Modern Substation Technologies

Taking the digital route to enable a smarter grid

The transmission segment, which is pivotal to the efficient operation of the power sector, is at the crossroads of higher efficiency, owing to the ongoing implementation and commissioning of digital substations, along with other technological upgrades. Digital substations incorporate intelligent electronic devices (IEDs) with integrated information and communication technology, non-conventional instrument transformers (NCITs), merging units, and phasor measurement units that are interfaced with the process bus and station bus architecture.

NCITs make a substation simpler, cheaper, smaller, more efficient and safer by replacing secondary wirings and eliminating the dangers associated with open current transformer (CT) circuits, and electrical hazards in general. The IED is a microprocessor-based protection and control device for power equipment such as circuit breakers, transformers and capacitor banks. The deployment of the IEC 61850-9-2 based process bus facilitates the replacement of traditionally used 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 the restoration time in case of an eventuality. Another benefit of the digital substation system is that the data names in an IEC 61850 device are not dictated by the device vendor or configured by the user, but are instead defined in a standard and provided in a power system context, hence making it convenient for an engineer to immediately identify its meaning without having to define mappings that relate index numbers and register numbers to system data. This gives the technology an advantage over conventional remote terminal unit-type communication.

For Power Grid Corporation of India Limited (Powergrid), the country’s largest power transmission company, modernising its substations has been a key area of focus. In a recent development, Powergrid, in collaboration with Bharat Heavy Electricals Limited (BHEL), successfully commissioned India’s first indigenously developed BHEL-made 400 kV optical current transformer and digital substation components at Powergrid’s

400/220 kV Bhiwadi substation and energised it on September 12, 2020. It comprised a switchgear controller, an NCIT (optical CT), GPS, Ethernet switches, a distance-protecting relay, and a capacitor voltage transformer (CVT) merging unit. This collaborative research and development project was a major step towards complete digitalisation of the substation automation system, as well as indigenisation. Meanwhile, a commercial 220/66 kV digital substation project is currently being implemented in Chandigarh, and a digital retrofit project for a 400/220 kV substation at Malerkotla in Punjab is expected to be commissioned soon, equipping the substation to meet the IEC 61850 standard.

There are several advantages of installing a digital substation. For instance, the IED, the CT, the CVT circuit and the DC control circuit can each be tested in isolation, allowing for better identification of problems, if any. Advanced diagnostics and visualisation can also be achieved this way. Furthermore, digital substations completely eliminate the need for switchyard panel rooms, as a result of which the project commissioning time is significantly reduced. They also permit remote administration, help to independently regulate voltage by utilising smart transformers, and provide real-time feedback on power supply parameters. Other, intangible benefits of digital substations include improved productivity and functionality, greater reliability of assets and substation operator safety, and lower cost and space requirements. It has also been observed that the installation of modern equipment to digitalise substations brings increased system availability while optimising manpower requirements.

Other emerging technology trends

Another technology trend shaping the substation segment is  hybrid gas-insulated substations (GIS). A hybrid GIS has an air-insulated substation (AIS) busbar with a GIS bay module that has rapid deployment and expansion capabilities. Transmission companies are also deploying fault current limiters in substations, essentially installing series reactors (air core dry type) on the line and bus to control power system fault levels. Interstation tele-protection communication is being used for long distance communication and signalling. In addition, online monitoring and diagnostic tools such as online dissolved gas analysis and online partial discharge monitoring for GIS are being used. The other interesting upcoming development in the substation sector is the introduction of prefabricated substation solutions, which allow for faster installation, reduced costs and dependence on civil works, and lower risk of cost and time overruns. In addition, these projects have a 95 per cent lower space requirement as compared to AIS solutions, owing to their compact layout and usage of gas-based insulation instead of air-based insulation.

Overall, the grid is undergoing a significant transformation. Substations, which are an integral part of the transmission grid, need to keep up with these changes and adopt advanced technologies to make the future grid more resilient and flexible.

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