Major foreign power equipment manufacturers have made unremitting efforts in exploring solid insulation materials and technologies, accumulating rich experience. For instance, high-performance epoxy resin and efficient epoxy casting technology developed by companies such as ABB, EATON, and Toshiba of Japan have been applied in the production of indoor/outdoor vacuum circuit breakers and solid-insulated switchgear, achieving remarkable social and economic benefits. The switchgear product series have been gradually improved with enhanced compatibility, and they are developing from 24kV to higher voltage levels.
Domestic research in this field started relatively late but has advanced rapidly in recent years. Domestic solid-insulated switchgear has been put into grid operation.
Looking at the solid-insulated ring main units (RMUs) from various manufacturers, most adopt a phase-separated structure where each phase is independently cast and molded. This structure greatly reduces the probability of phase-to-phase faults. In addition, the three-phase structure is designed to be as identical as possible, allowing the main components of each phase to be interchangeable. This not only lowers design and mold costs but also reduces the difficulty of production and stock preparation. Meanwhile, it avoids the problem of the entire device being scrapped due to a single circuit or phase fault—one of the primary concerns of users regarding solid-insulated RMUs.
The specific layout schemes of solid-insulated switchgear are diverse, each with unique characteristics. For example:
● EATON’s SVS ring main unit adopts an under-busbar design, with isolating switches arranged vertically front and rear.
● The solid-insulated RMU from South Korea’s Intec also features an under-busbar design but uses horizontally arranged vacuum earthing switches—a design not found in other solid-insulated switchgear. Its advantage is ensuring sufficient short-circuit making capacity in case of accidental closing of the earthing switch under live conditions. However, this design inevitably increases costs, and its acceptance in the domestic market remains to be seen.
The busbars of solid-insulated switchgear are usually circular, generally made of copper tubes. There are two types of busbar insulation:
1、Silicone rubber insulation or EPDM (Ethylene Propylene Diene Monomer) rubber insulation with a semiconductor layer on the surface.
2、Epoxy resin casting insulation.
Both ends of the busbar are equipped with fully insulated connection measures to ensure the reliability of connection with the main circuit of each phase.
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