Modern business requirements call for upgraded assets that can ensure safety, reliable power supply and continued business operations. Transformer technology has advanced enough to accommodate the changing needs of utilities and improve power system resilience. A key trend has been the use of dry-type transformers and K-class (ester) fluid-filled transformers, which reportedly have lower failure rates as opposed to oil-filled ones. Another key technology trend is the use of smart transformers becoming an important element of digital substations that autonomously control voltage and maintain communication with smart grids to allow remote administration and real-time feedback on power supply characteristics. These new-generation transformers use enhanced core materials, and have higher levels of safety (such as fire resistance), lower space requirements, cheaper prices, lower failure rates, lower noise levels and increased asset life. In addition, they are environmentally friendly and adaptable to smart grids.
Power Line takes a look at new and emerging technology trends in transformers…
HVDC converter transformers: High voltage direct current (HVDC) transmission is an economical process for the transmission of bulk power over long distances. Since all generating plants produce alternating current (AC), HVDC converter transformers are required to convert it into direct current (DC). These transformers also convert the DC back to AC for power consumption. They have AC windings connected to the AC system and valve windings connected to converters, which are further connected in a series circuit to build up the necessary level of DC voltage. The advantages of these transformers are high electricity transmission and low transmission losses.
In June 2021, Power Grid Corporation of India Limited (Powergrid) commissioned the 6,000 MW HVDC bipole between Raigarh in Chhattisgarh, Pugalur in Tamil Nadu and Trichur in Kerala. A consortium comprising Bharat Heavy Electricals Limited (BHEL) and Hitachi ABB Power Grids had won the order for the 800 kV Raigarh-Pugalur link in 2016. The consortium supplied major equipment including 800 kV converter transformers, converter valves, cooling systems, and control and protection technology for the project. This project marks the first usage of voltage source convertor technology in the country.
Ester-filled transformers: Conventional transformers use mineral oils as the insulating fluid, while ester-filled transformers use natural esters for liquid insulation of the transformer. As natural esters have about twice the fire point of mineral oil at 360 ºC, as well as a flashpoint of 320 ºC, these transformers have the significant advantage of being fire resistant. In case of leakage, ester-filled transformers fare better than their conventional counterparts because natural esters are biodegradable, and thus risks of soil contamination are minimised.
Last year in April, Tata Power commissioned India’s largest natural ester-filled 110/33/22 kV, 125 MVA power transformer at the BKC receiving station, as part of its Mumbai transmission network. More recently, in July 2022, BHEL commissioned a 100 MW floating solar photovoltaic plant at NTPC Ramagundam in Telangana. A major component of the solar plant is the use of biodegradable natural ester oil-filled inverter-duty transformers.
Dry-type transformers: Dry-type transformers are gaining traction. In these, the windings along with the core are kept within an air-filled, pressurised and sealed tank. They are motionless, solid-state devices without any moving or rotating components. They do not need to be stored in fireproof vaults and do not produce poisonous fumes. The two types of dry-type transformers are cast resin transformers and vacuum pressure impersonated transformers. They can reduce the risk of fire hazards and are thus ideal for areas such as residential buildings, offices, schools, hospitals and metro stations. BSES Yamuna Power Limited has deployed a dry-type transformer in East Delhi and BRPL has deployed a 1,500 kVA dry-type transformer at the Triveni Shopping Complex in Delhi. Dry-type transformers have also been deployed at the Kochi metro station.
Green transformers: Green transformers with low noise for ultra-low applications, that provide increased safety against fire with the use of ester oil, are emerging. Green transformers offer several benefits such as a lower carbon footprint and slower ageing compared to traditional transformers. Such transformers also have lower life cycle costs as they are equipped with hermetically sealed tanks, which require no oil conservator and no associated devices, thereby reducing maintenance requirements.
Smart transformers: Smart transformers are an integral component of digital substations. Smart transformers can independently regulate voltage while allowing remote operation by retaining contact with the smart grid. They change the voltage ratio using applied semiconductor technology and can achieve high power density. They also operate at a high frequency, thus reducing both cost and size, making them economical. In addition, smart transformers minimise energy consumption and greenhouse gas emissions. They can provide stable, optimal power supply, and protect electrical equipment from power fluctuations, thereby extending equipment life.
Others: A mobile transformer is a portable device used in mobile substations. It is used in emergency circumstances, when an interim grid connection or temporary power supply is required, such as during load peaks, substation replacement or equipment failure. It is a trailer-mounted, self-contained system that is preconfigured and ready to use, with short installation and commissioning times. Power utilities can use energy efficient transformers (EETs) to enhance the efficiency of the transmission and distribution (T&D) system, and as a result reduce T&D losses. These transformers are specially engineered for high performance. They use low resistance copper wires, suffer minimal heat losses, require less coolant and have longer running times. EETs can reduce losses by up to 60 per cent. In addition to these, in September 2020, Powergrid, in collaboration with BHEL, commissioned a 400 kV optical current transformer and digital substation components at the 400/220 kV Bhiwadi substation of Powergrid.
Transformer materials are being improved as well. New trends in core construction are helping in loss reduction and expediting the production process. Step-lap construction of transformer cores is being adopted instead of the conventional non-step-lap type to reduce the building factor in transformer cores by 5-8 per cent, as well as the no-load current and the noise level. Also, for transformer processing, a drying technique – vapour phase drying, which uniformly removes moisture – is gaining traction. Vapour phase drying, like hot oil spray drying, uses hydrocarbons to add heat concurrent with vacuum drying. The vapour phase process provides the most efficient combination of heat addition and vacuum application. This reduces the processing time by approximately 25 per cent over hot oil spray processing, and by 40 per cent over hot air processing. Further, the basic core materials utilised in transformer manufacturing are witnessing a gradual transition from CRGO M4 steel sheets to amorphous steel to laser-scribed core material-grade ZDKH. Additionally, the conductor materials used in transformer windings have shifted from paper-insulated regulator copper conductors to epoxy-coated continuously transposed conductors. This has resulted in space optimisation.
The adoption of modern transformer technologies will make the future grid more resilient and adaptable to the significant changes being experienced by the grid. The scale and pace of these emerging technologies’ adoption will, however, be driven by the extent of investments made by power utilities, going forward.
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