Measurements by Residual Gas Analysis Inside Vacuum Interrupters

For low- and medium-voltage applications, the vacuum-interruption principle has been well established over the past 30 years. Component materials for vacuum interrupters (VIs) have to be designed for very low gas content since this characteristic determines the quality of vacuum inside the VI for at least 30 years of service or shelf life. Vacuum integrity in a ldquosealed-for-liferdquo VI is needed, and, therefore, gas pressure measurements on VIs are conducted during production as a quality-control process. To limit the pressure resolution in the range of 10^-7 hPa for a long period, vacuum measuring systems are applied to assure the vacuum integrity (tightness) of the VI. Those measurements are performed during production by magnetron (Penning principle) measurements on each VI. In addition, some selected VIs are analyzed by means of residual gas analysis (RGA-mass spectroscopy) for further production control and improvement. The RGA analyzer system consists of a Quadrupole and an Omegatron analyzer in the ultrahigh-vacuum apparatus, which can be connected to the VI. This technique is used to detect residual gases, e.g., gas sources, and to investigate the diffusion of gases from the material into the vacuum. The measurements of magnetron and RGA are analyzed and compared herein, and a description of how to eliminate gas sources by selection of suitable materials for a VI will be presented.