Substations are indispensable equipment. Because of their role of receiving high-voltage electricity, moderating it and re-routing it to consumers, they are situated right at the crossroads of the transmission and distribution (T&D) segments. Emerging developments incorporating digital technology, artificial intelligence and machine learning are poised to enhance the efficiency and technical resilience of the substations, while optimising their workings costs. The ongoing technological advancements in the battery storage industry and the rapid growth of renewables have obliged players in the T&D segment to gradually upgrade their systems and move towards digital substations, which are simpler, more compact and safer than conventional substations. Digital substations have optical fibre communication backbones in place of traditional copper connections. With benefits such as increased flexibility and availability, reduced cost, and lower risk and environmental impact, digital substations are among the key emerging trends in the power industry.
Digital substation architecture
On the digital side, the operations begin from the station bus, which facilitates communication between station-level systems such as the supervisory control and data acquisition gateway and local human machine interface, digital instrument transformers (DITs), and bay-level equipment such as bay controllers and protection relays. The station bus is also equipped with Generic Object Oriented System-wide Event messaging, enabling a smoother information flow. DITs, unlike their conventional counterparts, can detect inaccuracy and range issues, and intelligent electronic devices (IEDs) use multicast transmission to local devices or remotely stationed control operators in order to visualise the operational status of the substation. In this manner, all components of the digital substation interact with each other to exchange data and communicate in real time.
In terms of the physical architecture and changes to digital substations, the biggest transformation has taken place in the re-organisation of substation design through the addition of several new components such as hybrid switchgear, non-conventional instrument transformers, merging units and phasor measurement units. The deployment of the IEC 61850-9-2-based process bus facilitates the replacement of traditional copper cables with fibre optic cables, and the usage of a common protocol allows for interoperability among various makes of IEDs. Process bus architecture can ease maintenance and troubleshooting in the future, significantly reducing restoration time in case of an eventuality.
Benefits of digital substations
Digital substations incorporate integrated information and real-time communication technologies, which are interfaced with process bus and station bus architecture. Installing digital substations will primarily enable integration of real-time data and data analytics into the system, thereby facilitating more accurate decision-making, reduced downtime and enhanced diagnostics. Real-time diagnostics, in turn, help eliminate the requirement of troubleshooting and reduce the cost and time expended on repairs and maintenance through timely diagnosis of problems in the substation.
Converting existing substations to digital substations also bestows a space advantage since digital substations require less space than conventional substations. Further, smart digital substations can especially be useful during extreme weather events, since they can determine methods of effectively rerouting electricity and thereby minimise damage and destruction to assets.
Digital substations are the need of the hour, given the rapid adoption of renewable power generation. Renewable energy technologies are intrinsically associated with intermittency and ramp-up issues, requiring substations to effectively manage load and demand, taking into account real-time developments – something that digital substations are capable of doing through seamless supply of electricity according to demand and supply dynamics.
Digital substations in India
Power Grid Corporation of India Limited (Powergrid) commissioned the first substation based on the IEC 61850 standard in 2007. The utility’s first pilot using the IEC 61850-based process bus was commissioned at the Bhiwadi 400/200 kV substation in 2014. In July 2020, Powergrid commissioned a 400 kV digital substation in Punjab, making it India’s first fully digital commercial substation. The complete digital upgrade of the Malerkotla substation required updating the protection and control systems – including the bus bar protection system – for the entire substation. This substation was constructed using the insights generated from the pilot digital substation in Bhiwadi.
The way forward
The consumers, the government, T&D utilities and the manufacturing companies should collaborate to devise norms and standards in order to ensure steady, phased execution of digital substation technology. They also need to astutely factor in the financial and operational costs and challenges that can potentially hinder its uptake, and effectively establish necessary incentives.