With cables underground, the traditional, large step-down substation with its overhead lines became impractical. Customers now required a compact piece of equipment that could be installed quickly with a minimum of site work while providing the same functionality as an overhead line substation.
Europe was one of the first markets to embrace the practice of undergrounding cables and installing CSSs built on site with either brick or concrete. Concrete is weather-resistant, but very heavy, difficult to work with and labour costs can be significant. However, if the unit is preassembled before shipment to site, the transportation and installation costs can be excessive as a concrete CSS weighs, on average, 24 tonnes.
In the search for lighter and more cost-effective solutions, a steel enclosure was found to fit the bill. With its comparatively light weight, transporting a steel CSS to rural locations is less expensive and heavy on-site installation work is not required.
However, while lighter than concrete, steel does not have the same strength and is more sensitive to ambient weather conditions. High levels of sunshine may increase the steel temperature to such an extent that a derated transformer has to be used, thus lowering the overall efficiency of the CSS.
ABB recognized that a new CSS enclosure solution was needed – one that combined the benefits of steel and concrete. Ideally, it would be robust enough to protect the equipment inside from the extremes of heat and cold, while being lightweight enough to be easily transported, even to remote locations.
The answer was found in UniPack-G, where G represents the use of low maintenance GRP. It is unaffected by extreme temperatures and withstands attack by salt and humidity. Furthermore, since a UniPack-G enclosure is much lighter (one third the weight of an equivalent concrete CSS) transportation costs are reduced and it is much easier to install in remote locations.
The UniPack-G design is tested to the highest standards in the GB and IEC ranges. In addition, the standard design has passed the internal arc classification (IAC) test, which ensures it offers the highest level of safety for operators and the general public.