ABB VD4 36 Installation And Service Instructions Manual page 27

10. Application of the X-ray emission Standards
One of the physical properties of vacuum insulation is the possibility of X-ray emission when the interrupter contacts are open.
The specific tests carried out at the PTB laboratories (Physikalisch-Technische Bundesanstalt, in Brunswick - Germany) show
that local emission at a distance of 10 cm from the interrupter or pole surface, does not exceed
1 mSv/h.
It follows that:
– at the rated service voltage the use of vacuum interrupters is absolutely safe;
– application of the withstand voltage at power frequency, according to the IEC 62271-100 and VDE 0670 Standards, is safe;
– application of a voltage higher than the withstand voltage at power frequency or of a test voltage in direct current, specified
in the IEC and VDE Standards, cannot be used;
– limitation of the above-mentioned local phenomena, with interrupters with open contacts, depends on keeping the specific
distance between the contacts.
This condition is intrinsically guaranteed by correct operation of the operating mechanism and by the adjustments of the
transmission system.
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