Permissible X - ray radiation emitted by vacuum - interrupters / - devices at rated operating conditions

In the medium voltage range, the vacuum interruption (VI) principle and vacuum devices (VD) are well established. Today, vacuum devices are available in the medium voltage range up to 52 kV rated voltage, as well as vacuum circuit breakers up to 80 kA short circuit current interruption ability. Besides the excellent interrupting performance, the vacuum interrupters and vacuum devices have to withstand at normal service condition and between the open contact system, while rated voltages and the corresponding test voltages applied according to the national and international standards. These are the power frequency voltages UPF and the lightening impulse voltages (Basic Insulation Level, (BIL)). Under the influence of a locally enhanced electrical field strength, electrons may be emitted from the cathode contact surface in vacuum and accelerated due to the applied rated voltage. Impacting the anode contact of the vacuum interrupter Bremsstrahlung (soft X ray emission) and the characteristic radiation of the specific material occurs. Therefore, VI and VD formally are considered as sources of stray radiation, which have to be controlled by the act of law and the standards. Given definitions and regulated limits are mandatory for the responsible manufacturer on Vis and VDs. According to the European law "Council Directive 96/29/EURATOM" of 13 May 1996, our Vis and VDs are subject to control by the German authorities with EU qualification approvals, provided that appropriate type verification is given by the "Physikalisch Technische Bundesanstalt (PTB)" in Braunschweig. Field optimized VI/VD designs and proper surface performances as well as modern manufacturing technologies are essential and matter of course in order to fulfil the radiological requirements and to keep VI and VD use save, even in the possible case of prospective high voltage applications.