Critical Components

Technology trends in substations, switchgear and transformers

The Indian power sector has evolved greatly over the past decade with the influx of renewables in the form of mega projects and small distributed set-ups, and the emergence of the electric vehicle (EVs) market. The transmission and distribution segment, too, has kept pace with this transition in the energy mix. Rapid technology advancements have been made in critical power system components such as substations, switchgear and transformers, which form the core of power transmission and distribution and make it possible for renewable power to be evacuated into the grid. The equipment is being made smarter, more robust and flexible so as to deal with the intermittent generation pattern of renewables and changing load profiles due to EV integration.

Substations and switchgear

Conventionally, air-insulated substations (AISs), which use air for insulation between various live parts, have been used for power transmission in India. However, in view of increasing space constraints, land cost, and renewable energy and EV penetration, the focus is shifting to substation and switchgear technologies that require less space and are more reliable. These include gas insulated, hybrid, digital, modular and underground substations.

Gas-insulated substations (GISs): They have emerged as a popular choice due to their many benefits over AIS. These substations use sulphur-hexafluoride (SF6) gas, which reduces the distance needed between active and non-active switchgear parts, resulting in lower space requirements. Further, GISs can be installed both indoors and outdoors. They also offer enhanced safety as all interior elements of GISs  are insulated and no cable or linkage can come in contact with the live parts. These require less installation time than their counterparts and are significantly easier to operate and maintain on a regular basis. Although they cost more than AISs, GISs offer several benefits with respect to land coverage, construction and maintenance costs and performance, making them better suited for high voltage applications.

Hybrid substations: These are a mix of AIS and GIS technologies, combining the benefits of both. Hybrid substations can be installed indoors as well as outdoors and are suitable for optimising space and cost. There is a growing deployment of hybrid substations in the country, mainly as future extensions of existing substations. These substations strike a balance between the cost of land and the facility construction cost. In addition, they ensure the desired power supply and provide flexibility by allowing a change in module configuration as per the required components.

Digital substations: With the increasing penetration of renewables and EVs into the grid, there is a need for digitally enabled substations and switchgear for better power reliability. To this end, digital substations with smart and automated switchgear are increasingly being adopted to enable the collection of real-time data. They help monitor, control and maintain assets. These also help in predictive maintenance and planning, thereby reducing asset downtime and enabling faster restoration of faults. Further, these substations can be remotely monitored and are equipped with a supervisory control and data acquisition system, bay controller units, a communication interface, phasor measurement units and other advanced digital equipment to help increase flexibility and provide automation.

Apart from this, there are various other types of substations being implemented as per requirement. For instance, underground substations are being increasingly deployed owing to rising land constraints and safety issues in busy locations. Underground substations typically deploy GIS solutions as these are fire resistant. Further, prefabricated and pre-commissioned modular substations are being deployed, mainly in remote locations with adverse weather or difficult terrain, to save installation time and costs. They come with pre-assembled control cables that have multi-plug connectors and are ideal for usage as auxiliary substations during the repair or maintenance of existing primary substations as they can be easily relocated.

Similar to modular substations are mobile substations that come in a ready-to-connect format with complete assemblies. They are designed for grid code compliance and easy mobility. These are ideal for providing interim grid connections and temporary power supply and are also useful for integrating distributed renewable energy assets.

Transformers

The transformer industry is on a growth trajectory with high investments in the transmission segment and ongoing reforms in the distribution segment. Transformer manufacturers are now focusing on increasing their manufacturing capacity and deploying advanced technology to create more efficient products. Further, owing to the greater focus on smart grids and the increasing share of renewables in the energy mix, there has been a growth in demand for smart and digital transformers.

The transformer market is broadly segmented into oil-immersed and dry-type transformers. Oil-immersed transformers with higher energy efficiency, lower sound level and longer operating life account for a higher share. Liquid-filled transformers require thinner conductor insulation than dry-type transformers and have smaller core and coils. However, with the increasing focus on safety and environment protection, there has been a growth in the demand for dry-type transformers as well. Predominantly, solar power plants use liquid-filled transformers as they dissipate heat more efficiently, whereas dry-type transformers are used only in certain indoor installations where liquid-filled transformers cannot be used. The key emerging technologies in the transformer space include high voltage direct current (HVDC) converter transformers, phase shifting transformers (PSTs), coupling transformers and smart transformers.

HVDC converters: HVDC technology can transmit large amounts of electricity over long distances with lower losses when compared to a high voltage alternating current system. It has gained prominence in recent years for transmitting power from mega power projects. In the renewable power space, large solar parks and wind farms are located far away from load centres and require transmission of power over significant distances. HVDC converters transfer power between an AC system and the DC transmission network and form the core of HVDC systems.

PSTs: They control the active power flow in the network by regulating the phase of line voltage and work independent of energy generation. These transformers are used in networks where intensive power wheeling takes place. They help ensure the optimum utilisation of transmission lines. PSTs protect the transmission equipment from thermal overload and help improve efficiency.

Coupling transformers: Coupling transformers are used to enhance the control and stability in flexible AC transmission systems (FACTS). These transformers connect the grid with a static synchronous compensator (STATCOM), which ensures the supply of a dynamic, precise and adjustable amount of reactive power to the AC power system.

Digital transformers: Smart and digital transformers are important components of digital substations  equipped with intelligent monitoring and diagnostics features. These can automatically regulate voltage in accordance with the smart grid and real-time power supply data. They enable remote monitoring of components such as the transformer core, windings, oil, tap changers and bushings.

Outlook

With the increasing penetration of intermittent renewable energy into the grid, there is a much greater need for reactive power support to avoid voltage disturbances in the grid. Excess reactive power lowers operational efficiency, whereas less reactive power results in a voltage drop, thereby making it impossible to transmit the required power. Thus, various static and dynamic devices are being deployed for the optimisation of reactive power and maintenance of grid stability. Apart from this, FACTS is being increasingly deployed.

Net, net, there have been a host of technology advancements in the power transmission and distribution space, especially with respect to substations and transformers. Apart from being made more efficient and safer, the focus is on making these critical components more automated and smarter. India aims to have 450 GW of renewable power capacity by 2030, most of which is expected to come from solar and wind. To integrate such a huge quantum of intermittent generation into the grid, there is a need for advanced and flexible systems so as to manage the sudden imbalances expected in renewable energy generation. Thus, efficient digital power systems can help monitor and maintain grid stability.

By Khushboo Goyal

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