Over the years, there have been significant advancements in substation technologies. New and emerging technologies aim to address the challenges faced in the transmission and distribution network, such as space constraints, high downtime in case of a fault, time constraints, safety concerns and power supply to geographically remote locations. Advanced substation technology solutions aim at providing reliable, uninterrupted and quality power, while ensuring minimum equipment downtime.
Power Line takes a look at the key emerging technologies in distribution and transmission substations…
Digital substations
One of the key emerging substation technologies is digitalisation. Under this, sensors are used to monitor substation operations and send signals to the control centre. Digitalised substations leverage communications through optical fibre cables (OFCs) that replace traditional copper connections. Digital substations are increasingly gaining traction in the country. In February 2017, ABB India secured an order from Technopark for setting up a 110 kV digital substation at an information technology park in Kerala.
A digital substation analyses performance data and provides recommendations on maintenance and repairs. It enables the identification of degradation in substation performance in real time, helping in predictive or reliability centred maintenance by capturing any anomaly in operations. This helps avoid unplanned outages, minimises emergency repair costs and lowers the risk of asset failure. There is also a reduction in material requirement owing to a reduced need for protection and control panels, making digital substations compact. Besides, these are faster to install as they use pre-tested process bus systems. Digital substations provide additional safety by eliminating open current circuits. Interoperable solutions and the use of OFCs instead of copper wires reduce the duration and the cost of onsite work for the refurbishment of secondary equipment.
GIS substations
Another substation technology that is witnessing wide uptake is gas insulated switchgear (GIS) substations. These substations use sulphur-hexafluoride (SF6) gas, which reduces the distance needed between active and non-active switchgear parts, resulting in lower space requirements, making these ideal for urban areas. A typical GIS substation needs one-tenth the space needed for conventional installations. Besides, these can be installed indoors and outdoors.
Another significant advantage of GIS substations is enhanced safety. As SF6 is five times heavier than air, it offers excellent extinction characteristics. All interior elements of GIS substations are insulated and no cable or linkage can come in contact with the live parts. Besides, arc flashes are rare in a GIS substation. These substations require lower installation time as compared to other options, primarily because of the smaller size and lower weight. Further, GIS substations are significantly easier to operate and maintain on a regular basis as they offer front instead of rear access, and are usually equipped with integrated testing instruments.
With regard to the cost of a GIS substation, its overall cost is 10-40 per cent more than that of an air insulated switchgear (AIS) substation. However, considering the land coverage, construction and maintenance costs, and better performance, GIS substations are more economical, especially for high and extra high voltage applications.
Hybrid substations
Hybrid substations are a combination of AIS and GIS substations. These substations strike a balance between the cost of land and the facility construction cost. Hybrid substations provide flexibility and customisation. A hybrid substation allows a change in the configuration of modules according to the components that are required to ensure the desired power supply. It is mainly used for the extension or substitution of any traditional substation operating on an air-insulated busbar.
There is also a growing deployment of hybrid substations in the country. The Gujarat Energy Transmission Corporation is deploying hybrid substations for extending and upgrading a number of its existing 66 kV and 220 kV substations. This particular technology was selected owing to its reduced land requirement, less installation time and absence of conventional disconnectors. In another instance, a 110 kV hybrid substation has been constructed by Cochin International Airport Limited at a cost of around Rs 220 million. The substation, set up by ABB, will cater to the power requirements of the airport and allied organisations for the next 15 to 20 years.
Modular substations
Modular substations comprise pre-fabricated and commissioned switch rooms. These are factory installed and pre-commissioned off-site, allowing simple onsite civil works, installations and commissioning. These are an ideal solution for remote sites that are exposed to inclement weather or are located in poor soil conditions. Besides, the mobilisation of site workers is reduced significantly with off-site switchroom construction. The modules are designed to allow easy transportation and quick installation time. Prior to its dispatch from the factory, the entire substation usually undergoes routine tests. Pre-assembled control cables with multi-plug connectors further reduce the installation time. These are ideal for customers requiring shorter overall delivery times and minimal onsite work. The customised and compact solutions have a smaller footprint, and include ready-to-connect primary and secondary cabling with plug-type contacts. Fast erection and dismantling make them easy to relocate and they are well suited for usage as auxiliary substations during the repair or maintenance of existing primary substations.
Underground substations
Another emerging technology is the deployment of underground substations. The purpose of underground substations is to provide the functionality of a conventional substation while minimising the area occupied above ground. Placing the substation underground reduces space requirements at downtown sites, and the free surface area can be used for other purposes. These substations are ideal for urban areas where compactness, reliability and safety are needed, while allowing easy maintenance and future expansions. Usually, underground substations deploy GIS solutions, as these are fire resistant.
The deployment of underground substations is fast gaining traction in the country. CESC Limited is developing the first underground extra high voltage 150 MVA substation at Park Circus in Kolkata, West Bengal. The substation entails an estimated cost of Rs 530 million and will be located 12 metres below the ground. It requires an area of nearly 600 square metres. The Delhi Metro Rail Corporation also operates two underground substations on Church Road near North Block and Rashtrapati Bhavan. These substations are located 6 metres below the ground and have been set up on an area of 5,000 square metres. The construction of these substations took over a year to complete, as underground substations require special ventilation, drainage and earthing systems.
Mobile substations
Mobile substations come in ready-to-connect form with complete assemblies and are designed for grid code compliance and easy mobility. Typically, mobile substations are available for voltage levels up to 420 kV. These are a perfect solution for utilities and industries needing to provide interim grid connections and temporary power supply. Mobile substations require a shorter installation and commissioning time and provide reliable and high-quality power supply. These substations enable temporary power supply during periods of high load, malfunctions, maintenance and replacement, mordernisation of substations, emergency and planned outages, etc. They are also useful for integrating distributed generation units and renewable generation sources.
Net, net, there are a host of technology solutions, which aim at addressing the challenges in the transmission and distribution network. For an optimal outcome, it is important to judiciously select the ideal option for meeting the power requirements, while keeping in mind local issues and problems.