基于超声脉冲反射法评估大电机定子绝缘的老化状态

INSULATION CONDITION DIAGNOSIS OF LARGE GENERATOR STATOR BARS BASED ON ULTRASONIC PULSE-ECHO METHOD

该文提出一种基于超声反射法的大电机(300MW,18kV)主绝缘状态诊断方法。用这种方法可以测量超声纵波在主绝缘中传播的统计最小声速,统计平均声速,声衰减和统计缺陷率。在实验室分别对已运行16年、18年、23年和新的定子线棒进行了试验研究,并在发电机现场进行 了定子绕组超声检测试验。试验结果表明,统计最小声速和统计平均声速随绝缘运行年数的增长不断减小,统计最小声速减小的趋势比统计平均声速更明显,严重老化的主绝缘由超声检测得到的统计缺陷率增大。大电机定子绕组的超声现场检测试验验证了超声反射法在发电机小修条件下的应用性。超声反射法是一种有效的、实用的大电机主绝缘状态诊断方法。

An ultrasonic pulse-echo method was put forward to diagnose insulation condition of generator stator bars. Based on this method, a statistical minimal velocity, a statistical average velocity, and an attenuation coefficient of ultrasonic longitudinal waves propagated in stator insulation were measured, and a statistical defect rate were measured also. Three sets of stator bars in-service for 16, 18 and 23 year periods respectively in three generators (300MW, 18kV) and a new stator bar were tested in laboratory, several stator windings in a generator were also tested to examine the on-site testing capability of this method. The experimental results indicated that statistical minimal velocity and statistical average velocity decrease with insulation in-service time, the decrease of statistical minimal velocity is larger than that of statistical average velocity, and that statistical defect rate measured on sever-aged insulation is greater. The on-site ultrasonic testing results demonstrated that two velocity parameters are measured practically in the condition of generator light maintenance. It is effective and practical to use ultrasonic pulse-echo method for insulation condition diagnosis of generator stator bars.