The role of vacuum in circuit breaker technology

Based on first installations of electrical energy systems at the second half of the 19^th century, apparatus were needed to close and open electrical circuits under load and short-circuit conditions. Looking back to the origin of the development of these apparatus very different media have been used in order to switch electrical currents with the focus to extinguish arising arcs after separation of the metallic contacts. Different arc quenching media like suitable gases or liquids have been applied. Recent developments are focussed to vacuum inside the tubes. The advantages and disadvantages, associated with the application of the above mentioned materials are reported. The important impact of vacuum application on switchgear technology is discussed. Different arc quenching media applied in switching apparatus need different conditions of commissioning, maintenance, repair and replacement as well as different supporting secondary equipment. All these points of view have to be taken into account in the design of the relevant switchgear which has to be in total as simple and reliable as possible under the aspect of a valuable asset to the user. Vacuum investigated first in the 17^th century by Otto von Guericke, Magdeburg, has proved in the meantime to be a powerful “material” for application in apparatus in electrical energy systems and is presently dominating the circuit breaker technology in the field of medium voltage networks with system voltages in the range of about 1 kV to 50 kV. However, apparatus using vacuum are invading the applications even in higher system voltages as well as down to the low voltage-range. A running CIGRE Working Group is dealing with this new trend. Some results as discussed in this international working group are briefly reported.