Effect of short circuit switching on dielectric properties of vacuum interrupters
Short circuit current interruption may change the dielectric properties of vacuum interrupters during their service life. Therefore, in this work effects of the current interruption on the dielectric properties and contact erosion of the interrupters have been investigated. Contact material's evaporation during the flow of the vacuum arc before current zero may change the contact surface and cause some erosion after each operation. With the help of field electron emission current measurement the surface conditions of the interrupter contacts are compared between the new vacuum interrupters and interrupters which were previously subjected to interruptions with different arc current amplitudes and arcing time. With the help of Fowler-Nordheim diagram, surface parameters i.e. field enhancement factor β and emission area Ae are calculated and compared for each case. Field electron emission current inception voltage and breakdown voltage are compared for these cases as well.
Electrical Life of Vacuum Interrupters
The breaking of currents from a couple of amperes to several tens of kilo-amperes is a main function of medium voltage circuit breakers. Vacuum has become the leading technology in this field with attributes such as high reliability and superior electrical endurance. Standards and specifications define testing procedures to demonstrate the electrical life of circuit breakers. The requirements vary from a couple up to several hundreds of interruptions. The paper discusses the results of electrical endurance tests on vacuum interrupters according to different procedures with emphasis on their severity and the actual life time expectancy of vacuum interrupters. The results show an almost unlimited electrical life at load current level and a short circuit life expectancy exceeding any standard. The arc control and current level turned out to have a strong influence, too. Differences could be shown with respect to the different test procedures
A new range of vacuum interrupters developed using latest modeling tools
Vacuum interrupters have been widely used for power distribution systems since the 1960s and hare proven their reliability in service. Work is continuing to improve this technology and to satisfy the growing requirements of the electrical power industry. A new family of vacuum interrupters, the so called VG range, has been developed covering power The key drivers for this project were an optimised design, reduced development time and expenditure and reduced environmental impact. To achieve these targets a maximum of modeling techniques was employed. Vacuum interrupters have many electrical functions such as interrupting short circuit currents, conducting the rated current and withstanding lightning impulse voltage. Furthermore, they also have to fulfill important mechanical duties. The heart of each vacuum interrupter is the are control geometry that is required to distribute the arc energy equally over the contact surface. In the course of the development three dimensional electro-magnetic modeling was applied to optimise the ohmic resistance of the interrupters and to extend the short circuit interruption performance up to 63 kArms. Electrostatic calculations were also used. Relevant areas were not only the dielectric design of the interrupters itself, but also the interrupter mounted in circuit breakers or the optimisation of the interrupter manufacturing process. Finite element calculations were used to optimise the mechanical performance by simulating and varying different geometries and taking into account a variety of materials and their properties. The paper presents the modeling approach taken for this development project by discussing some actual examples.