Structural Upgrade: New and emerging transformer technologies

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…

Transformer technologies

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.

Advances in materials

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.

Conclusion

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.