When it comes to bushings, almost all engineers think only of a linear-shaped device. But a project requiring HV equipment to be installed inside a cave 40 years ago triggered an idea that has since been refined into a novel U-shaped bushing now being used on a line of current transformers manufactured in China.
Unconventional thinking is in some respects the norm with this supplier of equipment since they have recently developed a second range of dry bushings that also relies on a technology different from the classical oil (OIP) or resin (RIP) impregnated paper insulation typically found on condenser cores for transformer applications.
INMR travels to an industrial suburb of Beijing to report on the products of TR Electric.
Huang Weishu and Wang Ruzhang are an elderly married couple who present an image quite inconsistent with what one usually finds today within the high voltage industry. Both have had distinguished careers as research scientists at China’s Electric Power Research Institute. However, after leaving EPRI, instead of focusing on retirement, they chose instead to return to an idea first conceived back in 1971 and to refine it into the basis for a fast-growing bushings and electrical equipment business.
In a model typical of many start-ups, the couple began their business about ten years ago under modest circumstances, operating from a single room and wrapping their bushings by hand. Today, they occupy a large factory complex about an hour’s drive from Beijing and bushings are now automatically wrapped in a special facility where a contamination-proof airlock is the only way in or out. Says Wang Xuedong, chairman of the company, “while our bushings may now be mature, we think that our technology continues to remain unique.”
According to Huang and his wife, the most obvious difference between their dry bushing and other types currently available in the market is the use of polytetrafluoroethylene (PTFE or teflon) as the principal core insulation material. Another key difference is how grading of the electric field is accomplished using special metallic foils placed in such a way that they offer high resistance against thermal shock.