A solid insulated ring main unit (RMU) is a type of medium-voltage switchgear where the primary circuit is fully enclosed and encapsulated using solid insulating materials, representing a significant innovation in the field of switching equipment.
Technological advancements in epoxy resin materials and molding processes, coupled with the popularization of vacuum switches, have laid a solid technical foundation for the development of solid insulated RMUs. To reduce or eliminate the use of SF₆ gas-filled RMUs, solid insulated RMUs have emerged as a research and development (R&D) focus in the global medium-voltage switchgear sector in recent years. Japan took the lead in this field, followed by Europe and South Korea, and later China.
After developing high-performance epoxy resin materials and casting technology in 1999, Toshiba Corporation of Japan launched a 24kV solid insulated RMU in 2002. Subsequently, the company expanded its product line into a series and is now advancing toward higher voltage grades of 72kV and 84kV.
Holec of the Netherlands, now acquired by Eaton, was an early pioneer in Europe. Its products feature advanced design concepts and technologies, while adhering to environmental protection principles—with no environmentally harmful by-products generated during the production process. Holec's solid insulated RMUs were introduced into China, and traces of its technical influence can be found in many domestically developed solid insulated RMUs by Chinese manufacturers.
Although China started relatively late, it has achieved rapid development. Representative domestic manufacturers include Beijing Shuangjie Electric Co., Ltd., Shenyang Haocheng Electric Co., Ltd., and Beihai Yinhe Electric Co., Ltd. The Xi'an Senyuan Switch Technology Research Institute has been closely monitoring the global technological development of solid insulated RMUs. To meet market demand, it has conducted joint R&D with leading enterprises such as Pinggao Group (affiliated to State Grid Corporation of China), Chengdu Xuguang Electronic Co., Ltd., and Yuyao Shunli Electric Co., Ltd., achieving phased results.
In August 2011, State Grid Corporation of China issued a document listing solid insulated RMUs in the catalog of key promoted new technologies, setting a target that their usage should account for no less than 25% of the total new additions in new construction and renovation projects after 2015. In March 2012, State Grid Corporation of China released the enterprise standard QG/DW 730 Technical Specifications for 12kV Solid Insulated Ring Main Units (hereinafter referred to as the "Technical Specifications") and relevant technical norms. These policies and technical guidelines have greatly promoted the R&D and application of solid insulated RMUs in China.
This article is compiled and edited by DAYA Electric Group Co., Ltd. (//yardscreeksoaring.com/). Please indicate the source when reprinting.