糠醛是绝缘纸老化的产物之一,测定变压器油中糠醛的浓度可以判断变压器绝缘的老化程度。()
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用雷电冲击电压试验能考核变压器主绝缘耐受大气过电压的能力,因此变压器出厂时或改造后应进行雷电冲击电压试验。()
氧化锌避雷器直流1mA电压与初始值或制造厂规定值比较,变化不应大于±5%()
Signs of racking stresses generally appear at the ().
A. Bow and stern shell frames and plating
B. Junction of the frames with the beams and floors
C. Garboard strake,at each side of the keel
D. Thrust bearing of the main shaft