X-ray radiation of a 126 kV vacuum interrupter

X-ray emission occurs between a pair of opened contacts in vacuum interrupters (VIs) while a rated voltage or a power frequency test voltage is applied. Therefore, VIs are considered as sources of stray radiation, which should be controlled by laws and standards. The objective of this paper is to understand what is the X-ray radiation level of a 126 kV vacuum interrupter and an influence of the radiation level by applied power frequency voltage. The X-ray radiation emitted by the 126 kV vacuum interrupter was measured by a FJ347 radiometer with a power frequency voltage applied on the 126 kV vacuum interrupter. The experimental results showed that the dose of X-ray radiation emitted by the 126 kV vacuum interrupter did not exceed the IEC 62271-1 standard requirements 5 μSv in case of a rated voltage at 126 kV and that of 150 μSv in case of a rated power frequency withstand voltage at 230 kV. The mean value of X-ray radiation dose increased from 2.9 μSv to 14.4 μSv and then 29 μSv with the applied power frequency voltage increasing from 126 kV to 150 kV and then 170 kV, respectively when contact gap was 20 mm. The mean value of X-ray radiation dose increased from 0.75 μSv to 3.3 μSv and then 11.5 μSv with the applied power frequency voltage increasing from 126 kV to 150 kV and then 170 kV, respectively when contact gap was 30 mm. During a conditioning course, the X-ray dose reached an average value of 4.49 mSv, which means if a worker conditioned 180 126 kV vacuum interrupters or less in a year, he or she is safe in case of a distance of 6.4 meters away from the conditioned 126 kV vacuum interrupters.