Modern business requirements call for upgraded assets that can ensure safety, reliable power supply and continued business operations. The substation and switchgear industry has witnessed technological advancements across all voltage levels. Industry players are constantly trying to develop different kinds of substations and switchgear that are more intelligent, compact, reliable and environment friendly, and require minimum installation and commissioning time. Towards this, digital substations are gaining traction across utilities. Digitalisation enables utilities to identify, prevent and rectify faults, thereby ensuring reliable power flow in the grid and to consumers. This has been made possible by the use of sensors and intelligent electronic devices (IEDs) throughout the substation including the switchyard. Further, the deployment of the IEC 61850 protocol has provided seamless communication and integration between IEDs of different manufacturers. Another key trend is the growing installation of gas-insulated switchgear (GIS) and hybrid substations in place of conventional air-insulated switchgear (AIS) substations. GIS substations are indoor type, wherein equipment is placed inside modules filled with sulphur hexafluoride gas (the insulating medium). The failure rate of a circuit breaker and a disconnecting switch in GIS is one-fourth that of AIS.
Power Line takes a look at new and emerging technology trends in switchgear and substations…
Substation technology
Digital substations: Digital substations are equipped with IEDs with integrated information and communications technology, non-conventional instrument transformers, merging units and phasor measurement units that are interfaced with the process bus and station bus architecture. These substations offer several benefits. Digital substations completely eliminate the need for switchyard panel rooms, thus significantly reducing project commissioning time. They also permit remote administration, help in independently regulating voltage through smart transformers and provide real-time feedback on power supply parameters. Other intangible benefits of digital substations include improved productivity and functionality, greater asset reliability, substation operator safety, and lower cost and space requirements. It has also been observed that the installation of modern equipment to digitalise substations increases system availability while optimising manpower requirements.
The Power Grid Corporation of India Limited (Powergrid) has successfully validated the performance of fully digital substation technology through pilot projects at Bhiwadi and Neemrana. The technology has helped in improvement of the overall availability of the system by online testing of control and protection schemes from a centralised access point. It also helps in advanced diagnostics, superior visualisation of information flow, reduced commissioning time and reduced environmental footprint. In 2020-21, it commissioned a fully digital 400/220 kV substation (including bus bar protection) with IEC 61850 process bus-based protection automation and control system at the 400/220 kV Malerkotla substation in Punjab. With this, Powergrid has become one of the very few utilities in the world to retrofit a complete substation with full digital technology. Currently, implementation of another fully digital substation project is under way at Chandigarh.
GIS and hybrid substations: A key trend is the growing installation of GIS and hybrid substations in place of conventional AIS substations as Indian utilities grapple with right-of-way and land acquisition issues. GIS substations have seen increased deployment among utilities, owing to their advantages such as less space requirement, better safety and low maintenance costs. GIS substations are indoor-type substations in which equipment is placed inside the modules filled with SF6. The GIS substations require less space (around 35 per cent less than an AIS substation), entail lower maintenance costs, have a lower outage rate, generate less noise and are safer to operate. Hybrid substations comprise a mix of AIS and GIS technologies. They can be installed indoors as well as outdoors and require a moderate land size. They are also good for optimising space and cost.
The adoption of variants such as hybrid substations and vertical GIS substations and the use of environment-friendly insulation materials have seen an increase in the past few years. Sterlite Power implemented the country’s first vertical GIS substations at Prithla, Kadarpur and Sohna as part of the Gurgaon-Palwal Transmission Project. These 400/220 kV GIS substations are multistorey substations with a rooftop 220 kV open switchyard, housing the 400 kV GIS equipment on the ground floor, the 220 kV GIS on the first floor and the open 220 kV switchyard on the roof. The entire GIS substation occupies just 3.8 acres, thus, reducing the land requirment by as much as 75 per cent.
Switchgear technology
AIS: AIS is the most widely deployed switchgear in India and worldwide. It uses air as the primary dielectric for phase-to-phase and phase-to-ground insulation. AIS is popular where space is not an issue. It has low construction and maintenance costs. AIS is easy to maintain as all the equipment is within view and faults can be attended to without much delay. However, it is vulnerable to faults since the equipment is open to external elements such as human intrusion, pollution, de-position of saline particles, lightning strikes and extreme weather conditions.
