Internal dielectric strength of vacuum interrupters in liquid nitrogen environment

In conventional applications vacuum interrupters are used in insulating gases like air or sulfur hexafluoride (SF6), but in combination with high temperature superconductive (HTS) equipment they are surrounded by liquid nitrogen. First of all, this changes the external dielectric strength. However, in previous experimental investigations it was not possible to determine the external dielectric strength of the tested vacuum interrupter because even with the maximum possible contact gap the breakdown would occur inside the vacuum interrupter. So the external dielectric strength is not part of this work. Because of the lower temperature of the switching contacts the inner dielectric strength may be affected. In the literature lower field emission currents are reported for lower contact…