Smart, Compact and Reliable: Innovations in switchgear and substation design

May 29, 2023

The new and emerging switchgear designs are focusing on digitalisation of operations and reducing the footprint of substations. One of the main cha­llenges faced by transmission and distribution utilities in network expansion is right-of-way (RoW) constraints. To ad­d­ress this issue, utilities are increasingly ad­opting new technological solutions. Gas-insulated switch­gear (GIS) is being increasingly adopted by utilities as it requires significantly less land vis-à-vis air-insulated switchgear (AIS). Hybrid substations, which combine GIS and AIS, also offer potential so­lutions for mini­mi­sing the space re­qu­i­re­­ments. Apart from this, the use of compact, flexible and reliable digital, intelligent and smart swit­ch­gears is gaining traction. With the support of internet of things (IoT), digital switch­gear enables data processing that can be used to detect errors and malfunctions in advance, thereby preventing system failure and minimising energy lo­sses and costs.

GIS: GIS is essentially compact and metal encapsulated, consisting of high voltage (HV) equipment such as circuit breakers and disconnectors. In GIS substations, all components including busbars, circuit breakers, current transformers and potential transformers and other substation equipment are placed inside modules filled with sulphur hexafluoride SF6 gas. Traditionally, GIS uses SF6 as the insulation medium.

The deployment of GIS substations is gaining prominence in India's power transmission and distribution segments in order to effectively address space co­n­s­traints. GIS substations require app­roximately 35 per cent less space than AIS substations, resulting in lower mainten­ance costs and outage frequency. Al­though the initial cost of GIS substations is about 50 per cent higher than of their AIS counterparts, the overall capital costs are comparable.

GIS is an attractive alternative for densely populated areas, with high reliability, reduced maintenance requirements and smaller environmental impact. GIS substations can be deployed either indoors or outdoors. They are reliable for medium and low voltage service and are particularly useful for industrial locations, hospitals and housing societies where space is limited. Further, due to the smaller size of GIS substations, they are well suited for ecologically sensitive areas as they minimise the environmental footprint. How­ever, one of the concerns with the growing deployment of GIS is the extensive use of SF6 as the insulating and arc quenching medium. SF6 has been classified as a greenhouse gas and is highly potent in terms of global warming.

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 the behaviour of SIS and AIS. There are also no visible live parts along the main circuit. However, the issue of electrical field variation arises in harsh environmental conditions. Shielded SIS (2 SIS) is a more advanced technology with three concentric layers: a live part (main conductor, insert and vacuum interrupter, which is permanently connected to the network and is subject to voltage variations), an insulating layer that ensures insulation in all operating conditions, and a conductive layer that 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.

Hybrid switchgear: The utilities are increasingly embracing hybrid switch­gear, which combines the components of AIS and SF6 GIS technologies. The compact and modular design is particularly useful for substations that require renovation and extension and currently use AIS switchgear. Hybrid switchgear is especially beneficial in areas where land is expensive or limited. In a hybrid substation, the busbars are air insulated and all other equipment, such as circuit breakers, bushings, busducts, connecting elements, disconnectors, current transformers and sensors, is gas insulated. Hybrid substations are charact­e­rised by a compact modular design, which combines a variety of functions in one module. The initial cost of hybrid substations is approximately 20 per cent higher than that of AIS, and these substations requi­re a moderate amount of land.

Vacuum switchgear: Vacuum switch­gear is rapidly gaining popularity. Vacuum interruption technology works efficiently in medium voltage applications. It is safer and more reliable where the levels of both faults and operations are high. Vacuum switchgear is nearly maintenance-free. It requires less driving energy in circuit breakers and has a longer mechanical life. For a given contact gap, vacuum provides about eight times more dielectric strength than air and four times more dielectric strength than SF6 gas at one bar. The dielectric str­ength of vacuum circuit breakers all­ows a very small contact gap to be maintained. This small contact gap enables safe arc quenching, due to the high dielectric strength of vacuum and its fast recovery to full dielectric value after arc interruption at current zero. This makes vacuum switchgear highly suitable for capacitor switching.

Eco-efficient switchgear: The conventional switchgear and substations em­ploy SF6 gas or a combination of fuels and oils in hydraulic mechanisms. The use of SF6 as insulating material, however, poses an environmental hazard. SF6 is a greenhouse gas with an atmospheric lifespan of 3,200 years and a global war­m­ing potential stronger than CO2 by 23,500 times, which causes potent damage to the environment. On an average, a typical switchgear contains 1 kg of SF6, making it crucial to safely dispose of SF6 switch­gear to prevent the release of the gas into the atmosphere as its toxic by-pr­o­ducts adversely impact human health.

Due to the detrimental environmental effects of SF6, which is commonly used as an insulating material in GIS, utilities and technology providers are actively seeking environmentally safe alternatives. New-age SF6-free switchgear has gained significant attention as part of our collective efforts to achieve climate goals. The alternative C5 fluoroke­to­ne/air gas mixture combines good electrical features while also reducing the global warming potential by almost 100 per cent compared to SF6. The good dielectric properties of C5-FK make it suitable as insulation material in switchgear.

Digital and intelligent switchgear: Sm­ar­­ter transmission and distribution equipment including digital switchgear is in high demand. Smart switchgear en­sures network stability, protects equipment and remains unaffected by network load fluctuations. The use of intelligent switchgear equipped with two-way real-time communication is gaining traction. Intelligent switchgear is capable of measuring various parameters and transmitting the readings to energy utilities and management centres on a real-time basis. The monitoring and configuration of systems can be carried out from a remote-control centre. The systems can quickly detect electric sparks and ot­her anomalies can prevent short circuits, overload, component failure, etc. In­te­lli­gent switchgear can also predict mo­nthly power demand within a load network. Intelligent switchgear is easy to maintain. It helps in smart energy management and reduction of power bills. The switchgear can be preconfigured and preprogrammed with the help of IoT.

Ultra high voltage (UHV) switchgear: The demand for increased transmission po­wer and reduced transmission losses per line is driving the adoption of UHV levels, which in­vol­ve rated voltages of 800 kV, 1,100 kV and 1,200 kV. The use of metal enclosures and SF6 gas insulation enables the de­velo­pment of more compact, HV switchgear. The Power Grid Corpora­tion of In­dia has set up a 1,200 kV test station at Bina to all­ow manufacturers to install and test the­ir UHV equipment. Typically, UHV AC grids require swi­t­chgear that can handle the switching de­mand for normal operations and provide protection in the event of a short circuit.

Net, net, the new switchgear designs fulfil the utilities’ needs to minimise RoW requirements and promote susta­inable operations. These advancements will fa­cilitate the rapid expansion of the country's transmission and distribution network, and support energy transitions. Ov­erall, upgrading obsolete infrastructure and digitalising substation and swit­ch­gear operations will go a long way in en­su­ring reliable power supply in the co­untry, while minimising operations and maintenance costs as well as outages.