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1.4号机于1972年12月投产发电。1974年预防性试验时(运行小时数为8077小时),测试中发现B相在2.0U_H直流耐压及泄漏电流,其泄漏电流达100微安。经查找未找出故障点仍投入运行。1979年大修期间,采用声测法查出B相第22槽上层线圈的上端部,距槽口170毫米处绝缘损坏,随即更换线圈,但对损坏原因未作分析。1981年6月17日4点,机组在正常运行情况下带有功负荷40兆瓦,无功负荷16兆乏时发出定子接地故障信号。经判断系发电机内部接地。停机拆除发电机引线及中性点连线,用2500伏摇表摇测发电机A、B相绝缘正常,C相绝缘为零。接着用3500伏脉冲电压对C相作加压试验时机架附近有放电声。将C相这一部分线圈包上锡箔后检查
Unit 1.4 was put into operation in December 1972. 1974 preventive test (hours of operation for 8077 hours), the test found that B phase at 2.0U_H DC withstand voltage and leakage current, the leakage current of 100 μA. After finding no fault point is still in operation. During the overhaul in 1979, the upper end of the upper coil of the 22nd slot of phase B was detected by acoustic measurement, the insulation was damaged at a distance of 170 mm from the slot, and then the coil was replaced without any analysis of the cause of the damage. At 4:00 on June 17, 1981, the unit issued a ground fault signal to the stator with a normal load of 40 MW and a reactive load of 16 MHz. It is judged that the generator is internally grounded. Stop and remove generator lead and neutral connection, with 2500 V shake shake generator A, B phase insulation is normal, C phase insulation is zero. Then with 3500 V pulse voltage on the C phase for pressure test discharge noise near the rack. This part of the C-phase coil wrapped in tin foil after inspection