What is HTC Transformer?

HTC transformers, consisting of the initials of the "High-Temperature Compact Transformer" nomenclature, are electrical machines designed with NOMEX insulating materials and Silicon or Midel oil blended with advanced technology, allowing larger power ratings to be used in smaller volumes. 

With the development of material technology, the sizes of transformers are getting smaller. However, special solutions need to be produced for some very narrow application areas. For example, places with narrow volumes, which we call machine housing (nacelle) in wind turbines, underground switchyards, historical areas which have old transformers in limited space, subway networks are just a few of the places where HTC transformer solutions can be applied. So why do we choose these transformers? What are the benefits for us? What should we pay attention to in the purchasing process regarding the disadvantages?

Graph-1 Relationship between environmental friendly and fire safety

As you have seen in the graph, it shows the Fire Safety – Environmental-Friendy relationship of the 5 types of transformer oil used today (askarel, mineral oil, synthetic ester, natural ester, silicone oil). With the HTC transformer design, a transformer with a high fire safety-environmental-friendly relationship is selected. The use of these oil types is gradually made compulsory in many specifications in Europe. 

Today, transformers have to operate at higher temperatures due to the increase in load demand in many places. When we take into account the atmospheric conditions, it is not enough for transformer oil to have a high specifications in terms of fire safety and environmental friendliness. It is also required that the insulation materials that determine the life of the transformer have advanced technology. This is where the NOMEX insulation solution comes into play. 

With the use of these two materials (NOMEX insulation paper and Silicone/Midel oil), transformers can be operated at higher temperatures without ageing. Because the less cooling surface is required for such transformers, transformers can be minimized in size by up to 30%. Compact, lighter, lower-sized HTC transformers can now carry more apparent power and be more overloadable than conventional transformers. At the same time, lower transportation costs will occur for these transformers due to their reduced sizes and weights. With the new technology insulation materials that technically offer the opportunity to operate up to 220 °C, the life span of the transformers is extended; these transformers require less maintenance and repair. As a result, lighter or the same weight, higher power capacity transformers can be obtained with the same people, the same machines, and the same production line as HTC transformers. During the days of environmental and fire susceptibility increases; transformers that almost never fail, require less maintenance, can be overloaded, and can be easily transported and assembled, can be integrated into the electrical system nowadays. 

The disadvantages of the HTC transformer solution are that the costs of NOMEX and new type oil materials are higher than standard insulations and oils. Prices of NOMEX insulation materials are approximately 20 times higher than cellulosic insulation materials; Midel and silicone oils are also approximately 4-5 times more expensive than mineral transformer oils. Of course, these price differences in raw materials can be compensated to some extent by reducing the size of the transformer (using less oil and less tank cooling material).

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