GIS: GIS is essentially compact and metal-encapsulated, consisting of HV equipment such as circuit breakers and disconnectors. In GIS, all components including busbars, circuit breakers, current transformer, potential transformers and other substation equipment is placed inside modules filled with sulphur hexafluoride SF6 gas. Traditionally, GIS uses SF6 as the insulation medium. It maintains atomic and molecular properties even at high voltages and has superior insulation properties.
It also reduces the distance needed between active and non-active switchgear parts, thereby reducing the size of the equipment and making these ideal for urban areas as well as indoor spaces. The other advantages of GIS are its high safety index and low maintenance requirements. The high capital cost of GIS as compared to that of AIS is an issue, but if land as well as construction and maintenance costs are taken into account, it proves economical. Further, with the increase in voltage, the incremental investment required for GIS is less than that required for regular switchgear. Further, SF6 is a greenhouse gas with high global warming potential. With environmental concerns associated with SF6, efforts are under way to replace it with an alternative medium.
Hybrid switchgear: Hybrid switchgear combines conventional AIS and modern GIS technologies, and can be installed both in indoor as well as outdoor areas. Some of the key advantages of hybrid switchgear are that it requires almost 30 per cent less switchyard area and lower foundations per bay. In a hybrid switchgear substation, circuit breakers, disconnector and earthing switches, voltage transformers and sensors, current transformers and fast-earthing switches are enclosed in a single-phase gas-insulated housing, while traditional air-insulated busbars are used to connect other equipment. As various functions in a hybrid switchgear substation are integrated, the distance between the components is reduced, thereby reducing the overall space requirement. They can be quickly installed (usually plug and play), are highly reliable and have a lower life cycle cost.
Vacuum switchgear: A vacuum circuit breaker is mostly suitable for medium voltage applications where the arc quenching takes place in a vacuum. It is now emerging as an alternative in high voltage applications as well due to various advantages – compact size, higher reliability, lower maintenance and faster restoration. Vacuum switchgear has also seen a renewed interest with focus on reducing the use of SF6. It is expected that the deployment of vacuum switchgear at higher voltages will increase in the times to come. However, a few challenges pertaining to capacitor switching, continuous current performance, voltage sharing, etc., still need to be addressed before vacuum switchgear can be successfully deployed at higher voltages.
Solid-insulated switchgear: In solid-insulated switchgear (SIS), the main MV circuit is generally encapsulated in insulating materials (such as epoxy resin). Fundamentally, there is no difference in behaviour in an SIS and AIS. There is also no visible live part along the main circuit. However, the issue of electrical field variation exists in case of harsh environmental conditions. Shielded SIS (2 SIS) is a more advanced technology with three concentric layers: a live part (main conductor, insert, or vacuum interrupter, which is permanently connected to the network and is subject to voltage variations), an insulating layer (ensures insulation in all operating conditions) and a conductive layer (ensures electrical continuity and an effective earth connection). 2SIS technology offers various advantages such as no ageing of infrastructure, no three-phase or two-phase faults and no internal arc effects.
Intelligent switchgear: Switchgear makers have started leveraging internet of things to enable real-time information flow, as well as improved predictive diagnostics that leads to higher energy efficiency and a more reliable grid. Intelligent switchgear can connect with the internet and provide comprehensive monitoring and protection functions, as well as measure all electrical parameters in real time. A smart switchgear has built-in protection and control IEDs. These new IEDs, combined with the latest information and communications technologies, form a base for enhanced protection, control and monitoring. Intelligent switchgear overcomes disadvantages of common electric switchgear power systems by performing functions such as system diagnosis, electric fire prediction and prevention, and electric power demand prediction.
Conclusion and the way forward
With the decarbonisation, decentralisation and digitalisation of the energy sector, utilities are taking steps to transition and upgrade their power systems to cater to future grid requirements. Market players are also making efforts to integrate new substation and switchgear technologies that use less space and have a lower outage due to a growing focus on providing uninterrupted power supply. Furthermore, the development of new infrastructure and the modernisation of the existing one will go a long way in establishing a secure and reliable transmission and distribution network, while driving the growth of technological advancements in the switchgear and substation market.