The country’s transmission segment is expected to grow considerably in the coming years to facilitate the integration of a large quantum of renewable energy. India has envisaged increasing its non-fossil fuel-based installed electricity generation capacity to 500 GW by 2030.
In order to meet the target, it is necessary to connect high solar and wind energy zones to the interstate transmission system (ISTS) to evacuate and transfer power to load centres. As per the Central Electricity Authority’s recently released Transmission Plan for Integrating 500 GW of renewable energy capacity, the length of the transmission lines and substation capacity planned under the ISTS for integration of additional wind and solar capacity by 2030 have been estimated as 50,890 circuit km and 433,575 MVA respectively, at an estimated cost of Rs 2,442 billion. With this addition, the interregional transmission capacity will increase to 150,000 MW by 2030 from 112,250 MW at present. Therefore, the transmission grid will grow significantly from the present level of 463,758 circuit km and 1,111,607 MVA.
Given the intermittent nature of renewable energy generation as it is dependent on weather conditions, it is likely to pose challenges to grid operators in terms of forecasting and meeting the load. Often, weather conditions change unpredictably and this requires grid operators to have enough flexibility to react to generation trends, failing which power shortages and blackouts could ensue. In addition, renewable resources lack an automatic frequency response mechanism, which are present in large rotating thermal turbine generators and, therefore, they cannot adapt to reactive power transients on high voltage transmission lines. Larger voltage swings due to changes in both generation and load can cause grid instability. To overcome this, technologies such as Flexible AC Transmission Systems (FACTS) with more real-time control, distributed energy resource management for utilities and energy storage solutions will be important.
The management of such a vast and complex transmission network requires the adoption of advanced digital solutions, supervisory control and data acquisition (SCADA), remote monitoring technologies and sophisticated sensors, as well as predictive maintenance strategies. Power Line takes a look at some of these network management technologies being implemented in the transmission segment…
Predictive asset management
Transmission utilities are increasingly moving to predictive maintenance strategies, which call for actions to be taken based on equipment health forecast through the use of data analytics tools for objective decision-making. Some of the key factors considered under the strategy include design and voltage class, past operational history, failure trend, service age and health index. For instance, Power Grid Corporation of India Limited (Powergrid) has taken pioneering initiatives in this regard. The utility has embarked upon a digital transformation journey, starting with the integration of online sensors at the equipment level in 2012, followed by the launch of the National Transmission Asset Monitoring Centre (NTAMC) in 2014. In 2017-18, GIS mapping of lines, tablet-based (Patrosoft) patrolling of transmission lines and automatic fault analysis system was implemented. In the ensuing years, the utility launched the Powergrid Asset Life Management System (PALMS), commissioned the first 400 kV digital substation at Malerkotla, adopted enhanced protection system control and introduced a predictive asset maintenance philosophy.
PALMS is a web-based portal developed in-house for real-time health assessment of about 3,600 transformers/reactors in Powergrid. It categorises critical equipment based on operational experience and latest international standards. Similarly, in-house apps and dashboards have been developed for network assessment and to provide a bird’s-eye view to the management of asset management issues. This includes the PG DARPAN app (Powergrid Digital Application for Routine Patrolling and Assessment of Network) for transmission line patrolling, which has been in use since August 2021. The portal features a rich, highly customisable dashboard, which facilitates ground patrolling of transmission lines and generation of reports helping asset managers monitor and take corrective action quickly.
Moreover, Powergrid’s NTAMC at Manesar, Haryana, facilitates 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 2021-22, two additional extra-high voltage (EHV) substations were integrated with the NTAMC for remote operation, taking the total remotely monitored substations to 264.
In addition, a centralised relay database management system has been introduced to improve the efficiency of relay settings management and save man-hours in the operation and maintenance of assets.
WAMS
The wide area monitoring system (WAMS) has emerged as an efficient solution for addressing reliability and operational concerns in power supply. It enhances real-time power transfer capabilities, enables automatic corrective actions such as adaptive islanding, allows better visualisation through accurate measurements as well as provides decision-support tools. The basic infrastructure of WAMS comprises phasor measurement units (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 SCADA 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 several control centres over the communication network.
Powergrid implementing smart grid technology in the power system through the installation of PMUs on 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 WAMS for the northern regional grid. This marks 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 (GETCO) is also implementing WAMS at its state load despatch centre (SLDC) to deal with challenges in systems 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 – 10 substations of 400 kV, 13 substations of 220 kV, two generating substations at Adani Power’s Mundra thermal power projects and at the Wanakbori 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.
FACTS
FACTS devices such as static VAR compensators and static synchronous compensators (STATCOM) are expected to play a key role in network management as greater integration of renewables into the grid is achieved. These power electronic devices provide dynamic voltage support, thereby ensuring grid reliability and voltage stability. Powergrid has already installed advanced STATCOMs in the 400 kV network as well as thyristor controller reactor (500 MVAR) in Kurukshetra to improve the static as well as dynamic voltage profile of the Kurukshetra high voltage direct current station.
SCADA
SCADA is a helpful tool in power transmission because of its applications in enabling complete visibility of the network for load management, reserve monitoring of generators, hydro-thermal coordination, economic load despatch, state estimator, EMS reactive power management, renewable energy handling, feeder-wise supply monitoring, distribution-side management and smart grid. It is an effective tool for utilising the power grid during contingencies and avoiding voltage collapse, cascade tripping, load generation mismatch and blackouts in the grid. GETCO has undertaken a smart grid project using SCADA. The system includes an automated distribution management system, a renewable energy management centre, an energy accounting and scheduling system and smart grid feeder management. Meanwhile, Karnataka Power Transmission Corporation Limited’s SCADA system has an automatic generation control (AGC) module, which helps to continuously balance the system, maintain a constant frequency and eliminate area control error.
Going forward, with the influx of more and more alternative sources of generation, network management solutions will play a crucial role in maintaining reliability and stability of the transmission grid.