In the field of digital substations, there has been a paradigm shift in the way control and protection systems are operated and maintained. The overall availability of these systems can be impÂroved through online testing of control and protection schemes from a centraÂliÂsed access point. This enables advanÂcÂed diagnostics, superior visualisation of information flow, reduced commissioning time and a reduced environmental footÂprint. In a digital substation, the opeÂrations are managed by intelligent electronic devices (IEDs), interconnected through communications networks. MiÂcroprocessors have been introduced into substation components to improve the performance of the main product.
Broadly, digital substation infrastructure comprises three levels. The station level encompasses substation control system equipment such as servers, human-maÂchine interfaces, gateways and GPS. This level supports data exchange within the substation as well as remotely. Next is the bay level, which covers system protection and control functions. It governs interfacing with field equipment and peer deviÂcÂes (GOOSE), as well as station-level deÂvices on the client server. Lastly, there is the process level, which covers primary equipment and interfacing devices. It manages analog signals from merging units to IEDs by sample value, and takes binary signals from the intelligent control unit by GOOSE to IEDs, and vice versa. A digital substation focuses on digitalisation of both the station level and the process level by converting analog measurement data and binary status information into digital data. This involves the use of ethernet-based communication to exchÂanÂge information for protection, monitoring, control and measurement. The process bus replaces hard-wired connections with communication lines, enabÂling the deployment of ethernet-based optical fibre networks instead of copper wiring between intelligent electronic deÂvices and various otÂher equipment. Due to the uniform comÂmunication protocol IEC 61850, interoperability of products across manufacturers and peer-to-peer services is now also possible.
Digital substations have numerous adÂvanÂtages. They are easier and simpler to install, as they require much less wiring. The process is standardised, which maÂkes it easier to deploy new applicatiÂons. There is no need for duplicating hardware, which reduces capex requirements. Digitalisation of substations also leads to improved system reliability, measurement accuracy and recording of information. Commissioning and operations improve as well. It becomes easier to inÂcorporate modern electronic current transformer and voltage transformer sensors. There are many upcoming technoÂlogies that can enable better digital adaptation. Technology providers have come up with advanced sensing techniques to detect, and assess the extent of, potential equipment degradation. These techniÂques convert substation equipment inÂforÂmation into digital formats to be anaÂlysed. The latest high-sensitivity seÂnÂsors study the partial discharge to idÂenÂtify signs of potential degradation that woÂuld otherwise be difficult to deÂteÂct, and that too, with precision.
Power Grid Corporation of India Limited (Powergrid) has been at the forefront of implementing process bus-based full digital substation technology in the coÂuntry. As early as 2020, Powergrid commissioned a 400 kV digital substation in Punjab, making it India’s first digital 400 kV substation. It uses IEC 61850 process bus technology, and was constructed by retrofitting the existing, conventional Malerkotla substation, which had been in operation since 1992. Powergrid is also setting up digital gas-insulated substations at the 765 kV level. Existing digital substations can undergo digitalisation without disrupting the operations while implementing and adopting newer technologies. This can be acÂhieved with well-planned capex and opex streams. BrownÂfield substations perform better with these technologies, which can also reduÂce maintenance expenses and eventually enable quicker returns on investment. They also help increase station lifespan and serviceability. Notably, Powergrid has initiated the upgradation of the conventional protection and control system at its old 400/220 kV Kanpur substation to an IEC 61850 process bus-based full digital system.
Conclusion
While digital substations have numerous benefits, their implementation comes with a set of challenges. Although digital substations do not have any direct imÂpact on the tariff, compared to conventional hardware technology, digitalisation is expensive. Digital substations have a single centralised system; hence, a cyÂberattack on any one substation can compromise the whole grid. This creates a need for islanding systems, which meÂans that each individual system needs to be enabled to isolate itself from the main grid. The main control system has to be placed away from the major networks, further protecting the distribution system and generation plants from intrusion. Apart from this, for efficient design and testing of any digital substation, selecting the right tools is important. OfÂten, the involvement of multiple vendÂors creates incongruencies in configuration. Thus, coordination and the use of evolÂved technologies are necessary. Training the workforce to operate these substations is another critical step in ensuring their successful uptake.
Overall, with adequate manpower training and improved cybersecurity, digital substations will go a long way in improving the overall management of substation operations, enhancing the reliability of power supply and minimising outages.