Significance of shields in high voltage performance of vacuum interrupters

Vacuum Interrupters use a metallic cylinder to shield the ceramic from the metal vapor during arcing. Rightly so, this metallic cylinder is termed as “shield” or “arcing shield” or “vapor condensing shield”. This shield plays an equally important role in the high voltage performance of the vacuum interrupter. The number, position, dimensions and profiles of these shields govern the electrostatic field distribution and hence the high voltage performance of the vacuum interrupter. The high voltage performance of the vacuum interrupter is evaluated through analytical means like FEM simulations and high voltage tests. This paper presents the significance of the shield through results of electrostatic simulations and experimental results of commercial vacuum interrupters with various combinations of shields. The paper also presents the role of multiple shields, especially for higher voltage interrupters. A case study, highlighting the importance of the annular gap between contacts and shield for the impulse voltage performance of the contacts is also presented in this paper.