Applicability of vacuum interrupters in liquid nitrogen environment

Due to its excellent overall electrical performance vacuum technology moves into the focus of further applications, for example in combination with high-temperature superconductive (HTS) equipment or in HTS subnets. For each new application the characteristics of vacuum interrupters have to be observed, which is done in this work. For operation in liquid nitrogen (LN2) the mechanical properties have to be investigated first. LN2 also changes the internal and external dielectric strength, another aspect that has to be taken into account. Another important characteristic of vacuum interrupters is the magnitude of chopping current. If the vacuum interrupter is used in a liquid nitrogen environment its contact temperature is close to that of liquid nitrogen. This could have an effect on the switching performance. However, main focus of this research project is to study the electrical contact resistance of vacuum interrupters in liquid nitrogen. Extremely low overall resistances of not more than 1 μΏ should be achieved, motivated by the expected high continuous operating currents of several kilo amperes in HTS systems, and are a prerequisite for economical use of vacuum interrupters in combination with superconductive equipment.