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
Effect of various kinematic parameters of mine hoist on fretting parameters of hoisting rope and a new fretting fatigue test apparatus of steel wires
The effect of various kinematic parameters of mine hoist on fretting parameters of the hoisting rope was investigated and a new fretting fatigue test apparatus was designed. A simulation model of the rope tension was presented to examine the role of various kinematic parameters on the rope tension and tension amplitude during lifting. Ranges of fretting parameters of the rope during lifting with different kinematic parameters were determined. The results show that different kinematic parameters induce different modal shapes of the vibrating systems during lifting, which results in distinct ranges of fretting parameters of the rope.