Transformer technologies have evolved considerably to meet the emerging requirements of utilities and adapt to the changing grid. New designs and features have been driven by considerations such as space optimisation, lowering costs, increasing asset life, improving core materials, adding appropriate levels of safety, addition of digital hubs, reducing failure rates and cutting noise levels, among other things. As utilities focus on grid modernisation, investments in new and advanced transformer technologies can provide an answer to their need for a safe, reliable and affordable grid.
Technology trends
Product-wise, the latest transformer technologies include 1,100 kV high voltage direct current (HVDC) converter transformers, 800 kV HVDC converter transformers as well as phase shifting transformers. Controlled shunt reactors through which we can control reactive power and thereby maximise efficiency of lines are also gaining traction. Transformers for renewable energy applications are also gaining traction. Coupling transformers for static synchronous compensator applications have also become important from the grid stability point of view. Other new technologies such as traction transformers for dedicated freight corridors and higher capacity generator transformers (for 800/1,000 MW) are still at a nascent stage in India. Further, there is an emergence of green transformers with low noise for ultra-low applications, along with increased safety against fire with the use of ester oil. Green transformers offer several benefits by promising a lower carbon footprint and reduced ageing, besides lower pollution risks. Such transformers also have lower life cycle costs as they are equipped with hermetically sealed tanks design, which requires no oil conservator and no associated devices, thereby reducing maintenance requirements. The vacuum tap changers prevent contact erosion and further reduce maintenance needs.
To further maximise operational management and prevent faults, use of digital technologies is increasing. Utilities are turning towards smart transformers, which are an integral part of digital substations, and they independently regulate voltage and maintain contact with smart grids in order to allow remote administration and real-time feedback on power supply parameters. These transformers are equipped with intelligent electronic devices, and monitoring and diagnostics features. Besides, they provide web and supervisory control and data acquisition interfaces. There are also a number of technology upgradations being made to improve overall reliability. The overall reliability of a power transformer depends, to a great extent on the sound operation of bushing. Oil impregnated paper (OIP) bushing is conventionally used in a power transformer. However, a new technology that has now replaced OIP bushing is resin impregnated paper (RIP) bushing, which has superior thermal and electrical performance. In RIP bushing the major insulation consists of a core wound from paper and subsequently impregnated with epoxy resin.
Materials used in transformers are also being upgraded. In terms of the basic core materials, which are used for transformer manufacturing, there has been a gradual change from CRGO M4 steel sheets to amorphous steel, to the use of laser scribed core material grade ZDKH. Further, the conductor materials used in transformer winding have also changed from paper-insulated regulator copper conductor to epoxy-coated continuously transposed conductor. This has resulted in better space utilisation, owing to the compact size. Further, new trends in core construction are leading to minimising losses and expediting the production process. Step-lap construction of transformer cores are now being adopted instead of the conventional non-step lap (NSL) type to reduce the building factor in transformer cores (by 5-8 per cent), reducing the no-load current and the noise level relative to conventionally stacked NSL cores. Also, for transformer processing, a drying technique, which is gaining importance, is vapour phase drying that uniformly removes moisture. Vapour phase drying, like hot oil spray drying, uses a hydrocarbon to add heat concurrent with vacuum drying. The vapour phase process provides the most efficient combination of heat addition and vacuum application. This results in the reduction of processing time by approximately 25 per cent over hot oil spray processing, and approximately 40 per cent over hot air processing.
Issues and challenges
One of the key challenges for the transformer industry is the lack of standardisation of transformer specifications, or online monitoring devices or transformer fittings. Difficulty in availability of indigenous material such as copper rods, insulation, CRGO and online devices still prevails. Also, the absence of infrastructure essential for transporting heavy equipment such as power transformers poses a big problem. To conclude, technologies available in the transformer space are constantly evolving to meet power system requirements and address challenges facing utilities and the right technology selection can help utilities improve power reliability, minimise faults and optimise asset management.