Cast Resin Transformers
While the term “dry type” transformer is often confused to only refer to transformers processed with varnish and cured in ovens, such as VPI transformers, cast epoxy resin transforms are also dry type transformers. Cast epoxy resin transformers are highest on the evolutionary scale of transformer design and offer the best combination of electrical and mechanical performance factors. Cast epoxy resin transformers offer higher performance than other dry type transformers and do not present the environmental risks and hazards found in liquid filled transformers. Cast coil transformers offer superior dielectric properties associated with their insulation system when compared to other dry type transformers and can be used to voltage levels in the 35kV class, basic impulse levels (BIL) to 200kV and partial discharge levels to 10 pico-coulombs and below. In addition, they run cooler that other dry types and are easily cooled by the addition of fans and cooling ducts in the casting which allows for operation at higher power ratings. The robust structure achieved by casting the windings in a solid shell of epoxy provides mechanical strength unsurpassed by any other transformer available on the market. This robust structure manifests itself in the ability to ward off damage due to electrical faults and heavy electrical surges. Short circuit faults have proved to be disastrous for transformer types other than cast epoxy resin transformers as the forces set up by the magnetic fields are too much for these other, less robust, transformer types to handle.
Other features of cast coil transformers are seen in the compact design allowing these to be designed in confined areas where space is limited and also allows for close coupling to switch gear which is a space savings scheme found in many applications. Little maintenance is required and for the most part it is a simple matter of keeping the smooth surface of the coils clean by wiping off any dirt and dust that may have accumulated over a period of time. The insulation system is self-extinguishing reducing the risk of damage from fire. In addition to being compact and low maintenance a higher degree of reliability is offered by cast epoxy resin transformers.
The positive attributes of cast epoxy resin transformers make them a popular choice for use in environments at the opposite ends of the spectrum. Cast coil transformers are used in some of the most pristine settings without fear of contamination to the surrounding area and considered to be less conspicuous than other types of transformers. Common applications for JST cast resin transformers include many college campuses, hospitals, and areas with public access. Going to the opposite extreme these transformers are well suited for some of the harshest environments as the robust mechanical structure and durability of the coils can stand up to the adverse conditions that are found in such places as factories foundries, and processing plants while offering superior performance. In either cast the fact that these transformers take up less space and are easy to maintain, lends credence to further support their use in any environment.
JST has been supplying cast epoxy resin transformers since their founding in 1993 and has emerged as a premiere supplier of these products sold on a global basis. Since their founding JST has continued to invest in R&D and to improve upon an already superb product. Prior to casting, the coils are precision wound in a clean room environment under the strictest controls and then placed in a mold for casting. Stringent controls are also used during casting when both the primary and secondary coils are vacuum cast with an epoxy resin compound that is structurally reinforced with fiber glass or a mesh to achieve a void free cast coil with the highest structural integrity. The coils are married with the cores that are fabricated with amount of rigor with respect to the manufacturing controls.
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