU data is also transmitted to the supervisory control and data acquisition system. WAMS technology requires a high bandwidth communication network for rapid data transfer, which should match the frequency of sampling of the PMU data. The communication infrastructure is a critical backbone in the WAMS architecture. The PMU devices are then connected to one or many control centres over the communication network.
Powergrid is carrying out the implementation of the smart grid technology in the power system through installation of PMUs on extra high voltage (EHV) substations on a pan-India basis, integrated with control centres for WAMS and real-time monitoring of grid parameters. In July 2018, Powergrid, in collaboration with GE T&D India Limited, commissioned the WAMS for the northern region grid. This marked the first leg of a mega grid stabilisation project (unified real-time dynamic state measurement) and will enable Powergrid to monitor power flow across 110 substations in the northern region grid and respond to fluctuations within a fraction of a second. Once fully commissioned in all five regional grids, the WAMS solution will be the world’s largest, comprising 1,184 PMUs, 34 control centres and 350 substations.
Gujarat Energy Transmission Company Limited is also implementing WAMS at its state load despatch centre (SLDC) to deal with challenges in system operations, owing to the increasing integration of renewable energy in the state grid. Under WAMS Phase I, 113 PMUs were installed in the state at 25 strategic locations – ten 400 kV substations, thirteen 220 kV substations, two generating substations at Adani Power’s Mundra thermal power projects, and at the Wankabori thermal power station. Under Phase II, 62 locations covering all 400 kV and major 220 kV interface points, and renewable-rich pockets will be covered to enhance monitoring of the grid. Upgradation of analytics with the implementation of WAMS Phase II PMU at the SLDC control centre is also being explored.
Remote monitoring of substations and other equipment is also gaining traction as it helps utilities reduce manual intervention. Powergrid has set up the National Transmission Asset Monitoring Centre (NTAMC) at Manesar, Haryana, to facilitate remote operation of the company’s transmission system and monitoring of various parameters on a real-time basis at regional and national levels. Likewise, regional transmission asset monitoring centres have been set up at various locations across the country. These state-of-the-art centres are manned round the clock by experts for effective monitoring and management of transmission assets. Remote management of substations has proved to be immensely beneficial during 2020-21 to ensure uninterrupted supply of power despite the Covid-19 pandemic. During financial year 2020-21, eight additional EHV substations were integrated with the NTAMC for remote operation, taking the total remotely monitored substations to 242.
Smart grid technologies can be deployed for asset management by transmission utilities. Condition-based monitoring of substation assets can be undertaken through a combination of intelligent electronic devices, smart sensors, fully secure communications/open protocols and intelligent head-end, which is a user-friendly software. A prerequisite is a detailed condition evaluation of the installed equipment. The actual equipment condition is continuously assessed by the online detection of significant working device parameters and their automatic comparison with average values and performance. Maintenance is carried out when certain indicators give the signal that the equipment is deteriorating and failure probability is increasing. This strategy, in the long term, helps in drastically reducing the costs associated with maintenance, thereby minimising the occurrence of serious faults and optimising the management of the available economic resources. Reliability- centred maintenance is the third method considered by utilities. Substation reliability modelling enables customers to understand the risk associated with each of its components. Reliability-centred maintenance is based on optimising maintenance investment by limiting the execution of unnecessary tasks while focusing on substation components, which represent a higher risk. This evaluation includes failure mode and effect analysis to determine the best maintenance strategy to maintain reliability. The life cycle cost-based evaluation of this strategy has to be derived from condition-based maintenance analysis.
The way forward
As the adoption of digital and smart grid technologies continues in the transmission segment, utilities need to focus on cybersecurity as well. Taking cognisance of cyberthreats that can hamper the power system’s functioning, the Central Electricity Authority released cybersecurity guidelines for the power sector in October 2021. The guidelines lay down a cyber assurance framework, strengthen the regulatory framework, put in place mechanisms for early warning of security threats, vulnerability management and response to security threats, and secure remote operations and services. Going forward, it is imperative for utilities to have cybersecurity as a critical element of their smart grid roadmap. N