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Nuclear Power Operation Safety and Environment Part 6

Tham khảo tài liệu 'nuclear power operation safety and environment part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Investigation of High Energy Arcing Fault Events in Nuclear Power Plants 139 Fig. 1. Scheme of the electric circuit affected Fig. 2. Cross section of the cable tray inside the cable cylinder blocks inside ground between the buildings SCMALTANLAGENGEBAUOE 140 Nuclear Power - Operation Safety and Environment Fig. 3. Photos of the cable damage left location of the damaged cable right damage by the cable fire evaporation Fig. 4. Cables with protection by intumescent coating left photo of the cable channel right photo of the coating Unfortunately the pressure value having really occurred during the event could not been determined. Damage to fire doors dampers or fire stop seals were not observed. The high energy short circuit did not result in any fire propagation the combustion was limited to the location where the short circuit occurred. The fire self-extinguished directly after the electric current had been switched off. The fire duration was only a few seconds however the smoke release was high. It has to be mentioned that all cables inside the cable channel were protected by intumescent coating see Figure 4 above . This coating ensured the prevention of fire spreading on the cables. The detailed analysis led to the definite result that the event was mainly caused by ageing of the 10 kV cables. The ageing process was accelerated by the insufficient heat release inside the cable cylinder blocks. As a corrective action all high voltage mainly 10 kV cables with PVC shielding being older than 30 years were replaced by new ones. Another effect of the event was the smoke propagation to an adjacent cable channels via a drainage sump. As a preventive measure after the event each cable channel was supplied Investigation of High Energy Arcing Fault Events in Nuclear Power Plants 141 by its own drainage system. Moreover all the channels were separated by fire barriers with a resistance rating of 90 min. 5.2 Arcing fault in an electrical cabinet of the exciter system of an .