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 improved through online testing of control and protection schemes from a centralised access point. This enables advanced diagnostics, superior visualisation of information flow, reduced commissioning time and a reduced environmental footprint. In a digital substation, the operations are managed by intelligent electronic devices (IEDs), interconnected through communications networks. Microprocessors 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-machine 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 devices (GOOSE), as well as station-level devices 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 exchange information for protection, monitoring, control and measurement. The process bus replaces hardwired connections with communication lines, enabling the deployment of ethernet-based optical fibre networks instead of copper wiring between intelligent electronic devices and various other equipment. Due to the uniform communication protocol IEC 61850, interoperability of products across manufacturers and peer-to-peer services is now also possible.
Digital substations have numerous advantages. They are easier and simpler to install, as they require much less wiring. The process is standardised, which makes it easier to deploy new applications. 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 incorporate modern electronic current transformer and voltage transformer sensors. There are many upcoming technologies 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 techniques convert substation equipment information into digital formats to be analysed. The latest high-sensitivity sensors study the partial discharge to identify signs of potential degradation that would otherwise be difficult to detect, 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 country. 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 achieved with well-planned capex and opex streams. Brownfield substations perform better with these technologies, which can also reduce 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 impact on the tariff, compared to conventional hardware technology digitalisation is expensive. Digital substations have a single centralised system; hence, a cyberattack on any one substation can compromise the whole grid. This creates a need for islanding systems, which means 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. Often, the involvement of multiple vendors creates incongruencies in configuration. Thus, coordination and the use of evolved 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.