The new and emerging digital technologies as well as artificial intelligence and machine learning solutions are increasingly being incorporated throughout the electrical system, including substations, to enhance efficiency and bolster technical resilience. Digital substations provide immense benefits in terms of grid safety and reliability as well as improved operational performance. Further, extraneous technological advancements in battery storage and rapid growth of variable renewable energy are increasingly driving transmission and distribution utilities to upgrade their equipment and adopt digital substations.
Digital substation architecture
Digital substation architecture comprises two types of components – digital and electrical – and modifies operations dynamically at two different levels. Integrating a digital substructure layer to the existing substation system results in improved granularity of informational flow at higher speed, helping the system to respond more promptly to changing demand and supply dynamics. Further, this substructure transforms the real operational dynamics by repurposing components such as switchgear, and current and voltage transformers connected to the control and protection layer of the substation so as to ensure superior performance.
In terms of the physical architecture, in a digital substation, one of the key transformations pertains to the reorganisation of substation design through the addition of several new components such as hybrid switchgear, non-conventional instrument transformers, merging units and phasor measurement units. Moreover, digital substations require the replacement of multitudinous copper wiring with efficient optical fibre, in turn, raising efficiency, reducing the carbon footprint and reducing costs. The hard-wired connection uses expensive copper wiring. However, replacing it with optical fibre cable embedded with sensors enables the substation to process data at source and communicate it to other devices.
Digitalised substations can continuously monitor high and medium voltage switchgear as well as substation transformers while performing real-time simulation and diagnostic functions. Consequently, they ensure proactive management of assets and contribute towards enhancing the life of equipment. Digital substations offer a space advantage as they require less space than conventional substations. For instance, a hybrid switchgear is compact. It combines the functionality of air-insulated switchgear and SF6 gas-insulated switchgear (GIS).
The digital solution eliminates the requirement for conventional relays and protection equipment, resulting in a reduction in the number of control panels. Further, space saving can be achieved through optimised engineering design using digital assets. The net result is the ability to offer a more compact substation control building, reducing the overall footprint of the substation, limiting civil construction activities and generating further cost savings. It also reduces the cost of construction and potentially reduces the right-of-way requirement, especially in urban areas. Moreover, the compactness of equipment aids in reducing the copper cable length in substations by 80 per cent while accelerating the pace of installation by 60 per cent.
Digital substations in India
Powergrid, in collaboration with BHEL, has successfully commissioned India’s first indigenously developed 400nkV optical current transformer along with digital substation components (IEDs and SCADA) at the 400/220 kV Bhiwadi Substation. Earlier, in July 2020, Powergrid commissioned a full digital substation (including busbar protection) with an IEC 61850 process bus-based protection automation and control system and successfully demonstrated it by retrofitting a conventional control and protection system at the 400/220 kV Malerkotla substation. This technology provides a lot of flexibility in engineering, faster commissioning, reduced downtime and cost, enhanced diagnostics and ease of troubleshooting during asset management. The complete digital upgrade of the Malerkotla substation required updating the protection and control systems, including the busbar protection system, for the entire substation. This substation in Malerkotla was constructed using the insights generated from the pilot digital substation in Bhiwadi. Based on its experience from recent projects on process bus technology, Powergrid has initiated a project for retrofitting conventional protection and control schemes with advanced automation systems.
In April 2022, ABB India commissioned a digital substation product and digital system factory in Vadodara, Gujarat. This factory will manufacture products such as relays, while the solutions range from centralised protection and control systems and distribution automation, to bus transfer systems and arc protection for the electrical distribution network. The establishment of reliable domestic supply chains for the production and maintenance of digitalised substation components such as disconnector circuit breakers and fibre optical sensors will ensure that the prices are affordable and make it easier to source, maintain and repair equipment for these new technologies.
Issues and challenges
The process of installing and retrofitting substations and transforming them into digital substations took much longer than expected because of a combination of financial, technical and operational issues encountered by Indian utilities.
The augmentation of substations was a major challenge as utilities had IEDs from different vendors and thus integrating them to interoperate was an economic and technical problem. In some cases the control command from the HMI to the bay controllers of different vendors did not work, whereas in other cases, the IEDs had subscription issues. Utilities also faced the obstacle of ensuring Windows version compatibility with the new version of IEDs. The lack of coordination between the IEDs and GOOSE also added to the difficulties. The non-availability of devices was another pressing issue. The non-availability of proper logical nodes and sufficient ports for IEDs had an impact on the pace of installation and subsequent operations of the entire network.
Moreover, adherence to IEC 61850 standards has proved to be burdensome considering their rigid specifications and complex requirements, which have rendered it extremely difficult for manufacturers to devise components that are cost effective and tailored to meet customer expectations.
Meanwhile, the emaciated financial condition of Indian discoms has prevented them from investing in digital substations. This is further compounded by the reluctance of financial institutions to lend to discoms given their extant non-performing assets.
The way forward
Digital substations have paved the way for utilities to deploy substation-related infrastructure rapidly while occupying less space. Additionally, these utilities are expected to witness improvement in their operational performance given the enhanced efficiency, superior reliability and safety offered by these substations. These advantages will also permeate across the grid system. The trajectory of India’s renewable energy transition will be determined to a great extent by the rate at which digital technologies are deployed across the rest of the grid as solar and wind energy are intermittent and increase load volatilities in the grid. Hence, the extent of digital substation adoption in India will improve system resilience and efficiency substantially without necessitating full-scale modernisation of all the components in the grid architecture.
Overall, it is vital for consumers, government, distribution utilities, transmission utilities and manufacturing companies to collaborate and devise a mutually beneficial set of institutional norms and standards to ensure steady and phased adoption of digital substation technology.